Induced resistance as a putative component of compost suppressiveness.

Abstract Compost made of tomato-plant residues mixed with the coarse fraction of separated cattle manure, suppressed wilt disease caused by Fusarium oxysporum f. sp. melonis in melon. This compost also mitigated the effect of the foliar pathogen Botrytis cinerea in cucumber and melon plants, suggesting that induced resistance mechanism may possibly be involved in the suppression phenomenon. To study the possible involvement of induced resistance in the suppression of Fusarium wilt, we used a split-root system, based on side-grafted melon plants. This enabled us to obtain a well developed root system split into two different parts, both serving the same plant. When the peat part of the root zone was inoculated, compost that formed the other half of the root zone reduced disease severity, as compared with the case where both parts of the root system were grown in peat. When both parts of the root system were grown in compost, disease severity was further reduced, possibly because of the direct effect of compost microflora. It is suggested that induced resistance could be an additional mechanism involved in Fusarium disease suppression by composted manure and tomato residues. The side-grafted split-root system is an efficient method to study the phenomenon of induced resistance against soil-borne pathogens, which prevents interference by artefacts caused by the wound effect.