Studies On Isolation, Identification, Virulence Comparison And Fungicide Screening Of Pathogenic Alternaria On Rapeseed

A large number of pods of rapeseed Fengyou730F1were covered with black molds and more than90%disease area occurred in Liling city of Hunan Province, in May of2012. Study was especially carried out in order to diagnose and to control the disease. The innovations and results of this study are as follows:(1) Pod black mold is a kind of special symptoms of rapeseed black spot. Several strains were isolated from the pods and seeds of rapeseeds collected from diseased plants, and they have the same spore morphology. These strains were identified to be Alternaria sp. by microscopy. Spraying inoculation with spore suspension of the strain FY730F-01reproduced black mold on pods and strains same as FY730F-01were separated from inoculated pods. Therefore FY730F-01was proved by the rule of Koch to be the pathogen of this disease. FY730F-01was identified to be A. brassicae by microscopy and rDNA-ITS sequence analysis.(2) Seed-borne Alternaria on36tested commercial rapeseed cultivars of Hunan Province were examined in this study. Alternaria spp. were isolated from35rapeseed cultivars except Heshengyou868. Huaxiangyou12had the highest isolation rate (66.00%). Isolates were proved to be A. brassicicola and A. brassicae respectively by rDNA-ITS sequence analysis, A. raphani was not detected. All of isolates from Huaxiangyou12were A. brassicicola. However, as for A. brassicae, Changyouza61had the highest isolation frequency (15.00%). A. brassicicola showed slightly higher isolation rate than A. brassicae.(Chinese journal of oil crop sciences accepted)(3) A. brassicicola is more virulent than A. brassicae obviously. This study detected the virulence of14strains by in vitro inoculation on rapeseed leaves with the spore suspension. The inoculation test showed that YY817-15and YY817-14had the strongest virulence, the average spot diameter of25.00mm and21.13mm. YY10-1and YY50-4had the weakest virulence, with average spot diameters of8.88mm and9.63mm.(4) dsRNA is first reported of in A brassicicola. The dsRNA, which extracted by the cellulose CF11method, followed by treatment of enzyme digestion, agarose gel electrophoresis showed the presence of the dsRNA in2strains:YY817-14and YY817-15.(5) Difenoconazole showed the best inhibitory effects. In vitro inhibitory effects of11 fungicides to strains A. brassicae FY730F-01and A. brassicicola YY817-15were tested. The inhibitory effects of Difenoconazole and Flusilazol were the best to FY730F-01, followed by Propiconazole and Prochloraz. The inhibitory effects of Prochloraz and Difenoconazole were the best to YY817-15, followed by Flusilazol and Propiconazole. The inhibitory effects of Chlorothalonil and Thiophanate-methyl were the worst to both two strains. This study offered a guide for the prevention and treatment of rapeseed black spot.