MORPHOLOGICAL, BIOCHEMICAL AND MOLECULAR VARIABILITY OF SCLEROTIUM ORYZAE ISOLATES ASSOCIATED WITH STEM ROT OF PADDY IN KARNATAKA

Abstract

Sclerotium oryzae isolates obtained from stem-rot-affected rice in Karnataka were characterized for cultural, sclerotial, biochemical and molecular variability. Isolates were compared on potato dextrose agar (PDA), Sabouraud dextrose agar, nutrient agar, Richard's agar and Hanson's agar. Considerable isolate-to-isolate variation occurred in colony colour, texture and radial growth. On PDA, SO-1 and SO-2 reached 84 mm after 48 h, whereas several isolates remained slow growing even after 96 h. Sclerotial initiation generally occurred within 4-6 days; 23-69 sclerotia plate-1 were produced, sclerotial diameter ranged from 1.6 to 3.6 mm and 100 sclerotium dry weight ranged from 36.8 to 77.8 mg. Glucose was utilized by all isolates and was the most consistently preferred carbon source; indole production was frequent whereas methyl-red reduction occurred in fewer isolates. Of 45 ITS-region sequences generated, 30 high-quality sequences were retained, identified as S. oryzae and deposited in GenBank. Phylogenetic analysis resolved two principal groups, demonstrating substantial phenotypic and molecular heterogeneity within the Karnataka population.