Prevalence, characterization and cross infectivity of Rhizoctonia species causing rice sheath blight complex in Tamil Nadu

Sheath blight of rice is a significant biotic stress caused by various Rhizoctonia species, including Rhizoctonia solani (sheath blight), Rhizoctonia oryzae-sativae (aggregate sheath spot) and Rhizoctonia oryzae (sheath spot). The presence of these diverse Rhizoctonia species highlights the complexity of sheath diseases and emphasizes the need for management approaches to mitigate their impact on rice production. In the current study, 37 isolates of Rhizoctonia spp. were collected from various rice-growing regions of Tamil Nadu, India during 2021-22. The isolates were characterized phenotypically and for their virulence pattern. The cultural characteristics including mycelial and sclerotial morphology of the isolates were recorded, aiding in the identification and characterization of the pathogens. An amplicon size of 265 bp was obtained in PCR analysis of R. solani isolates which confirmed their belonging to anastomosis group AG1-IA. Further differentiation using species-specific primers GMRS-3, GMRO-3 and GMROS-2 revealed that 30 isolates belonged to R. solani and 7 to R. oryzae-sativae. The highly virulent isolates of R. solani and R. oryaze-sativae were selected for host range studies in different hosts and the results indicated that all the plant and weed species were found to be infected by both R. solani and  R. oryzae-sativae except pig weed and khaki weed.