GENETIC RELATEDNESS WITH SPECIAL REFERENCE TO VIRULENCE AMONG THE ISOLATES OF RHIZOCTONIA SOLANI CAUSING SHEATH BLIGHT IN RICE

摘要

Seven field isolates of the rice sheath blight pathogen (Rhizoctonia solani) collected from different rice-growing areas in South India, shelved morphological and physiological variations. For each isolate, the virulence index was calculated for the symptom expression based on mean disease grade. The isolate collected from Thiruvanandapuram (RS7) was highly virulent. The phytotoxin produced by each isolate was purified and the electrolyte leakage from rice leaf bits by respective toxin fractions was assessed. The activities of pectic enzymes, viz., exo-polygalacturonase, endo-polygalacturonase and pectin methylesterase were assayed. The variation among the isolates in the mycelial and extracellular protein profiles were studied by SDS-PAGE analysis. The field isolates varied in their cultural characters, pectic enzymes activity and virulence. There was no association between pectic enzymes production and virulence, while the toxin production was associated with che virulence. The genetic relatedness among the field isolates regarding virulence has been discussed.