| sclerotinia stem rot caused by Sclerotinia sclerotiorum is the most devastating disease on oilseed rape(Brassica napus) in China. As the pleasantly warm and moist climate, sclerotinia stem rot occur in Sichuan Provence become profoundly severe, leading to huge economic loss. In this paper, to elucidate the differentiation of 77 isolates of S. sclerotiorum from three areas of Sichuan Province, the biological characteristics, anastomosis groups, genetic diversity and and pathogenicity were investigated. Main results are summarized below.1、77 S. sclerotiorum isolates were collected from three regions (Mianyang, Chengdu and Yaan) in Sichuan province, and biological characteristics were determined. reusults showed that all strains were significant differences in the colony morphology, growth speed of hypha, matrix color, the number and size of Sclerotium. based on the colony morphology,77 isolates could be divided into 12 colonies form; after cultured on PDA, the cultivatable matrix four different color including white, light grey, light brown and green; the growth rate of hypha was in the range of 2.08cm/d-5.04 cm/d, and 70.13% of them were greater than 4.001cm/d in the diameter; The growth rate of hypha in Mianyang was significantly less than those in Yaan and Chengdu; The number of sclerotium ranged from 1 to 58, and there were no significant difference among three areas; The fresh weight of sclerotium was in the range of 0.13～1.37 mg per culture dish, and they in Yaan were significantly greater than those in Mianyang and Chengdu. Analysis of the characteristics of biology demonstrated that mycelium growth rate was remarkably significant correlated with fresh weight of sclerotium, however, there were no significant correlation between other biological factors2、 mycelium compatibility of 77 isolates was analyzed, and results showed that 77 strains were divided into 66 compatibility groups (MCGs); 57 groups were composed of single strain, and others were divided into 9 MCGs with 2-3 strains each group. It was demonstrated that mycelium compatibitity groups were significantly related to geographical locations of S.sclerotiorum.3、SRAP markers was used to analyse the genetic diversity of 77 S.sclerotiorum isolates. A total of 127 polymorphism fragments were amplified using 10 primer paris of SRAP, and proportion of polymorphic bands was 87.58%. UPGMA analysis (Unweighted Pair Group Method with Arithmetic Mean) indicated that the genetic similarity coefficient was 0.83～0.98. When the similarity coefficient was 0.877,77 strains were divided into 7 categories. Clustering results were roughly identical to geographical location of S.sclerotiorum, and 82.61% of strains from Yaan were classified as category II when 59.10% from Chengdu and 96.88% from Mianyang were classified as category I. Cluster analysis fitted mycelium compatibility groups, but was not siginificantly related to the growth rate of hypha.4、According to the results of biological characteristics and genetic diversity,50 strains from 77 isolates of S.sclerotiorum were used for pathogenicity test on the detached leaves of two rapeseed cultivars Chuanyou 58 and Zhongshuang 7. The length of disease spot was around 1.60～6.10 cm, we found that pathogenicity of 50 isolates were significantly different between each other, but there were no significant correlation between pathogenicity and geographical origins. In general, this study proved that pathogenicity differentiation is significantly positively correlated with the mycelium growth rate and fresh weight of sclerotium, but not related to genetic clustering. |
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