Genetic Diversity and Virulence Variation of Rice Sheath Blight Pathogen ( Rhizoctonia solani AG-1 IA) from Different Rice Varieties

Forty isolates of rice sheath blight pathogen ( Rhizoctonia solani AG-1 IA) from six rice varieties were analysed for genetic diversity by using random amplified polymorphic DNA (RAPD) technique. Of 98 RAPD bands that were amplified with 10 arbitrary decamer primers, 82.65% were polymorphic. Analysis of amplified polymorphic DNA fragments showed that Nei's genetic identity were 0.564 4～0.930 7, the tested isolates were classified as 4 RAPD groups(Ⅰ,Ⅱ,Ⅲ,Ⅳ), and the isolates from the same host were fallen into the same group by using UPGMA cluster analysis. The results of virulence test in greenhouse indicated that all isolates were virulent to rice variety Tetep, and the range of disease index varied from 0.40 to 11.83. It was suggested for genetic analysis that there was abundant genetic diversity existing in rice sheath blight fungal population, and that the genetic variation was very significant within populations from different rice varieties( F ST =0.632), and that host selection affected the population genetic structure of Rhizoctonia slani AG-1 IA. The RAPD cluster groups were in line to some extent with host origin of isolates, but virulence variation was not related to host origin of isolates and RAPD groups.