This work aimed to identify the best isolates of Magnaporthe grisea from Brazil to be used as testers for mating type determination of the fungus. The method used was based on the parents that allowed the mating type identification of the greatest number of isolates of M. grisea from wheat (Triticum aestivum). The sexual relationship between the wheat blast fungus and blast strains from other hosts was examined according to the following parameters: determination of mating type (MAT1-1 and MAT1-2), sexuality (hermaphrodite, female, and male), fertility (number of perithecia), and production of sexual organs (perithecia, asci, and ascospores). The testers Bp3a and Br118.2D determined the mating type of 72,7% of the wheat blast isolates and are recommended for mating type determination. Among the gramineous species, the blast isolates from Brachiaria plantaginea as well as T. aestivum may possibly play a role in the variability of the wheat blast disease. As genetic variability was observed within isolates from Setaria geniculata, blast strain from this weed may also be important in the variability of the wheat blast fungus. The rice (Oryza sativa) blast strain showed low sexual fertility.
