Morphological and pathological variability in rice isolates of Rhizoctonia solani and molecular analysis of their genetic variability

Nineteen isolates of Rhizoctonia solani collected from different rice varieties grown in various regions of Punjab were studied for their morphological and pathological characterization. Majority of the isolates were fast growing with raised and fluffy colonies and hyphal width of 9.6 mu m while four exhibited moderate growth rate. Colony colour in all except two isolates was light yellowish brown. While sclerotial number per 5.0 mm culture disc of the test isolates ranged between 2.1 and 11.2 mm, their size varied between 1.31 and 2.08 mm. Sclerotial colour in all except two isolates was dark brown and most of these were found scattered in the colony. There was no relationship between morphologically similar isolates and their pathogenic behaviour. Majority of the isolates produced lesion length between 45.6 and 58.2 mm on detached rice leaves (cv. PR116). Molecular characterization of genetic diversity in the test isolates was studied by using 10 inter simple sequence repeats (ISSR) and eight random amplified polymorphic DNA (RAPD) markers. The size of amplified DNA bands ranged from 0.25-3.0 to 0.5-4.0 kb with ISSR and RAPD markers, respectively. Combined data set of 155 DNA markers were analysed with UPGMA resulting five clusters with 49-89% genetic similarity. Most of the isolates showed grouping specific to the host variety. Out of these two types of DNA markers, RAPD markers were able to detect more genetic variability when compared to ISSR markers.