丝核菌的分类系统:现状及存在问题

Taxonomy of Rhizoctonia fungi:status quo and problems

以重要植物病原菌为特征的丝核菌是一类在土壤中广泛分布的丝状真菌,通常不产孢,以菌丝或菌核的形式存在,多样性非常丰富。本文基于国内外最新研究进展,对依据菌丝体的细胞核数目、菌丝融合、有性生殖和系统进化等方面的基本特征展开的丝核菌分类体系及分类现状进行了综述。基于菌丝的细胞核数目,丝核菌被分为单核、双核和多核丝核菌三大类群。自然界中单核丝核菌数量极少,多核和双核丝核菌在全球分布广泛,占丝核菌的绝大多数。基于菌丝融合试验的结果,目前多核丝核菌被分为13个菌丝融合群,双核丝核菌被分为18个菌丝融合群。部分融合群内又根据一些稳定的特征分了亚群,但亚群的建立标准并不统一。目前的分子系统学研究结果基本支持丝核菌的菌丝融合群及亚群的分类。基于部分有性世代被发现的菌株的形态特征,多核和双核丝核菌分别被鉴定为亡革菌属和角担菌属。此外,目前已有分属重要植物病原菌和兰科菌根菌类群的至少9个融合群或亚群的17个菌株完成了基因组测序,比较基因组学和线粒体组学开始在丝核菌分类和进化研究中发挥作用。丝核菌分类系统特殊且复杂,作者在文末提出了目前丝核菌分类学研究面临的问题和今后研究的趋势,期待更多的学者参与到这个重要菌群的研究中来。

Plant pathogens Rhizoctonia spp.,which include diverse organisms,are soil inhabitants.They produce no spores and survive as hyphae and sclerotia.This paper reviewed classifications(according to number of nuclei,anastomosis,sexual reproduction,phylogeny,ect.)of Rhizoctonia fungi and analyzed the status quo of the taxonomy.Based on the number of hyphal nuclei,Rhizoctonia spp.are classified into uninucleate(UNR),binucleate(BNR),and multinucleate fungi(MNR).BNR and MNR are omnipresent,while UNR are rarely found in the nature.According to the result of anastomosis reactions,MNR and BNR are respectively categorized into 13 and 18 anastomosis groups(AGs).Some AGs are further divided into subgroups based on some stable characteristics,but the standards for the subclassification are not uniform.The results of molecular phylogenetic research also support the classification of AGs and subgroups.Based on the morphological characteristics of some Rhizoctonia isolates with sexual reproduction,MNR and BNR are identified as Thanatephorus and Ceratobasidium,respectively.At present,genome sequencing has been completed for at least 17 isolates of 9 AGs or subgroups which are important plant pathogens and orchid mycorrhizal fungi.Comparative genomics and mitogenomics have played an important role in the classification and phylogenetic research of Rhizoctonia.In summary,the classification systems of Rhizoctonia are special and complex.The authors also analyzed the problems in the taxonomy of Rhizoctonia and the future research trend,hoping to provide a reference for the future research on Rhizoctonia.