Interaction of a biological control agent, Chaetomium globosum, with seed coat microflora

The mechanism by which Chaetomium globosum, applied as ascospores to squash, snap bean, and pea seeds, reduces damage caused by larvae of the seed-corn maggot, Hylemya platura (Meigen), and soilborne plant pathogens was investigated. Chaetomium globosum ascospores germinate rapidly and cover the seed coat with a dense mat of mycelium soon after seeds are planted in soil. However, if seeds are not treated with C. globosum before planting, other organisms rapidly colonize the seed coat during germination. Seed flies oviposit near seeds in response to the growth of pseudomonads on the seed surface. Studies employing a selective medium indicate that Pseudomonas become the most prevalent genus occurring on the seed coat during seed germination. Treatment of seed with C. globosum suppresses the logarithmic growth of pseudomonads on the seed coat but affects neither bacterial populations in the soil surrounding the seed nor germination of Fusarium solani f. sp. pisi chlamydospores, either on the seed coat or in the soil surrounding the seed. A water-insoluble antibiotic was extracted from C. globosum treated seeds. After systemtic examination of other possibilities, it was concluded that this nondiffusable antibiotic substance produced by C. globosum suppresses pseudomonads responsible for stimulation of oviposition by seed flies as well as the soilborne plant pathogens.