BIOASSAY TO SCREEN TOMATO SEEDLINGS FOR TOLERANCE TO METRIBUZIN

Abstract

Studies were carried out to develop a nutrient culture technique to select tomato (Lycopersicon esculentum Mill.) genotypes for tolerance to metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)-one], The bioassay consisted of growing tomato seedlings from seed in styrofoam cups modified with cheesecloth bases. The cups were floated on half-strength Hoagland’s solution with metribuzin and placed in controlled environment cabinets maintained at 25 °C, with a light intensity of 24.2 klx for 14 h/day and 80% RH. The nutrient–herbicide solution was changed every 5 days, Metribuzin at 0.25 ppm was the optimum concentration for selection between tolerant and susceptible cultivars, under the environmental conditions described. The seedlings were harvested 15 days after sowing and scored for phytotoxic symptoms; seedling height to the terminal bud was measured. It was possible to screen a large number of seedlings in a confined space, using this technique. Significant differences were noted between tolerant Fireball and Vision cultivars and susceptible Heinz 1706 and Trimson cultivars.