Grape marc compost: microbial studies and suppression of soil-borne mycosis in vegetable seedlings

Compost suppression of soil-borne diseases in horticultural crops has been attributed to the activities of antagonistic microorganisms. A great diversity of microorganisms, capable of suppressing pathogens naturally colonize compost. A large number of microbes appeared in microbiological analyses of grape marc compost. Most microorganisms were bacteria. Average percentages were 31% mesophilic and 28% thermophylic bacteria, 16% mesophilic actinomycetes and 20% thermophylic actinomycetes. Only a few mould and yeast morphologies were obtained, 4% and 1% respectively. Antagonist in vitro assays were performed with 432 microbial morphologies isolated from grape marc compost. The microbes isolated were extremely effective antagonists in in vitro assays against all the fungal pathogens tested. Seven microorganisms were selected for further bioassay with Rhizoctonia solani in radish, Fusarium oxysporum f. sp. radicis-cucumerinum in melon, and Phytophthora parasitica in tomato and two microorganisms with Pythium aphanidermatum in cucumber. Those experiments indicate that grape marc compost reduces the severity of Pythium damping-off in cucumber, but does not reduce the severity of Phytophthora root rot in tomato, Fusarium oxysporum f. sp. radicis-cucumerinum in melon and Rhizoctonia solani in radish. Better suppressive effects were not demonstrated by either compost or vermiculite amended with microbes selected from grape marc compost.