Diversity and Molecular Characterization of Fungal Pathogens Associated with Paddy in the Cauvery Delta Region
Fungal diseases severely threaten rice productivity and food security across the Cauvery Delta. This study investigated the prevalence, morphological variation, pathogenicity, and molecular identities of three primary fungal pathogens Bipolaris oryzae, Pyricularia oryzae and Rhizoctonia solani collected across Tamil Nadu and Karaikal U.T. Field surveys revealed wide spatial variation in disease intensity, with maximum percent disease index (PDI) recorded for sheath blight (54.00% in Nannilam), blast (42.34% in Aduthurai) and brown spot (30.40% in Pattukkottai). In vitro characterisation of ten isolates per species demonstrated notable diversity in mycelial growth rates, colony pigmentation, conidial features, and sclerotial formation. Controlled greenhouse evaluations on susceptible rice cultivar BPT-5204 confirmed varying degrees of virulence among isolates, identifying Bo8 (mean PDI 28.95%), Pg7 (mean PDI 38.99%) and Rs6 (mean PDI 36.85%) as the most aggressive pathotypes for brown spot, blast, and sheath blight, respectively. PCR amplification and Sanger sequencing of the ribosomal DNA internal transcribed spacer (rDNA-ITS) region definitively confirmed species identities for the hyper-virulent isolates: B. oryzae Bo8 (558 bp; ON556554), P. oryzae Pg7 (541 bp; ON556555) and R. solani Rs6 (514 bp; ON556551). These characterised pathotypes provide critical reference strains for regional resistance breeding and targeted disease management strategies.