The segregation of virulence among progenies of a cross between wheat isolates of Magnaporthe grisea on five wheat (Triticum aestivum) varieties was studied. The segregating population was formed by 37 progenies resulting from the cross between two field isolates that differed in virulence. The results showed 1:1 avirulence/virulence segregation to the varieties CNT 8, BR 17, and OR 1 indicating the segregation of a single avirulence gene that was specific to each variety. On the other hand, the segregation of avirulence/virulence of the varieties BR 31 and Iapar 3 was 1:3 indicating the segregation of one avirulence gene and the suppressor of this gene. Furthermore, the sexual recombination between fungal isolates under laboratory conditions produced isolates virulent to all varieties, which might be one of the causes for varietal resistance breakdown.
