Seed treatment improved seed quality, seed production and controlled downey mildew disease on sweet corn

Abstract

Downy mildew is a major disease in sweet corn caused by Peronosclerospora maydis, a seedborne pathogen. An effort to get successfully field production is by using high quality seeds. Seed quality consists of physical, physiological, genetical, and pathological (seed health) quality. The aims of this research were to evaluate the effectiveness of seed treatment using synthetic fungicide and biological agent to control downey mildew disease, to improve plant growth, seed production, and seed quality of harvested sweet corn. This study consistsed of 3 stages: pre experiment, experiment 1, and experiment 2. In pre experiment, the compatibility among the biological agents, the compatibility between biological agents and synthetic fungicides, phytotoxicity and hypersensitivity were tested. The optimum matriconditioning ratio and the time of conditioning were also evaluated. All the pre experiment activities were conducted in laboratory. Experiment 1 was done to evaluate the effect of seed treatments on seed physiological quality, disease incidence, and plant growth of sweet corn. Seed physiological quality test was conducted in laboratory, whereas disease incidence and plant growth were done in plastic house. Experiment 1 was conducted using completely randomized design with one factor which was seed treatment. The best result of experiment 1 was used as seed treatment in experiment 2 which was conducted in the field. Split plot design with two factors was used in this experiment, sweet corn line as main plot and seed treatment as sub plot. Experiment 2 was conducted to evaluate the effect of seed treatments on disease incidence, plant growth and seed production. The result of compatibility test showed that Bacillus megaterium did not inhibit growth of Brevibacillus laterosporus, and vice versa. The growth of biological agents (B. megaterium and B. laterosporus) were not inhibited by synthetic fungicide. Hypersensitivity test of B. megaterium and B. laterosporus isolates showed negative result. The ratio of seed : burned rice hull (100 mesh): solvent = 3: 0.5: 1 and 24 hours conditioning at 20 0C was optimum, resulting the highest seed physiological quality. In experiment 1, the best vigor index and germination speed resulted from B. laterosporus biological agent treatment. The lowest disease incidence (64%) was by synthetic fungicide treatment without matriconditioning, whereas control and all non fungicide treatments produced 100% disease incidence. All treatments except matriconditioning and control increased plant growth. Matriconditioning + mixture of synthetic fungicide + B. laterosporus was the best seed treatment in increasing plant dry weight. In experiment 2, line 07 was more resistant to downy mildew attack. Line 07 also produced better growth than line 06. Seeds of line 07 applied with matriconditioning + mixture of fungicide treatment + B. laterosporus resulted the highest ear weight per plant (53 g). Application of all seed treatments on line 07 were not able to increase the quality of harvested seed, but matriconditioning + mixture of synthetic fungicide + B. laterosporus on line 06 was able to increase physiological quality of harvested seed.