Genetic variability of the wild incompatibility alleles of the tetrapolar basidiomycete Agrocybe aegerita.

The variability of the sexual incompatibility genes of Agrocybe aegerita was investigated in the homokaryotic progeny of 13 wild dikaryotic strains from five distinct European geographic origins. Results of mating tests allowed identification of 18 A alleles and 16 B alleles out of a possible 26 different alleles for each in the sample. The determination and the comparison by a contingency χ (2) test of the frequencies of allele replications between intra- and interregional matings showed no departure from a random distribution of incompatibility alleles. The allelic series estimated for the incompatibility genes of the entire population of A. aegerita, 30 A and 25 B aleles, are significantly less extensive than those already hypothesized for other tetrapolar hymenomycetes. However, the low variability of incompatibility genes has little effect on the outbreeding efficiency (92.6%) of this mushroom. The low variability of the incompatibility alleles and the apparent absence of intrafactorial recombination could relate to a single-locus structure of the incompatibility genes in A. aegerita.