Morpho-genetic variability of Rhizoctonia solani population causing sheath blight disease in rice (Oryza sativa L.)

Abstract

Aim: The present study aims to investigate the morpho-pathological and molecular variability among the R. solani isolates from different geographical regions of India. Methodology: R. solani isolates were collected from sheath blight infected rice plants from diverse regions of Western Uttar Pradesh and Uttarakhand. Morphological variability among the isolates was studied in-vitro on PDA medium. The anastomosis grouping was determined by hyphal fusion reactions paired with tester strain and confirmed by AG-specific-PCR assay. Pathogenicity assay was conducted in-vivo on four rice varieties using artificial inoculation method under greenhouse conditions. Evolutionary relationship among the isolates was determined using rDNA-ITS-PCR with ITS1 & ITS4 primers. Further, genetic variability among the isolates was assessed using ISSR primers. Results: A total of 21 isolates of R. solani were recovered and based on morphological and sclerotial features, significant variation was observed among the isolates. All the isolates belonged to AG1-IA group which was confirmed by AG-specific PCR assay. Based on pathogenicity, eight isolates were found highly virulent, eight were moderately virulent and six were less virulent. ISSR markers showed high level of polymorphism and grouped all isolates into three major clusters showing partial correlation with geographical origin of the isolates. Sequence variations in ITS region were observed in the form of insertions or deletions of the nucleotide when rDNA-ITS sequences were compared that led to the interspecies diversity and diversity was observed in clad-specific manner. The phylogenetic tree separated the isolates into ten distinct clades showing high level of genetic diversity. Interpretation: The results of the present study may be helpful for the phylogenetic classification of complex R. solani species and provide information on the genetic divergence and occurrence of pathogenic races. This information will be helpful for the development of effective disease management strategies based on the molecular breeding and other approaches. Key words: Anastomosis, Genetic diversity, ISSR, Pathogenicity, R. solani, Sheath blight