Genetic Structure of Natural Populations of Agaricus bisporus, the Commercial Button Mushroom

Agaricus bisporus (Lange) Imbach, the familiar button mushroom of commerce, 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 collection of 342 isolates from 12 locations. For 10 nuclear toci marked by RFLPs, we found high genetic diversity in all geographic populations. Among the 342 isolates, three different analyses of genetic diversity were carried out: the first on the total sample of 342 isolates, the second on a subset of 108 “cultivar-like” isolates shown previously to carry either of the two mitochondrial DNA haplotypes found in cultivated strains, and the third on the other 234 isolates that carry a diversity of mtDNA haplotypes not found in cultivated strains. We found that the samples of cultivar-like isolates from various locations were genetically more similar among themselves and to the cultivars than to the samples of other isolates from the same locations. Furthermore, the cuitivar-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 frequencies was consistent with the occurrence of hybridization between the cuitivar-like and the other strains in the coastal California population. Analyses of genetic diversity and genetic distance were all consistent with the historical record that cultivars and cultivar-like strains in the wild originated from Western Europe.