The virulence of the population of Magnaporthe grisea collected from eight upland rice farms of cultivars 'BRS Bonança' and 'Primavera', located in five municipalities in the State of Goiás was studied. A total of 681 isolates, 321 collected from BRS 'Bonança' and 360 from 'Primavera' were utilized for the analysis. The genotypes included for characterizing virulence were nine Japanese race differentials, six near-isogenic lines of 'IAC-25', five near-isogenic lines of 'CO-39' and the rice cultivars 'Primavera', 'BRS Bonança', 'IAC-25' and 'CO-39'. The isolates of M. grisea from 'BRS Bonança' were more virulent than those of 'Primavera' on NIL's of 'IAC-25'. The majority of isolates from leaf and panicle of both cultivars were avirulent to the near-isogenic line 'CNA 8212'. The virulence was present in low frequency in the pathogen subpopulations of 'BRS Bonança' and 'Primavera' to the genes Pi-z t (Toride-1) and Pi-z (Fukunishiki) of the Japanese race differentials. A low percentage of isolates were virulent on 'C101 LAC' (Pi-1) e 'C101 A 51'(Pi-2). Considering the compatible and incompatible reactions on the NIL's of 'IAC-25' to the population of M. grisea retrieved from 'BRS Bonança', the dedrogram showed one group (90% similarity coefficient), distinct from its recurrent parent. On the other hand, the population from 'Primavera', with the exception of 'CNA-8199' formed one group (93% similarity coefficient), including its recurrent parent. The resistance genes Pi-z and Pi-z t of cultivars 'Fukunishiki' and 'Toride-1', respectively, Pi-1 and Pi-2 of NIL's and the unidentified genes in NIL's of 'IAC-25', that showed broad spectrum of resistance to the populations tested can be used for developing near-isogenic lines of rice cultivars 'BRS Bonança' and 'Primavera'.
Oryza sativa; Pyricularia grisea; rice blast
