Assessing natural relationships in the Basidiomycetes by DNA analysis

DNA was isolated from mycelia and basidiomes of 44 different mushrooms and characterized by physical methods and reassociation kinetics. The GC contents of the genera Hypholoma, Pholiota, Stropharia, Psilocybe and Kuehneromyces ranged from 42.2 to 45.9 mol%. The Polyporus species gave GC contents between 50.4 and 54.1 mol %. The average genome sizes of species within the Stropharia aeruginosa complex ( S. aeruginosa, S. caerulea, S. albocyanea and S. ochrocyanea ) were approximately 22.2 × 10 9 dalton; 12–15% of the genomes consisted of repetitive DNA. DNA-DNA hybridization studies were performed by a fast spectroscopic method and on membrane filters using radioactively labelled DNA. DNA-DNA hybridizations were performed in the genera Polyporus, Psilocybe, Stropharia and Kuehneromyces . The spectroscopic method was used for the first time for investigations of the relatedness of Basidiomycetes. Good agreement between both DNA-DNA hybridization methods was observed only at high homology values. It was demonstrated on whole-cell DNA that both methods are useful for investigations of close relationships at the species level. Homology values between 95 and 100% obtained with the spectroscopic DNA-DNA hybridization method indicated conspecificity, whereas homology values between 40 and 60% indicated distant relatedness. Stropharia albocyanea and S. ochrocyanea were considered conspecific due to DNA-DNA homologies of close to 100%. The same was true for Stropharia squamosa (= Psilocybe squamosa) and S. thrausta (= Psilocybe squamosa var. thrausta ).