Relatedness of three species of Agaricus inferred from restriction fragment length polymorphism analysis of the ribosomal DNA repeat and mitochondrial DNA

The ribosomal DNA (rDNA) repeat of Agaricus brunnescens (= A. bisporus) was cloned and mapped for six restriction endonucleases. The map positions of the 26S, 18S, and 5.8S rRNA genes on the 9.2 kilo base pairs (kbp) repeat were determined by alignment of sites conserved in the rRNA genes of other fungi. The rDNA restriction site maps for six isolates of A. brunnescens, five isolates of A. bitorquis, and three isolates of A. campestris were compared using cloned A. brunnescens (Ag 50) rDNA as a hybridization probe. The rDNA restriction patterns for all six A. brunnescens isolates were identical. The A. bitorquis and A. campestris isolates were subdivided into two groups each, according to rDNA restriction-site polymorphisms. The A. brunnescens and A. bitorquis rDNAs were distinguished by a 0.7 kbp length difference in the noncoding spacer between the 18S and 26S rRNA genes. Despite the almost perfect conservation of the coding region between species, the noncoding spacers of A. campestris and the other two Agaricus species were too divergent to propose a simple series of mutational events to account for the differences. Interstrain and interspecies variation in the mitochondrial DNA was also surveyed. Strain-specific mitochondrial DNA restriction patterns were recognized and fewer differences were observed between the A. brunnescens and A. bitorquis isolates than between A. campestris and the other two species.Key words: Agaricus brunnescens (= A. bisporus), Agaricus, rDNA, mitochondrial DNA, restriction fragment length polymorphism analysis.