Control of Soilborne Pathogens on Vegetables Grown in Greenhouse by Microorganisms Isolated from Compost

Compost suppressiveness depends on its 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 and organic domestic 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: selective for Fusarium sp., selective for Trichoderma sp., potato dextrose agar (PDA) for isolation of fungi, lysogeny broth (LB) for isolation of bacteria. In total, 74 colonies were isolated from plates and tested in greenhouse on potted plants against Fusarium oxysporum f. sp. basilici/basil, Pythium ultimum/cucumber and Rhizoctonia solani/bean. Antagonistic microorganisms were blended into a peat substrate at 10 g L-1 or 10 ml L-1 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 R. solani and one of them was effective against Fusarium oxysporum f. sp. basilici. Among all isolated microorganisms, bacterial strains showed to significantly control the pathogens better than Trichoderma and other fungi.