Parasexual Recombination in Magnaporthe oryzae

Parasexual recombination is thought to be one of the causes of variation in the pathogenicity of rice blast fungus, Magnaporthe oryzae, which breaks down resistant rice varieties. In this study, the virulence and fitness of parasexual recombinants of M. oryzae were examined in vitro and in the field. According to the results of the genetic analysis of the pathogenicity of parasexual recombinants of the fungus, the segregation ratios of avirulence and virulence among recombinants on rice cultivar Hattan 3 and line K59-1 were consistent with those of the sexual progeny of the fungus. This indicated that the avirulent genes of the parasexual recombinants were segregated in a manner similar to that in sexual reproduction. The fitness of parasexual recombinants derived from co-cultures of parental isolates was also investigated. The recombinants produced intermediate-sized lesions and intermediate numbers of spores between the parents on the host. Plants inoculated with the recombinant also showed intermediate disease severities between the parents in the field. Parasexual recombinants can attack a rice multiline system because their virulence and fitness is inherited from the parents. Discipline: Plant disease Additional key words: aggressiveness, fitness, Pyricularia oryzae