Possible role of xanthobaccins produced by Stenotrophomonas sp strain SB-K88 in suppression of sugar beet damping-off disease

Three antifungal compounds, designated xanthobaccins A, B, and C, were isol ated from the culture fluid of Stenotrophomonas sp, strain SB-K88, a rhizob acterium of sugar beet that suppresses damping-off disease. Production of x anthobaccin A in culture media was compared with the disease suppression ac tivities of strain SB-K88 and less suppressive strains that were obtained b y subculturing,train SB-K88 was applied to sugar beet seeds, and production of xanthobaccin A in the rhizosphere of seedlings was confirmed by using a test tube culture system under hydroponic culture conditions; 3 mu g of xa nthobaccin A was detected in the rhizosphere on a per-plant basis. Direct a pplication of purified xanthobaccin A to seeds suppressed damping-off disea se in soil naturally infested by Pythium spp. We suggest that xanthobaccin A produced by strain SB-K88 plays a key role in suppression of sugar beet d amping-off disease.