| In order to analyze population genetic diversity of Verticillium dahliae on cotton, 308 islolates were recovered from Verticillium-wilt-symptomatic cotton grown in 12 provinces including 96 counties of China. Population genetic diversity was studied based on cultural characteristics, SSR and ISSR fingerprint. SSR and ISSR fingerprint were further analysed compared with the results of pathogenicity and geographical origin. Some V. dahliae isolates with special cultural characteristics were identified according to their physiological characteristics and specific PCR products. And the relationship between physiological characteristics and pathogenicity was studied according to 12 isolates of different aggresiveness. This study will provide the basis for further research of genetic variation of cotton verticillium wilt in our country, pathogenic mechanism,resistance cotton breeding,rational distribution of resistant varieties,the causes of resistant reduction etc.. The main results were shown as following.1. V. dahliae of cotton in China showed five different cultural types(A, B, C, D and E)on PDA medium. Type B which accounted for 72.9% produced plenty of uniformly distributed microsclerotia and ringed white circle edge of colonies; Type C which accounted for 23.6% had less microsclerotia around of colonies, formed black circle ring, and had white mycelia with no or little microsclerotia in the middle of the colonies. The isolates obtained from the Yangtze River basin varied most in cultural characteristics, followed by the Yellow River basin, and the isolates from XinJiang province had the lest variation in cultural characteristics. Single spores of the same wild isolate showed obviously different cultural characteristics on PDA medium, witch indicated that all wild isolates are heterozygotes.2. There were 14 of 308 isolates showed special cultural characteristics on PDA medium. All the 14 isolates were identified based on temperature reaction and specific PCR products to V. nigrescens, V. albo-atrum, deofliating and non-defoliating V. dahliae (D-1/D-2, ND-1/ND-2). Resluts showed that all of the 170 isolates belong to V. dahliae .155 isolates were deofliating V. dahliae which accounted for 91.2%, and the rest 15 isolates were non-deofliating V. dahliae which accounted for 8.8%. 11 of 15 non-deofliating V.dahliae isolates were from XinJiang province, which accounted for 45.8% of all tested XinJiang isolates. This indicated that most of V. dahliae of cotton in China were deofliating V. dahliae.3. Under specific growth condition, growth rate, yield of conidia and secretory toxin of 12 isolates with different aggressiveness to cotton were tested. The results showed that there was a significant difference among these isolates in growth rate, conidia and secretory toxin yield, and these threee parameters exhibited certain positive correlation with pathogenicity. In addition, there is no correlation between growth rates or conidia yield of isolates and deofliating phatotype, but there is certain positive correlation between the yield of secretory toxin and deofliating phatotype of isolates. 4. SSR primers were designed based on the genome database of V.dahliae on lettuce and SSR reaction system was established and optimized. 13 pairs of SSR with higher polymorphism were selected for molecular fingerprint analysis. The results of UPMGA cluster showed that 170 tested isolates of V. dahliae from China were distinctly classified into two groups. Groupâ… contained 26 isolates, of which 18 isolates were from Xinjiang province, accounting for 69.2%. Groupâ…¡contained 144 isolates, of which 138 isolates were from the inland, accounting for 95.8%. So there is significant difference between the isolates from Xinjiang province and other provinces. SSR fingerprinting had a significant correlation with geographical origin of isolates. The isolates from Xinjiang province were significant different with those from the inland, but there was no correlation between SSR fingerprinting and the pathogenicity. Isolates with weaker aggressiveness may be easier to produce genetic variation. To our knowledge, this is the first report in China about SSR fingerprint of V. dahliae on cotton.5. Nine ISSR primer pairs were used to amplify genome DNA of 170 tested isolates of V. dahliae from China to analyze genetic diversity in this study. Clustering analysis results showed that 170 tested isolates were classified into three different pathogenicity groups. The isolates in Groupâ… showed weak virulence to cotton. Strong pathogenicity isolates constituted Groupâ…¡, and most of Groupâ…¡were medium pathogenicity. The study indicated that there was a significant correlation between ISSR fingerprint and the pathogenicity, but no correlation between ISSR fingerprint and geographical origin .
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