Systematics, mating compatibility, and ribosomal-DNA variation in Agrocybe section pediadeae.

摘要

Mating systems, crossing compatibility, morphology, and restriction site polymorphisms in ribosomal DNA (rDNA) were examined as part of a systematic and phylogenetic analysis of Agrocybe pediades (Fries) Fayod (Homobasidiomycetes, Bolbitiaceae) and five intersterile but phenotypically similar species.;Unlike most species of Agrocybe, which have bifactorial heterothallic mating systems, the mating system of A. pediades is unifactorial heterothallic. Inter-isolate crosses between collections of A. pediades demonstrated the existence of two rigorously intersterile mating groups (I, II) in North America and Europe. A single isolate from eastern North America, constituting a third intersterility group (III), was incompatible with all other A. pediades isolates. Isolates originating from Asia were intercompatible with both mating groups I and II but the degree of compatibility and stability of resultant dikaryons varied. Due to overlapping macro- and micromorphology and the absence of distinguishing characteristics between the mating groups it is concluded that A. pediades constitutes a single taxonomic species.;A single rDNA unit repeat from A. pediades R 665 was cloned and characterized. Fifty-eight restriction site positions were surveyed among isolates from the mating groups of A. pediades. Four polymorphic restriction sites, each with the enzyme Bam HI, were observed. Combinations of the polymorphic Bam HI restriction sites produced six different restriction profiles (haplotypes). Only the Asian isolates were characterized by a unique haplotype whereas the North American and European isolates shared four haplotypes in common.;The rDNAs of A. pediades and five species of Agrocybe with unifactorial mating systems, were mapped with eighteen restriction enzymes. Seventeen restriction sites were phylogenetically informative and a cladistic analysis yielded a single most parsimonious tree indicating. A. neocoprophila, A. subamara, A. platysperma, and A. pediades are monophyletic. Thus, the unifactorial mating system characterizing these taxa probably originated in a common ancestor. The close relationship of A. pediades to the pleurocystidiate taxa A. neocoprophila, A. subamara, and A. platysperma, indicates that the absence of pleurocystidia in A. pediades is a derived character.