Sexuality and Genetic Identity in the Agaricus Section Arvenses

Abstract

Twelve wild collections and one commercial strain were used to characterize breeding systems and to develop molecular identities in the Arvenses section of the genus Agaricus, which includes the "horse mushroom" A. arvensis. Two morphotypes were identified based on macro-and micromorphological features. However, not all collections could be delimited by conventional taxonomic characters. Sequencing of the small subunit intergenic spacer (ITS) region (368 to 370 bp) of the rRNA genes clearly resolved the 13 collections into two clusters consistent with the identified morphotypes. Single-spore progenies and mating type testers were established and used to test intra-and interstock compatibility. The two compatibility groups identified were consistent with ITS clusters. Compatibility group I stocks readily interbred within the constraints of a unifactorial heterothallic system with a multiallelic mating type factor. Compatibility group II had a more restricted breeding pattern, and interactions were difficult to predict on the basis of mating type. Morphological data, ITS sequences, and the ability to interbreed suggest that these collections are part of a complex of interrelated species. Single-spore, homokaryotic isolates from both compatibility groups were able to fruit in compost culture, and two of the collections may represent natural homokaryotic fruiting. We conclude that species from the section Arvenses have versatile unifactorial heterothallic life cycles that permit both interbreeding and homokaryotic fruiting.The genus Agaricus has a worldwide distribution, with up to 90 species recorded in Europe (2, 10) and more than 40 species recorded in the United Kingdom (13). Estimates for the worldwide totals of Agaricus species vary, but are likely to exceed 200. These species, which include the cultivated white button mushroom Agaricus bisporus (Lange) Imbach, exhibit a variety of breeding systems. Examples of both homothallic and heterothallic life cycles have been found (7,20). Mushrooms from the Arvenses section of Flavescentes (10) have medium to large white sporophores with a yellowing surface, double pendent annular ring, and an aniseed or almond-like odor (10, 28). The section Arvenses contains 19 defined species within six subgroups: Aestivalis, Arvensis, Augustus, Macrosporus, Spissicaulis, and Sylvicola (10). These morphologically similar species include A. sylvicola (Vitt.) Sacc., the wood mushroom; A. arvensis Schff. ex. Fr., the horse mushroom; A. nivescens (Möll.) Möll.; A. macrocarpus (Möll.) Pilat; and A. essettei Bon. (syn. A. abruptibulbus Peck sensu auct. europ) (10). Several species from the Arvenses section have commercial potential (23,(25)(26)(27). Morphological features used to distinguish taxa within the Arvenses section include sporophore color, the presence of a "cogwheel" structure on the lower surface of the double ring, and a swollen base to the stipe (e.g., A. abrubtibulbus), the size of spores and/or cheilocystidia, and habitat of the specimen (10, 15, 28).Identification within...

Differentiation of Agaricus species and other homobasidiomycetes based on volatile production patterns using an electronic nose system

“…Interestingly A. avensis (93-7) was differentiated from A. nivescens (W6I). These two species are inter-related but can be distinguished by morphological, compatibility and DNA analyses (Calvo-Bado et al 2000). Although some minor overlapping occurred between samples within the Agaricus genus, the differentiation between diverse homobasidiomycete genera was more obvious based on volatile production patterns.…”

“…In this study, the CA cluster groups were not always consistent with relationships determined from the molecular analysis. In terms of genetic identity, A. arvensis and A. nivescens are closely related, both fall within the section Arvenses and although different species, they are capable of limited interbreeding (Calvo-Bado et al 2000). A more striking difference is the comparison between A. bisporus and A. subfloccosus.…”

Spore behaviors reveal a category of mating-competent infertile heterokaryons in the offspring of the medicinal fungus Agaricus subrufescens

“…With two replicates for each mating test, it was not rare to observe a positive reaction in only one of the two replicates. False negative reactions are common in A. bisporus (Kerrigan et al 1994) as in some species of Agaricus section Arvenses to which A. subrufescens belongs (Calvo-Bado et al 2000).…”

RAPD molecular differentiation of the cultivated strains of the jelly mushrooms, Auricularia auricula and A. polytricha

“…This makes strain protection problematic, and impedes strain improvement. Molecular markers of rDNA sequencing, RFLP (restriction fragment length polymorphism), RAPD (random amplified polymorphic DNA), microsatellite and mitochondrial genotypes have all been used to discriminate mushroom species and/or strains of Agaricus (Castle et al 1987;Sonnenberg et al 1991;Khush et al 1992;Barroso et al 2000;Calvo-Bado et al 2000;Ramirez et al 2001), Auricularia (Yan et al 1999), Ganoderma (Hseu et al 1996), Lentinula (Chiu et al 1996), Stropharia rugoso-annulata (Yan et al 2003), and Volvariella (Chiu et al 1995). These technologies provide ways to obtain reliable data for mushroom strain identification and protection.…”