Abstract: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.
