Species clarification of oyster mushrooms in China and their DNA barcoding

Species of the Pleurotus ostreatus complex (oyster mushrooms) are one of the main groups of cultivated edible mushrooms in China, with abundant strains and a complex genetic background. Although the cultivation of oyster mushrooms is a very important industry in China, the inconsistent nomenclature of the complex is controversial and has led to much confusion and economic loss in the mushroom industry. In this study, we performed molecular identification of the species complex based on sequences of the internal transcribed spacer region (ITS), translation elongation factor 1-alpha (TEF1), and two genes that encode subunits of RNA polymerase II (RPB1 and RPB2). A total of 284 samples with different commercial names gathered from different mushroom spawn preservation centers, companies, and field isolations were investigated via phylogenetic analyses inferred from a single locus or multi-loci. Our analyses indicated that 56% of the strains were labeled with improper scientific names and that all of the strains could be divided into seven lineages, representing one morphological species each, namely P. abieticola, P. eryngii, P. cf. floridanus, P. ostreatus, P. placentodes, P. pulmonarius, and P. tuoliensis. Reference sequences for accurate identification of the taxa were developed or suggested. Meanwhile, we evaluated the suitability of the four candidate segments as DNA barcodes. Our analyses indicated that RPB2 was the most promising candidate segment of DNA barcode for the P. ostreatus species complex, taking into consideration the polymorphisms and other aspects of the four markers.