Control of soil-borne pathogens on potted vegetables with microorganisms isolated from suppressive compost.

Compost suppressiveness depends on chemical, physical and microbiological composition and antagonists can be isolated from high quality composts. The objective of the present work was to isolate microorganisms from a suppressive compost and to test them for their activity against soil-borne pathogens on vegetable crops. A compost from green wastes that showed a good suppressive activity in previous trials was used as source of microorganisms. Serial diluted suspensions of compost samples were plated on different media for isolation of fungi and bacteria. Colonies were isolated from plates and tested in greenhouse on potted plants against Fusarium oxysporum f. sp. basilica-basil, Pythium ultimum-cucumber and Rhizoctonia solani-bean. Antagonistic microorganisms were blended into a peat substrate at 10 g L−1 fungal biomass or 10 ml L−1 liquid culture 14 days before seeding. Pathogens were mixed into the substrate at 1 g of wheat kernels L−1 7 days before seeding. Seeds of basil, cucumber and bean were sown into 2 L pots in greenhouse. The number of alive plants and above ground biomass were measured 20-30 days after seeding. Four fungi and three bacteria were able to significantly control P. ultimum and F. oxysporum F. sp. basilici. None of them was effective against R. solani. Among all isolated microorganisms, bacteria significantly controlled the pathogens better than Trichoderma and other fungi.