BIOLOGICAL-CONTROL OF PYTHIUM DAMPING-OFF AND APHANOMYCES ROOT-ROT OF PEAS BY APPLICATION OF PSEUDOMONAS-CEPACIA OR P-FLUORESCENS TO SEED

Certain rhizosphere bacteria screened in a growth chamber bioassay for control of Pythium damping-off and Aphanomyces root rot of peas (Pisum sativum) also controlled these diseases in field-grown plants. Three bacterial species-Pseudomonas cepacia (strain AMMD), P. fluorescens (strain PRA25), and Corynebacterium sp. (strain 5A)-were tested at three field sites for performance as seed dressing either alone or in combination with captan. Seed treatment with P. cepacia and P. fluorescens, alone or in combination with captan, effectively controlled disease. In 1989, when Aphanomyces root rot was moderate to severe, seed treatment with the bacteria resulted in significant increases in emergence and yield at all three sites and in reduced disease severity at two sites, regardless of captan treatment. P. cepacia was the most effective bacterium, increasing emergence by an average of 40% and yield by 48% compared with captan alone. P. fluorescens without captan was also very effective, increasing both emergence and yield by an average of 33% compared with captan alone. Corynebacterium sp. without captan increased emergence by 23% and yield by 12% compared with captan alone. In 1988, when severe drought limited disease development, yield was generally increased by application of all three bacteria, with or without captan, but these differences were not statistically significant.