A novel homothallic variety of Agaricus bisporus comprises rare tetrasporic isolates from Europe

Abstract

Among 400 wild specimens of A. bisporus collected in Europe, only three were tetrasporic. In the case of two of them from France, a previous study showed that one was homokaryotic and hypothetically belonged to a homothallic entity while the other was heterokaryotic and possibly resulted from hybridization between a member of this entity and a classical bisporic strain. A third tetrasporic specimen recently was discovered in Greece. Morphological and genetic comparisons, using alloenzymatic markers, molecular markers and ITS polymorphisms, reveal that this third specimen is homokaryotic and belongs, with the homokaryotic specimen from France, to the same entity. Dissimilarity analysis confirms the hybrid origin of the heterokaryotic specimen. Varietal status is proposed for this homothallic, highly homogeneous entity, and A. bisporus var. eurotetrasporus is described. This novel variety clearly differs from var. bisporus by its tetrasporic basidia and from var. burnettii by its longer spores. It has a complex story because it can interbreed with var. bisporus and shares the same habitat; however, because of its homothallic life cycle and its partial intersterility, it is probably in the process of speciation.

• Agaricus bisporus var. eurotetrasporus
• basidial spore number variation
• cultivated mushroom
• evolution
• homothallism
• ITS polymorphism

The authors are grateful to Richard W. Kerrigan, who performed the characterization at the βGLU locus at Sylvan Inc. and who provided the subfloccosus sequence data; to Mark Loftus (Amycel), who provided primer sequences of the PR 19 (= L36) marker; to Mike Challen (HRI), who contributed to the detection of the ITS polymorphisms; and to Régis Courtecuisse, who improved the diagnosis. We thank Lucette Pirobe and Simone Rextoueix for technical assistance. This research was supported by INRA and CTC under joint contract. Financial support from the BRG (Bureau des Ressources Génétiques) is also gratefully acknowledged.