The predominant causers of root rot in Vojvodina are fungi from ... 2000â2005, on the territory of Vojvodina, the frequency of Rhizoctonia solani in phytopat-.
Zbornik Matice srpske za prirodne nauke / Proc. Nat. Sci, Matica Srpska Novi Sad, ¥ 110, 103—108, 2006 UDC 633.63:632.4(497.113)
V e r a B. S t o j š i n1, F e r e n c F. B a g i1, S t e v a n M. J a s n i ã2, F e r e n c F. B a l a ÿ1, D r a g a n a B. B u d a k o v1 1 2
Faculty of Agriculture, Department of Plant and Environmental Protection Dositeja Obradoviãa 8, 21000 Novi Sad, Serbia and Montenegro Scientific Institut of Field and Vegetable Crops, Maksima Gorkog 30, 21000 Novi Sad, Serbia and Montenegro
RHIZOCTONIA ROOT ROT (RHIZOCTONIA SOLANI K Ü H N.) OF SUGAR BEET IN PROVINCE VOJVODINA* ABSTRACT: Sugar beet root rot appears regularly each year, but its intensity depends on agro ecological conditions. The predominant causers of root rot in Vojvodina are fungi from Fusarium genus and species Macrophomina phaseolina. Over the last couple of years, more intense occurrence of Rhizoctonia root rot has been observed. Rhizoctonia solani, the causal agent of root rot is present in sugar beet fields. During 2000—2005, on the territory of Vojvodina, the frequency of Rhizoctonia solani in phytopathological isolations from rotted sugar beet roots was between 0,0—18,2%. The intensity of the disease depends on localities, agro ecological conditions and genotypes. Symptoms of Rhizoctonia root rot were registered at some localities in all regions of Vojvodina: Srem, Banat and Baåka. The disease appearance is above all local. It occurs in small patches, on heavy, non-structured soil and on depressed, wet parts of plots. Individual diseased plants can be found during July. Brown rot appears on sugar beet roots, with dried tissue on surface, which is present on the tail as well as on the middle part and the head of root. Tissues with described symptoms are deeper regarding the healthy part of root. On vertical root section, the necrotic changes are clearly visible comparing to tissue section without symptoms. The heavily infected tissue forms fissures on roots in most cases. Besides the above-mentioned symptoms on roots, the plant wilting and leaf handle necrosis as well as leaf dying are also observed. When rot spreads to the whole root head, plants quickly die. KEY WORDS: distribution, aetiology, Rhizoctonia root rot, Rhizoctonia solani, sugar beet, Vojvodina
INTRODUCTION Various types of rot on sugar beet root have become more and more frequent in the last couple of years and have caused economically significant losses in our country (S t o j š i n, 2003, M a r i ã and S t o j š i n, 2004). * The paper was presented at the first scientific meeting IV INTERNATIONAL SYMPOSIUM ON SUGAR BEET Protection held from 26—28 september 2005 in Novi Sad.
There are a lot of available data on parasites that cause root rot. The first noteworthy occurrence and greater losses were registered during 1960s in Banat and the north part of Baåka (M a r i ã et al., 1970). Later, in the last decade of 20th and at the beginning of 21st century, root rot occurred, usually in dry years, when it caused economically significant losses which manifested in decrease of yield and digestion. According to many authors (M a r i ã et al., 1970, S t o j š i n et al. 2001, J a s n i ã et al., 2001, J a s n i ã et al., 2004, P e j o v i ã et al., 2003, M a r i ã and S t o j š i n, 2004, S t o j š i n, 2003), Fusarium root rot is the most important root disease in our country. This one, together with charcoal root rot (Macrophomina phaseolina) causes huge damages on sugar beet, especially in dry years (M a r i ã et al., 1970, S t o j š i n, 1993, S t o j š i n, et al., 1999). Other species like Thanatephorus cucumeris (anamorphic Rhizoctonia solani) — Rhizoctonia root rot, Erwinia carotovora — causal agent of bacterial soft rot, Streptomyces scabies — the causal agent of scab root, Pleospora bjoerlingii (anamorphic Phoma betae) — seedling damping-off, etc. appear from time to time on individual plots or isolated plants and they are not harmful to sugar beet in Vojvodina (M a r i ã and S t o j š i n, 2004). Nevertheless, some authors claim that Rhizoctonia root rot (Rhizoctonia solani) is spread in Vojvodina and that it can cause significant losses in some years, especially in Srem (V i c o et al., 2004). MATERIAL AND METHODS Collecting root samples Root rot was evidenced in more localities in Vojvodina and was being followed during vegetative periods in years from 2000 to 2005. In order to diagnose and identify the cause of root rot and to examine symptoms of decay, sample roots with symptoms of the rot were collected from different localities. The roots were selected randomly and the part of roots with typical symptoms was used for isolation and determination of parasites that cause rot. Isolation Phytopathological isolations were done by standard procedure, which means isolation on Potato Dextrose Agar (PDA) medium, in Petri dishes and incubation in thermostat at 25°C. After the colony development, isolates were transferred in order to get pure cultures and to determine the fungus. Determination Isolates were determined as Rhizoctonia solani on the base of morphology of vegetative and generative organs (B a r u c h, S. et al., 1998). 104
THE RESULTS AND DISCUSSION Phytopathological isolations During experimental period, Fusarium species were predominant pathogenes which caused sugar beet root rot in Vojvodina (40,8%). Species like Macrophomina phaseolina (2,86%), Rhizoctonia solani (8,94%) and other fungi genera were registered in lower percentage (19,76%) (Table 1). Table 1. Isolation from diseased sugar beet roots in different locations in Vojvodina (2000—2004) Isolated fungi (%)
Number of diseased roots
Others saprophytic organisms
Symptoms of Rhizoctonia root rot The first symptoms which could be noticed on diseased plants are sudden chlorosis and wilting of leaves. Black necrosis of leaf stems appear, especially on leaves close to the root head. Faded, wilted leaves quickly collapse and form brown to black rosette, which is present throughout the whole vegetative period. Root rot can be complete or partial. Brown to black parts of tissue appear on diseased root. They can unify and capture one part or the whole root. Deep fissures are usually located near the head of the root. In humid conditions, tissue can soften and symptoms of wet rot are present then. Another type of symptom is dry rot, which manifests itself in lesions which are light and dark brown, in the shape of concentric circles. Under the lesions, parasite mycelium is formed with clearly distinguished margins between healthy and diseased tissue. DISCUSSION Intensity of Rhizoctonia root rot depends on the large number of biotic and abiotic factors. The degree of disease caused by R. solani depends on the amount of inoculum in the soil, time of infection, environmental conditions (temperature and humidity) and include physical, chemical and biological characteristics of the soil (B u d d e r m e y e r and P e t e r s e n, 2004). Rhizoctonia root rot more frequently appears on heavy, non-structured soils as well as on depressed, wet parts of the soil with high level of underground water. Para105
site causes greater losses when sugar beet is grown (B u d d e r m e y e r and P e t e r s e n, 2004) in monoculture (inadequate crop rotation) or in frequent breeding on one parcel only (M a r i ã, 1992, B u d d e r m e y e r and P e t e r s e n, 2004, W e s t e r d i j k et al., 2004). Therefore, concerning all these reasons, it is necessary to use integrated control to fight Rhizoctonia root rot, caused by R. solani. These means that control should include improved cultivation practice, then the use of fungicides as well as biological means of control against the disease. One of the most important measures concerning cultivation practice is crop rotation. On the parcels where sugar beet is grown in monoculture, the percentage of Rhizoctonia root rot is significantly higher, while on those parcels with preceding cereal crops (wheat or barley) or grasses, the frequency of diseased plants is much lower (W e s t e r d i j k et al., 2004). On compacted soil the intensity of the disease is higher. That is why soil impacting and compressing should be avoided. Soil for sugar beet breeding needs to be loose and well-aerated. Also, it is recommended to breed resistant sugar beet variants, since the resistant genotypes exist. However, environmental conditions and the amount of inoculum can effect the resistance degree. Seedlings of resistant sugar beet variants are usually very susceptible to the parasite (W e s t e r d i j k et al., 2004). With the purpose of seedling protection chemical measures are recommended. These measures include fungicide treatment of the seeds as well as chemical treatments of young plants. The treatment of young plants with the fungicides on the basis of strobilurin (active substance is azoxystrobin, commercial product Quadris) turned out to be a very successful one. According to the results of S t u m p and F r a n c (2003), the use of strobilurin decreases the appearance of root rot in 41—81% and increases yield 3—4 times comparing to non-treated control in the conditions of artificial inoculation of sugar beet in field. Seed treatment with protective fungicides (Maneb, Mankozeb and Tiram) is efficient in seedling protection. Biological measures against damping-off and flattening of the seedlings, since they are non-resistant to R. solani are usually recommended and they include seed treatment with spore suspension of Trichoderma virens fungus. Some of these isolates express high efficiency against seedling damping-off ( H a n s o n, 2003). It is well known that fungus from Trichoderma genus form antibiotics, which inhibit the development of other fungi species (H o w e l l et al., 1993). T. harzianum manifests activity against Rhizoctonia root rot, but it does not affect damping-off and flattening of seedlings (R u p p e l et al., 1983).
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RHIZOCTONIA SOLANI K Ü H N. PROUZROKOVAÅ MRKE TRULEŸI KORENA ŠEÃERNE REPE U VOJVODINI Vera B. Stojšin1, Ferenc F. Bagi1, Stevan M. Jasniã2, Ferenc F. Balaÿ1, Dragana B. Budakov1 1 Poqoprivredni fakultet, Trg D. Obradoviãa 8, Novi Sad, Srbija i Crna Gora 2 Nauåni Institut za ratarstvo i povrtarstvo, Maksima Gorkog 30, Novi Sad, Srbija i Crna Gora Rezime Truleÿ korena šeãerne repe javqa se svake godine u slabijem, ili jaåem intenzitetu, pre svega u zavisnosti od agroekoloških uslova. Dominantni prouzrokovaåi truleÿi korena šeãerne repe u našoj zemqi su gqive iz roda Fusarium i Macrophomina phaseolina. Posledwih godina uoåena je intenzivnija pojava mrke truleÿi korena šeãerne repe prouzrokovane od strane Rhizoctonia solani. Rhizoctonia solani, prouzrokovaå mrke truleÿi korena, prisutna je na poqima pod šeãernom repom. U periodu 2000—2005. na teritoriji Vojvodine zastupqenost gqive Rhizoctonia solani u fitopatološkim izolacijama iz korena sa simptomima truleÿi bila je u intervalu 0,0—18,2%. Intenzitet pojave oboqewa zavisi od lokaliteta, vremenskih uslova i genotipa. Simptomi mrke truleÿi korena registrovani su na pojedinim lokalitetima Srema, Banata i Baåke. Oboqewe se pre svega javqa lokalno, u mawim oazama na parcelama, na teÿim nestrukturnim zemqištima, kao i zabarenim delovima wiva. Pojedinaåne obolele biqke se nalaze tokom jula. Na korenu šeãerne repe javqa se tip simptoma mrke, suve truleÿi na površini tkiva, koja se javqa kako na repnom, tako i na sredwem delu i glavi korena. Tkivo sa opisanim simptomima je ugnuto u odnosu na zdravo. Na uzduÿnom preseku korena uoåava se smena mrkog, nekrotiånog tkiva, sa tkivom bez vidqive promene boje. Jaåe zaraÿeno tkivo kod veãeg broja uzoraka puca stvarajuãi pukotine na korenu. Pored opisanih simptoma, uoåava se i pad turgora, nekroza i truleÿ osnova lisnih drški i sušewe lišãa. Kada truleÿ zahvati åitavu glavu korena, biqke ubrzo ugiwavaju.