Evidence for amphithallism and broad geographical hybridization potential among Agaricus subrufescens isolates from Brazil, France, and Thailand

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

“…burnettii correlatively to their basidial phenotypes which are highly bisporic and tetrasporic, respectively (Raper et al 1972;Callac et al 1993;Kerrigan et al 1994). In A. subrufescens, Thongklang et al (2014) observed that the ratio of heterokaryotic spores was also quite variable but genetic determinants are unknown and might be completely different. This variable ratio of heterokaryotic spores indicated that the rate of postmeiotic mitoses occurring in basidia must be also variable.…”

“…A. subrufescens is, to our knowledge, the Agaricus species having the broadest climatic and geographical range (Peterson et al 2000;Kerrigan 2005;Wisitrassameewong et al 2012a, b;Parra 2013;Gui et al 2014). Interfertility between isolates from South America, Europe, and Asia has been recently demonstrated (Thongklang et al 2014), indicating that a broad genetic base is available for the genetic improvement of this species.…”

“…For instance, of approximately 500 species of Agaricales, about 8 % were considered amphithallic (Lamoure 1989). Thongklang et al (2014) showed that A. subrufescens, like A. bisporus var. bisporus, has a multiallelic unifactorial (bipolar) system of sexual incompatibility with a single mating type locus (MAT) tightly linked to a centromere and an amphithallic life cycle.…”

“…In A. bisporus, such sister nuclei heterokaryons are infrequent (Summerbell et al 1989); the spatial position of the spindles of the second meiotic divisions (Evans 1959) and/or their asynchrony (Kamzolkina et al 2006) could explain the preferential migration in the same spore of two non-sister nuclei, each one per second meiotic divisions. In A. subrufescens, Thongklang et al (2014) reported the following three primary categories of single spore isolates that are represented in the theoretical tetrasporic random model of Fig. 1a:…”

“…The more the loci are centromere-linked, the more stringent this test is. In A. subrufescens, cultivated strains have been compared but breeding strategies are not reported in literature except the hybridizations performed by Kerrigan (2005) and Thongklang et al (2014). For developing such strategies in this species, the test for identifying mating-competent single spore isolates has to be reassessed.…”