Characterisation of viruses of pepper (Capsicum spp ...

Alemu, Tameru (2004): Characterisation of viruses of pepper (Capsicum spp.) and sweet potato (Ipomoea batatas) from Ethiopia. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 126 pages. High disease incidence of viruses in pepper and lack of research on viral diseases of sweet potato in Ethiopia led to initiatives to conduct this study. The investigations on pepper viruses had the objectives to determine field incidence of viral diseases, to identify the viruses and to map their distribution. Further, the most important virus had to be characterised biologically and serologically and its variability should be determined. The epidemiology as well as the sources of resistance against the virus had to be investigated. In sweet potato, this study was undertaken to identify and characterise the occurring viruses on biological, serological and molecular level. Diagnostic surveys were conducted in two cropping seasons in major pepper growing districts in the rift valley of Ethiopia. The highest (89%) and the lowest (15%) viral disease incidences were recorded at Awassa and Meki respectively. Of 503 pepper samples analysed, 88% were infected with one or more viruses. Ethiopian pepper mottle virus (EPMV, ~60%) followed by Potato virus Y (PVY, ~23%) were the prevailing viruses. Investigations on biological variability revealed the presence of two EPMV pathotypes. The first pathotype induced severe symptoms on Nicotiana benthamiana in early stages of infection. It also infected tomato and produced severe symptoms on most pepper genotypes. The second pathotype produced only mild symptoms on N. benthamiana, did not infect tomato and caused mild and latent infections on some pepper genotypes. Cytopathological investigation of infected tissue by the severe pathotype showed massive development of pinwheels and scrolls as well as inclusions of virions. Isolates of EPMV were serologically indistinguishable. Aphids transmitted the severe EPMV isolate more efficiently than the mild isolate. Seed transmission of EPMV isolates was not found. Nicandra physalodes, Datura stramonium and Solanum nigrum were the main wild reservoirs of EPMV and other viruses Previously undescribed resistance sources against EPMV were found in pepper genotypes PBC 972, PBC 559, PBC 223 and Bakolocal. 318 collected sweet potato cuttings were indexed for virus infections. 62.8% of the cuttings revealed infections. Sweet potato feathery mottle virus (SPFMV) occurred commonly in all locations. The highest (86%) and lowest (32%) incidences were found in cuttings from the districts Humbo and Sodo Zuria respectively. Cuttings of the cultivar ‘Gadissa’ had a higher percentage of SPFMV infections than those of ‘Kogansengan’. Similarly, cuttings from farmers’ planting stocks revealed a higher percentage of SPFMV infections than those originated from the production fields. Among 13 cuttings examined with SPVG antiserum in DAS-ELISA, three cuttings were found to be positive. The host range of Ethiopian SPFMV and SPVG isolates was limited to Ipomoea species. Coat protein (CP) gene and untranslated region (3’UTR) sequences of two and the 3’UTR of another two Ethiopian SPFMV isolates were determined. Analysis of the sequences revealed the presence of the DAG- and other conserved motifs, which are features of the coat protein gene of potyviruses. Sequences of deduced amino acid (aa) and nucleotide (nt) of CPs and 3’UTR were compared with sequences of other SPFMV isolates in gene banks. The Ethiopian isolates humb1 and sodo19 had a similarity of >95% and ~83% with SPFMV-Russet Crack (SPFMV-RC) and SPFMV–Common (SPFMV-C) strains from America respectively. In a similar comparison,

the isolates ark21 and bod24 showed sequence identities of ~82% and >94% with SPFMVRC and SPFMV-C strains respectively. Phylogenetic analysis of the coat protein amino acid and 3’ UTR nucleotide sequences clustered the Ethiopian humb1 and sodo19 as SPFMV-RC and ark21 and bod24 as SPFMV-C strains accordingly. Furthermore, the Ethiopian SPFMVRC isolates were genetically closer to other East African SPFMV-RC isolates than to isolates from other parts of the world. Sequence analysis of the CP gene fragments of the Ethiopian SPVG isolates ark15 and sodo20 showed features of the CP gene of potyviruses. Alignment of sequences revealed that SPVG isolates had longer CPs (355aa) and 3’UTR (221nt) compared to other potyviruses infecting sweet potato. Alignment of CP amino acid and 3’UTR nucleotide sequences showed >90% similarity among Ethiopian-, Egyptian- and Chinese SPVG isolates, demonstrating, that all are isolates of the same virus species. Furthermore, phylogenetic analysis grouped all SPVG isolates together. Both analyses showed that Ethiopian- and other SPVG isolates had a closer relationship to Sweet potato virus II (SPVII) and SPFMV from Zimbabwe (SPFMV-Z) than to other potyviruses infecting sweet potato.

Arnold, Christian (2003): Studies on the biological control of the Horse Chestnut Scale Insect Pulvinaria regalis Canard (Hom., Coccidae) on urban trees. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 97 pages. This study aimed to investigate biological control measures against the Horse Chestnut Scale Insect Pulvinaria regalis Canard (Hom., Coccidae), a pest of urban trees. Of particular interest were observations and investigations on biological and ecological aspects of P. regalis and four native enemies of the Horse Chestnut Scale Inscect, the coccinellid predator Exochomus quadripustulatus L. (Col., Coccinellidae) and the parasitic wasps Coccophagus semicircularis (Förster), C. lycimnia (Walker) (Hym., Aphelinidae) and Microterys flavus (Howard)(Hym., Encyrtidae). The main part of this study was the release of E. quadripustulatus and C. semicircularis in Bonn and Duisburg as well as M. flavus in Duisburg. The duration of larval development of E. quadripustulatus decreased with increasing temperatures as well as food consumption and weight of larva and pupa. Predation rates of adults were low within the first 30 days after the hibernation had ended but increased thereafter. Freshly hatched adults consumed considerable amounts of food directly after hatching. The mean number of eggs laid at 9/19°C was 96,8 per female, which was less compared to 12/24°C with 139,1 eggs. Adult E. quadripustulatus preferred unparasitized P. regalis nymphs 12 days after parasitation. C. semicircularis and C. lycimnia parasitized P. regalis nymphs with a minimium body size of 0,98 mm and 0,92 mm, respectively. Higher numbers of C. semicircularis lead to an overall increase of parasitized P. regalis nymphs but to a decrease of the individual parasitation rate. M. flavus could complete a full life cycle with instars (N2) and adult P. regalis as hosts. Field observations revelead that infestation levels of P. regalis varied between the cities as well as between the trees species within one city. Highest levels were observed in Duisburg on Chestnuts with 57406 nymphs/m2 leaf area. Lowest levels were found in Bonn on maple

with 851 nymphs/m2. In the urban area of Bonn P. regalis has one generation per year. Eggs are laid in spring. During the summer month P. regalis nymphs can be found on the leafs, during the winter on twigs and branches. Climatic variations were identified as reason for the postponement and prolongation of various developmental stages of P. regalis. Until now 65 plant species are known as host plants. P. regalis is distributed all over Germany but can be found mainly in the rhineland area. The appearance of all natural enemies observed coincided with the life cycle of P. regalis during the whole experimental period. The release of 20 and 30 E. quadripustulatus larva in Duisburg lead to a reduction of P. regalis numbers up to 47,7%. After the release of 20 and 30 C. semicircularis females an increased number of parasitized P. regalis of 12,9% was observed. The indigenous parasitoid C. lycimnia parasitized a maximum number of 21,8% nymphs. A combined release of 20 C. semicircularis (14,2%) and E. quadripustulatus (46,2%) decreased infestation levels up to 60,4%. M. flavus females parasitized 19,6% of adult P. regalis and layed up to seven eggs into one scale insect. The number of eggs deposited by parasitized P. regalis was lower (217,9) compared to unparasitized P. regalis females which layed a mean number of 1272,4 eggs.

Badi, Marcela (2001): Importance of Basidiomycetes for the biological control of the root-knot nematode Meloidogyne incognita with emphasis on the mode-of-action of nematicidal active metabolites. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 111 pages. Ten Basidiomycete isolates out of forty tested in the present greenhouse screening on tomato plants, achieved significant levels of biocontrol towards Meloidogyne incognita. The most successful isolates: Marasmius spp. 90019, Lycoperdon pyriforme 79131, Omphalotus olearius 90170 and Lentinus lepideus 82019 were shown to affect the penetration of M. incognita juveniles. Furthermore, the reduced penetration rate in case of Marasmius spp. 90019 and O. olearius 90170 could be correlated with the reduction in nematode activity in the potted soil. Nematode inactivation in the soil suggested the production of fungal metabolites with nematistatic reaction which reduce movement to the roots, penetration and further nematode development resulting in a low infestation level. The isolate O. olearius 90170 was not found to produce the active compounds omphalotins in the wheat powder substrate used as carrier in the screening. Therefore, the high level of control achieved with this isolate was assumed to result from a high level of rhizosphere colonisation. Nine isolates increased significantly root and shoot weight of tomato plants promising success also in promoting plant growth. The possible practical use of those active isolates as biocontrol agents towards M. incognita justify further testing under field conditions. Among the four fungal compounds tested in the present study, omphalotin A (OMP A) isolated from O. olearius 90170 showed the highest nematicidal activity towards M. incognita juveniles. This was followed in effectiveness by 4methoxybenzene-1-ONN-azoxyformamide (MBONNAF) isolated from L. pyriforme 79131. Furthermore, OMP A showed a species specific activity among plant parasitic and non-parasitic nematodes and both compounds,

OMP A and MBONNAF had a stage specific activity towards Radopholus similis and Pratylenchus zeae where the second and third stage juveniles were most affected. Investigations to the mode-of-action of the two compounds OMP A and MBONNAF were conducted on the enzymatic activity in nematode nervous system (acetycholinesterase AChE), lipid, carbohydrate (pyruvate) and energy (adenosinthiphosphate ATP) metabolism. OMP A did not inhibit AChE activity in M. incognita extract and concluded no action similarity with the standard nematicide aldicarb. Lipase activity in OMP A treatment decreased parallel with the loss in juvenile mobility. The results obtained with OMP A on carbohydrate/energy assays showed significant reduction in pyruvate and ATP levels after longer exposure of juveniles and not shortly after the onset of nematicidal activity. The results with MBONNAF suggested that its action is more targeted toward energy metabolism (ATP) and this could correlate to the slower onset of its nematicidal activity. Different tests are still needed in order to obtain a comprehensive picture of the mechanism of action of OMP A and MBONNAF.

Block, Torsten (1997): Field and Laboratory Studies on Side-Effects of Plant Protection Products on Beneficial Arthropods in Apple Cultivation. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 97 pages. Apart from their effect on pathogens, plant protection products also have side-effects on nontarget organisms such as beneficial arthropods. Especially in apple cultivation, efforts are made to maintain the natural control potential of beneficial arthropods by selecting preparations, spray sequences or application dates that are compatible with beneficials. The objective of the present thesis is to study the side-effects of broad-effect insecticides used at different dates, in integrated and conventional spray sequences, and of different fungicide spray sequences on beneficials in apple cultivation. In laboratory trials, the side-effects of pesticide mixtures on three beneficial arthropod species relevant to fruit cultivation were compared with those of individual preparations. The application of the broad-effect insecticides ‘Decis’ (Deltamethrin) and ‘Bulldock’ (betaCyfluthrin) just before apple blossom was less harmful to predatory mite Typhlodromus pyri (Acari, Phytoseiidae), and the population recovered faster than with the application after blossom, with differences among varieties and a higher spider mite abundance observed in the post-blossom variant. ‘Perfekthion’ (Dimethoate) strongly decimated predatory mites at both application times, with a somewhat faster re-population in the pre-blossom variant. Other beneficial arthropods were not damaged substantially. The apple trees treated with conventional spray sequences showed a markedly lower level of predatory mite and spider infestation than the trees treated by way of an integrated sequence, whereas spider mite abundance was the other way round. The beneficials were not affected by the three spray sequences in which the fungicides ‘Omnex + Delan/Polyram Combi’, ‘Rondo M’ or ‘Omnex plus’ were used alternatively. The preparation mixtures tested in T. pyri, i.e. ‘Dithane Ultra + Benocab’ and ‘Delan + Pirimor’ showed an additive increase in mortality, ‘Systane 6W + Polyram WG’, ‘Omnex plus + Rubitox’ and ‘Systane 6W + Rubitox’ a synergistic increase in mortality. The combinations ‘Dithane Ultra + Benocap’, ‘Polyram Combi + Karathane’, ‘Omnex plus + Rubitox’, ‘Systane 6

W + Rubitox’ and ‘Insegar + Pirimor’ reduced the reproductiveness more markedly than the individual preparations. Related to the mortality of L2-larvae of Coccinella septempunctata- (Col., Coccinelidae), ‘Delan + Pirimor’ showed synergistic side-effects. In mortality trials with Orius majusculus (Het., Anthacoridae) L2-larvae, ‘Bayfidan + Euparen’ and ‘Delan + Pirimor’ had synergistic effects, while ‘Polyram Combi + Karathane’ showed antagonistic effects.

Bölling, Nina (2004) Phytopathological characterization of isolates of cucumber mosaic virus. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 149 pages. The biodiversity of 9 isolates of cucumber mosaic cucumovirus (CMV), including the well known isolates K-, Fny- and Q-CMV, were compared by RT-PCR, dsRNA electrophorese, host plant reaction, DAS- and TAS-ELISA under identical con-ditions. There-fore a purified virus suspension of defined concentration was used to inoculate Nicotiana rustica, N. glutinosa, N. clevelandii, N. tabacum “Samsun-NN”, Lycopersicon esculentum (Rheinlands Ruhm), Capsicum annum (Yolo Wonder B) and different varieties of Cucumis sativus and Valerianella locusta. RT-PCR with two sets of primers specific for subgroup I (S-I) and subgroup II (S-II), allowed the classification of the isolates within S-I and S-II. RT-PCR with primers specific for CMV RNA 3 followed by digestion with MspI substantiated the above re-sults. Distinct and different patterns were not found. Association of all isolates with satellites were detected by RT-PCR with primers specific for satellite-RNA and con-firmed by dsRNA analysis, indicating a high level of accumulation in infected plant cells. The isolates induced symptoms of different phenotype and severity, varying from complete systemic necrosis to no symptoms at all, but no correlation was found with sub-group type. In mixed infections, between two isolates within one subgroup or from sub-group S-I and S-II each, no synergistic or antagonistic effect was evident. Examinations of histological and cytological changes in infected host plant tissue elucidated the extent of damage caused by the infection but neither isolate- nor CMV-specific effects were observed. There was no general relationship between the severity of systemic symptoms and virus accumulation. By ELISA high levels of virus accumulation were detected in plants with none or mild symptoms as well as in plants with severe symptoms. In all host species the sensitivity of both ELISA-variants was satisfactory. Virus was detected even in plants, which appeared to be not infected at all. The results of the present work confirm, that there is no correlation between symptom expression, incidence and subgroup type of the CMV-isolates, and non of them are reliable guides to assess the actual amount of damage caused by infection.

Brinkmann, Olaf (2003):

Effect of several resistance proteins on phytopathogenic fungi in vitro and the resistance effect of these proteins in transgenic potato and tobacco plants. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 107 pages. The development of plant transformation and cloning techniques has opened new possibilities in plant breeding research. With these new techniques now it is possible to transfer genes from different organisms into plants. The objectives of molecular plant breeding are to optimise crop quality and to increase the disease resistance of plants to phytopathogenic fungi. Especially, the basic resistance of plants can be improved by the transfer of foreign genes coding for pathogenesis related proteins. In this paper transgenic potato and tobacco plants expressing the PR-proteins glucanase, chitinase, RIP, or a combination of two of these proteins, respectively, were studied for their resistance to several fungal plant diseases using a leaf disc assay. Tobacco lines expressing glucanase or chitinase, resp., showed significantly reduced infection with the pathogens Botrytis cinerea and Phytophthora nicotianae. In comparison to these lines, the combination of the two PR-proteins led only to a slight further enhancement of resistance of tobacco plants. Furthermore, the co-expression of glucanase/chitinase, glucanase/RIP or RIP/chitinase, resp., in the potato variety Désirée resulted in significantly reduced disease symptoms after infection with Phytophthora infestans but not to a resistance increase higher than the resistance of lines expressing only one foreign protein. The lysozyme of the T4 bacteriophage is known to be bactericidal. Using in vitro assays, an inhibitory effect on germinating spores of phytopathogenic fungi was detected in this work. The same effect was shown for enzymatic inactive T4-lysozyme and for the synthesised peptides A4 and A23 of the C-terminus of T4-lysozyme. Thus, the fungistatic effect is likely ascribed to the membrane disturbing activity of amphipathic helices these peptides are coding for. Using a fluorescence test the membrane disturbing activity of T4-lysozyme on fungal spores could be proven. The expression of T4-lysozyme in potato plants (var. Désirée) under control of the 35Spromoter confers significantly increased resistance to Phytophthora infestans. Whereas potato plants expressing the T4-lysozyme gene under control of the mannopine-synthase promoter showed no significant Phytophthora resistance. Further resistance tests indicate that transgenic T4-lysozyme expressing potato lines of the varieties Panda and Secura, which have high or low natural resistance to Phytophthora leaf blight, resp., show significant enhanced resistance, too.

Diab El-Arab, Hanan (2001): Rhizosphere specific microbial communities in wheat: characterization using fatty acid extraction methods and possible role in maintenance of root health status. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 139 pages. The results obtained in the research on the determination of the rhizosphere specific microbial communities and their possible role in maintaining proper root health of wheat are presented in three chapters. In the first chapter, the disease reaction of six wheat genotypes having different geographical origins to specific soil-borne pathogens was studied. In

addition, the degree of genetic relatedness of those wheat genotypes was determined using RAPD-PCR. Results of pathogenicity tests conducted in growth chambers showed that: German wheat genotypes were tolerant to most root-rotting fungi, Middle East genotypes were moderately susceptible while the South Asian genotypes were susceptible. On the other hand, results of the UPGMA cluster analysis of the genetic relatedness among wheat genotypes showed separate clustering of the Middle East genotypes from each other and from the other genotypes which had no distinct clustering. In the second chapter, the role of plant genotype on the composition of the rhizosphere specific microbial communities (RSMC) of wheat was elucidated. Different approaches were used to determine RSMC under controlled environmental conditions: the traditional culturing technique, colony forming units and the advanced fatty acid methyl ester extraction methods. Multivariate analyzes, including principal component analysis and cluster analysis combined with different fatty acids techniques revealed distinct RSMC of the Middle East wheat genotypes versus closely related microbial communities of the other four genotypes. Targeted characterization of the microbial communities was accomplished using select fatty acid biomarkers for specific microorganisms. The third chapter describes the influence of an introduced biocontrol agent Pseudomonas fluorescens 2-79 in controlling the take-all pathogen Gaeumannomyces graminis var. tritici and on the composition of the RSMC of wheat. Results showed suppression of the take-all pathogen with the rhizobacterium. Furthermore, phospholipid fatty acids and fatty acids profiles of the microbial communities revealed distinct treatment effects on the structure of the microbial communities. Distinct clustering of fatty acid biomarkers was observed between microbial communities in the presence of the pathogen versus the control treatments. The results indicated that the distinct composition of the rhizosphere specific microbial community was not only influenced by the introduced biocontrol agent, but also by the plant genotype of the wheat cultivar. This study showed that a number of interrelated factors influence overall plant resistance to fungal root-rot pathogens. Future research into the role of plant genes involved in hosting beneficial plant-associated microbes will provide greater insight into the interaction between genotype and rhizosphere specific microbial communities and provide new tools to improve root health management.

Diédhiou, Papa Madiallacké (2001): Investigations on the occurrence of arbuscular mycorrhizal fungi and importance for plant health and vitality. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 97 pages. The importance of arbuscular mycorrhizae for plant growth and vitality as well as for plant health was studied under field and greenhouse conditions. AM-fungi were isolated from soil samples taken in fields at different locations in Northrhine-Westphalia, Germany. Seven of them were used after propagation on maize for further studies. The identification of the isolates was based on morphological features of the spores. The taxonomical methods were combined with results from DNA sequence analysis of the ITS and the 5.8S rDNA of ribosomal genes. Comparison of the DNA sequences of the isolates with those from data banks gave evidence for AM identification, which could be confirmed or completed by the morphological methods.

The ability of the AM-fungi to improve plant growth depends on many factors among which the genotype of both partners plays an important role. Not only the plant species, but also the cultivar and the AM-isolate were essential for the efficiency of the symbiosis on plant growth. Experiments were carried out to study the effect of a co-inoculation of AM-fungi with other beneficial rhizosphere micro-organisms on plant growth. The combination between AM-fungi and Bacillus subtilis or a non-pathogenic isolate of Fusarium oxysporum gave neither a synergistic nor an additive effect on plant growth. Nevertheless, root colonization with the AM-fungi was improved by the presence of F. oxysporum. Glomus coronatum proved to be antagonistic to Meloidogyne incognita on tomato and reduced the nematode damage. F. oxysporum also reduced disease severity and nematode damage. The combination between G. coronatum and F. oxysporum showed, however, neither an additive nor a synergistic effect against the disease due to M. incognita. Under field conditions mycorrhization of wheat roots was very low indicating a lack of importance of this symbiosis in intensive wheat production. Fungicides, mainly strobilurins, and growth regulators, when applied at growth stages as usually, are not implicated in the reduction of the AM-fungi in these biotopes. Wheat mycorrhization was significantly higher under organic farming conditions. Complementary greenhouse studies showed that spray application of strobilurins negatively influenced root mycorrhization only in early stages of establishment. Later applications did not affect mycorrhization. In contrast, herbicide applications led to different results: Metsulfuron-methyl was very toxic to mycorrhizae, whereas prosulfocarb and fluroxypyr had a weak negative effect on mycorrhiza.

Dietrich, Stephan (1998): Investigations on the development of a preparation of the entomopathogenic fungi Metarhizium anisopliae and M. flavoviride for control of the African Locust Locusta migratoria and the Desert Locust Schistocerca gregaria. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn,172 pages. The fungi Metarhizium anisopliae and M. flavoviride are well documented pathogens of locusts and promising candidates for biocontrol of these pest insects. However, the commercial utilisation of the fungus as a mycoinsecticide necessitates the development of practical production, formulation and application techniques. A liquid fermentation technique was developed in order to produce high concentrations of submerged spores (Ss) of Metarhizium spp. using extremely cheap media. For M. flavoviride, isolate Mfl 5, the best medium was 4% sugar-beet syrup and 8% Naturpur® (composted chicken droppings) resulting in a maximum yield of 6,3 x 108 Ss/ml. Within a laboratory batch-fermenter a maximum yield of 1x109 Ss/ml was obtained. The production in fermenters with a capacity of up to 350 l was possible. Light- and scanning electron microscope investigations were conducted to study the formation of Ss. A spray-drying technique was developed which allowed drying of submerged spores of M. anisopliae and M. flavoviride without a significant loss of viability. The best protective agents for Ss were skim milk powder (20%) + sugar-beet syrup (2,5%). Finally, the virulence of spray-dried submerged spores of M. anisopliae (Ma 97) and M. flavoviride (Mfl 5) was tested

in bioassays using L3-4 of Locusta migratoria. Results showed that there was no significant difference in the mortality curve between spray-dried and undried submerged spores of M. anisopliae but of M. flavoviride. For long-term storage, spray-dried submerged spores were incubated at different constant temperatures between 5° and 50° C under dry and oxigen reduced conditions. After 52 weeks of storage at 5°, 20° and 30° C, the germination rate of Mfl 5 was 73.1, 68.0 and 38.3%, respectively. Storage at 40° and 50° C for about eight and two weeks, respectively, resulted in a loss of viability of 50%. In semi-field trials in Mauritania three different formulations of Mfl 5 were tested against Schistocerca gregaria using ULV-application. Spray-dried submerged spores were highly infective in a water-based formulation, an oil/water emulsion and an oil formulation. In contrast to laboratory trials, the highest mortality of nearly 100% after 15 days was observed with the water-based formulation (20% sugar-beet syrup in water). This formulation was also effective against adults using concentrations of 1.2 x 1012 Ss/ha.

Drescher, Karsten Erich (2005): Studies on the possibilities of biological control of Thrips tabaci Lind. (Thys., Thripidae) using different, predatory arthropod species in the production of vegetables. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 67 pages. The common vegetable pest Thrips tabaci Lind. (Thys., Thripidae) can hardly be controlled by using large amounts of chemical insectizides. Therfore, it was the aim of the present study to investigate the possibilities of ecologically safer biological control methods by releasing different predatory arthropod species. For this purpose, beneficial arthropods were tested for use in biological control under standard laboratory conditions. During this evaluation special interest was put on developmental times, predation rates and reproduction. Suitable beneficial organisms were then mass released under a standard crop production setting. Their efficacy measured in reduction of crop pests found per plant was evaluated in the field. The beneficial arthopods were released as single species, combined with plant protection netting, as well as in combination of different species. Of the beneficial arthropods studied in the laboratory predatory bugs (Heteroptera, Anthocoridae), predatory Thrips (Thysanoptera, Thripidae und Aeolothripidae), as well as predatory mites (Acari, Phytoseiidae und Hypoaspidae) were, in general, able to be used in the biological control of T. tabaci. Orius majusculus REUTER, Franklinothrips vespiformis CRAWFORD, Amblyseius cucumeris OUDEMANS, Amblyseius degenerans BERLESE, Amblyseius umbraticus CHANT, Amblyseius andersoni CHANT , Amblyseius limonicus GARMAN und MCGREGOR were evaluated. The predatory mites A. cucumeris, A. degenerans, A. andersoni, A. limonicus were used in the field studies. The reduction of T. tabaci caused by the mass release of the different beneficials varied in respect to the beneficial used, the year of the study, as well as through additional use of the plant protection netting. An increase in efficacy of the mass release

could not be observed by varying the dates for the mass release or a combination of used species. In conclusion, A. cucumeris and A. andersoni were able to reduce the number of pest per plant.

Durmusoglu, Enver (1997): The evaluation of the dislodgeable foliar residues and exposure of workers in pesticide-treated apple and rose cultures. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn,110 pages. The most common way that operators and workers can be exposed to pesticides is during the application or afterwards by contact to residues remaining on the foliage. Particularly for workers in treated crops, these residues are the main source of exposure to pesticides during their manual work activities. In this study, firstly the dislodgeable foliar residues and exposure of workers after application of Triflumuron and Bitertanol in apple culture as well as after application of Methiocarb and Bitertanol in rose culture were measured. The level of exposure of the workers during thinning and harvesting in an apple orchard and during break of shoot cutting in a greenhouse roses production was determined. Following a transfer coefficient was calculated representing the relationship between determined residues and the level of exposure of the workers. The amounts of the dislodgeable foliar residues of each pesticide measured in the two different crops varied greatly. The residues of Triflumuron and Bitertanol detected on the leaves in the apple orchard amounted to 0,06 to 0,24 µg/cm2 and 0,06 to 0,65 µg/cm2 respectively. The amounts of Methiocarb and Bitertanol found on the leaves of the roses could be determined to range from 0,21 to 2,6 and 0,24 to 1,54 µg/cm2. The level of exposure of the workers varied depending on the pesticide used, the kind of work conducted and the time after the application of the pesticides at which it was conducted as well as the characteristics of protective clothing worn. The range of the determined levels of exposures varied between 0,1 to 12,4 mg/h. The measured rates of exposure to both pesticides during the thinning of the apple orchard were clearly higher than during harvest, whereas in the rose greenhouses the measured exposure rates for the harvest were higher than during breaking of twigs. A transfer coefficient for the thinning out in apple orchard which is the activity that results in the most contact with pesticide treated material was calculated to amount from 1000 to 10000 cm2/h. The transfer coefficient for the harvesting of the roses was determined to be between 200 and 10000 cm2/h. The results of this study clearly show that the values of the level of exposure of the worker to all examined pesticides were distinctly below the values considered to be tolerable without danger to the health of the worker. It was also shown that use of gloves and wearing suitable clothing greatly reduces the level of exposure.

Faber, Thomas (1998):

Studies on biology and ecology of the newly imported horse chestnut scale Pulvinaria regalis Canard (Hom., Coccidae) and on its native natural enemies on urban trees in Germany. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn,77 pages. In this study the biology, ecology and spreading of the newly imported horse chestnut scale Pulvinaria regalis Canard (Homoptera, Coccidae) a pest of urban trees was examined in the open land and in the laboratory. Of particular interest were observations and examinations on the biological and ecological aspects of two native natural enemies of the horse chestnut scale, the coccinellid predator Exochomus quadripustulatus L. (Coleoptera, Coccinellidae) and the parasitic wesp Coccophagus scutellaris Dalm. (Hymenoptera, Aphelinidae). It was the purpose of this work to record data for the development of a biological control strategy. In the urban area of Bonn P. regalis laid eggs on stems and branches from end of April to mid May. From mid May to end of June first instar crawlers hatched and established themselves on leaves for the rest of summer. Until autumn males reached second and females third instar and migrate to twigs before leaf fall. In April they developed to adults. A suitable method for separation of different developmental stages was to measure the anal plate length of P. regalis individuals. The development of body length as well as the dispersion and density of P. regalis individuals on the leaves seemed to be influenced by the host plant species. In the year 1995 the German pest area extended in the North to Dortmund, and in the South as far as Frankfurt and Offenbach. In the West the pest extended to Aachen and in the East to Offenbach. Horse chestnut, lime and maple trees were observed as main hosts. In the laboratory the development of P. regalis was heavily affected by warm temperatures of 26°C. On P. regalis infested urban trees the eggs of E. quadripustulatus were found from end of April to mid June, the larvae from mid May to mid July, pupae from end of June to end of July and adults during the whole period of investigations. In the laboratory E. quadripustulatus larvae fed on an amount of about 7899 and 9424 P. regalis eggs. Decreasing temperatures caused a higher uptake of feed. Directly after their last moulting E. quadripustulatus adults started distinct feeding activity. On the 10th day at 20/14°C (16/8 h) the daily predation rate reached its maximum of an average number of 120 P. regalis settlers. From the 40th day onward, the daily predation rate decreased to about 3 to 6 scales. The parasitic wesp C. scutellaris passed winter in the larval stage in P. regalis third instar nymphs and had at least 2 generations per year. Fertilized eggs of C. scutellaris were laid in the alimentary canal of the exposed third instar nymphs. At a set temperature of 25°C C. scutellaris larvae hatched on the 3rd and 4th days. Prepupae were observed from 11th, pupae from 13th and adults from 14th day onward. Virgin C. scutellaris females laid their eggs only in C. scutellaris larvae before they had reached prepupal stage. Temperature conditions had distinct effects on the duration of development of both sexes and on the number of male progeny. Honey from bees and honey dew from P. regalis had similar positive effects on the longevity of C. scutellaris adults. At alternating temperatures of 16/12°C (12/12 h) females of C. scutellaris parasitized an average number of 63.7 third instar nymphs of P. regalis.

Faupel, Annekathrin (2003): Characterization of potato-associated bacteria and their potential for the biological control of the root-knot nematode Meloidogyne incognita (Kofoid & White) Chitwood. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 136 pages. Plant associated bacteria are able to improve plant growth and health but little is known about their diversity, abundance and antagonistic potential for the biological control of soilborne pathogens. Samples of roots and leaves of potato plants var. 'CILENA' were taken at three different growth stages (establishment, flowering, maturity) and 2716 bacteria were isolated from the microhabitats rhizosphere/endorhiza and phyllosphere/endosphere. The isolates were characterized using FAME gas chromatography. Data obtained were used for calculation of richness (R1) and diversity (N1, N2) and evenness (E5) to compare population spectra between habitats and growth stages of the potato plant. Composition and diversity of bacterial populations changed significantly over time in all habitats. In general Bacillus and Pseudomonas were the most dominant genera. Further dominant genera were Stenotrophomonas in the rhizosphere and endorhiza, Arthrobacter in the phyllosphere and Agrobacterium, Curtobacterium and Micrococcus in the endosphere. Bacterial isolates were then tested for their antagonistic potential against the soilborne pathogens Verticillium dahliae and Rhizoctonia solani in vitro. The highest antagonistic activity with 14-15 % of all isolates occurred in the rhizosphere and endorhiza at flowering. Eighty eight percent of this antagonistic bacteria belonged to the genera Pseudomonas and Bacillus. A total of 156 antagonistic bacteria were screened against Meloidogyne incognita on potato in the greenhouse. Forty seven bacterial isolates reduced the number of galls and egg masses for more than 25 %. Bacterial isolates effective against M. incognita predominantly belonged to the genera Pseudomonas (47 %), Streptomyces (15 %) and Paenibacillus (12 %). The best isolates with multiple effects against all the three pathogens were Streptomyces violaceusniger RR76 and Pseudomonas putida 3R2-12 originally isolated from the rhizosphere. Both isolates reduced the number of galls caused by M. incognita for more than 50 % and caused a strong growth inhibition of V. dahliae and R. solani and might be potential candidates for the development of new biocontrol agents against these soilborne pathogens.

Fischer, Bärbel (1996): Contributions to environmentally safe plant protection systems in grapevine cultivation. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 166 pages. Experiments were conducted under laboratory, greenhouse and field conditions to study the effects of watery compost extracts on the control of major fungal diseases of grapevine, such as Plasmopara viticola, Uncinula necator and Botrytis cinerea. Field experiments from 1992 to 1994 under practical production conditions in the vinegrowing region of Baden should allow a definitive judgement of effects and potential of compost extracts in disease management. The application of reduced copper concentrations against Plasmopara viticola

was also tested. Rapeseed oil was applied to study its use in environmentally safe plant protection systems. Possible side effects on predatory mites were observed. Grape and vine moths (Lobesia botrana and Eupoecilia ambiguella) were controlled by Bacillus thuringiensis. Test plots sprayed with water or unsprayed were maintained in conventionally-produced and organically-managed vineyards. Wines were produced from selected plots and tested analytically and by winetasters. Uncinula necator was well controlled by compost extracts if the infection pressure was not extreme, reducing the disease severity by 96 to 98% on ripening berries (veraison; EichhornLorenz Stage 35). However compost extracts did not control Uncinula necator sufficiently under heavy infection pressure. Copper sprays cannot be replaced by compost extracts. The population of predatory mites (Typhlodromus pyri) was hardly influenced by compost extracts whereas eriophyid mites (Calepitrimerus vitis and Eriophyes vitis) were stimulated. Other substances used as sprays by organic growers, such as Natriumsilicate, Ulmasud® and Mycosin® (two clay mineral preparations) suppressed predatory mites. Rapeseed oil effectively reduced the incidence of Uncinula necator by 66 to 99% and the severity of disease by 96 to 99,9% on ripening berries. Against Plasmopara viticola however, rapeseed oil was only marginally effective. Copper concentrations could be reduced significantly, but in the high Plasmopara viticola infection pressure of 1994, control was not reliable. Compost extracts and rapeseed oil did not have any negative effects on wine quality. The experiments demonstrated that even under difficult conditions, practical alternative production strategies are available both for conventional and organic grapevine growers.

Girma, Adugna Senbeta (2004): Diversity in Pathogenicity and Genetics of Gibberella xylarioides (Fusarium xylarioides) Populations and Resistance of Coffea spp. in Ethiopia. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 81 pages. The coffee wilt disease (CWD) is a typical tracheomycosis caused by the fungal pathogen Gibberella xylarioides (Fusarium xylarioides). The disease in Ethiopia is endemic and widespread on Arabica coffee (Coffea arabica) and re-emerged as a major threat to Robusta coffee (Coffea canephora) in Congo, Uganda and Tanzania recently. The major objectives of the study were to assess and determine the occurrence and distribution of CWD, collect sexual and asexual forms of the pathogen and investigate the fungus population structure and biology. CWD was prevalent in semiforest, garden and plantation coffee production systems with significantly varying incidence. The disease is more important in plantation followed by the garden-based production. There were implications of variations in resistance levels of Arabica cultivars in the field. Agronomic practices such as close spacing, replanting and slashing or hoeing were among the factors aggravating CWD. G. xylarioides was isolated from almost all fields being the main cause of wilting trees although other Fusarium spp., namely, F. oxysporum, F. solani, F. stilboides and F. lateritium var. longum were identified. The cultural appearances of G. xylarioides isolated from Arabica coffee on potato sucrose agar are grayish white to bluish black or dark purplish, which varied from those strains with orange pigments from Robusta and Excelsa coffee. In mating tests, some crosses produced

fertile perithecia with extruded ascospores in culture. The pathogenic diversity of G. xylarioides was studied by inoculating 10 isolates colleted in 10 major Arabica growing districts in Ethiopia and one from Robusta coffee; in seedlings of 9 Arabica cultivars and one Robusta line in the greenhouse. All Arabica isolates were pathogenic only to seedlings of C. arabica with varying degrees of aggressiveness, but incompatible with seedlings of C. canephora. In contrast, the Robusta strain was specifically compatible with seedlings of C. canephora without showing any infection symptom in all C. arabica cultivars. This result is the first cross inoculation evidence proving host specialization of G. xylarioides populations to the two coffee species. There existed highly significant (P < 0.001) differences among cultivars, isolates and cultivar-isolate interactions. The cultivar-isolate interactions indicate vertical resistance and virulence combinations. Among cultivars, Catimor-J19 and Kurme were resistant to all isolates except one; while F-59, Caturra, Dega and Wolisho manifested susceptibility to all Arabica isolates. The isolate from garden coffee in Yirgacheffe (Gx11) was the most aggressive with being virulent to all cultivars. Jimma (Gx1), Gechi (Gx4) and Tepi (Gx7) isolates proved to be also aggressive, whereas Yayo (Gx5) and Mettu (Gx6) both from semiforest coffee were less aggressive. RAPD-PCR analysis showed that Ethiopian Arabica isolates formed a genetically homogeneous population but distinctly polymorphic to strains from C. canephora and C. excelsa. The historic Arabica strain was slightly different from the recent collections illustrating little genetic change in the population over the last 3 decades. This in turn implies that the sexual teleomorphic state of the fungus contributed only less to diversity of the pathogen populations instead serving as survival and disseminating structure. The RAPD fingerprinting revealed that the coffee wilt pathogen populations are genetically diverse related to Coffea spp. and geographic origin in Africa. The present investigations employing cultural comparisons, pathogenicity tests and RAPD-PCR markers corroborated existence of host specialization into at least two pathogenic forms within G. xylarioides populations. Thus two formae speciales, namely; Gibberella xylarioides f. sp. abyssiniae (anamorph: Fusarium xylarioides f. sp. abyssiniae) for the fungus strains attacking only C. arabica; and Gibberella xylarioides f. sp. canephorae (anamorph: Fusarium xylarioides f. sp. canephorae) pathogenic to C. canephora and C. excelsa were proposed. This subdivision enables to design effective CWD management strategies, develop resistant cultivars/lines and formulate further breeding programs towards each population group.

Griesbach, Matthias (2000): Occurrence of mutualistic fungal endophytes in bananas (Musa spp.) and their potential as biocontrol agents of the banana weevil Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae) in Uganda. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 129 pages. The results are presented in five chapters. The first chapter gives a comprehensive literature review on banana production in East Africa and describes the major insect pest Cosmopolites sordidus as well as the occurrence and mode-of-action of fungal endophytes in different plant species.

In the second chapter the oviposition behavior of the banana weevil is described in the context of integrated pest control. Oviposition rates, egg size and eclosion rates were all positively related to adult size. In addition, oviposition rates and larval development were influenced by the banana cultivar as well as by the adult population density. The subject of the third chapter is the isolation and screening of fungal endophytes for biological control activity on banana weevil eggs and larvae. Two hundred isolates were obtained from healthy banana rhizomes of different cultivars in Uganda. Twelve of these isolates caused in-vitro mortality rates of 80-100% on weevil eggs and up to 48% on weevil larvae. The effective isolates were mostly Fusarium and Acremonium species. The mode-ofaction of these isolates included both direct colonization and production of secondary metabolites. The fourth chapter describes the colonization of banana plants by fungal endophytes. In-vitro tests with excised banana roots showed that fast growing Fusarium isolates were the best colonizers. These observations were confirmed in-vivo with tissue cultured plants of different cultivars. The rhizome and older root parts were generally higher colonized than the root tips and the shoot of the plants. The results of container and field trials with different banana cultivars and fungal endophytes are presented in the fifth chapter. A significant reduction in damage of up to 64% was observed on endophyte-inoculated plants. The reduction in damage is attributed mainly to antifeedant effects in inoculated plants resulting in retarded development of weevil larvae. The results demonstrated the potential of fungal endophytes in the biological control of the banana weevil.

Gulati, Mukesh Kumar (2001): Studies on biocontrol of crown rot (Phytophthora cactorum) and red stele (Phytophthora fragariae var. fragariae) disease of strawberry. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 134 pages. The present work is divided into four chapters. The first chapter gives a comprehensive introduction, its contents include a brief literature review on soil borne crown rot disease (Phytophthora cactorum) and red stele disease (Phytophthora fragariae var. fragariae) of strawberry. In the second chapter dual culture and culture filtrate tests as well as greenhouse and field studies were conducted to evaluate the potential of pre-selected rhizobacteria against crown rot (Phytophthora cactorum) and red stele disease (Phytophthora fragariae var. fragariae) of strawberry. Three antagonistic bacteria isolates: Erwinia herbicola isolate G-584, Paenibacillus macerans isolate G-V1 and Pseudomonas putida isolate I-112 proved to be potential biocontrol agents in dual culture, culture filtrate and greenhouse studies. In greenhouse experiments following bacteria treatment the disease symptoms of crown rot and red stele disease of strawberry were significantly reduced after 72 days and significant increases in both root and shoot weights were also recorded. Field experiments revealed that root dip bacterization against crown rot and red stele disease of strawberry can be successfully combined with a foliar spray of Aliette.

The third chapter describes the spread of bacteria in the rhizosphere of strawberry. The investigations revealed that the applied rhizobacteria could successfully colonize strawberry roots. Alternative methods of characterizing microbial communities, including gas chromatography and BIOLOG plating were conducted. In further observations using LowTemperature-Scanning-Electron-Microscope it was shown that colonization patterns of applied rhizobacteria differed between strains. The fourth chapter deals with the mode of action of antagonistic bacteria used in this study. Results revealed that the production of antifungal metabolites depended directly on culture media and initial pH value. In the present study it was shown that King’s B Broth was the most suitable culture media for the production of secondary metabolites from P. putida I-112 and Tryptic Soy Broth for the production of secondary metabolites from E. herbicola G-584 and P. macerans G-V1. Amplification of genomic DNA from P. putida I-112 by PCR with the specific primers Phl2a and Phl2b yielded a 745-bp fragment indicating the presence of genes for the synthesis of phloroglucional compounds. In HPLC analysis the presence of 2,4diacetylphloroglucinol was confirmed. On TLC plates the antifungal bands produced from P. macerans G-V1 and reference isolate BSA85 had identical Rf values. In HPLC analysis results showed that P. macerans G-V1 is capable of producing the antifungal peptide “Bacillomycin D”. To determine whether secondary metabolites of selected rhizobacteria play a role in biocontrol of soil borne Phytophthora diseases of strawberry, plant roots were treated with cell free extracts of bacteria. Following treatment with cell free extracts of isolate E. herbicola G-584 and P. macerans G-V1, P. putida I-112 and Aliette the disease level was significantly reduced compared to the untreated control. The results confirm a direct effect of the applied rhizobacteria on the soil borne Phytophthora diseases of strawberry.

Gutberlet, Volker (2001): Studies on the suitability of the encapsulation of the nematophagous fungus Hirsutella rhossiliensis for biological control of Heterodera schachtii and Meloidogyne incognita using renewable resources. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn. The suitability of the encapsulation of the nematophagous fungus Hirsutella rhossiliensis for biological control of plant-parasitic nematodes was studied in laboratory tests, bioassays, and greenhouse and field trials. The fungus was encapsulated in sulfoethylcellulose together with various additives. Fungal capsules with corn gluten and yeast extract as nutrient sources had nematicidal and phytotoxic effects in bioassays with Heterodera schachtii and sugar beet seedlings. It was not possible to re-isolate H. rhossiliensis from nematode juveniles or from soil. Similar nematicidal and phytotoxic effects were observed with pure corn gluten meal, which was also nematicidal to Meloidogyne incognita on tomato in the greenhouse. The short-term increase of ammonia up to cytotoxic concentrations during the microbial decomposition of corn gluten is considered to cause the nematicidal and phytotoxic effects. Therefore corn gluten was removed and yeast extract kept as the sole nutrient source. Capsules of this new formulation degraded much slower in soil than the former and caused no detectable ammonia production. Their application resulted in parasitism of nematode juveniles by H. rhossiliensis, reduced invasion of H. schachtii into beet roots, and

improved root length of sugar beet seedlings. In a field trial with sugar beet in microplots containing soil naturally infested with H. rhossiliensis, the rate of parasitism of H. schachtii juveniles in the soil was enhanced when fungal capsules with H. rhossiliensis were applied. Sugar beet yield was also improved, indicating a reduction in nematode early root invasion. The reproduction rate of H. schachtii, however, was not substantially influenced. The application of fungal capsules in the greenhouse showed no effect on M. incognita on tomato. In a bioassay the introduction of Aphelenchus avenae as an additional host for H. rhossiliensis did not increase the efficacy of the fungal capsules against H. schachtii. Fragmentation of the fungal mycelium during the fermentation process, as well as replacing yeast extract by autoclaved yeast cells improved the efficacy of the fungal capsules. The control of H. schachtii was positively correlated with increasing content of yeast in the capsules, thus demonstrating the importance of an organic nitrogen source. The encapsulation technique is considered to have significant potential for improving biological control of plant-parasitic nematodes with H. rhossiliensis or other nematophagous fungi.

Hagner-Holler, Silke (2002): Occurence and biology of Septoria petroselini (Desm.) on parsley (Petroselinum crispum). Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 90 pages. Septoria petroselini causes Septoria leaf spot of parsley and is in Germany one of the major diseases in parsley. In rainy years the disease spreads epidemically and provokes serious losses of yield and quality. Until now control strategies were mainly based on general preventive measures. No data were available on the biology and epidemiology of the pathogen which are essential to be able to fight the blight efficiently. S. petroselini exclusively infected P. crispum, whereas wild growing herbs, including celery, did not show any leaf-symptoms, a prove for the straight specialization on its host plant. In vitro the fungi showed optimal growth at 20-25°C. For the infection of parsley plants an incubation period at 100% humidity after inoculation was necessary. Under optimal conditions the sporulation of the pathogen started 14-21 days after inoculation. The isolates showed differences in virulence, the investigated varieties of parsley showed differences in suspectibility for S. petroselini. No variety was completely resistant against the pathogen. On many seeds pyknidia with conidia were found, which were not capable to infect parsley plants. On dried plant residues infection structures of S. petroselini were found to be vital for 3 years, on dead leafs the pathogen stayed infectious for weeks. Spreading of pathogen on a parsley field took place from leaf tissue and remnants of harvest by irrigation water onto the undersurface of leafs from surrounding plants. S. petroselini infected the plants trough their cavity openings and grew intrecellular in the leaf tissue, before development of pycnidia and sporulation took place or the fungi grew out of the cavity openings onto the leaf surface and caused further infections. Plants on parsley fields were regulary strong infested with S. petroselini, mostly off middle of august. The increase of infestation correlated with the time of production of dew, caused by great differences between temperatures of day and night. The number of cuts did not influence the development of the pathogen on parsley fields, even measures like removing the cut and hoeing the parsley field were not sufficient for a

significant reduction of infestation. Considerable reduction of infestation has been achieved by using an azol-containing fungicide. Initially the infestation took place through infected seeds, from this focus of infection the pathogen was spreaded all over the parsley field. For practice it should be strived to develop a model of prediction for the probability of infection out of the acquired data, to facilitate a purposeful protection of plants. Moreover it has to be attached great importance to the hygienic status of fields and seeds.

Hasky-Günther, Katja (1996): Investigation of the mode of action of antagonistic rhizosphere bacteria Agrobacterium radiobacter (isolate G12) and Bacillus sphaericus (isolate B43) against the potato cyst nematode Globodera pallida in potato. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn,138 pages. A number of rhizobacteria applied to seed or planting material have been shown to significantly reduce G. pallida early root infection of potato. To improve the effectiveness of that biological control system it is necessary to determine the mechanisms of action. Two bacteria strains, Agrobacterium radiobacter (isolate G12) and Bacillus sphaericus (isolate B43) were used representatively. Mechanisms that could be involved include bacterial production of specific metabolites or metabolism of root exudates which reduce hatch, mobility or disrupt host finding behaviour. The third main feature was the investigation of a bacterial induced systemic resistance. Bacteria treatment of the potato roots showed no reducing effect on the attraction of larvae to the roots. A lot of rhizobacteria produce antibiotics, siderophores, HCN and other toxic compounds, which are discussed as one mode of action in biological control. Culture filtrates of B. sphaericus lead to a high percentage of larvae inactivation. The culture filtrate of A. radiobacter showed a minor effect. Bacteria fermented potato root exudates, which should simulate nutrient conditions in the soil lead to no significant inactivation of nematode larvae. Systemic effects of the bacteria strains were checked in a split root system by applying bacteria to one part of the root system. After one day nematodes were inoculated either to both parts of the roots or to the untreated part only. Both strains showed a significant systemic effect. Nematode penetration was reduced both on the bacteria treated part of the root and on the untreated one. This systemic effect could be induced not only by vivid bacteria but also by dead bacteria. Furthermore, culture filtrate of B. sphaericus showed the strongest systemic effect. The culture filtrate of A. radiobacter, however, had no systemic effect at all. Both bacteria strains not only had an influence on larvae penetration of nematodes but also a systemic effect on the phytopathogenic fungus Phytophthora infestans. Biochemical investigations of the physiological reactions of potato plants to the bacteria showed a quantitative and qualitative difference in protein expression. These different proteins, however, could not be identified as one of the common PR-proteins in potato. Endophytically growing cells could only be identified with A. radiobacter. For the first time it has been proven that rhizosphere bacteria are able to induce a systemic resistance against cyst nematodes.

Ismail, Suha (2001): Host-parasite interaction between the Mediterranean cereal cyst nematode (Heterodera latipons) and barley (Hordeum vulgare) with emphasis on biological control. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn,118 pages. This work is divided into eight chapters. The first chapter is on introduction consisting of a brief literature review on the importance of cereal crops and cereal cyst nematodes in the Mediterranean regions, control strategies and the importance of antagonistic fungi in the control of nematodes. The second chapter deals with general material and methods used throughout the research program. Studies on the hatching behaviour of H. latipons are covered in the third chapter. The results showed that dormancy of H. latipons eggs is broken by exposure to a pretreatment temperature of 27°C but not by exposure to cold temperature. It was further shown that cysts were first pre-treated at 5°C, hatching with root exudates of both barley cultivars was significantly greater than in the water control. This suggested that root exudates also may play a role as an external signal, inducing hatch of H. latipons eggs at low temperature. In the fourth chapter, further studies were conducted to elucidate the life cycle of H. latipons. It was demonstrated that H. latipons required 350 degree-days to complete its various life stages from second stage juveniles to the appearance of female at 15°C. In the fifth chapter, the spectrum of H. latipons egg pathogenic fungi in semiarid and temperate soils was examined in two fields. Eighteen fungal strains present in either German or Syrian soils were isolated from uninfested eggs of a Syrian isolate of the barley cyst nematode H. latipons. Fusarium and Acremonium were the most common fungi isolated from both soils. A slightly higher level of antagonistic potential and a greater level of fungal egg pathogen diversity were present in the semiarid soil from Syria. This is important for the natural control of the Mediterranean cereal cyst nematode H. latipons common in this climatic region. Investigations on the biological control potential of fungal egg antagonists towards Heterodera latipons and H. schachtii are presented in the sixth chapter. The fungal isolates from the barley cyst nematode H. latipons were re-tested on water agar for their pathogenicity towards eggs of both H. schachtii and H. latipons. Only in four isolates, from eighteen, was H. schachtii more susceptible to the egg pathogenic fungi than H. latipons, while H. latipons was more susceptible in eight isolates than H. schachtii. These isolates were screened in the greenhouse for their potential in reducing H. schachtii and H. latipons densities in soil and subsequent nematode infection of sugar beet and barley, respectively. Only two of the isolates significantly reduced H. schachtii density and caused an early root infection in comparison to the untreated control. Conversely, all the isolates except Chaetomium (SHL-3) reduced the densities of H. latipons. The seventh and eighth chapters deal with the mode-of-action of the antagonistic fungi. The results indicated that besides mechanical penetration, enzymatic processes also play a role in eggshell destruction. The negative effect of some fungal isolates on the penetration and/or on the hatching of nematode eggs and juveniles, implies the existence of toxic and/or lytic secondary metabolites acting before or during egg infection.

Jende, Gabriele (2001): The cell wall of the oomycete Phytophthora infestans as a target of fungicides. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn,114 pages. The influence of ‘Iprovalicarb‘ as a novel fungal compound from the new class of amino acid amidecarbamates, on the development of Phytophthora infestans, causing late blight of potatoes and tomatoes, was characterised and compared to the activity of other fungicides. The infestation of Phytophthora infestans on tomato plants was effectively limited after a protective or curative application of ‘Iprovalicarb‘ in concentrations of 5 ppm a.i. and the formation of symptoms was prevented successfully. Microscopical investigations, which were carried out with a confocal laser scanning microscope, could demonstrate that early developmental stages of Phytophthora infestans on the surface of tomato plants were inhibited after a protective application of ‘Iprovalicarb‘. Morphological changes of the germ tubes, especially the lysis of cell wall structures, indicated that the cell wall lost stability substantially. ‘Iprovalicarb‘ was found to affect mainly the infection structures of Phytophthora infestans in the tissue of tomato leaves. The spread of the pathogen into deeper tissue layers was suppressed to a high extent. The swelling of fungal structures and the lysis of hyphal cell walls indicated that ‘Iprovalicarb‘ influenced the fungal cell wall. Compared to other oomycete-fungicides, with different modes of action, only ‘Azoxystrobin‘, an electron transport inhibitor, and ‘Dimethomorph‘ had an excellent effect in vitro like ‘Iprovalicarb‘. Both ‘Iprovalicarb‘ and ‘Dimethomorph‘ caused similar morphological changes in the hyphae of Phytophthora infestans like a ‘beaded morphology’ of the hyphae and swollen hyphal tips, but they interfered differently with the cell wall structure. ‘Iprovalicarb‘ showed an influence on the evidence of mono- and polysaccharides in the cell wall, which was not observed after an application of ‘Dimethomorph‘. Futhermore, ‘Iprovalicarb‘ caused structural changes of the cytoskeletal components, which probably influenced their regulation of the alignment of the cellulose microfibrills. Electron microscopical investigations showed that the cell walls became thicker and had a higher marking density for cellulose after an ‘Iprovalicarb‘-treatment. However the cell walls lost stability under the influence of ‘Iprovalicarb‘. This might be due to the fact that the state of crystallisation of cellulose had changed. After a ‘Dimethomorph‘-treatment abnormally thickened cell walls appeared as well, but in contrast to ‘Iprovalicarb‘ the structure of the cytoskeletal elements was not affected. The present investigations indicated that ‘Iprovalicarb‘ is different from other oomycetesfungicides concerning it’s effects despite similar changes in the fungal cell wall and by this ‘Iprovalicarb‘ broadens the instrumentarium of plant protection.

Khan, Imtiaz (2003): Biological and ecological studies on Typhlodromus pyri Scheuten (Acari, Phytoseiidae) as an efficient biological control agent of the European red mite Panonychus ulmi (Koch) (Acari, Tetranychidae).

Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 89 pages. The present research aimed to study in the laboratory biology and prey consumption by Typhlodromus pyri Scheuten (Acari, Phytoseeidae) with Panonychus ulmi (Koch) (Acari, Tetranychidae) nymphs as prey at different high temperatures. Preference and consumption on apple pest mite species and production of scars on apple leaves as well as fruits by T. pyri was determined. Toxicity of some pesticides to T. pyri was evaluated. Prey preference and consumption by Chrysoperla carnea (Stephens) (Neur., Chrysopidae) on apple pest mite species was recorded. Biology of P. ulmi at the different high temperatures and effectiveness of some pesticides against the pest mite was investigated. Finally, in the field experiments on T. pyri seasonal population dynamics; within tree- as well as on leaf distribution during vegetation period; within-tree distribution as well as density/twigs during winter; fecundity during different generations and mortality during autumn was studied in apple orchards region Meckenheim. The results of the laboratory experiments showed that T. pyri was able to develop, consume prey and reproduce at both the higher temperatures, but, duration of all life stages, prey consumption and fecundity decreased significantly as the temperature was increased from 25∀2°C to 30∀2°C. T. pyri preferred all stages of Aculus schlechtendali Nalepa (Acari, Eriophyidae) than P. ulmi or Tetranychus urticae Koch (Acari, Tetranychidae). The adult T. pyri females produced longitudinal irregular scars on the leaves and fruits of apple. Metasystox, ordoval and telmion were found harmful to T. pyri and the predatory mite showed 5.3-17.0-fold resistance against the different pesticides. C. carnea also showed preference for A. schlechtendali than P. ulmi or T. urticae. With the increasing temperature duration of different life stages and fecundity in P. ulmi were significantly reduced. Apollo, metasystox, masai and ordoval were found highly toxic to P. ulmi. The pest mite showed 1.723.3-fold resistance against the various pesticides. It was found in the field experiments that density of T. pyri peaked each year in mid-July. More than 50% of the predatory mite population congregatted in bottom layer of the trees. About 90% of the eggs, 75% nymphs, 60% females and 50% males were found in the inner area of apple leaves. About 50% of the T. pyri overwintering population was found in bottom layer of the trees in winter. Fecundity of T. pyri was significantly higher each year in June generation than August or winter. Falling on apple leaves of T. pyri in autumn results in about 10% mortality each year.

Klinkenberg, Hans-Josef (2002): Phytopathological characterization of oomycetes with different field resistance to fungicides. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn,151 pages. Oomycetes can spread rapidly within fields of cultivated plants. The fungal disease attack is associated with severe economic losses. Currently an effective control of the pathogen is only possible with few fungicides. The efficacy of these fungicides is often limited by the development of fungicide resistant isolates of the pathogens. The objectives of the following work were: 1. to describe the fungal stages affected by various fungicides, 2. to evaluate the

occurrence of fungicide resistant fungal isolates in the field and 3. to develop a sensitive method for early detection of the pathogen in potato plants. The work was carried out on the economically important host-pathogen-systems: potato / tomato – Phytophthora infestans, grape – Plasmopara viticola and pickling cucumber – Pseudoperonospora cubensis. The inhibiting effect of the fungicides on different developmental stages of the pathogen such as sporangia, zoospores and encysted zoospores was determined in laboratory assays. Additionally, the fungicide effect on disease reduction was evaluated in situ. The non systemic active compounds mainly affected zoospores and encysted zoospores. The systemic active compounds primarily inhibited mycelial growth and to a lower extent zoospores and encysted zoospores. At lower concentrations the strobilurine azoxystrobin gave better control than all other compounds tested. Fungicide resistance was only shown for systemic active ingredients, i.e. metalaxyl and cymoxanil against Phytophthora infestans and Plasmopara viticola and to some extent for fosetyl-al against Pseudoperonospora cubensis. Fungicide resistant pathogen populations only cause a problem in agriculture if they outcompete sensitive fungal populations. Field populations of Phytophthora infestans were sampled and tested for vitality, aggressiveness and fungicide resistance. The following scenarios were considered: potatoes grown organically, potatoes grown following the IPM standards and potatoes collected from refuse piles. Fungicide resistant isolates with high vitality and aggressiveness could pass the winter on plant debris and represent an important inoculum source in next years spring. In organically grown potatoes, fungicide resistant pathogen populations developed despite any selection pressure due to fungicides indicating air-borne migration of fungicide resistant populations. Fungicide resistance was also commonly observed in IPM farmed fields and even enhanced by the repeated use of fungicides with similar mechanisms. It is concluded, that the development of fungicide resistance in fungal field populations can be delayed or even inhibited by alternating use of fungicides with different mode of action. Prerequisite for an early and reliable detection of the fungus in the field is a sensitive and specific diagnosis. Therefore a serological test based on tissue printing was developed for pathogen detection within potato plants.

Kranz, Joachim (2002): Laboratory and field studies on the attractiveness of different wild and cultivated plant species to some polyphagous predators. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 94 pages. In the present study, laboratory and field experiments were conducted in order to investigate the attractiveness of different wild, ornamental and cultivated plants as well as of their allelochemical secretions to the adults of the polyphagous predators Coccinella septempunctata L., Adalia bipunctata (L.), Propylea quatuordecimpuctata (L.) (Col., Coccinellidae) and Chrysoperla carnea (Steph.) (Neur., Chrysopidae). A modified 4-armed olfactometer was used in the experiments on both laboratory and field strains of the predators. Results showed that the differences between the predatory individuals from laboratory and field strains remains low. Furthermore, no remarkable differences were found

among the individuals from different sexes or age groups. In the laboratory experiments by the olfactometer, clear differences were found in the attractiveness of the different plants to the four predatory species tested, where it ranged, for instance, from 6 % with Centaurea cyanus to 32 % with Artemisia vulgaris for the laboratory-individuals of C. septempunctata. Maximal attractiveness level of 38 % was achieved for C. septempunctata with Fagopyrum esculentum as an odour source, 42 % for A. bipunctata with Medicago sativa, 34 % for P. quatuordecimpunctata with M. sativa and 38 % for C. carnea with Urtica dioica. The fieldindividuals showed a relatively more readily attracted to the different plant species than those individuals obtained from the laboratory rearings. In the field experiments, the population density of the predators was studied on different cultivated plants in the presence of accompanying plants from these species. On the other hand, the population density of the aphids, which were most commonly encountered, was also determined. The presence of accompanying plants, which have a considerable olfactory attractiveness, had lead to a partially significant increase in the population density of the predators on neighbouring vegetable plants, while the differences among the different variants remained low. Some wild plants such as A. vulgaris, U. dioica and Tanacetum vulgare as well as F. esculentum, M. sativa and Phacelia tanacetifolia had remarkably enhanced the predatory population, which resulted in a partially significant reduction in the population density of the vegetable specific aphid species in the variants with accompanying plants. In conclusion, the results of present study showed a combination of laboratory and field experiments on the olfactory attractiveness of plants, and clarified the effect of olfactory attractive accompanying plants on the population density of predators and aphids on vegetable plants. The results are discussed with a special consideration of their implementation possibilities for the conservation and augmentation of natural enemies.

Lamprecht, Sybille (2002): Effect of different ozone exposure patterns on the pathosystem wheat-Mycosphaerella graminicola. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 122 pages. The impact of ozone on the pathosystem wheat-Mycosphaerella graminicola was investigated by exposing wheat plants to various concentrations of the air pollutant in controlled growth chambers. Furthermore, two different ozone exposure patterns with the same total dose were compared; one with short-term peak concentrations representing urban areas and the other one representing rural areas containing a relatively constant ozone concentration. The effects of ozone during day/night cycles on leaf injury due to chlorosis and necrotization as well as on photosynthetic activity, biomas and yield were investigated. Results showed that exposure to both ozone patterns led to acute leaf injury and considerable yield reduction. These effects were strongest after exposure to the pattern with short-term peak concentrations. Ozone exposure before inoculation influenced the disease rate of M. graminicola. The constant concentration pattern always induced significantly higher infection rates in all cultivars tested. The effect of the short-term peak concentrations on infection rate was strongly related to the cultivar-specific susceptibility to ozone injury. The

concentration of antioxidants in wheat leaves led to the assumption that the cultivar-specific susceptibility to ozone damage depends on differences in the genetically based level of antioxidants in each cultivar. An additive effect of ozone and infection with M. graminicola could be demonstrated only for grain weight. In general, damage caused by ozone was more significant than that caused by M. graminicola infections. The results of these exposure models indicate that increased tropospheric ozone, which nowadays usually occurs in summer, can inhibit plant growth, reduce yield and alter the predisposition of wheat to M. graminicola. Therefore, the exposure pattern seems to play a key role in the type and severity of ozone damage to plants.

Le, Huong Thi Thu (2003): The role of Pythium aphanidermatum (Edson) Fitzp in tomato sudden death in the tropics with emphasis on integrated disease management. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 114 pages. Sudden death causes severe damage to tomato grown under field conditions following flooding at high soil temperatures. P. aphanidermatum plays a key role in sudden death. The fungus damages the root cortex, which causes wilting and plant death. In a field experiment conducted in the hot growing season between June and September 2002 in Taiwan, 51, 72 and 93-day-old tomato plants were flooded and tested for susceptibility to sudden death. Three isolates of Trichoderma harzianum, two of Trichoderma virens and one of Streptomyces saraceticus were evaluated for biological control of tomato sudden death due to P. aphanidermatum in the greenhouse and in the field. The results revealed that neither Trichoderma spp. nor Streptomyces gave significant biocontrol of tomato sudden death. The percentage of diseased tomato plants growing in soil treated with either Trichoderma isolates or Streptomyces after flooding was not significantly different when compared to the soil treated with P. aphanidermatum alone. The soil amendments, SFMC, FNB-5A and S-H Mixture tested in this study also showed little promise for controlling tomato sudden death due to P. aphanidermatum. In both greenhouse and field experiments conducted in the summer of 2001 in Taiwan, the number of wilted and dead tomato plants was not significantly reduced over the control. The Trichoderma aureoviride added to the soil amendment treatments also gave no significant improvement in control of P. aphanidermatum with respect to tomato sudden death. Similar poor results were observed in treatments with the fungicide Mefenoxam. Grafting tomato onto eggplant rootstocks successfully protected the plants against tomato sudden death. The eggplant roots were colonized by P. aphanidermatum, but no extensive damage was caused to the plant. The results of the present study indicate that, with exception of grafting with eggplant rootstocks on biocontrol or the use of organic amendments would not give adequate control in the field. More research on biocontrol and organic matter for control of tomato sudden death is thus required.

Lennartz, Burkhard (2001): Biologische Bekämpfung von Septoria spp. an Weizen mit Chaetomium cochliodes und Ulocladium atrum durch Einschränkung der epidemischen Entwicklung des Erregers. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 140 pages. Although the biological control of plant diseases with fungal antagonists had been frequently described, there are only few details known about the application of biological agents in field cultures. In most cases strategies of biological control on aerial parts of plants are directed on the elimination of the pathogen. Another promising strategy is the retardation of the epidemiological development by competition for nutrients and space. It was investigated if fungi that were isolated from wheat leaves are able to reduce colonization, reproduction, and epidemic spread of the necrotic pathogens Septoria nodorum (Phaeosphaeria nodorum) and Septoria tritici (Mycosphaerella graminicola) on wheat. The aim was to control Septoria spp. by reduce of the epidemic development with antagonists and to find forms of application that are appropriate for agriculture. Chaetomium cochliodes and Ulocladium atrum proved to be proper of antagonists because of their efficiacy against different growth stages of Septoria spp., their apathological features, their high potential of spread, and their fast colonisation of necrotic tissue. The antagonists are able to colonize wheat leaves and reduce the development of Septoria nodorum or Septoria tritici. Competition for nutrients and space seems to be the antagonistic mechanism of U. atrum because interactions like hyperparasitism or antibiosis could not be detected in microbiological studies. In contrast C. cochliodes produced antibiotic metabolisms and displaced the pathogen by competition and antibiosis. The efficiency of the biological control was proved in field trails. Both antagonists controlled the development of Septoria spp.. They reduced the necrotic leave tissue and the reproduction of the pathogen. The production of pycnidia and pycnospores was considerable lower. This was proved on different locations under different intensities of production. Applications of fungicides led to a reduction of yield losses between 10 and 25 % depending on location. Three to four treatments with C. cochliodes or U. atrum resulted in a yield increase up to 9 % and 17 %, respectively. A cheap medium was found with oat kernels, on which C. cochliodes and U. atrum produced a large amount of spores. The spores of the antagonists could be stored for more than one year without any greater loss of vigour. Different oils and oil products used as formulation improved the distribution and adherence of the spores at the plant. Both antagonists were relatively insensible against agrochemicals. Herbicides and insecticides had no or only small effects on sporulation and growth. Against fungicides C. cochliodes und U. atrum showed a lower sensitivity than S. nodorum and S. tritici. The application of a combination is possible after an interval of several days.

Lienemann, Kerstin (2003): Incidence of Fusarium species in winter wheat in the Rhineland and possibilities of control with special reference to wheat cultivar. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 152 pages.

In 1998 – 2000 incidence of Fusarium head blight (FHB) in integrated and organic farming considerably depended on year, weather conditions, location and wheat cultivar. In 1999 and 2000 infection rate of kernels by Fusarium spp. was three times higher (18 – 20%) than in 1998, the incidence of Microdochium nivale was significant only in 1998. Despite same tillage system and previous crop, kernel infection varied considerably with location, similar as the composition of Fusarium species. F. avenaceum and F culmorum prevailed on the kernels harvested, whereas infections with F. graminearum and F. poae occurred less frequently. Incidence of some Fusarium species was promoted by previous crops as winter wheat or sugar beet, but not by minimum tillage. Because of its ecological flexibility F. culmorum seems to be highly adapted to growth conditions in the Rhineland. Similar demands on growing conditions can be obviously assumed for F. avenaceum and F. tricinctum while infection levels of F. avenaceum and F. culmorum indicated antagonistic interactions. Ear infection occurred by successive – and symptomless – infection of the leaf levels, which was important for all Fusarium species except F. graminearum and F. poae. In a three years trial under field conditions `Charger`, `Bandit`, `Rialto` and `Haven` showed high susceptibility to FHB, `Hybnos`, `Convent` and `Residence` were least susceptible. Low susceptibility of cultivar `Atlantis`, `Kanzler` and `Ludwig` was due to plant height, whereas kernels of `Atlantis` had a low infection rate additional when inoculation was done at anthesis. Genotypes `Bandit`, `FR 444/06` and `Hanseat` showed also high susceptibility to FHB but it was remarkable that the breeding line ‘FR 444/06’ gave high yields despite of high infection level. The morphological resistance mechanism was plant height (r = -0,66), in contrast to spikelet density within the ear. A short distance between flag leaf and ear and an erectophile leaf position at the same time promoted ear infection. Fungicide treatment of wheat leaves resulted in a significant increase in kernel infection by Fusarium spp. in 40% of trials. In some cases also mycotoxin content of the kernels was increased. Ear treatment with the azoles metconazole or tebuconazole resulted only in 40% of the experiments in a significant decrease in the incidence of Fusarium infection of the kernels harvested. There was a selective effectiveness of the tested azoles against the occurring Fusarium species.

Mahdy, Magdy (2002): Biological control of plant parasitic nematodes with antagonistic bacteria on different host plants. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 171 pages. Root-knot nematodes, Meloidogyne spp., are recognized as the most economically important genus of plant parasitic nematodes worldwide. The nematode causes severe damage and yield loss to a large number of cultivated plants and especially on vegetable crops in the tropics and subtropics. In the investigations conducted in this study, the potential control of plant parasitic nematodes using different antagonistic bacteria was studied with particular reference to the control of species of Meloidogyne on tomato. The results obtained from the research are presented in four chapters. The first chapter gives a: comprehensive introduction to the problems associated with root-knot nematode attack, outlines the major

control methods being used and and gives an inside into integrated pest management now as well as the potential use of biological control in future integrated strategies for nematode management. In the second chapter the results of experiments on the biological control activity of the plant health promoting rhizobacterium Bacillus cereus strain S18 for biocontrol of the three major species of Meloidogyne are discussed. The results showed that B. cereus introduced either as a soil drench or as a root dip, reduced the number of galls and egg masses of M. incognita on tomato significantly. B. cereus applied 10 days before nematode inoculation caused significant reductions in root galling and number of galls. No differences, however, were detected between the different application times in the number of egg masses produced. It was also shown that B. cereus does not control all three major species of Meloidogyne to the same degree. B. cereus had little to no biological control activity toward M. arenaria, but gave significant control of M. incognita and M. javanica. Furthermore, the results demonstrated that B. cereus is an effective biological control agent of M. incognita on a broad spectrum of host plants. In the third chapter the plant health promoting rhizobacterium Rhizobium etli strain G12 was tested for control of different genera of plant parasitic nematodes on a broad spectrum of crops. R. etli exhibited strong biocontrol activity towards M. incognita on different host plants. The reduction rates varied however between crops. Results showed that R. etli had the ability to control three economically important species of Meloidogyne. The highest reduction was against M. incognita and M. javanica, whereas it had little effect on M. arenaria. It was also demonstrated that increasing inoculum densities of R. etli caused increased reductions in nematode infection. Reduction in the number of galls occurred at 1010 cfu/ml whereas reductions in egg mass number were detected at 106 to 1010 cfu/ml. R. etli also caused significant reductions in sugar beet cyst nematode, Heterodera schachtii infection. R. etli reduced significantly the number of cysts/plant and number of eggs and juveniles/plant. The bacteria, however, did not affect the number of eggs and juveniles/cyst. The experimental data also showed that R. etli can reduce infection of the cyst nematode Globodera pallida on potato, but had no activity towards the migratory endoparasitic root-lesion nematode Pratylenchus zeae on maize. In the fourth chapter the spore-forming endoparasitic bacterium Pasteuria penetrans (Pp3) was used as a biocontrol agent for the biological control of M. javanica on tomato. The results revealed abiotic factors affect attachment. Culture filtrates of the two antagonistic rhizobacteria B. cereus S18 and R. etli G12 reduced attachment of Pp3 spores to the cuticle of M. javanica juveniles at 100 strength and dilutions of 10 percent of the original fermentation broth. The experiments also demonstrated that percolates of chicken manure compost treated soil had a strong negative effect on the attachment of Pp3 spores to M. javanica juveniles. In greenhouse tests P. penetrans multiplied quickly and within 6 months and gave good biological control of M. javanica when initially introduce into the planting soil during seedling production. The seedlings with P. penetrans in the potting soil were then grown for two additional tomato cropping cycles in a sand substrate previously infested with root-knot nematodes, at temperatures above 25 C. The overall results of these studies demonstrated the importance of three different bacterial antagonists for root-knot nematode control and supplied new information on how to improve activity of the bioloigcal control agents as well as ideas on their use in integrated management under field conditions

Makumbi-Kidza, Nakato (2002): Studies on the distribution, pathogenicity and control of the root-knot nematode (Meloidogyne incognita) on cassava (Manihot esculenta). Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 172 pages. The study is organized in seven chapters. Cassava is presented as a staple of the tropics with outstanding features that have made it the most important root crop in Africa. Major pests and diseases occurring on cassava are listed. Nematode damage is dealt with in more detail. Field surveys were made in major cassava growing regions of Uganda. Root-knot nematode incidence and damage on cassava was investigated in two regional surveys in northern and western Uganda, and in two local surveys in central and eastern Uganda. Although Meloidogyne spp. and susceptible cassava cultivars occurred at all locations the differences in nematode damage observed were considerable. The environmental causes for increased nematode damage were identified as: sandy soils, susceptible alternate host crops (particularly Nicotiana tabacum L. and Solanum aethiopicum), an alternate weed host (Ageratum conyzoides L.) and an annual rainfall regime that allowed for a permanent presence of vegetation on agricultural land. Pot experiments were conducted in which cassava was screened for resistance to M. incognita (race 2). The nematode infected and reproduced on all clones tested. The predisposition of second stage juveniles (J2) to hatch from nematode egg masses was dependent on the cassava clone on which the egg mass had been formed, significant differences occurred between clones. The total number of J2 hatching per egg mass was also cultivar dependent. There was a significant difference in reaction of the cassava clone tested to the different root-knot nematode species M. incognita and M. javanica. Experiments were carried out to examine the effect of M. incognita on yield and root cyanogenic potential (RCNp) of cassava. M. incognita reduced sprouting (shootemergence) of cassava (TMS 30572) significantly. Cassava was most vulnerable to nematode attack during and before the time of storage root initiation. Infection during this time greatly reduced the number of storage roots formed. RCNp was raised in most nematode infected plants, for some clones the increase was significant. A field experiment lasting 12 months showed that nematodes significantly reduced the number and the size of storage roots formed by some of the clones tested. The effect on yield of different nematode inoculum densities was investigated at three, six and nine months after planting. Some clones were able to compensate early losses with later growth increases. Based on the results obtained an integrated pest management (IPM) strategy, TRAP, for the control of nematodes on cassava was developed. It focuses on pest, host and site as the three factors that need to be targeted by IPM in order to effectively reduce root-knot nematode damage to cassava. The control measures are limited to specific ‘high risk areas’ that are identified with help of the Geographic Information System (GIS).

Meier, Anja (2003): Towards the impact of environmental conditions and plant cultivation measures on Fusarium infection and mycotoxin contamination of wheat. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 180 pages.

The influence of plant cultivation measures on plant health of wheat in organic and conventional farming systems in the Rhineland was investigated in studies of several years. The effect of site, weather, cultivar choice, fungicides, soil preparation (tillage), crop rotation, previous crop, intensity of cultivation and weed on infection of wheat ears with different Fusarium species and Microdochium nivale as well as on mycotoxin contamination was investigated. Valuation of ears was only partly suitable for the assessment of infection rate with Fusarium species, as distinct symptoms were only visible when infection was caused by a single Fusarium species. The major proportion of grain infection with all Fusarium species investigated occurred at the time of flowering. However, danger of infection before inflorescence (BBCH 49) and until wax-ripe stage respectively should not be underestimated when the weather is appropriate. The spectrum of Fusarium species isolated was the same for all sites, only the infection rate with each Fusarium species varied. The species F. avenaceum, F. culmorum, F. poae, F. graminearum, F. tricinctum, F. sporotrichioides as well as Microdochium nivale were identified. Soil preparation in interaction with the previous crop, such as G. aparine, had significant impact on infection potential of the soil. Some weed population was also infected and might thus be an alternate host; especially those weed varieties developing within the standing crop were partly showed heavier infection than the wheat. Comparing wheat varieties of different environmental conditions ‘Bold‘, ‘Zentos‘ and ‘Petrus‘ were least susceptible to Fusarium infection. Susceptibility to Fusarium infection of different varieties was not correlated with susceptibility to Microdochium nivale infection. Wheat from organic farming in comparison with wheat from integrated farming showed by 10% lower infection rates and with 100-350 µg/kg also lower DON contents which is probably mainly due to lower intensity of cultivation and different crop rotation. In conventional farming, Fusarium infection and mycotoxin contamination could be reduced by up to 60% when azole fungicides were applied on schedule. Application of a strobulurin fungicide could lead to increased DON content. Fungicide treatment alone is not sufficient to assure quality of grains, so that further plant cultivation measures have to be included. As a large variety of Fusarium species was identified, other mycotoxins than DON should be included in analysis.

Mekuria, Tadesse (2003): Characterisation and Mode of Action of Natural Plant Products against Leaf Fungal Pathogens. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 144 pages. The medicinal uses and chemical diversity of bryophytes, spices and herbs are long known, but their potential application in crop protection seems largely unexplored. The objectives of this study were to find crude extracts, new fungicide leads, and resistance inducers to meet the current uprising demands in the discovery of biopesticides. Research schemes were carried out to isolate and determine antifungal compounds from 20 bryophytes and from 23 spices and herbs. These were used as crude ethanolic extracts to investigate their bioactivity on globally important 16 different pathogens and 8 important host plants under in vitro and in vivo conditions.

The screening of extracts for their antifungal effects exhibited that activity of products varied significantly according to their sources. Extracts of bryophytes, especially Bazzania trilobata, Diplophyllum albicans, Sphagnum quinquefarium, Dicranum denudatum and Hylocomium splendens showed higher antifungal efficacy against Botrytis cinerea, Alternaria solani, Phytophthora infestans, and Blumeria graminis. Similarly, extracts of Piper nigrum, Carum carvi, Cassia spp., Artemisia dracunculus, Urtica dioica, Foeniculum vulgare and Coriandrum sativum were found as the best antifungal products among spices and herbs. The extracts of B. trilobata and P. nigrum were investigated in more detail. The B. trilobata extract inhibited fungal stages like germination of conidia, germ-tube formation, elongation and mycelial growth. Plants received the product (1% m/v) at different time intervals before inoculations with pathogens. Application of the extract 2 days before fungal inoculation showed reduction of disease severity against diverse pathosystems up to 98%. Under such circumstances, the extract gave high efficacy in 9 of the 13 tested pathosystems, though the biotrophic pathosystems were more sensitive than the perthotrophic ones. The extract of P. nigrum showed both protective and curative mode of action, whereas the efficacy of the extract from B. trilobata was reduced by 50 % for its curative application against Puccinia recondita on wheat. Bioassays determining systemicity of the B. trilobata extract demonstrated that the product showed a translaminar and at distant effectivity against P. infestans, Podosphaera leucotricha, Uncinula necator and Uromyces appendiculatus. The active guide component of P. nigrum extract had a similar molecular structure as piperine as detected by different chromatographic techniques. The extract of B. trilobata was composed of unidentified metabolites like flavonoids and procyanidins. But its major bioactivity was linked to the hydrophilic fraction and lysosome like organelles (LLOs). Lysosome like organelles (LLOs) described as vesicles, vacuoles, lysosomes, spherosomes and melanosomes which were bounded with a single membrane. They had positive reactivity with acridin orange and showed lysosomal acidic hydrolase activity. There were positive reactions with specific dyes staining nucleic acids. Incubation of LLOs with different substrates detected their phagolysosomal enzymatic activities. Chitinase endocytosis activity was recognised by the formation of electron dense granules at the interface, vesicles and specific loci on the body of LLOs. Incubations were proceeded using LLOs with sporangia and zoospores of P. infestans, conidia and mycelia of A. solani, urediospores of U. appendiculatus and teliospores of Ustilago nuda. Unspecific degeneration of fungal cell walls and entire protoplasms were detected. Germination, basidia formation and sporidia differentiation of teliospores of Tilletia caries were delayed on a medium amended with the LLOs. The protective spraying of LLOs significantly impaired the infection structures of pathogens on the leaf surfaces and in tissues, locally and systemically. Infection, disease development and propagation of leaf pathogens were reduced irrespectively of variations in their taxonomy and host pathogen interactions. Thus, pretreatments of susceptible plants with LLO preparations of mosses provide a new perspective for an integrated disease management of fungal pathogens of different crop plant.

Metz, Claudia (2003):

Influence of pathogen genotype on the antagonistic efficacy of Ulocladium atrum in the control of Botrytis cinerea. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 131 pages. The necrotrophic fungus Botrytis cinerea (Pers.) is a pathogen with a wide host range causing economical losses in many crops worldwide. Effective control of the pathogen using fungicides with the same mode of action is restricted by the fast development of resistant isolates. Biocontrol may offer a supplementary or alternative crop protection tool and also can be used for the management of fungicide resistance. The saprophytic hyphomycete Ulocladium atrum has been described for its antagonistic potential against gray mould in various crops. The efficacy of U. atrum depends on the saprophytical competition with B. cinerea during the colonization of necrotic plant tissue, affecting the epidemic spread of the multicyclic pathogen. In this work the efficacy of U. atrum in the biocontrol of various genotypes of B. cinerea was investigated. The strains were differentiated for their morphological and physiological characteristics, as well as on their sensitivity against common botryticides from different chemical groups. The antagonistic potential of U. atrum has been proven under controlled conditions on necrotic grapevine leaves, in greenhouse crops such as begonia, sweat pepper and grapevine plantlings as well as under field conditions in grapes on different cultivars and at several locations over several years. The aggressiveness of B. cinerea strains differed in various crops indicating specific interactions between pathogen and host species. The efficacy of the antagonist U. atrum was also influenced by the genotype of the pathogen strain to be controlled. The differences in vulnerability to the antagonistic activity of U. atrum were neither correlation to strain specific characteristics like spore size, growth or aggressiveness nor to fungicide sensitivity. Furthermore, efficacy of disease control depended on the reasonable coordination of application parameters like spore concentration applied, timing and number of U. atrum applications, as well as the growth media used for spore production of the antagonist. Neither the crop development nor the quality of the wine fermentation was negatively affected by the application of U. atrum. Alternate applications of U. atrum and the botryticide fenhexamid reduced the gray mould infection on berries significantly, whereby the number and dosage of fungicides decreased. However, at high disease pressure like in 2000, the efficacy of U. atrum was not able to reduce significantly the rapid spread of B. cinerea on the grapes, because the incidence of U. atrum on berries decreased before harvest and the antagonistic activity depending on nutrient competition became insufficient. The antagonist showed low sensitivity against pesticides and may be integrated in existing crop protection strategies in viniculture.

Mulawarman (2002): Use of natural products based on renewable raw materials to stimulate soil health and control Meloidogyne incognita. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 115 pages. New products based on renewable raw materials as well as various sources of Chitin and Chitosan were screened to control plant parasitic nematodes. Chandler Check (20 kg/ha)

and TerraPy® (200 kg/ha) significantly suppressed Meloidogyne incognita infection by 21 % to 28 %. For chitinuous compounds, Chitosan oligosacharides suppressed nematode infection by 23 % to 70 %, while those with higher molecular weight were most efficient. All Biosol treatments in general suppressed nematode infestation by 65 %. Control efficiency was even enhanced by combining Biosol with Oligo-Chitin and Oligo-Chitosan resulting in an average increase in control of 62 %. Regarding its origin, Chitosan originated from India and Canada and NM 9316 were shown to give best control of nematodes up to 48 %. The application of organic amendments was optimised by varying application rates, forms and using combinations of organic amendments or combinations of organic amendments with antagonistic microorganisms. Both, high and low rates of Chitosan incorporated into soil at 28 days before planting and at planting caused a reduction in nematode infection and enhanced plant growth, while no effects were observed with application of Chitosan after planting. In an approach to reduce total amounts of application, Chitosan applied as a seed treatment significantly reduced Pratylenchus zeae infection on maize. Similarly, Chitosan also reduced Heterodera schachtii on sugar beets 21 days after inoculation and 35 days after inoculation. Infection of Globodera pallida was significantly reduced by all treatments of potato treated tubers at 35 days after inoculation. The application of Chitosan on tomato as a seed treatment caused only a slight reduction in Meloidogyne incognita infection. An additional reduction of nematode infection was observed for the combination of TerraPy with mycorrhiza. The organic amendments significantly affected soil microorganisms and nematode communities. TerraPy®, Chitosan and to a lesser extent Magic Wet® reduced plant parasitic nematode densities and improved plant growth. The application of N and P in equivalent amounts present in the formulations did not affect plant growth promotion in the same degree. Properties of the amendments such as improved soil structure, increased soil water retention or increased plant nutrient availability may play a key role in plant growth promotion. Furthermore, modifications of the microbial community also might contribute to plant growth stimulation and nematode control, in that all three compounds TerraPy®, Chitosan and Magic Wet® significantly increased certain genera in the soil. Acinetobacter, for example, plays a key role in the solubilization of phosphate in soils. Therefore, increasing densities of Acinetobacter might result in improved supply of phosphate to the plant. The highest increase of Pseudomonas, a bacterial genus with plant growth promoting activity was observed following Chitosan application. Other, not yet identified bacteria, might have also contributed to plant growth or health promotion by mechanisms such as stimulation of phytohormones, N-fixation or suppression of deleterious microorganisms. The potential mode of action of Chitosan as an inducer of systemic resistance against Meloidogyne incognita was studied on tomato using a split-root system and foliar spray. Chitosan application to one-half of a split-root system caused a significant reduction of egg masses on the other side of the split root system. Similar result were achieved when Chitosan was applied as a foliar spray, indicating that a downward movement of signals associated with the resistance reaction occurs. It is concluded that TerraPy®, Magic Wet® and Chitosan contribute significantly to plant growth and health by stimulating soil microorganisms and thereby suppression of plant parasitic nematodes.

Munif, Abdul (2001): Studies on the importance of endophytic bacteria for the biological control of the rootknot nematode Meloidogyne incognita on tomato. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 120 pages. A total of 670 strains of endophytic bacteria were isolated from tomato plants grown in temperate and tropical soil from Germany and Indonesia. The isolation procedure was done using surface-sterilization and trituration method with 3% and 6% sodium hypoclorite (NaOCl). The total population density of endophytic bacteria recovered from tomato roots ranged between log 0.45 and log 4.45 cfu/g root fresh weight. Endophyic bacteria were identified based on their fatty acid profile using FAME-GC-MIDI system. Thirty-eight bacterial species in 21 genera and 50 bacterial species in 32 genera were found in association with tomato roots in Germany and Indonesia, respectively. The most abundant endophytic bacterial species in Germany were Pseudomonas putida (11.8%) followed by Bacillus megaterium (10.59%) and in Indonesia B. megaterium (14.31%) followed by P. putida (12.44%). Species richness and diversity was 7.08 and 3.29 for bacteria from Germany and 8.44 and 3.01 for bacteria from Indonesia. A total of 181 bacterial strains in 51 bacterial species were physiologically characterized. Bacterial traits most commonly observed were protease activity (55.74%), cellulose activity (41.53%), solubilization of phosphate (40.44%), chitinase activity (25.14%), HCN (18.03%), fluorescense activity (18.03%), and lipase activity (10.93%). None of the bacteria showed pectinolytic activity. The 181 bacterial strains were tested for their in vitro antagonism towards Rhizoctonia solani, Fusarium oxysporum f.sp. radicis-lycopersici and Fusarium oxysporum f.sp. lycopersici and their biocontrol activity against Meloidogyne incognita. Fourteen strains (7.7%) showed antagonism against R. solani, 9 strains (5.0%) against F. oxysporum f.sp. radicis-lycopersici and 7 strains (3.9%) against F. oxysporum f. sp. lycopersici and 21 strains (11.6%) significantly reduced the number of galls produced by M. incognita on tomato in screenings studies. Four out of 21 strains, i.e. Pantoea agglomerans MK-29, Cedecea davisae MK-30, Enterobacter spp. MK-42 and Pseudomonas putida MT-19, significantly reduced M. incognita infestation on tomato either as a seed treatment or as a soil drench application. The four endophytic bacteria also significantly reduced early root penetration of Meloidogyne juveniles into tomato roots up to 56%, when applied as a root dipping or soil drench. Combination of the four bacterial strains gave a higher reduction in the number of galls than the application of a single strain. Investigation on the mode of action of endophytic bacteria showed that the culture filtrates of endophytic bacteria were able to inactivate and kill M. incognita juveniles in vitro and reduce early root penetration and the number of galls and egg masses of M. incognita on tomato. Application of endophytic bacteria in a split-root system resulted in a significant reduction of the early root penetration and number of galls and egg masses of M. incognita. These results suggest a combination of two active mechanisms by endophytic bacteria, i.e. direct mechanisms through the release of metabolites with nematicidal/nematistatic activity and indirect mechanisms based on induced systemic resistance. The population dynamics of endophytic bacteria in the rhizosphere and within plant tissue showed that the introduced endophytic bacteria colonized the tomato rhizosphere

continuously over 28 days after bacterial application and significantly increased the total bacterial population density. The introduced endophytic bacteria were able to colonize the root interior for a minimum of 6 weeks. The internal population densities of introduced endophytic bacteria in tomato roots ranged between log 1.2 and log 5.9 cfu/g root fresh weight. The population densities of introduced endophytic bacteria were higher in the presence of M. incognita than in the nematode-free control but the differences were not significant. With the exception of Enterobacter spp. MK-42, the applied endophytic bacteria were not detected in the stem of tomato.

Mwangi, Maina (2003): Mechanisms of action in biological control of Fusarium oxysporum f.sp. lycopersici in tomato using rhizobacteria. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 159 pages. Seven bacteria isolates with known antagonistic effects against nematodes were evaluated in the greenhouse for ability to reduce Fusarium wilt in tomato. The effective isolates Pseudomonas fluorescens T58, P. putida 53 and Bacillus sphaericus B43 were selected for further study and their mechanisms of action were investigated. Results showed that induced systemic resistance (ISR) was the main mechanism of action for all three effective rhizobacteria while antibiosis did not play a major role. To characterise the ISR changes in phenolic compounds, lignin content in roots, and activities of the pathogenesis-related (PR-) proteins peroxidase, chitinase and ß-1,3-glucanase, and structural changes in cells were investigated. A new phenolic compound was detected in plants treated only with Fusarium. This new phenol was not detected when the plants treated with P. fluorescens T58 or B. sphaericus B43 were infected with Fusarium. Isolate P. putida 53 did not suppress the occurrence of the new phenol. Lignin content in roots was non-significantly increased in plants treated with isolate T58 and B43. Peroxidase activity in stem was increased by all isolates, but the increase due to B. sphaericus B43 occurred earlier and was short-lived. Changes in chitinase activity in leaves were induced by isolates 53 and B43, while ß-1,3glucanase activity was not affected by any of the rhizobacteria. Isolate T58 induced callose deposition on cell walls while isolates 53 and B43 induced extrusion of occluding material into the lumina of xylem vessels. P. fluorescens T58 was observed to be a producer of HCN. The role of HCN and other volatile metabolites produced by this isolate in biocontrol of Fusarium was investigated. The volatile metabolites reduced Fusarium spore germination but not mycelia growth, although mycelia lost pigmentation when exposed to the volatiles. The volatiles produced by isolate T58 could significantly reduce the densities of competing bacteria in plant growth substrate while fungal densities were not always significantly reduced. In addition, the volatiles induced increased peroxidase activity in tomato plants which may contribute to biocontrol. The ability of ISR to reduce tomato damage by Fusarium toxin was also investigated. Ion leakage and chlorophyll degradation in the leaves was studied in relation to the content of superoxide anions (O2-) and H2O2, which are active oxygen species (AOS). Superoxide dismutase, catalase, ascorbate peroxidase and guaiakol peroxidase activities, which regulate AOS metabolism were also studied. Plants treated with isolate T58 had significantly less ion leakage and chlorophyll degradation after treating with

Fusaric acid. Isolates 53 and B43 did not effectively protect plants from damage by the toxin. On the overall the effect of toxin on chlorophyll degradation and ion leakage from leaves could be related to the AOS content and the activities of the enzymes regulating AOS metabolism.

Niere, Björn Ilja (2001): Significance of non-pathogenic isolates of Fusarium oxysporum Schlecht.: Fries for the biological control of the burrowing nematode Radopholus similis (Cobb) Thorne on tissue cultured banana. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 118 pages. Bananas are an important commodity in international fruit trade but they are far more important as a starchy staple in East Africa. Banana production is threatened by a complex of pests and diseases. The burrowing nematode Radopholus similis is the major root rot pathogen in Africa as well as worldwide. In this study, possibilities for the biological control of the burrowing nematode on tissue cultured banana were investigated. Major parts of this study were conducted at the International Institute of Tropical Agriculture (IITA), Eastern and Southern Africa Regional Center (ESARC) in Uganda. Fungal endophytes were isolated from healthy banana root and rhizome tissue after surface sterilization. Identification of the 285 isolates obtained, revealed that the majority of fungi could not be considered mutualistic fungal endophytes. Species of Acremonium and Fusarium were most commonly isolated at a frequency of 20 % and 30 % of all isolates, respectively. Fusarium oxysporum was the predominating fungal species and constituted 10 % of all endophytic isolates. Although the majority of F. oxysporum isolates are non-pathogenic soil colonizers, a number of specialized forms causing wilts or root rots of crop plants exist. To distinguish isolates of F. oxysporum targeted for the biological control of banana nematodes from F. oxysporum f. sp. cubense, the causal agent of banana wilt, vegetative compatibility grouping (VCG) was applied to the biocontrol strains. None of the strains proved to be genetically related with known tester strains of the banana and tomato pathogens as detected by VCG. The majority of strains was also not compatible with each other, indicating that non-pathogenic endophytes of banana roots represent a heterogeneous fraction of the F. oxysporum population. Nonpathogenic isolates of F. oxysporum were selected for the inoculation of tissue cultured banana plants. The fungal strains tested exhibited various degrees of activity that led to reduced nematode reproduction in roots of up to six months old banana. Nematode control was considered to be dependent on the host plant genotype and could never be observed on the East African highland cultivar Mbwazirume. Reductions in nematode densities were related to a significant reduction in development of females in roots of inoculated banana. Plant growth in endophyte treated plants was generally not affected. Reduced height was observed on the cultivars Enyeru and Valery but at the same time number of nematodes were significantly reduced. Root necrosis in general decreased in plants inoculated with fungal antagonists followed by nematode challenge inoculation supporting the nonpathogenic nature of the fungal isolates. The mechanisms of action responsible for nematode control could not be established. Direct microbial antagonism of the nematodes by F. oxysporum, however, seems not to be the cause leading to nematode control. Further

studies are needed to elucidate the mode-of-action responsible for nematode control. Inoculation of non-pathogenic isolates of F. oxysporum on tissue cultured banana is currently seen as a technology that complements and can improve tissue culture of Musa spp.

Ortega, Felipe (1994): Influence of induced resistance on the host-parasite-interaction MalusXDomestica Borkh.-Venturia inaequalis (Cke.) Wint. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 124 pages. In the work presented, the efficacy of induced resistance against pathogen strains with different genotypes and mixed populations out of them was investigated. For this purpose MalusXDomestica Borkh.-Venturia inaequalis (Cke.) Wint. was used as a model system. First it was necessary to find appropriate induction methods and to characterise induced resistance in this host-parasite-interaction. The application of 2,6-Dichlorisonicotinic acid and 3,5-Dichlorsalicylic acid on apple plants lead to a reduction in their scab infestation that amounted to 60-70%. The subcuticular growth of the pathogen was reduced, the latency period prolonged and the sporulation restricted. The effect of induced resistance on the infection cycle of the fungus was investigated by fluorescence microscopy. Induced resistance interfered with all stages of infection except conidial germination and appressorium formation, but the most relevant effect to the restriction of the disease was the impairment of the first infection stages of the pathogen. The investigations strongly suggest that the main effect of induced resistance on Venturia inaequalis in apple is due to the interference with the pathogen nutrition. To evaluate the variability in pathogen populations towards this crop protection principle, the efficacy of induced resistance was evaluated against pathogen strains with different genotypes. Their sensitivity to triazole-fungicides and Vf-virulence were used as distinctive marks for their differentiation. The investigations resulted in important differences in the activity of induced resistance, but no correlation between its efficacy against a certain strain and the sensitivity of this strain to triazol fungicides nor its Vf-virulence could be identified. When induced resistant plants were challenged with a mixed population of these pathogengenotypes its activity was, either comparable or clearly superior to the efficacy reached against the best controlled strain in the mixture. No selection processes could be identified in competitive studies. The investigation of the dose-response relationship of triazole fungicides against Venturia inaequalis on induced resistant plants allowed the identification of a clear synergism between both active principles. The enhancement of the efficacy of the fungicides on induced resistant plants could be proofed under field conditions as well. This observation delivers a further concept for the use of induced resistance in crop protection. Despite that the utilisation of resistance-inducers in practical crop protection is difficult to handle, due to their indirect mode of action, the active principle of induced resistance widens the possibilities with which plant diseases can be controlled.

Pocasangre, Luis (2000): Biological enhancement of banana tissue culture plantlets with endophytic fungi for the control of the burrowing nematode Radopholus similis and the Panama disease (Fusarium oxysporum f.sp. cubense). Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 95 pages. A total of 132 endophytic fungal isolates were recovered from internal tissues of surface sterilized roots and corms from 21 banana cultivars in Central America and Cuba. The antagonistic activity of 25 endophytic fungi towards Radopholus similis was studied on micropropagated banana plantlets of the cultivar Gran Enano (AAA) under greenhouse conditions. Five of these endophytic isolates caused reduction in the number of R. similis /g root greater than 90% in comparison to endophyte-free plantlets. The antagonistic activity of the effective endophytic isolates was retested on different banana cultivars: Williams (AAA), Gros Michel (AAA) and FHIA-23 (AAAA). Reduction in the number of R. similis /g root greater than 76% was recorded on all banana cultivars tested. Also the population density of R. similis in the soil was significantly reduced by the endophytic fungi. Endophytic fungi effectively colonized the roots and corms of the plantlets. Frequency of reisolation greater than 46% in the roots was recorded on three banana cultivars. The presence of endophytic fungi in the roots reduced the penetration of R. similis into the root tissue up to 74% on the commercial cultivar Gran Enano (AAA) 5, 10 and 15 days after nematode inoculation. In addition in the absence of R. similis inoculation with endophytic fungi increased shoot and root weight as well as root length of the banana cultivar Gran Enano (AAA) Williams (AAA) and FHIA-23 (AAAA) 3 months after inoculation. The Antagonistic activity of endophytic fungi towards race1, 2 and 4 of Fusarium oxysporum f.sp. cubense (FOC) was studied on micropropagated plantlets under greenhouse conditions. The pathogenicity of FOC race 1, 2 and 4 was confirmed on race indicators cultivars. Typical symptoms of Panama disease were observed 6 weeks after inoculation. Antagonistic tests conducted with high and low inoculum densities of FOC race 4, 1x106 and 1x103 cfu/ml respectively showed that there were no differences in disease severity between inoculated plantlets with endophytic fungi and control under high inoculum densities of FOC race 4. However, disease severity, internal and external symptoms, was significant different between inoculated plants with endophytes and control under low inoculum density.

Prange, Alexander (2004): Food mycological and X-ray absorption spectroscopic investigations on the influence of phytopathogenic, mycotoxin producing moulds on the gluten protein structure and baking quality of wheat. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 156 pages. The influence of phytopathogenic, mycotoxin producing moulds on the sulfur speciation of the gluten proteins and thus the baking quality of wheat was systematically investigated. To characterise the sulfur speciation in situ, XANES spectroscopy was established as method for the "wheat gluten" system. XANES spectra were analysed quantitatively using the MINUIT fitting routine. To deal with this interdisciplinary subject comprehensively, different

methods and aspects pertaining to mycology, mycotoxinology, molecular biology and cereal chemistry were applied and considered for the investigation of mould infected wheat in several field and storage trials. XANES spectroscopic measurements allowed for the first time a description of the sulfur speciation of wheat gluten proteins and flours in situ. The oxidation of reduced LMW subunits of glutenin with atmospheric oxygen led to an increased formation of disulfide bridges; in LMW subunits stored in ambient air and temperature conditions for more than two years, virtually nothing but sulfoxide and sulfonate were detected. The investigation of LMW subunits which were reoxidised with potassium bromate and iodate at different pH values showed that these oxidising agents do not only cause an oxidation of thiol groups to disulfide bridges, but also an (unwelcome) oxidation of the cysteine residues to sulfoxide and sulfonate; sulfur as sulfone was not detected. The strongest oxidation was observed with acidic pH values. Field fungi of the genus Fusarium have hardly any influence on the sulfur speciation of the wheat gluten proteins. A reduced functionality of the gluten network and a reduction of the baking volume have not been observed. From the perspective of food safety and consumer protection this is of great importance because the baking quality of flours that were heavily loaded with DON did not allow detecting their contamination with fusaria and/or mycotoxins. Storage fungi of the genera Aspergillus and Penicillium have a direct influence on the sulfur speciation of gluten proteins. In baking tests with flours from the storage trials (20% moisture content/20°C) a considerably reduced baking volume was observed. In this context, an increased proportion of sulfonate was found, which is not available for the thiol/disulfane exchange reaction in the gluten network. From these changes of the composition of the mould flora during suboptimal storage of wheat and from the trichothecene contents it is concluded that microbial interactions play an important role in the development of the mould flora and the mycotoxin contents.

Reissinger, Annette (2000): The interaction of the fungus Chaetomium globosum with the powdery mildew fungus Erysiphe graminis f. sp. hordei on barley (Hordeum vulgare). Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 95 pages. Fungal endophytic colonization of plants can change their metabolic activity leading to a modified defense response to subsequent pathogen attack. It could be shown that the saprotrophic fungus Chaetomium globosum is able to grow endophytically in barley roots (Hordeum vulgare). The colonization included symptomatic discoloration of the root cortex if a synthetic culture substrate was used for plant growth. The colonization of the root tissue by C. globosum was investigated with histological and serological techniques. The fungus colonized the epidermis intracellularly, while the outermost cortex layer was colonized interand intracellularly. The colonization always originated from the rhizosphere. The inter- and intracellular growth was accompanied by host responses including autofluorescence and brown discoloration of cell walls adjacent to hyphae and hemispherical or papilla like protuberances of cell walls. Additionally, an anamorphic substance which was found in the intercellular spaces, seemed to block the intercellular growth of the fungus. In contrast to

these findings C. globosum could not be reisolated from the roots by means of surface sterilization techniques. The only sterilant being effective to ascospores on the plant surface penetrated the epidermal root tissue and caused damage to this area [1]. Consequently, C. globosum hyphae growing in this tissue could not be detected. Using microscopical and serological methods, no colonization of leaf blades could be found. To determine the mode of action leading to the reduced disease severity of Erysiphe graminis f. sp. hordei, which was described previously [2], increased plant defense responses in the primary leaves induced by the defense of C. globosum in the roots were investigated. However, on a microscopical level no increased defense responses could be found in plants colonized by C. globosum. Additionally there was no indication for a modified infection process of E. graminis konidiospores 41 h post inoculation. The conidial germination of the pathogen, as well as the appressorium and haustorium formation, i.e. the successful penentration of the epidermis, and the reproduction was not altered. However, a general reduction of attached conidia was found on the leaf surfaces of plants colonized by C. globosum compared to mock treated controls. This observation indicates for a C. globosum inducible, and systemically diffusible signal which acts on early stages of pathogenesis, i.e. the attachment of konidiospores to the leaf surface, via an altered conidial germination. References [1] Reissinger, A., Vilich, V., Sikora, R.A. (2001). Detection of fungi in planta: effectiveness of surface sterilization methods. Mycological Research, in press. [2] Vilich, V., Dolfen, M., Sikora, R.A. (1998). Chaetomium spp. colonization of barley following seed treatment and its effect on plant growth and Erysiphe graminis f. sp. hordei disease severity. Journal of Plant Diseases and Protection 105, 130-139.

Richter, Sabine (2002): Laboratory- and field-investigations about the efficacy and the insertion of Diadegma semiclausum Hellen against Plutella xylostella L. and Pteromalus puparum L. against Pieris rapae L. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn. The two lepidopterous pests small cabbage white, Pieris rapae (L.) (Lep., Pieridae), and diamondback moth, Plutella xylostella (L.) (Lep., Plutellidae), are able to destroy a large amount of the cabbage, which is cultivated in the region of the Rhein-valley. Increasing resistence of the pests against insecticides and the lack of indications for pesticides in the production of vegetables enlarge the further development of alternative methods to suppress the pests. To keep care to the farmer and the customer as well as to save the environment it is necessary to develop alternatives for the only use of chemical insecticides. The use of beneficial arthropods therefore reaches more and more importance as a harmless and purposeful method to control the pests. The present study deals with the biology, the ecology and the parasitation of two parasitoid wasps, which occur naturally in the Rhein-valley: Diadegma semiclausum Hellen (Hym., Ichneumonidae) is a solitary larvae-parasitoid of the diamondback moth, the gregarious parasitoid Pteromalus pupa-rum L. (Hym., Pteromalidae) attacks the pupa of the cabbage

white. The investigations were done to get information for the development of biologic strategies against both the lepidopterous pests. Aspects of the biology and the parasitation capacity of both parasitoid species were investigated under laboratory conditions with the aim of obtaining basic information for the biological control on cabbage. The maximum parasitation of D. semiclausum and P. puparum was observed at the beginning of the oviposition period. In the first half of the oviposition female offspring predominated over the male one, whereas more male parasitoids were produced towards the end of the oviposition. D. semiclausum showed the highest parasitic capacity when P. xylostella-larvae in the stages L2-L3 were offered. The number of hatched P. puparum-offspring was influenced by the age of P. rapae-pupae. Furthermore the reduced number of parasitized host-pupae dependent on the increasing interval between hatch and copulation of the parasitoid female was perceived. The studies with both parasitoid species leads to the use of those parasitoid females in the pest management, which are at the beginning of the oviposition. Their progeny is female biased and may parasitize further generations of the pest. In field trials the results of the laboratory studies were taken to get the optimum parasitoid density and the most favourable moment of release of the parasitoids. In all the three years of research a parasitation of the cabbage white and the diamondback moth was noticed in the week after the release. An important difference between the number of individuals in the single treated cabbage plots and in the control plots could be registered just at one place. The repeated releases of the parasitoids showed a better effect than to double the number of the inserted wasps, at which these results are statistically not significant. The combination of a parasitoid release and a chemical plant protection could be carried out at one place. A complete reduction of the pests was achieved only in the parts with insecticide spraying. In 1998 a distinct increase of parasitized pest individuals could be noticed in the plots with parasitoid releases against the control plots. During the three years a complete suppression of the population of both pest species in the field trials couldn t be achieved.

Saleh, Azzam (2002): Biological and ecological studies on the polyphagous predatory bug Dicyphus tamaninii WAGNER (Heteroptera: Miridae) as a natural enemy of the melon aphid Aphis gossypii GLOVER (Homoptera: Aphididae). Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 79 pages. The present research aimed to study the biology and prey consumption by Dicyphus tamaninii WAGNER (Heteroptera: Miridae) by feeding on different age groups of Aphis gossypii GLOVER (Homoptera: Aphididae) as prey at different temperatures in the laboratory. The host plant spectrum for oviposition by the predator was also investigated. Moreover, experiments were conducted to study the interaction of D. tamaninii with other natural enemies and the potential damage it might cause to cucumber. Finally greenhouse experiments were carried out in order to investigate the efficiency of the predator under more natural conditions. The results of the laboratory experiments showed that D. tamaninii was able to successfully feed, develop and reproduce when exclusively fed on A. gossypii as prey at a wide range of

low and high temperatures, however a constant temperature of 35+1°C was fatal to the predator. The predatory bug was able to adapt smoothly to fluctuating prey offer and maintain its capability of oviposition even when the prey was relatively scarce. The average daily prey consumption by the late nymphal instars as well as the adult stage of the predator on A. gossypii was high, where it reached up to 60 aphid/day by the adult female. Although D. tamaninii showed a clear affinity toward A. gossypii, it accepted also other important pest species offered as prey. Although cucumber, tobacco and tomato were preferred, the predatory bug seems to occupy a wide plant host range for oviposition. Despite being polyphagous, the predatory bug is not likely going to disrupt the efficiency of some other natural enemies in a biological control program. Investigating the plant-feeding habit of the predator showed that, D. tamaninii preferred leaves to cucumber fruits, a fact that leads to the conclusion that the potential damage to cucumber fruits by the phytophagous predator remains low. In the greenhouse experiments, it was found that the release of 2 D. tamaninii adults per plant was sufficient to achieve up to 90% reduction in A. gossypii population, when the predator was released 1 week after infestation with the aphid. Nevertheless, it is speculated that an earlier release of D. tamaninii would be more effective in the biological control of A. gossypii. In conclusion, D. tamaninii exhibited under laboratory as well as greenhouse conditions many features, which make the predatory bug a very promising natural enemy to be used in framework of a biological control program of the melon aphid on cucumber.

Schade-Schütze, Anja (2000): Occurrence and biological characterization of Fusarium species in wheat. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 161 pages. In 1995 - 1997 the incidence of Fusarium species and Microdochium nivale in conventional and organic wheat production in the Rhineland area was investigated. The influence of cultivar, nitrogen fertilization and application of fungicides on Fusarium head blight severity and mycotoxin contamination was assessed. The isolation rate of various Fusarium species and M. nivale from plant material was optimized using a selective growth medium (Czapek-Dox-Iprodion-Dicloran-Agar). Especially, for low infection levels the isolation rate of pathogens from grain samples was increased significantly. At harvest, the infection rate of wheat kernels by Fusarium species averaged less than 10 % for all trial sites, whereas kernels were infected by M. nivale by up to 30 %. In organic wheat production “Toronto” was the most susceptible cultivar tested, whereas “Batis”, with a satisfactory yield level, showed medium susceptibility. During the three years study F. avenaceum was the most common species detected in grains harvested at all sites; there was a tendency of increasing infection rates with F. poae. In organic farming the mycotoxin level of most of the grain samples was less than 40 µg deoxynivalenol /kg. An increase in the infection rate for Fusarium spp. was observed in crops that either received a higher amount of nitrogen fertilization or had been treated with fungicides including active

ingredients belonging to the strobilurines. In the latter case increased levels of deoxynivalenol were also assessed. For the biological characterization of Fusarium species and M. nivale the pathogenicity and virulence of five Fusarium species and M. nivale on leaves of different wheat cultivars and barley were measured. This method revealed a wide range in virulence among Fusarium species decreasing in the order, F. cerealis, F. culmorum, F. graminearum, F. avenaceum, F. poae and M. nivale. Furthermore, 27 isolates of F. culmorum were characterized using disease severity of had blight of wheat in inoculation experiments, the effect on thousand kernel weight, the virulence of isolates on primary wheat leaves as well as the growth rate on selective media. Analysing these parameters correlations between disease severity at BBCH and the reduction of the thousand kernel weight as well as between thousand kernel weight and the total amount of mycotoxins could be established. In general, deoxynivalenolproducing isolates of F. culmorum reduced the thousand kernel weight to a greater extent than nivalenol-producing isolates.

Schoene, Philip (2003): Ulocladium atrum as an antagonist of grey mould (Botrytis cinerea) in grapevine. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 104 pages. Plant diseases inhibiting cultivation of crops are typical of intensive agriculture and plant protection measures with frequent applications of pesticides are therefore required. Problems occur by using chemical pesticides: e.g. development of resistance to pesticides and sideeffects on beneficials and the environment, which calls for new strategies of crop protection. Botrytis cinerea (Pers.), one of the main pathogens in grapevine, Vitis vinifera L., is capable of infecting leaves, stems, flowers and fruits and reduces quality and quantity of yield. The saprophytic hyphomycet Ulocladium atrum (Pers.) proved to be antagonistic to B. cinerea in some crops, reducing growth and sporulation of the pathogen by competition for nutrients and space, limiting the epidemic spread of B. cinerea on plants and within the crop. The efficacy of U. atrum for biological control of grey mould in grapevine was assessed under controlled conditions and in field studies. The antagonist reduced the development of B. cinerea in vitro and on necrotic and healthy grapevine leaf material, respectively. U. atrum reduced spore production of the pathogen on mature grapevine berries as well as sporulation of sclerotia. Competition for nutrients and space proved to be the principal mode of action. The antagonist showed, similar to the pathogen, an ecological fitness persisting unfavourable climatic conditions under controlled conditions and in field experiments. Moreover, a low sensitivity of U. atrum to many pesticides enabled an integration of the antagonist into conventional crop protection measures. Direct combination with some pesticides as tank mixture resulted in a lower vitality of the antagonist and therefore reduced its efficacy. Nonetheless, alternating treatments with pesticides and the biocontrol agent are a potential strategy to enrich strategies of integrated crop protection. Large-scale experiments on biological control of grey mould by U. atrum were carried out in white grapes in 1997-99 in three German vine-growing areas. Three to four applications of the antagonist reduced B. cinerea effectively on plant tissue during the season and on berries at harvest. Furthermore, a reduced air-load of B. cinerea conidia was measured

before vintage in 1997. This indicates that an effect of U. atrum could be enhanced when the antagonist is applied over a much larger area. The potential of this biocontrol agent was shown applied alone or combined with botryticides. In all three seasons with low to moderately high disease pressure, grey mould was reduced by U. atrum alike chemical botryticide treatments. Nonetheless, at a high disease pressure of grey mould, an integrated approach together with chemical control and biological control measures should be envisioned. Negative effects of U. atrum were observed neither on plants, inflorescences and berries nor on vinification. Hence, the antagonist provides a suitable biocontrol agent for grey mould in grapevine, and it can be used in both, biological and integrated crop protection.

Scholz, Uwe (2001): Biology, pathogenicity and control of the cereal cyst nematode Heterodera latipons Franklin on wheat and barley under semiarid conditions, and interactions with common root rot Bipolaris sorokiniana (Sacc.) Shoemaker [teleomorph: Cochliobolus sativus (Ito et Kurib.) Drechs. ex Dastur.]. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 159 pages. The results are presented in eight chapters. The introduction (Chapter I) gives an overview about the agro-ecological conditions for cereal production in the Near East as well as literature review specifically related to the research topics investigated in this work. The second and third chapter describes the hatching behavior and life cycle of H. latipons. Experiments demonstrate the adaptation of H. latipons to low temperatures (5°C - 10°C) with maximum hatch of 45% of the cyst content per vegetation period. The juveniles of H. latipons emerge from the cysts in December and reach the highest concentration in soil in January and February. H. latipons multiplies on seminal and nodal roots of barley. The host range status of barley, oat, durum and bread wheat varieties is investigated in the fourth chapter. Almost 40% of the barley and most oat varieties of the International Differential Set for cereal cyst nematodes as well as the majority of barley varieties adapted to the Mediterranean environment are good hosts for H. latipons from the dry agro-ecological zone. All wheat varieties investigated are resistant to this population. Pathotype I from the dry zone is prevalent on barley and pathotype II from the wet zone is able to attack barley and wheat. In chapter V the pathogenicity of B. sorokiniana to barley under controlled conditions is demonstrated for the application of mycelium and conidia of the fungus. Pathogenicity is accompanied by severe infection of the crown of barley. The joint and separate impact of nematode and fungus on barley is investigated in chapter VI, VII and VIII. The early infection by H. latipons followed by B. sorokiniana nine weeks later as well as the simultaneous attack of nematode and fungus result in the strongest reduction of grain and straw yield and increased the B. sorokiniana infection of crown and subcrown internode compared to the application of the fungus alone. Under the presence of B. sorokiniana, the multiplication of H. latipons was reduced. H. latipons has a severe impact on grain and straw yield of barley under unrestricted water supply and a slight impact under drought stress, while the pathogenicity of B. sorokiniana is only expressed under drought stress conditions. Root length and root weight is reduced by the nematode under unrestricted

water supply and the fungus reduces root weight and root length as well as the number of heads under drought stress. H. latipons reduces the water use efficiency related to grain and straw yield regardless the water supply level, while B. sorokiniana reduces the water use efficiency only at unrestricted water supply. The damage threshold of H. latipons for barley and durum wheat is 5 e+j/g and 10 e+j/g soil in the dry and wet zone respectively. Barley and durum wheat grain yield is reduced in the dry and wet agro-ecological zone, respectively, while bread wheat tolerated the infection in both zones (Chapter IX).

Skrobek, Anke (2001): Investigations on the effect of entomopathogenic fungi on whiteflies. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 128 pages. The entomopathogenic fungus Paecilomyces fumosoroseus is well-known for its broad hostspectrum and efficacy against many kinds of insects. Although its effectiveness against soilborne arthropods has already been described over 100 years ago, Metarhizium anisopliae has only recently been cited as pathogenic to homopteran pests. In the present study different isolates of both microbial control agents were evaluated for their potential to control the whitefly species Trialeurodes vaporariorum and Bemisia argentifolii. Whiteflies are one of the most important arthropod pests of greenhouse and field crops, B. argentifolii occurring mostly in tropical and subtropical climates and T. vaporariorum being the pre-dominant species in Northern Europe. Many isolates of P. fumosoroseus and M. anisopliae, originating in different climatic regions, were found to be effective against all larval stages of both whitefly species. For the integration of this biological control agent into crop protection systems, a possible synergism between the entomopathogens and insecticides from the group of the chitin synthesis inhibitors was investigated. Although fungi and insecticide acted synergistically when applied with a time interval, control of whiteflies was not sufficient for an effective, practical pest control. In contrast, corresponding investigations on Spodoptera littoralis, the Egyptian cotton leafworm, gave high mortality levels and thus offered good prospects for reducing the pesticide input. Different oils, waxes and polymeric additives were examined for their ability to enhance the efficacy of the biological control agents. Two polymeric additives were found to increase the shelf-life at room temperature of conidia of M. anisopliae when conidia were dried within the formulation. Microscopical studies using fluorescence, low temperature scanning electron and confocal laser scanning microscope indicated positive effects of Addit ® (Koppert, Netherlands) and a polymeric additive on the distribution of formulations –and hence conidiaon leaf and insect surfaces. Spore germination, speed of kill and mortality of the target insect were also found to be enhanced. Both additives offered good prospects for optimising the efficacy of entomopathogenic fungi against B. argentifolii and T. vaporariorum, thus indicating high potential for the integration in the framework of an IPM strategy.

Stierl, Reinhard (1999): Comparative Investigations of the Mechanisms of Induced Resistance. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 107 pages. The mechanisms of chemically induced resistance to Alternaria solani, Phytophthora infestans and Oidium lycopersium in tomatoes were investigated and compared. These phytopathogenic fungi differ fundamentally in their life-cycles and modes of nutrition. The resistance inducers used were Dichlorosalicylic acid (DCSA), Dichloroisonicotinic acid (DCINA), Benzothiadiazole (BTH), ß-Aminobutyric acid (BABA) and a synthetic inducer designated RI 108. In greenhouse experiments with P. infestans all the inducers caused clear reductions in the severity of infection, which were also largely reproducible in field trials. With the exception of RI 108, the inducers were also able to reduce infection by O. lycopersium. They were least effective against A. solani and in some experiments no effects could be observed with this organism. The application of BABA invariably failed to induce any degree of resistance to A. solani. The mechanisms of induced resistance at the cellular level were investigated using conventional light and fluorescence microscopy and confocal laser scanning microscopy. On DCSA-, DCINA- and BTH-treated leaves the penetration of O. lycopersium was almost completely prevented by the increased formation of papillae, whereas BABA treatment reduced penetration without any visible plant reaction. Reduced penetration by P. infestans could also not be attributed to stronger papillae formation. The limited development of both O. lycopersium and P. infestans on induced resistant plants could mainly be attributed to the hypersensitive response of infected cells. In contrast, hypersensitive responses were not able to restrict the development of A. solani. Timed investigations revealed that cytoplasmic aggregation and alterations in the cytoskeleton were already evident in the cells of induced plants during the penetration phase. These reactions, which are probably the earliest symptoms of the defence mechanism, occurred sooner and more strongly in induced plants. This indicates improved pathogen recognition in induced plants. The differences in the frequency and efficacy of papillae formation and of the hypersensitive response to different pathogens indicate that, in addition to the penetration event itself, induced defence reactions are also influenced by the life cycle and mode of nutrition of the pathogen. It must therefore be concluded that induced resistance cannot be attributed to a single mechanism.

Terhardt, Josef (1999): Influencing microbial communities of the rhizosphere through the treatment of plant leaves and biological control of Fusarium oxysporum f. sp. lycopersici and Meloidogyne incognita with bacterial antagonists. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 136 pages. The text is divided into four chapters. Chapters A an B deal with influenncing microbial communities of the rhizosphere through the treatment of plant leaves. Chapter A refers back

to the plate count method. Individual variations in leaf treatment led to the changes in the combination of the rhizosphere community, in that a portion of the pseudomonads in the total amount of bacteria increase over time. In chapter B, alternative methods of characterizing microbial communities, including gas chromatography analysis of fatty acids, will be presented. The potential of double analytical approaches will be tested in thorough examinations, for example, analyzing the fatty acid composition of the phosholid fraction previously extractet from bulk soil or combining fatty acid analysis with the dilution plate count method, and compared to various microorganism communities from soil extracted from both potato und bean plots. With assistance from principal component and cluster analysis, the differences in the fatty acid spectra can be identified, and thereby the relevance of individual fatty acids can be derived. The resulting information would then be used as follows in the examinations to determine the influence of leaf treatments. The effects of individual leaf treatment substances (Milsana and Bion) on the microbial rhizosphere communities could be shown with the aforementioned techniques. Possibilities and limits of the fatty acid analysis method will be discussed. Chapter C describes the examinations to biologically control Fusarium oxysporum f. sp. lycopersici with the help of antangonistic bacteria. Of the 62 tested bacteria types, three showed a repeated reduction in the re-isolation rates of the pathogenic mold from the plant tissue when compared to the control group. Expanded examinations of the gas-exchange, chlorophyll content, and chlorophyll fluorescence as well as the organic substances of the plants will be caried out. Chapter D describes an ad planta test against the root-knot nematodes Meloidogyne incognita following the application of bacteria in the rhizosphere of the plants. Here, one bacteria type led to a reduction in root galls. Five samples reduced the number of egg sacs. A completed leaf treatment test with Bion and jacmonic acid had no impact on the intensity of nematode root infestation.

Weickel, Barbara (1997): Studies on the isolation, identification and biological characterization of arbuscular mycorrhizal fungi. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 116 pages. Arbuscular mycorrhizal fungi show differences in their infectivity and symbiotic activity. The aim of this study was to identify criteria for the biological characterization of mycorrhizal fungi that are relevant for practical use of the symbiosis. The influence of various factors on mycorrhizal formation where investigated to demonstrate their impact on the symbiotic efficiency. Arbuscular mycorrhizal fungi of the genus Glomus were isolated from different soils and cultivated using trap plants. Taxonomic classification was carried out on the basis of morphological and biochemical characteristics of the chlamydospores. Morphological features were described using the Expert System of the European Bank of Glomales (BEG) as a reference. The isozyme profiles after native polyacrylamide gel electrophoresis (PAGE) and the RFLP patterns of PCR-amplified ITS-DNA were used for molecular identification of Glomus-species.

In greenhouse experiments, the isolates were differentiated in their dynamics of development, infection rates and symbiotic efficiency. The inoculation of different host plants with a Glomus caledonium isolate significantly increased plant growth. Differences in the metabolic activity of mycorrhizal fungi were detected after histochemical staining for enzyme activities in the intraradical and extraradical fungal structures. The expression of fungal metabolic activity in relation to plant development is discussed. Isozyme analysis was used for isolate-specific detection of mycorrhizal fungi in the roots of the host plant. Mycorrhizaspecific malate dehydrogenases showed clear differences to host plant isozymes. Their occurrence and intensity were related to the fungal development stage. The pre-inoculation of Allium cepa with an isolate selected on the basis of the greenhouse data clearly improved mycorrhizal formation and plant growth in the field. The described approach can be useful in screening-programs for inoculation potential of mycorrhizal fungi.

Wissing, Albert (2000): Movement of Vydate (a. i. oxamyl) at insecticidal and nematicidal/nematostatic concentrations to the site of action and the effect on pests and the plant. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 150 pages. The integration of several control strategies for managing plant-parasitic nematodes and foliar feeding pests is a necessary approach to minimise potential environmental contamination with chemical plant protection agents. The possibility of a multiple delivery of pesticides via a drip irrigation system provides an effective strategy to position minimised amounts of the active agent by means of the tubing close to the plants near the target soil region of highest root and nematode abundance. Oxamyl (Vydate, E. I. Du Pont de Nemours & Co. Inc.), as a highly water-soluble and systemic nematicide, insecticide and acaricide provides an effective tool in this drip irrigation strategy to give agricultural and horticultural crops an all-round protection against sub-terrestrial nematodes and a wide range of aerial sucking and piercing pests. To optimise this strategy for effective pest control and a minimum burden for the environment it is imperative to understand the systemic movement capabilities of oxamyl in the crop itself. It is necessary to quantify the amount of active ingredient moving in time acropetal in the apoplast (upwards in the xylem) and basipetal in the symplast (downwards in the phloem) of the plant. This study demonstrates very pronounced systemic properties of the active agent oxamyl. Applied to the soil it is taken up passive and quantitatively very efficient by the plant root system. The translocation in the plant flows primarily to the sites of highest transpiration, the main metabolic source regions of the growing plant. The subsequent accumulation of oxamyl in the vascular tissue above the applied concentration level guaranties a high lethal effect against pests at the site of action in the foliage. The foliar pest control after soil application is obtained in a short time. A comparison of the extent of pest control after a corresponding foliar application reveals limited systemic translocation between different foliar plant levels at insecticidal concentrations, but apparent sufficient basipetal movement of oxamyl for root protection against nematode invasion. For effective plant protection against nematodes a prophylactic treatment is imperative.

These conclusions on the movement of oxamyl in the plant are based on various analytical and in vitro experiments. Furthermore ad planta bioassays in a special designed, multifunctional test system, in which several pest groups (nematodes, insects and acaria) were combined on different test plant species, demonstrated the oxamyl distribution in the plant. Studies on insects and acaria in a ‘biomembrane feeding system’ and experiments with radiolabelled 14C-oxamyl, inter alia in a ‘split-root system’ on tomato against Meloidogyne incognita, provided intrinsic information on the unique systemic properties of oxamyl. According to the results with radiolabelled oxamyl in the ‘split-root system’; it was evidenced that not only oxamyl or any radioactive degradation product elicits the plant protection against nematode species at the roots. Based on this conclusion different hypothesis on possible supplementary modes of plant protection against nematodes by oxamyl are described. Plant growth stimulation has been reported to take place after a treatment with oximecarbamates in absence of nematodes or other major pests or pathogens. This “carbamate effect“ was examined for oxamyl and other nematicides, but it has been shown to occur not in all plant growth situations.

Zegula, Thorsten (2004): Suitability of different predatory arthropod species for the biological control of Frankliniella occidentalis (PERGANDE) (Thysanoptera: Thripidae) and a survey of the spreading of Thrips palmi KARNY (Thysanoptera: Thripidae) in European greenhouses. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 89 pages. The aim of the present study was to assess the suitability of different predatory arthropod species for the biological control of the western flower thrips Frankliniella occidentalis (PERGANDE) (Thysanoptera: Thripidae) under greenhouse conditions. Furthermore, the introduction of the melon thrips, Thrips palmi KARNY (Thysanoptera: Thripidae) - a quarantine pest - into Europe was investigated via literature reviews and a survey of the quarantine offices of various European nations. In the laboratory experiments, twelve predatory mites, two predatory thrips and five predatory bugs were taken into stock culture as potential beneficial arthropods. Later on, experiments on the biology, reproduction and predation with F. occidentalis and T. urticae as prey were conducted. All the predatory mites developed by exclusive feeding on F. occidentalis larvae, except C. fortis, C. malaccensis and E. addoensis. Reproduction of A. cucumeris was highest by exclusive feeding on F. occidentalis larvae and lowest for A. womersleyi and A. degenerans. C. malaccensis was not able to lay eggs with this prey. Despite their small size the predatory mites showed good predation success. During the 18-day experimental period, the prey consumption was highest in E. addoensis and A. cucumeris. The predatory thrips F. vespiformis developed with F. occidentalis larvae as prey. On the contrary, A. intermedius could not develop with this prey species. While F. vespiformis was able to lay eggs with F. occidentalis larvae as prey, A. intermedius was not able to do so. Both the thrips species proved themselves to be more efficient predators against F. occidentalis larvae than the predatory mites during the experimental period. The five predatory bugs could develop completely by feeding alone on F. occidentalis larvae. The daily reproduction period was

lower in D. tamaninii and M. pygmaeus than in the three Orius species. The prey consumption was clearly higher in the predatory bugs than in the predatory mites and predatory thrips. In the greenhouse experiments, population development of F. occidentalis was recorded in the years 1999 - 2001. Infestation by the pest thrips showed great differences in the threeyear study period due to the variations in plantations and operations. For the experiments on the suitability of the biological control of F. occidentalis under greenhouse conditions a predatory thrips (F. vespiformis), a predatory mite (A. cucumeris) and two predatory bug species (D. tamaninii, M. pygmaeus) were selected. In the present studies, the predatory mite showed no effect against the pest thrips. However, the release of the predatory thrips F. vespiformis as well as that of the predatory bugs D. tamaninii and M. pygmaeus yielded satisfactory results. The results of the survey of the introduction of and damage by the quarantine pest T. palmi revealed that this pest has been introduced to the Netherlands, Slovakian Republic and in England. Additionally, sporadic appearances have been reported in Poland. However, since all infested crops were properly disposed of, establishment of the pest has not been recorded in Europe, to date.

Zens, Irene (2000): Occurrence and control of root of sugar beet caused by Rhizoctonia solani. Institute for Plant Diseases, Faculty of Agriculture, University of Bonn, 120 pages. The symptoms of root rot of sugar beet frequently affect single plants and cause losses that are negligible. For a few years in Germany extensive damages become apparent. The causative agent is member of the complex of pathogens Rhizoctonia solani. It is a world-wide known and extremely diverse fungus occurring in numerous biotypes. In this paper the root rot pathogen was characterised and first attempts of control were elaborated. The german pathogen was assigned to anastomosis group AG 2-2. This AG was even isolated in very early stages of growth of sugar beet. The AG 2-2 can be subdivided according to the most common host plants into AG 2-2IIIB, a ´gramineae-type´ and AG 2-2IV characterised as ´chenopodiaceae-type´. Investigations into the root pathogen by means of RAPD-PCR showed that further subgroups within AG 2-2 can be differentiated. Out of these the majority was assigned to the ´gramineae pathogen´. This type furthermore was isolated from fields with high losses much more frequently. Biological characteristics supported the importance of differentiating several types. They did not only differ in temperature tolerance but also in fungicide sensitivity and especially virulence. In a single attacked field in spite of distant disease patches a very homogenous population was proofed. This population consisted of a single pathotype remaining unchanged over a period of several years. The reason could be that either the predominant type suppressed other ones or these types occurred in so small frequencies that detection was impossible with the employed methods. Corresponding types appeared not only within different fields but also in different sites of Germany and the Netherlands. Distant fields showing the same pathotype showed further common qualities. With a high percentage of maize in the rotation isolation frequency of type 4 increased. This type was classified as particularly aggressive against sugar beet seedlings in ´mini tests´ and

caused the largest damages in the fields. Rhizoctonia solani AG 2-2 owns a great potential of damage. However in Germany hitherto protection of plants is restricted to indirect control. The occurrence of diverse pathotypes is problematic for control means. It is imaginable that even resistant sugar beet cultivars become less effective when a new pathotype becomes predominant. Spraying of fungicides showed some success but only with high application rates. For this reason seed treatments with the antagonistic bacterium ´FZB24´ and several fungicides were tested. The disease suppressive effect of seed dressing was provable up to the end of the growing season. Combinations of fungicides and antagonist especially were effective. Spraying of fungicides targeted on the seed line a few centimetres under the soil surface, the depths where sugar beets are attacked first, was evenly successful.