Agricultural waste-based composts exhibiting suppressivity to diseases caused by the phytopatogenic soil-borne fungi Rhizoctonia solani and Sclerotinia minor

On-farm composting is an efficient, environmentally safe and cost-effective process for recycle vegetable residues into productive cycles. Benefits of these composts could include their ability to mediate soil-borne plant pathogen suppression with a significant impact on eco-friendly crop management. In this work, on-farm composts were assayed for ability to control, both in vitro and in vivo, damping-off causing pathogens Rhizoctonia solani and Sclerotinia minor. Tomato and escarole-derived compost was the most suppressive and, furthermore, together with that derived from artichoke wastes, exhibited multi-suppressive activity. Compost communities, characterized at metabolic and global level by Biolog system, microbial counting, CO2-release and FDA hydrolysis rate, play a major role in compost-based biological control. The complete biotic inactivation by autoclaving composts, has, in fact, reduced or eliminated their ability in pathogen suppression. Solid state 13C-CPMAS-NMR spectroscopy revealed that spectrum areas typical for phenolic C, as well as methoxyl C, may be associated to suppressivity mechanism(s). These evidences suggested that the ecological relatioships between organic carbon molecular distribution and microbial structure may contribute to discriminate suppressive composts from null and conducive ones. Nutritional microniches in the composts can have profound effects on the community functions, including those linked to the suppressiveness.