GENETIC-STRUCTURE OF NATURAL-POPULATIONS OF AGARICUS-BISPORUS, THE COMMERCIAL BUTTON MUSHROOM

Agaricus bisporus (Lange) Imbach, the familiar button mushroom of comm erce, is a major vegetable crop around the world, In the past 10 years a significant worldwide effort has been made to collect Agaricus germ plasm from the wild, Here we report the genetic analysis of a collect ion of 342 isolates from 12 locations, For 10 nuclear loci marked by R FLPs, we found high genetic diversity in all geographic populations. A mong the 342 isolates, three different analyses of genetic diversity w ere carried out: the first on the total sample of 342 isolates, the se cond on a subset of 108 ''cultivar-like'' isolates shown previously to carry either of the two mitochondrial DNA haplotypes found in cultiva ted strains, and the third on the other 234 isolates that carry a dive rsity of mtDNA haplotypes not found in cultivated strains. We found th at the samples of cultivar-like isolates from various locations were g enetically more similar among themselves and to the cultivars than to the samples of other isolates from the same locations, Furthermore, th e cultivar-like samples showed no evidence of genetic differentiation between continents and between regions within a continent, In contrast , samples of other isolates showed significant differentiation at the same levels of the geographic hierarchy, A comparison of gene frequenc ies was consistent with the occurrence of hybridization between the cu ltivar-like and the other strains in the coastal California population , Analyses of genetic diversity and genetic distance were all consiste nt with the historical record that cultivars and cultivar-like strains in the wild originated from Western Europe.