Evidence of Sexuality in the Cultivated Mushroom, Agaricus Bisporus

The cultivated mushroom, Agaricus bisporus (Lange) Imbach, has been reported to be homothallic (4, 5, 11) because mycelium from a single basidiospore usually produces a normal fruiting body. Raper (7) distinguished among three types of homothallism in the basidiomycetes: (a) primary, the fertile dikaryon originating from a uninucleate (hence homokaryotic) spore; (b) secondary, the fertile dikaryon originating from a spore containing two nuclei of different mating types (heterokaryotic); (c) unclassified, the absence of a distinct dikaryotic stage. In spite of cytological studies on the presumed meiotic division in the basidium of A. bisporus, which show that two nuclei migrate into each of the two basidiospores produced (2, 3, 4, 8, 9, 10), the genetic basis for the self-fertility of this fungus has remained obscure. Several investigators (1, 3, 5) have noted that individual basidia of A. bisporus occasionally produce one, three, or four basidiospores, but two spores per basidium are most common. Most monosporous isolates are fertile, but some (20 to 30% of isolates) are reported as sterile (5, 11). Pairings conducted by Sinden (11) and Kligman (5) among these sterile isolates in some cases yielded sporophores and in others did not. However, no particular pattern of sexuality was recognized, and Kligman (5) stated, There is good evidence that the interaction between sterile strains is not sexual.