Pathotypes and virulence of Xanthomonas oryzae causing bacterial blight disease of rice in Peninsular Malaysia

A study was conducted on Xanthomonas oryzae isolates collected from major granary areas in Peninsular Malaysia. Study on the 346 isolates indicated that most of them (29.5%) could be grouped into pathotype P1.0. Pathotype P1.0 was only virulent against rice variety IR 8 which carried the resistant gene Xa-11 but remained avirulent against other differential varieties. Pathotype P1.0 was detected in all states. The most virulent pathotype was P7.7 which was capable of causing severe lesion on all differential varieties tested. However, most of the virulent pathotypes were only represented by a small number of isolates and limited to certain localities only. Rice variety MR 84 which was popular in the 90s was susceptible to the common isolates. However, other differential varieties such as Cempo Selak, Zenith, IR 20, DV 85 and Patong 32 were resistant, and most of the tested isolates remained avirulent against them