The objective of this investigation was to examine the virulence diversity of Pyricularia grisea isolates collected from the Experimental Station of IAC, Mococa in the state of São Paulo. The composition of races and their compatibility with known resistance genes were studied using the Japanese rice (Oryza sativa) differentials. Fifty single spore isolates were obtained from diseased panicles of rice cultivars IAC 201 and IAC 4440. Two races affecting upland rice cultivar IAC 201, JP 137 and JP 177, and one race (JP 200) affecting the lowland rice cultivar IAC 4440 were identified. The results showed low frequency of physiologic races in this breeding site. While all 25 isolates from IAC 4440 were compatible to one resistance gene, pi-ta², the isolates from IAC 201 were compatible to seven out of nine known resistance genes in the Japanese rice differentials. Furthermore only one resistance gene (pi-z t) was effective to all isolates of P. grisae collected from rice cultivars IAC 201 and IAC 4440.
