CHARACTERIZATION OF RICE FALSE SMUT PATHOGEN USTILAGINOIDEA VIRENS AND ITS USTILOXIN TOXIN IMPACT ON BRINE SHRIMP

Abstract

Survey on rice false smut disease has been conducted at Erode, Tanjore, Perambalur and Coimbatore districts of Tamil Nadu, India. Among the areas surveyed, higher disease incidence was recorded in the paddy variety bhavani cultivated in Bhavanisagar, Erode district in which the rice false smut disease incidence was recorded as 40%. The pathogenicity test revealed the symptom development within 12-15 days of conidial suspension injection. In order to characterize the fungal isolates of Ustilaginoidea virens, a causal for rice false smut disease was cultured on Potato Sucrose Agar (PSA) medium. The pathogen was characterized morphologically which exhibits white mycelium that turns yellow and becomes olive green on maturity. Molecular confirmation was carried out among the collected isolates that were amplified at 380 bp region which is found specific for the pathogen Ustilaginoidea virens using the primers US 1-5 and US 3-3. The extraction and purification of ustiloxin was carried out using flash chromatography. On purification 100% water and 30% ethanol fraction was collected separately. The cytotoxicity assay of ustiloxin in brine shrimp resulted that the mortality at 1% concentration of ustiloxin was 96% and the lowest mortality (26%) was observed at 0.2% concentration. The lethal dosage 50(LD50) was confirmed at the concentration of 0.4% ustiloxin having the mortality rate of 52% using brine shrimp bioassay