The development of tan spot (Pyrenophora tritici-repentis) in natural field conditions to Agricultural Research and Development Station Simnic area

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1 Field Crop Production ORIGINAL SCIENTIFIC PAPER The development of tan spot (Pyrenophora tritici-repentis) in natural field conditions to Agricultural Research and Development Station Simnic area Marius Paraschivu 1, Mirela Paraschivu 2, Gabriela Păunescu 2 1 Horticulture Faculty, University of Craiova, A.I.Cuza Street, no.13, Craiova, Romania (paraschivum@yahoo.com) 2 Agricultural and Research Station Simnic, Balcesti road, no.54, Craiova, Dolj, Romania Abstract The pathogen that caused tan spot is Pyrenophora tritici-repentis (Died.) anamorph Drechslera tritici-repentis (Died.) Shoemaker (synonym Helminthosporium triticirepentis). In recent years tan spot has become an important wheat disease in ARDS Şimnic area. During two years ( ), twenty-five winter wheat cultivars were evaluated for their response to natural infection under field conditions. Weather conditions were observed from April to June when tan spot pathogen spreads. A severe epidemic of tan spot occurred in 2008 when there was a sufficient amount of rainfall and the air temperature was close to optimal. In 2009 the disease started faster, but the evolution was slower than in The highest AUDPC values were recorded in 2008, comparatively with Investigations of tan spot development patterns under field conditions enable wheat growers to better forecast tan spot and achieve better timing of fungicide applications. Key words: weather conditions, tan spot, winter wheat, AUDPC Introduction The fungus Pyrenophora tritici-repentis (Died.) anamorph Drechslera tritici-repentis (Died.) Shoemaker (synonym Helminthosporium tritici-repentis) is a foliar fungal pathogen of many gramineous species and a foliar pathogen of wheat (Triticum sp.) that causes tan spot on leaves. The fungus produces two types of spores, which are wind-borne. Ascospores are forcibly ejected from pseudothecia, whereas the conidia are positioned in the air steam by elevated conidiophores on diseased leaf tissues. Wind speed as low as 2 m /s is sufficient to cause 100 percent conidial dispersal. Maturation of pseudothecia and ascospores occurs from 5-20 o C, but optimal temperature ranged from o C (Wright and Sutton, 1990). Conidia are produced at temperatures between o C; the optimum is 21 o C (Luz and Bergstrom, 1986). Ascospores are the major source of primary inoculums, followed by repeated cycles of conidial production, on diseased leaf tissue. Conidia might be a source of primary inoculums as well. Prolonged wet periods of 48 h longer are favorable to saprophytic growth of tan spot (Hosford et. al., 1987). The fungus produces lens-shaped necrotic lesions with chlorotic halo on susceptible cultivars. Yield losses attributed to this disease ranged between 3-50 percent. The pathogen can over-season on diseased seed, infected crop residue, and overwintering grass hosts (De Wolf et al., 1998). Shorter rotations, continuous wheat cultivation and especially conservation or minimum tillage systems increased the incidence of this disease (Lamari and Bernier, 1994; Ciuffetti and Touri, 1999). The objective of this study was to determine the effects of the weather conditions (temperatures and amount of rainfall) on the development of Pyrenophora tritici-repentis and to evaluate the response of the wheat cultivars to pathogen attack in ARDS Simnic area th Croatian & 5 th International Symposium on Agriculture

2 Ratarstvo Material and methods The experiment was conducted in the Breeding and Plant Protection Laboratory field from ARDS Simnic on brown reddish soil (ph 5.6; 1.8% humus). The same treatments were applied for both years. Thus, the field was plowed and disked prior to planting and weeds control was realized using 1 l/ha recommended dose Dicopur Top herbicide. Twenty-five winter wheat cultivars were evaluated for their response to Pyrenophora tritici-repentis natural infection under field conditions. Plots were fertilized at sowing with 40 kg/ha of N and 40 kg/ha of P 2 O 5 basal applyed and top-dressed with 60 kg/ha of N on early spring (March). The layout was a randomized complete block design in a strip-plot system with three replications. Plot size was 7 m 2. Seeding was on October 10 th 2007 and October 15 th 2008 using a seed rate of 550 grains/ m 2. The data on the weather conditions (temperatures and amount of rainfall) were collected during the main disease-spreading period (from April to June) for both years. The growth stages of plants were recorded according to the Zadoks scale (Zadoks et al., 1974). Disease evaluation was started when initial necrotic symptoms were noticed in the canopy of the wheat cultivars (Z39-ligule of the last leaf just visible) and continued on stages Z53 (1/4 of head out) and Z61 (the beginning of flowering). The diseased area was vissualy assessed on 10 randomly selected main tillers from each plot. Visual scoring of percent diseased area was done using a quantitative rating scale based on lesion size and necrotic leaf area (Raymond et al., 1985). Individual leaf-disease rating were averaged to obtain a mean score for each replication. To determine the diseases severity for each cultivar was used Area under Disease Progress Curve - AUDPC (Shaner and Finney, 1977): a Yi Y( i 1) A.U.D.P.C. = x( t( i 1) ti) i1 2 Where: Yi = the disease score at t i time; t (i+1) - t i = days between two consecutive disease scoring times. Area under Disease Progress Curve - AUDPC express the quantitative measure of epidemic development of disease (Reynolds and Neher,1997). Results and discussion Production of primary inoculums of tan spot depends on the successful survival and saprophytic growth of Pyrenophora tritici-repentis in the residues. In 2008 during April to May the weather conditions were suitable for the release of ascospores from pseudothecia and in the following months the second conidia-infection cycle was produced (Fig.1). Researchers determined that levels of primary inoculums have been correlated with the development of the tan spot epidemics in the field (Zhang and Pfender, 1993). Our experiment evidence suggests that optimal temperature for the incidence of ascospores in April and the beginning of May lead to a severe epidemic of tan spot in the field. 45. hrvatski i 5. međunarodni simpozij agronoma 869

3 Field Crop Production Figure 1. The optimal temperatures for the development of tan spot and weather conditions during the 2008 growing season Because of the humidity caused by the amount of rainfall in May and the first part of June, tan spot disease develops faster due to the conidia infections, which are considered secondary inoculums. The conidia were produced in cycles and this aspect assures the new infections and spreads the diseases in the field. A longer wet period can be observed in Fig.1 form May to June. Researchers detected that a longer post-inoculum wet period and optimal temperature increased conidial germination, the number of germs per conidium, teenght of germ tubes, appressoria production, papillae production and percentage of appressoria colonization host cells (Hosford et al., 1987; Summerell and Burges, 1989; Sah, 1993). In 2009 the optimum temperature for ascospores was realized at the beginning of April comparatively with the same period in The amount of rainfall did not have any significant effect during this period, because for the primary infection of the Pyrenophora tritici repentis fungus, soil moisture has a major role (Bockus and Shroyer, 1998). The lack of rainfall in the second part of April (Fig.2) made the disease evolution slower, but in the first part of May the weather conditions become suitable for the pathogen development. In the second part of May the conidia infections occurs and the symptoms of pathogen attack become more visible on the cultivars leaves. In June the lack of rainfall in the second part of month avoided the pathogen spread on the flag leaves, even the optimum temperature for conidia was touched th Croatian & 5 th International Symposium on Agriculture

4 Ratarstvo Figure 2. The optimal temperatures for the development of tan spot and weather conditions during the 2009 growing season The cultivars behavior to the Pyrenophora tritici-repentis attack was different depending on their susceptibility. Among all tested cultivars in 2008 only sixteen developed tan spot symptoms on the leaves (Briana, Glosa, Josef, Autan, Enesco, Renan, Serina, Cubus, Meunier, Exotic, Orion, Martina, Mariska, Renesansa and Isengrain), while 9 cultivars didn`t show any symptom (Frini, Dunai, Carolina, Capo, Fridoline, Aztec, Bercy, Cezanne, Cordiale). In 2009 eleven cultivars (Briana, Glosa, Josef, Autan, Apache, Enesco, Renan, Meunier, Exotic, Orion and Mariska) showed symptoms on the leaves and fourteen didn`t show any symptom (Frini, Dunai, Carolina, Capo, Fridoline, Aztec, Bercy, Cezanne, Cordiale, Serina, Cubus, Martina, Renesansa and Isengrain). In 2008 the pathogen was more aggressive comparatively with 2009 and the AUDPC values recorded in each year confirm this aspect. The AUDPC values in 2008 ranged between 92,46 (Renesansa) and 685,03 (Autan) (Table no.1). The highest AUDPC values were recorded by Autan, Renan,Exotic, Mariska and Apache, while the lowest AUDPC values were recorded by Renesansa and Meunier. The highest AUDPC values showed a higher susceptibility of the cultivars. Comparatively with control the cultivars Briana, Glosa, Josef, Autan, Enesco, Renan, Serina, Exotic, Orion, Mariska, Isengrain and Apache recorded differences statistically assured as very positive significant. Comparatively with experience mean all the cultivars affected by pathogen in 2008 recorded positive or negative differences statistically assured. Table 1. The values of Area under Disease Progress Curve (AUDPC) recorded by wheat cultivars in the conditions of Pyrenophora tritici-repentis attack in 2008 No. Cultivar AUDPC 1 Diff. Diff. control Mean 1 Briana 185,35 89,64 *** -77,67 ooo 2 Glosa 185,16 89,45 *** 77,86 *** 3 Josef 297,73 202,02 *** 34,71 *** 4 Autan 685,03 589,32 *** 422,01 *** 5 Enesco 173,49 77,78 *** 65,05 *** 6 Renan ,25 *** 321,98 *** 7 Serina 173,49 77,78 *** -89,53 ooo 8 Cubus 105,16 9,45-157,86 ooo 9 Meunier 95,71 control -167,31 ooo 45. hrvatski i 5. međunarodni simpozij agronoma 871

5 Field Crop Production 10 Exotic 443,18 347,47 *** 180,16 *** 11 Orion 175,16 79,45 *** -87,86 ooo 12 Martina 87,41-8,3 175,61 *** 13 Mariska 423,22 327,51 *** 160,2 *** 14 Renesansa 92,46-3,24-170,56 ooo 15 Isengrain 172,66 76,95 *** -90,36 ooo 16 Apache 328,07 232,36 *** 65,05 *** MEAN 2 263,02 DL 5% = 13,056 DL 1% = 17,600 DL 0,1% = 23,360 1 Mean AUDPC on three replications for each cultivar 2 Mean AUDPC of the experience In 2009 the AUDPC values were lower than in 2008 for all affected cultivars. Compratively with 2008 the cultivars Serina, Cubus, Martina, Renesansa and Isengrain didn`t show any symptom. In 2009 the AUDPC values ranged between 52,66 (Meunier) and 489,47 (Renan) (Table no.2). Comparatively with the control the differences recorded by Enesco and Orion were distinct positive significant and for all other cultivars were very positive significant. Comparatively with the experience mean only Autan, Renan, Exotic, Mariska and Apache recorded positive differences, while Briana, Glosa, Enesco, Meunier and Orion recorded negative differences. The difference recorded by Josef didn`t have any significante. Table 2. The values of Area under Disease Progress Curve (AUDPC) recorded by wheat cultivars in the conditions of Pyrenophora tritici repentis attack in 2009 No. Cultivar AUDPC 1 Diff. Diff. control Mean 1 Briana 156,68 104,02 *** -88,94 ooo 2 Glosa 120,87 68,21 *** -124,75 ooo 3 Josef 256,75 204,09 *** 11,13 4 Autan 486,53 433,87 *** 240,91 *** 5 Enesco 78,22 25,56 ** -167,4 ooo 6 Renan 542,13 489,47 *** 296,51 *** 7 Meunier 52,66 control -192,96 ooo 8 Exotic 392,18 339,52 *** 146,56 *** 9 Orion 80,61 27,95 ** -165,01 ooo 10 Mariska 261,76 209,1 *** 16,14 * 11 Apache 273,48 220,82 *** 27,86 ** MEAN 2 245,62 DL 5% = 15,450 DL 1% = 21,020 DL 0,1% = 28,250 1 Mean AUDPC on three replications for each cultivar 2 Mean AUDPC of the experience Conclusions The pathogen attack evolution was different for each cultivar depending on weather conditions, infection moment and cultivar resistance. The highest AUDPC values were recorded by Autan and Renan cultivars for both years. Looking closer at the figures presenting weather conditions we can point out that the air temperature in May is similar for all investigated years, but the amount of rainfall differed from season to season. A severe epidemic was observed during the 2008 growing season when the number of rainy days was highest. Our study indicates that both rain and temperatures play a major role in the incidence of tan spot pathogen in winter wheat under natural field conditions. The infection source and cultivar susceptibility are also important th Croatian & 5 th International Symposium on Agriculture

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