Blast samples were collected during 2004-2006 in different rice growing regions in São Paulo State, Brazil. The 71 monosporic isolates of Pyricularia grisea obtained were grouped into physiologic races based on the reaction type on a set of eight international and nine japanese differentials. Twenty-one pathotypes were identified among the 71 blast isolates according to the international set. The IB, ID and IG groups were most frequently detected (23, 21 an 17 times each, respectively). The virulence frequency of isolates to the genes in the international differencials varied from 0 (Raminad Str.3 variety) to 90.1 % (Sha-tiao-tsao). Based on the reaction of japanese differential set, 36 pathotypes or races were identified. None of the 71 isolates were capable of overcome the resistance of the gene pita², and only one isolate the resistance gene pi-z t. On the other hand, 63.4%, 59.1% and 53.5% among these isolates were virulent respectively on varieties Aichi Asahi (gene pi-a), Yashiro-mochi (gene pi-ta) and Ishikari-shiroke (gene pi-i).
blast; physiologic races; resistance genes; Oryza sativa
