Distribution of incompatibility factors in natural populations of Hypsizygus marmoreus in Japan.

Hypsizygus marmoreus (bunashimeji in Japanese) is a major cultivated edible mushroom in Japan. Characterizing its mating incompatibility factors in natural populations is essential for improving breeding efficiency. In this study, 71 wild isolates of H. marmoreus collected from different regions in Japan were analyzed to determine the composition and distribution of incompatibility factors. Mating tests using tester monokaryotic strains identified 82 cases of monokaryons that were carrying different alleles at both the A and B mating locus, whereas another 60 factors were shared among isolates. Several A and B factors were found in isolates from multiple regions, with one B factor detected in isolates from regions separated by approximately 1500 km. Chi-square analyses of the frequencies of shared incompatibility factors revealed the random distribution of incompatibility factors within regions, but significant differences among regions, particularly for B incompatibility factors. These findings indicate diversity in incompatibility factors within natural populations of H. marmoreus and imply that their geographical distribution has been shaped by ecological and evolutionary processes, including basidiospore dispersal and balancing selection.