Abstract:Forty-eight rice sheath blight strains (Rhizoctonia solani AG 1-IA) from seven counties in Guangdong province were analyzed for genetic diversity using RAPD technique. Ninety-eight RAPD bands were amplified with 10 arbitrary decamer primers, among which 89.9% were polymorphic. Analysis of amplified polymorphic DNA fragments showed that the Nei's similarity coefficients of isolates were 0.560 -0.949. The tested isolates could be classified into 5 RAPD groups (A, B, C, D, and E), and most of the isolates from the same area clustered in a same group by using UPGMA analyses. THe virulence test carried out in greenhouse showed that all isolates were virulent to rice variety Tetep, the disease index (DI) ranged from 0.73 to 18.7, the mean DI was 5.24, and the virulence variation was significant(α=0.05).The analysis showed that there existed abundant genetic diverdsity among rice sheath blight fungal popilations, and the genetic variation was very signficiant in R. solani AG 1- ⅠA population from different counties in Guangdong province (FST=0.579). The RAPD clustering groups had obvious correlation with geographical origin, but the virulence variation had no significant correlation with geographical origin and with RAPD groups.