Population Diversity Of Bipolaris Maydis And Their Sensitivities To Diniconazole In Sichuan Province

Maize is the thirdth most worldwide crop in the world after wheat and rice, which plays an important role in food security now. Southren leaf blight of maize that was caused by Bipolaris maydis(Nishik.et Miyabe) Shoemaker is the most devastating disease to maize production in Sichuan. In this study, the toxicity of8kinds of fungicides were measured against the Bipolaris maydis, Physiological race, Diniconazole sensitivity and the DNA diversity of Bipolaris maydis population that were isolated from Sichuan during2010to2011, and this study will set up the foundation for Maize late blight control and prevention.The178tested Isolates were single spore isolation from maize the192leaves which appear Bipolaris maydis located in different regions of Sichuan Province.The toxicity of6kinds of fungicides was measured against the Bipolaris maydis by growth velocity in lab.The suppression rate of Diniconazole on the hyphal growth was the best, its EC50was3.39μg/mL;The second was Dimethachlone, the EC50was5.96μg/mL; Mancozeband and Chlorothalonil, the EC50were19.30μg/mL and12.30μg/mL, respectivety.The lowest were Sanmate and Mildothane, EC50were843.00μg/mLand625.00μg/mL, respectivety.The sensitivity of113Bipolaris maydis from Sichuan Province to diniconazole was determined by growth velocity in lab.The results showed that these strains showed difference in their sensitivities to diniconazo.The most sensitive strains was Q100collected from QingShen, EC50was0.1μg/mL, the least sensitivemost was Q145collected from BaoXing,the EC50was9.98μg/mL, sensitive to the value was99.8times.EC50above9.00had two areas:Bazhong (9.05μg/mL)、Dazhou (9.28μg/mL), located from high latitude in the northern of Sichuan. EC50below4.00had two areas:Leshan (3.01μg/mL)、 Yibin (3.43μg/mL), locatde from low latitude in the southern of Sichuan.The physiological races of73Bipolaris maydis were identified by the differential host which had same nuclear background but with N, T, C, and S4different cytoplasmic.The result showed that the4physiological races O, C, S and T existed in Sichuan province, and among them, the race O was dominant, it was accounted for61.60%, the frequency of race T was15.10%. The frequency of race S and C races were12.30%and10.96%.Simultaneously, the pathogenicity of46Race O from different areas was different. The isolation frequency of strong pathogenic strains of Race O was more than that of the weak pathogenic strains. The frequency of medium pathogenic strains was 47.83%, the strong pathogenic strains and the weak pathogenic strains were28.26%and23.91%.Using random amplified polymorphic DNA technique,139Bipolaris rnaydis isolates on maize that from Sichuan province were tested for DNA diversity.The results showed that the genetic dissimilarity coefficient of139isolates were between0.0769and1.0. Among them, the least was0.0769, they were Q124and Q30, Q107and Q65, Q112and Q117etc.14combinations,showed their genetic material were minimum difference.The largest genetic dissimilarity coefficient was1.0,they were Q109and Q33,Q109and Q62,Q79and Q24etc.10combinations.Based on genetic genetic distance calculation and cluster analysis by UPMGA,the result showed that the genetic distance of139single spore strains was ranged from0.00to0.74.They werw clustered into two categories at0.74, one was constituted by Q104, Q115, Q79, Q109, another kind was constituted by the rest135strains.139strains were divided into multiple sub-categories in the different genetic distance, their genetic diversity was more complicated.Simultaneously, the dendrogram showed that the Bipolaris maydis which was isolated from the same corn field the same corn varieties didn’t have the same genetic traits, dividing group had no direct relationship with area source. Using RAPD divided genetic groups also hadn’t directly linked with physiological races.