Abstract
The sclerotia of Wolfiporia cocos are a kind of traditional medicine and food with excellent benefits and are widely used in China, Japan, and other Asian countries. The mating system of fungi is not only of practical importance for breeding but also has profound effects on genetic variability and molecular evolution. However, the lack of clamp connections in W. cocos increases the difficulty of research on mating systems. In this study, homokaryons and heterokaryons were distinguished by comparing the characteristics of culture, fruiting tests, and molecular markers, which was further demonstrated by k-mer analysis based on Illumina sequencing. Uninucleate, binucleate, and nuclei-free condition basidiospores of W. cocos were observed, and binucleate basidiospores were the most predominant. Brown-type colonies, slow growth rates in both PDA medium and sawdust substrate, and neutral pH after the growth of mycelia and unfruiting were found to be the morphological and growth characteristics of homokaryotic strains. Primers SSR37 and 38 were screened to identify homokaryons. K-mer analysis based on Illumina sequencing exhibited different heterozygous ratios for homokaryons and heterokaryons. The results revealed that pseudo-homothallism was the predominant mode of reproduction in the Chinese population of W. cocos, and heterothallism also existed in all probability. This study will be helpful for the cross-breeding of this precious medicinal mushroom and for understanding its evolution and population structure.
Highlights
IntroductionDried sclerotia are widely used as traditional crude drugs in China, South Korea, and Japan, whereas they are used as food by Native Americans
Homokaryon is the basic material for cross-breeding, and the existence of homokaryon and heterokaryon makes it difficult to determine the mating system of W. cocos
This report identified the homokaryon from numerous single spore isolates (SSIs) by comparing culture characteristics, fruiting tests, and molecular markers, which was further demonstrated by k-mer analysis based on Illumina sequencing of strain SS20
Summary
Dried sclerotia are widely used as traditional crude drugs in China, South Korea, and Japan, whereas they are used as food by Native Americans. It was first recorded in Shennong Bencao Jing, which is the earliest authoritative monograph on pharmacy in China (Gu, 2007), and in each edition of the Chinese pharmacopoeia. During the life cycle, fruiting bodies were rarely found in the field; the scientific description of the sclerotia was given in 1822 (von Schweinitz, 1822), but the sexual stage remained unknown until 1922 (Wolf, 1922). There is no evidence of rhizomorphs in the soil surrounding the sclerotia (Wolf, 1922), and the life cycle of this fungus is yet to be clarified (Li et al, 2019)
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