Evolutionary biology and interaction among the anastomosis groups of Rhizoctonia spp.

Abstract

Rhizoctonia solani Kuhn and other Rhizoctonia spp. are the plant pathogenic fungi widespread in the world and in both cultivated and noncultivated soils. Rhizoctonia spp. are readily isolated from diseased plants and soils, which differ in their pathogenicity, cultural, morphological and physiological characteristics. Identification of species and intraspecific groups (ISGs) is sometimes very difficult, due to the absence of the authentic cultures, which hinders mycological and pathological studies. The genus Rhizoctonia can be identified using various techniques such as, sequence analysis of ITS regions, DNA fingerprinting and the rDNA coding sequence. The introduction of the concept of anastomosis groups (AGs) or intraspecific groups has also aided species and subspecies identification. There are 13 different anastomosis groups exists in Rhizoctonia solani of which AG 1-4 were strong pathogenic on many plants and AG 6-10 were orchid mycorrhizae. Analysis of restriction fragment length polymorphisms (RFLPs) and the sequences within ribosomal RNA genes (rDNA) among different anastomosis groups of R. solani isolates exhibited DNA base sequence homology and diverging evolutionary affinities for hyphal anastomosis. More recently, ribosomal DNA (rDNA) sequences have been used to study the genetic relationships between AG of R. solani. The ecology and epidemiology of each ISG of R. solani must be investigated in order to gain a better understanding of this important group of fungi.