No abstract

Agaricus bisporus is known from field collections in several parts of southern Canada and the border states of Washington and Idaho. In Ontario, the species is associated with urban horticultural sites, agricultural areas, and thoroughfares. In British Columbia, Washington, and Idaho, the species is less well documented but occurs in habitats similar to those in Ontario. All studied isolates from these two regions were genotypically similar to those collected in Europe and also to a representative sample of cultivar isolates believed to be of European origin. In contrast, a population from forests of Picea in the Rocky Mountains of Alberta had genotypes that are very different from European and cultivar groups, including the putatively introduced populations in other parts of Canada. To a lesser extent, the Albertan individuals also differed from three other isolated natural populations, two in California and one in Israel. Two of 35 isolates from Alberta had nuclear genotypes that were partially or entirely consistent with European ancestry, indicating that foreign (probably cultivar) germ plasm has become established in the native habitat. Thirty of 35 isolates from the Alberta field sample had one of six mitochondria1 DNA (mtDNA) haplotypes known only from Alberta; the remaining five had an mtDNA type known from cultivar strains. However, nuclear genotypic similarity to other Albertan or European-cultivar isolates was not significantly correlated with presence or absence of this latter mtDNA type. The genetic diversity represented by the previously unknown Albertan population, and to a lesser extent by the heirloom varietal lineages and their derivatives that have become established in Ontario, British Columbia, Washington, and Idaho, is an important resource for breeders of this valuable fungal crop species. Threats to resource populations of this species, and possible responses, are discussed.

No abstract

This study employed nuclear and mitochondrial markers to assess the present‐day composition of the population of Agaricus bisporus in coastal California. Favourable weather in the fall, winter and spring of 1990–91 furnished an uncommon opportunity to collect and study field material of the ‘button mushroom’A. bisporus, a cultivated species, from the region. The previous such season occurred 13 years earlier. Ninety‐five nonredundant cultures from field material were prepared and genotypically characterized. These data were combined with data from earlier studies. Multilocus nuclear and mitochondrial genotypes were determined for 123 individuals. Genotypes were compared in pairwise fashion both within the sample and between this sample and others of diverse geographical origin or commercial provenance. Using parametric analysis and cluster analysis of nuclear similarities, and also mitochondrial data, two elements – indigenous and European – were apparent within the sample. This was consistent with our earlier results on a much smaller sample. At least 10 mitochondrial haplotypes (MTs) were present; based on genotypic similarities of associated nuclei, five (or six) MTs were Californian, four were European, and one was ambiguous. Based on MT origins, 54% of the 121 classifiable individuals in California were of European ancestry; natives constituted a minority at 46%. Even in the indigenous Monterey cypress habitat, where 84% of all individuals from California were sampled, non‐native A. bisporus appeared to have achieved parity (at 48–49%) with the native population. In all other habitats, which are far more extensive, European individuals outnumbered Californian natives by 4:1. Some evidence of hybridization between the two ancestral groups was found. European strains appear to have been resident in California for approximately one century. The extensive occupancy of the native habitat by non‐native germ plasm, the apparent inability of native strains to occupy or compete in non‐native habitats, and the disproportionately large inoculum reservoirs represented by non‐native habitat and agronomic activities all suggest that the native population is under considerable competitive pressure in what may be a very dynamic situation. If this surmise is correct, the native population may be at serious risk of further contraction, irreversible dilution through interbreeding, and possibly even extinction.