Breeding of edible fungi with emphasis on the variability among French genetic resources ofAgaricus bisporus

Our laboratory (INRA) has developed breeding programs for several species of edible fungi. For example, "sporeless" strains were obtained by mutagenesis for Pleurotus ostreatus and Pleurotus pulmonarius, a hybrid strain of Lepista nuda has been marketed, and genetic variability has been studied in Tuber melanosporum. At present, the largest program concerns Agaricus bisporus, for which a collection of about 200 French isolates from 44 sites has been gathered. High genetic polymorphism appeared even within each site. Nine genetically different isolates from the same site were studied in experimental culture. Variability was observed for color of the cap, susceptibility to bacterial blotch, and the elevated basidial spore number trait. A single isolate, Bs 261, gave sporocarps having a majority of tetrasporic basidia, and spores which, for the most part, were homokaryotic. This strain was interfertile with typical bisporic strains. The resulting hybrids were either bisporic or tetrasporic, according to which homokaryon of Bs 261 was used. More investigations will be necessary to understand the presence of a rare tetrasporic strain in a bisporic population and also to study the relationship between Bs 261 and the tetrasporic strains of the previously described A. bisporus var. burnettii.