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A selectable marker gene conferring resistance to bialaphos (BI) was introduced into rice blast isolate Y90-71B1 and another conferring resistance to blasticidin S (BS) into isolate 3514-R-2BS of Magnaporthe oryzae to demonstrate exchange of DNA. Colonies obtained from co-cultures of these two isolates were resistant to both BI and BS and had both resistance genes as shown by Southern blot analysis of their genomic DNA. Conidia from these Bl-BS-resistant isolates had only one nucleus per cell after staining with 4′,6-diamidino-2-phenylindole (DAPI). Using flow cytometry, however, these Bl-BS-resistant isolates were found to be haploid. Segregation of Bl-BS-resistant isolates for pathogcnicity (avirulence to virulence) on rice line K59-1 was consistent with a 1:1 ratio, as was segregation for mating type. These Bl-BS-resistant isolates were thus apparently derived from parasexual exchange of DNA and the segregation of pathogenicity and of mating type of the parasexual recombinants might correspond to that of the progeny of the offspring of the sexual cross. [ABSTRACT FROM AUTHOR]