Use of Isozyme Variation to Identify Genotypic Classes of <i>Agaricus Brunnescens</i>

Abstract

Thirty-four commercial and 162 research-maintained lines of Agaricus brunnescens deposited in The Pennsylvania State University Mushroom Culture Collection were examined electrophoretically for isozyme variation. Based on the variability at five structural gene loci (Gpt, Adh, Mpi, Pep-LLL-1, and Pep-LLL-2) they were partitioned into 27 genotypic classes. The allelic variability observed in mycelial extracts of these lines potentially allows the recognition of over 20,000 unique genotypic classes. The fact that only five genotypic classes were actually observed among commercial lines examined is evidence that the common mushroom is a near monoculture. Data from single spore-derived cultures of A. brunnescens revealed that most of these cultures retained heterozygosity at those loci heterozygous in the parental line. A limited number of recombinants were noted, i.e., heterozygous for some loci and homozygous for others. A small fraction (<5%) were homozygous at multiple loci suggesting that they may be homokaryotic. These observations support the contention that low levels of meiotic recombination occur and the chromosomal segregation is nonrandom in A. brunnescens.