The indigenous coastal Californian population of the mushroom Agaricus bisporus, a cultivated species, may be at risk of extinction

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.

Survival of an introduced ectomycorrhizal Laccaria bicolor strain in a European forest plantation monitored by mitochondrial ribosomal DNA analysis

“…In this population, neither nuclear migration (Casselton & Economou, 1985) nor invasive nuclear replacement (Rizzo & May, 1994), reported during in vitro mating of basidiomycetes, led to detectable coexistence of introduced LrDNA haplotype with local nuclei or vice-versa. This contrasts with the only intercontinental introgression reported so far, on Californian Agaricus bisporus (Kerrigan et al, 1998), where both introduced mitochondrial and nuclear markers often coexist with indigenous markers. However, typing mitochondria with LrDNA does not give a whole genomic fingerprint, and mitochondrial recombination after hyphal fusion (Baptista-Ferreira et al, 1983 ;Matsumoto & Fukumasa-Nakai, 1996 ; Barroso & Labare ' re, 1997), which would not preserve the LrDNA haplotype, cannot be excluded.…”

Fine-scale genetic analyses reveal unexpected spatial-temporal heterogeneity in two natural populations of the commercial mushroom Agaricus bisporus

“…Unfortunately, fruiting is an uncommon event for A. bisporus in nature and no method is available to directly isolate and analyse spores and mycelia from its natural habitats. Putative hybrids have also been reported in a coastal Californian population of A. bisporus (Kerrigan et al, 1998).…”

“…An earlier report based on samples from different areas in California suggested evidence of pseudohomothallic reproduction in the Californian populations of A. bisporus (Kerrigan et al, 1998). Those inferences were tentative, not supported by direct observation of mushroom from the same site over time (Kerrigan et al, 1998).…”

Genetic and Phylogeographic Structures of the Symbiotic Fungus Tuber magnatum

“…Artificial fungal plantations often are established in naturally productive areas to counterbalance a sharp decline in wild truffle harvests. Potential problems related to microbial competition are largely unexplored with respect to truffle cultivation, and the consequences of the deliberate introduction of nonnative strains into an indigenous population have been serious for other edible mushrooms (16,36). Hence, the profitable commercial practice of artificial fungal plantations may cause a loss of fungal biodiversity, and local strains with unique commercial characteristics might become extinct.…”