Variability of Pyricularia oryzae Cav. in irrigated rice genotypes

Rice blast, caused by the fungus Pyricularia oryzae Cav., is one of the most important diseases of rice. The understanding of its different strains allows a more efficient breeding towards resistant cultivars. This work aimed to determine the variability of the fungus and the prevalence of strains in irrigated rice genotypes, to evaluate the reaction of near isogenic lines of CO 39 to the collected P. oryzae isolates and to identify rice genotypes having complementary resistance genes to these isolates. The study was performed with 36 P. oryzae isolates collected in 18 irrigated rice cultivars from four counties in Rio Grande do Sul State, Brazil. A total of 21 strains were identified, with a prevalence for the IA group strains, in all collection sites, especially the IA-1 strain. A resistance reaction was observed for the cultivars BRS Firmeza, Bluebelle, Te-tep and BRS 7 (Taim), while a susceptible reaction was observed for Fanny, Dawn, BRS Pelota and BRS Atalanta. The series of near isogenic lines obtained from the CO 39 cultivar showed resistance to the isolates in the following order: C101 A51 (resistant to all isolates); C101 PKT (12); C104PKT (11); C105HP4L23 (8); and C101-LAC (3). From the studied isolates, it was concluded that there is variability of P. oryzae, prevalence of the IA strain, a higher tolerance for the cultivar BRS Firmeza and that the Pi-2 gene confers resistance to rice blast in all isolates analyzed