Effect of Common Cultural Practices on Septoria Leaf Blotch Disease and Grain Yield of Irrigated Durum Wheat Salah Rezgui, Institut National Agronomique de Tunisie, 43 Avenue Charles Nicolle, 1082 Tunis, Tunisia, Mohamed Moez Fakhfakh, Centre Technique des Céréales, 8170 Bou Salem, Tunisia, Samah Boukef, Azza Rhaiem, Mohammed Chérif, Mejda Chérif, Institut National Agronomique de Tunisie, 43 Avenue Charles Nicolle, 1082 Tunis, Tunisia, and Amor Hassine Yahyaoui, International Center for Agricultural Research in the Dry areas, P.O. Box 5466, Aleppo, Syria ____________________________________________________________________________ ABSTRACT Rezgui, S., Fakhfakh, M. M., Boukef, S., Rhaiem, A., Chérif, Mo., Chérif, Ma., and Yahyaoui, A. H. 2008. Effect of common cultural practices on Septoria leaf blotch disease and grain yield of irrigated durum wheat. Tunisian Journal of Plant Protection 3: 59-67. Using alternative cultural practices could be an attractive option to reduce fungicide without impairing Septoria leaf blotch disease (caused by Mycosphaerella graminicola, anamorph: Septoria tritici) control in irrigated durum wheat fields. Association between common cultural practices and disease related traits were assessed from data collected on a sample of 48 durum wheat fields. Results suggested that relying exclusively on one component rather than integrating a combination of practices is not cost effective to alleviate Septoria leaf blotch disease impact on grain yield. Disease severity increase was attributed to the extensive use of a susceptible cultivar “Karim”, early sowing, higher seeding rate, on farm produced seeds, greater nitrogen rates, and an ineffective fungicide application explaining 81.7% of the total variability of the surveyed durum wheat fields. Fungicide application reduced Septoria leaf blotch disease infection and its spread in treated fields but did not prevent infection. Fungicide application effect was lower for both low (less than 10%) and high (greater than 60%) severity, but it was effective when severity ranged from 40% and 50%. Lower critical Septoria leaf blotch disease threshold ranging between 10 to 20 % appeared to be adequate in reducing Septoria leaf blotch disease impact on grain yield. The study shows that lack of disease damage assessment is the most important component of farmers’ decision-making process with regard to the treatment dates and number of fungicide applications. Implementing a suitable integrated Septoria leaf blotch disease management program in irrigated durum wheat areas should be sought by varying cultural practices options. Keywords: cultural practices, durum wheat, Septoria leaf blotch disease, yield
____________________________________________________________________________ Durum wheat (Triticum turgidum subsp. durum) is commonly grown in the sub-humid and semi-arid areas of Tunisia. The new cultivars are often characterized
by a high grain yield and are more responsive to increased seeding rates, added nitrogen fertilizer use, additional irrigation and a relatively appropriate weed control techniques. These practices are commonly encountered in the sub-humid and irrigated farming systems. However, these crop management practices could
Corresponding author: S. Rezgui
[email protected] Accepted for publication 13 May 2008 Tunisian Journal of Plant Protection
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enhance disease severity caused by Septoria leaf blotch disease of durum wheat caused by Mycosphaerella graminicola (anamorph: Septoria tritici) and reduce grain yield. This effect is more pronounced when integrated control measures are lacking causing grain yield losses ranging from 30% to more than 70% (6, 7, 12). Farmers in Tunisia have substantial difficulty in managing Septoria leaf blotch disease despite the significant yield losses attributed to this disease. Septoria leaf blotch disease incidence and severity are partly attributed to changes in cultural practices and to the extensive use of early and semi-dwarf high yielding durum wheat cultivars (4). It has been reported that increased nitrogen application and early seeding date are among the principal factors that enhance disease development (14, 16, 22). This investigation aims to determine potential association between farmers’ practices and Septoria leaf blotch disease related traits and to estimate the relationship between Septoria leaf blotch disease severity and grain yield loss assessed in treated and untreated durum wheat fields using survey based data.
Mornaguia, Tebourba and Djedeida where the rainfall during 2006/07 cropping season ranged from 550 to 620 mm. Most of the surveyed farmers used supplemental irrigation. The average irrigated area ranged from 5 to 285 ha depending on the farm size. Data relative to farm size, common cultural practices such as nitrogen and phosphorus rates, cultivar used, planting date, seeding rate and fungicide application were considered in the data matrix for each farmer’s field. Septoria leaf blotch disease incidence was estimated based on 10 to 20 sample units selected from spots scattered throughout each field area. Disease density and severity were estimated based on a sample of 20 plants randomly selected from the middle of each field. Leaves were collected from different leaf plant tiller using a fine scale transect scheme. The 20 sample units were achieved along four parallel transects separated by 20 meters (15).This sampling was carried out twice during the wheat growing season, at flowering and prior to maturity. Average disease scores from both sampling dates were assessed for each field. Twenty flag leaves from each sample taken from fungicide-treated and from untreated fields were evaluated using an evaluation scale (17), describing the relative proportion of the size of lesions compared to the total of leaf area, and average percentages of necrosis were used to estimate Septoria leaf blotch disease severity. At harvest, grain yield was estimated based on samples of 4 to 6 independent scores of each field. Yield estimates from each field were provided by two extension service personnel and by three to four farmers. Average grain yield was then adjusted to the field’s owner estimation. In order to characterize durum wheat fields based on cultural practices, disease components and grain yield, and to determine potential correlations between
MATERIALS AND METHODS A data based on a survey of 48 irrigated durum wheat farmer’s fields located in the sub-humid region of Northern Tunisia were used in this investigation. These areas were selected based on the prevalent occurrence of Septoria leaf blotch disease across years to determine possible associations between the common cultural practices used by farmers and Septoria leaf blotch disease severity. All surveyed areas are characterized by rainy and mild to cool winter season; humid and warm spring conferring favorable conditions for the development of Septoria leaf blotch disease. These farms are located at Tunisian Journal of Plant Protection
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these three factors, factorial correspondence analysis using the “Proc Corresp” procedure of SAS (18) was carried out. Quantitative data included farm size (ha), disease components (incidence, severity, disease density (%), grain yield (q/ha), and total production costs (TD/ha), along with qualitative data included as binary values (0,1) (cultivar used: susceptible durum wheat cultivar “Karim” used:1 and 0 otherwise; sowing date: early sowing:1 and 0 otherwise; seed source: certified seeds used:1, farmers’ seeds used: 0; seeding rate: equal to recommended (140 kg/ha):1 and 0 otherwise; fungicide treatments where a value of 1 is attributed to treated fields and 0 to untreated fields) were considered in this analysis. Correlation coefficient between the size of the area sown, fertilizers (nitrogen and phosphorus rates expressed as units/ha) and seed rates as well as disease components was carried out using the “Proc Corresp” procedure of SAS (18). In order to estimate the relationship between grain yield and severity, the “Proc Nonlin” procedure of SAS (18) was used and the decay function GY=αe-rSEV , where α is the grain yield at the zero severity level and r the relative grain yield loss per unit of severity increase, was estimated.
represent only 13% and 3% respectively. The responsiveness to additional inputs and greater yielding ability explained partly the adoption of this susceptible cultivar “Karim” to Septoria tritici. The associations between the total sown area, cultural practices (seeding rates, phosphorus and nitrogen application rates) and disease related traits (Septoria leaf blotch disease incidence, density and severity) are summarized in Table 1. Increased sown area is negatively associated with seeding rates, nitrogen application and all Septoria leaf blotch disease related traits with a correlation coefficient ranging from -0.34 to -0.47. Seeding rate is positively associated with nitrogen and all disease related traits with a correlation coefficient (r) ranging from 0.76 to 0.85, and it is negatively associated with grain yield (r = -0.63) . Negative correlation coefficients are noted between grain yield and Septoria leaf blotch disease severity (r = -0.87), incidence (r = -0.82) and density (r = 0.69); whereas all the disease related traits are positively associated. Results of factorial correspondence analysis describing the contribution of cultural practices on Septoria leaf blotch disease severity and grain yield variability in the sampled durum wheat fields are summarized in Table 2. The results of correspondence analysis showed that two factors explained most of the variability (82.7%). The area sown to durum wheat, disease severity, nitrogen rate, and grain yield are highly associated with the first factor explaining 63.02% of the total variability (Table2). Moreover, farm produced seeds and early sowing are associated with the first factor (with r = 0.663 and r = 0.667 respectively) and appeared to promote Septoria leaf blotch disease development on the cultivar “Karim”. The second factor contributed with only 19.7% to the total variability and
RESULTS Survey data showed that over 61% of the total cereal area is sown to durum wheat (Fig. 1) whereas the area sown with bread wheat, barley and oat represents 12%, 15%, and 12% respectively. The crop diversification in the irrigated cereal growing areas is very limited because of a lack of forage crops and food legumes crops. Fig. 2 showed that among the durum wheat cultivars used by farmers, the cultivar “Karim” covers over 84% of the total durum wheat area whereas areas sown with “Razzak” and “Khiar” cultivars Tunisian Journal of Plant Protection
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Proportion of crop area (%)
is particularly explained by total input costs (r = 0.537), fungicide frequency (r = 0.203) and to a lesser extend grain yield variability (r = 0.537). However, the application of fungicide and its contribution to the total production cost is found the most discriminating component. Differences in the relationships between disease severity and grain yield for both fields were illustrated in Fig. 3. A negative non linear relationship between grain yield and Septoria leaf blotch disease
severity in these fields is obtained. The average grain yield decrease per severity unit in untreated fields represented twice as much as that noted in treated fields. However, at severity levels ranging from 0 to 10%, a grain yield of 6 t/ha is obtained in both treated and untreated fields. Greater fungicide efficiency is obtained at severity level less than 20%. Maximum grain yield losses of 2 and 0.7 t/ha were noted at severity ranges of 30% to 55% and superior to 70% respectively.
70 60 50 40 30 20 10 0 Durum Wheat
Bread Wheat
Barley
Oat
Cereal crops
Fig. 1. Distribution of the area sown with the main cereal crops.
Fig. 2. Proportion of durum wheat cultivars used by farmers.
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Table 1. Correlation coefficients between Area sown (A),Seeding rate (SR), Phosphorus rate (P), Nitrogen rate (N), Disease severity (S), Disease incidence (I), Disease density (DD) and Grain yield (GY) A SR P N S I DD (ha) (kg/ha) (kg/ha) (kg/ha) (%) (%) (%) SR - 0.39* P 0.04 0.16 N - 0.34* 0.85** 0.20 S - 0.47** 0.83** 0.12 0.85** I - 0.42* 0.80** 0.06 0.82** 0.94** DD - 0.39* 0.76** 0.13 0.86** 0.87** 0.93** GY 0.44** - 0.63** -0.12 -0.58** -0.87** -0.82** -0.69** **; *: Correlation coefficient significant at p≤0.01 and p≤0.05 respectively N = 48
GY (t/ha)
-
Table 2. Correlation coefficient of the variables with the first two dimensions Variables Durum wheat area sown to “Karim” Seeding rate Fungicide application Nitrogen rate Severity Early sowing Seed source Grain yield Total production cost Variability explained
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Factor 1 0.663 0.275 0.075 0.779 0.672 0.630 0.667 0.679 0.061 63.02
Factor 2 0.331 0.296 0.203 0.197 0.196 0.008 0.091 0.537 0.537 19.7
Treated Yt = 98.53e-0. 047 SEV . R2=0.91
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Untreated Y ut = 76.27e-0. 019 SEV . R2 = 0.99
Grain yield (q/ha)
50 40 30 20 10 0 5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
Septoria disease severity (%)
Fig. 3. Association between grain yield and Septoria disease severity.
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blotch disease periods is greatly affected by early sowing. Moreover, under irrigated growing condition, prolonged vegetative stage and favorable humidity conditions may have accelerated the progression of Septoria leaf blotch disease. The average number of treatment ranged from three to five treatments in sprayed fields and appeared to be independent of sowing time. These factors would favor Septoria leaf blotch disease occurrence (6, 11) and therefore could cause major grain yield loss. Foliar fungicide contributed significantly to increased grain yield in most durum wheat fields. However, both treated and untreated fields showed varying levels of grain yield response to varying levels of Septoria leaf blotch disease severities. The delayed sowing as a practice option used by few farmers (15%) in this sample, was found to be associated with increased grain yield and reduced Septoria leaf blotch disease infection levels as previously reported (1, 5). Epidemics revealed by the association of Septoria leaf blotch disease severity and incidence with the first factor of the correspondence analysis in untreated fields may have been attributed to an increased built up of primary inoculum of the Septoria tritici from previous cereal crops particularly when favorable conditions are prevailing (20, 21). Correlation coefficient indicated that disease parameters were negatively associated with grain yield. The increase of Septoria leaf blotch disease severity with increased nitrogen application is not consistent with other reports (8, 10). These discrepancies might be attributed to cultivar response (its relative resistance/tolerance levels to Septoria leaf blotch disease) and prevalent cropping system, particularly planting date and seeding rate. The lack of correlation of applied nitrogen with grain yield in the
DISCUSSION The total durum wheat area of the surveyed fields is 1670 ha and contributed around 62.5% of the cereal crops (Fig. 1) at this site. Biannual rotation system based on wheat/barley or oat is the main rotation system. This practice may have contributed to a large extend to the overexploitation of soil resources. Greater use of nitrogen and phosphorus are commonly used to compensate for soil depletion and to achieve economical grain yield as depicted by the correspondence analysis. However, several authors (20, 23) reported that higher nitrogen fertilization rate consistently produced greater grain yield only under low Septoria leaf blotch disease pressure in treated field for both tolerant and susceptible cultivars. In this study, most of farmers (73%) used a nitrogen mean rate of 350 kg/ha, whereas only 27% used nitrogen rate ranging from 175 to 250 kg/ha in irrigated wheat. Moreover, the cultivar “Karim” that is highly susceptible to Septoria tritici, covers 83.8% of area of the total durum wheat area (Fig. 2). Although nitrogen is required for achieving high yield, it appears to enhance Septoria leaf blotch disease progression in the flag leaf mainly under irrigated growing conditions (8, 10, 20, 24). Early sowing date (from 15 October to 1 November) is frequently encountered in this sample (59.45%) whereas only 37.8% of the farmers use mid-early sowing date ranging from 1st to 15 of November. These results suggest that early sowing would favor the impact of Septoria leaf blotch disease that might alter translocation from leaf tissue leading to yield reduction. Investigating agronomic and meteorological factors affecting Septoria leaf blotch disease severity in commercial wheat in England, (3, 9) reported that high risk of Septoria leaf Tunisian Journal of Plant Protection
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surveyed farmers’ fields could be high Septoria leaf blotch disease pressures, attributed to the residual nitrogen sources effective fungicide application would be in the soil from the previous crops. important to farmers growing susceptible Yield decreases more rapidly in durum wheat cultivars under optimum unsprayed fields as compared to treated cultural practices in irrigated wheats. A fields with comparable disease severity. critical threshold of fungicide application Fungicide applications usually suppress would lie within a range of 10 to 15 % of the disease for up to 25 days depending on severity level. Within this range, the the fungicide molecules, the rate, and the application of fungicide would be effective frequency of applications but did not in valorizing the total production factors. provide a full protection from Septoria leaf However, fungicide application beyond blotch disease attacks in treated fields. The 20% Septoria leaf blotch disease severity delays in invading new fresh green tissue level appeared to be cost ineffective to by Septoria leaf blotch disease in treated prevent significant grain yield reduction. fields may have contributed to the Management of Septoria leaf blotch accomplishment of grain yield in near disease, in particular and foliar diseases in normal path without significantly general, presents a challenge when disrupting the translocation of metabolites tackling individual disease components. and therefore the source-sink relationship. Modifying the micro-environment Hence, the rate decrease of grain yield combined with a canopy changes using (Fig. 3) in untreated fields (r = -0.047) was different tillage and stand density practices almost twice of that noted in treated fields would provide an additional opportunities (r = -0.019). to efficiently control foliar diseases (13). Although grain yield in both treated These practices would assume a and untreated fields are comparable at comprehensive understanding of the lower severity percentages (10 to 20%), complex interaction between pathogens, major differences for grain yield between plant, residue management, both fields are noted for higher disease microorganisms and diversification of the severity. At lower Septoria leaf blotch cropping system (2, 13). Hence involving disease severity percentages (from 10% to farmers in processes aimed to improve 30 %) average grain yield loss was 1.23 agricultural practices and generating t/ha. Greater mean grain yield loss of 2.03 suitable technologies within an integrated t/ha was observed when severity ranges pest management program, would offer a from 31% to 50% whereas, 2.53 t/ha mean better management of foliar diseases and grain yield loss was noted when severity particularly Septoria leaf blotch disease exceeds 51%. At lower disease severity, that would be relevant to farmers’ needs farmers are not able to decide on threshold and enhancing their decision making level of the disease and consequent yield process. loss in their decision making for the fungicide application. Hence, at extremely ____________________________________________________________________________ RESUME Rezgui S., Fakhfakh M. M., Boukef S., Rhaiem A., Chérif Mo., Chérif Ma. et Yahyaoui A. H. 2008. Effet des pratiques culturales communes sur la maladie de la septoriose et le rendement du blé dur en irrigué. Tunisian Journal of Plant Protection 3: 59-67.
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La lutte intégrée permet de réduire l’utilisation accrue de fongicides et mieux contrôler la septoriose du blé dur irrigué, causée par Mycosphaerella graminicola (anamorphe: Septoria tritici). L’association entre les pratiques communes et quelques paramètres de la septoriose a été évaluée en utilisant des données d’enquête menée sur 48 champs de blé en irrigué. Les résultats montrent qu’une combinaison de plusieurs pratiques pourrait limiter les effets négatifs de la septoriose sur le rendement de blé. En outre, les valeurs élevées de la sévérité de la septoriose obtenues seraient attribuées à la culture de la variété sensible “Karim”, la précocité de la date de semis, l’utilisation des densités de semis élevées et des semences de ferme, l’application des doses élevées d’azote et l’inefficacité des traitements fongicides. Ces facteurs expliquent 81.7% de la variabilité totale des données observées. Les résultats indiquent que l’application des fongicides a permis de réduire la sévérité de la septoriose sans pour autant avoir assuré une protection complète. Les fongicides semblent être inefficaces quand la sévérité est inférieure à 10% et supérieure à 60% et paraissent efficaces pour des niveaux de sévérité compris entre 40% et 50%. Des niveaux critiques d’attaque de l’ordre de 10 à 20% ont été proposés comme indicateurs permettant de limiter l’impact de la septoriose sur le rendement en grain. Cette investigation montre que le manque de critères d’évaluation des dégâts de la septoriose est une composante majeure du processus de prise de décision chez les céréaliculteurs quant à la date et le nombre d’interventions avec des molécules fongicides. Afin de réduire l’impact de la septoriose, une lutte intégrée contre cette maladie utilisant des options de conduites culturales variées pour le blé en irrigué devrait être adoptée. Mot clés: Blé dur, pratiques culturales, rendement, septoriose
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ملخص .حسٍن ٌحٍاوي صالح ومحمد معس فخفاخ وسماح بوكاف وعسة رحٍم ومحمد الشرٌف وماجدة الشرٌف وعمر،ًرزق ًالقاس/ تأثٍر الممارساث السراعٍت الشائعت على مرض التبقع السبتوري لألوراق واإلنتاج الحبً للقمح الصلب.2008 Tunisian Journal of Plant Protection 3: 59-67. .المروي ٍح أفعم يٚح ٔزًاٚذاخ انفؽشٛاساً خزاتاً نخفط االسرعًال انًفشغ نهًثٛهح خٚ ح تذٛكٌٕ اسرخذاو يًاسساخ صساعٚ ًٌكٍ أٚ (انؽٕسMycosphaerella graminicola سثثّ انفؽشٚ ٘يشض انرثمع انسثرٕس٘ ألٔساق انمًر انصهة انًشٔ٘ انز ٍح انشائعح ٔتعط خصا ئص انرثمع انسثرٕس٘ يٍٛ انًًاسساخ انضساعٛى انشاتؽح تٛٛ ٔلع ذم.)Septoria tritici :ٙانالخُس فحُٛد انُرائح أٌ االعرًاد عهٗ يكٌٕ ٔازذ فمػ تذالً يٍ يكايهح ذٕنٛ ت. ٘ٔ زمم يٍ انمًر انًش48 ٍُاخ يدًٕعح يٛاَاخ عٛت ٙادج فٚ ذى عضٔ انض. ًاٚش يدذ الرصادٛ لنمًر غٙ اإلَراج انسثٙح نهًشض فٛشاخ انسهثٛح نخفض انرأثٛيٍ انًًاسساخ انضساع ، اسرعًال يعذل عال يٍ انثزٔس، انضساعحٙش فٛ انرثك،ى " انسساطٚاإلصاب تانرثمع انسثرٕس٘ إنٗ صساعح صُف "كش ج شذج فسشخ. حٚذاخ انفؽشٛ ٔعذو َداعح انًثُٙٛرشٔخُٛذ انًٛ اسرخذاو يعذالخ أعهٗ يٍ انرس، انًضسعحٙاسرعًال تزٔس يُردح ف ح إنٗ خفط اإلصاتحٚذاخ انفؽشٛ أدٖ اسرخذاو انًث. زمٕل انمًر انًًسٕزحٙ فٍٙ اإلخًانٚ يٍ انرثا%81.7 ْزِ انعُاصش ح يُخفعح (ألمٛح يُخفعاً عُذ شذج يشظٚذاخ انفؽشٛش اسرخذاو انًثٛ كاٌ ذأث. بانرثمع انسثرٕس٘ ٔنكٍْا نى ذًُع يٍ زذٔثٓا الدسزد عرثاخ.%50ٔ 40 ٍٛذ أَّ كاٌ فاعال عُذيا ذشأزد شذج انًشض تٛ) ت%60 ٍ) ٔيشذفعح (أكثش ي%10 ٍي ٌُد ْزِ انذساسح أٛ ت. لنمًرٙش انرثمع انسثرٕس٘ عهٗ اإلَراج انسثٛح نخفط ذأثٛ عهٗ أَٓا كاف%20 ٗ إن10 زشخح ذماسب دٛخص ذٕلٚ ًاٛح اذخار انمشاس عُذ انًضاسع فٛ عًهٙح فًْٛى أظشاس انرثمع انسثرٕس٘ ْٕ انًكٌٕ األكثش أٛٛاب عالياخ نرمٛغ ٙك تشَايح إداسج يركايم يُاسة نًشض ذثمع األٔساق انسثرٕس٘ فٍٛ انرًاط ذؽثٛرعٚٔ . ح ٔعذدْاٚ ذاخ انفؽشٛانرذخالخ تانًث . حٛع خثاساخ انًًاسساخ انضساعُٕٚك ذٚح نضساعح انمًر عٍ ؼشٚٔانًُاؼك انًش انمًر انصهة،حٛ انًًاسساخ انضساع، انرثمع انسثرٕس٘ نألٔساق، إَراج:حٚخاذ كهًاخ يف
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