Morpho-Cultural, Pathological and Genetic Variability in Rhizoctonia solani Isolates Infecting Crops in Rice Based Cropping Pattern of Punjab State; India

Abstract

Rhizoctonia spp. which was earlier considered a minor disease causing pathogen under Punjab conditions now is a major threat to crops grown in Punjab. The present study investigated the morphological and cultural variations in Rhizoctonia population, pathogenic behaviour and extent of genetic differentiation between infecting populations of R. solani from different hosts. By species specific primers, Rhizoctonia species in Punjab were identified as R. solani (87.8 %), R. oryzae (11.1%) and R. oryzae-sativae (1.1 %). Morphological characterization of Rhizoctonia spp. based on the growth rate, colour of mycelium and sclerotial characters. A high degree of variation among these R. solani isolates was established. Potato isolates belonging to the different geographic areas of the state were clustered together and cotton isolates also related. R. solani isolates from maize, rice, wheat and chilli formed two major cluster groups. The molecular data on AG specific primers revealed that 46.8% of the isolates belonged to AG1-1A, while AG1-1B (10.1%), AG2-1 (13.9%), AG3 (12.7%). Using interspecific sequence repeat primers, isolates were clustered into three major groups (I, II, III). Group III consisted of isolates, mostly from Ludhiana irrespective of the hosts, indicating existence of genetic similarity among these isolates. Isolates were also found to partially group according to place of origin and the host. Further a partial relationship between the level of severity on rice was observed. The diversity and relatedness in hosts of R. solani isolates from Punjab indicates the need to consider the cropping pattern to reduce the inocula in the soil.