Microbial communities involved in suppression of Fusarium wilt of lettuce by a municipal biowaste compost

Compost suppressiveness depends primarily on microbiological composition and antagonists can be isolated from high-quality composts. The objective of the present work was to evaluate the suppressive effect of compost against Fusarium oxysporum f. sp. lactucae, and to study the microbial communities involved. A compost from municipal bio-waste that showed good suppressive activity in previous trials was added at 1% to a steamed sandy soil inoculated with the pathogen. Compared to the same soil not treated, compost showed a 40% disease control of Fusarium wilt of lettuce. Microbial activities, bacterial and fungal concentrations were quantified and correlated in a principal component analysis in order to clarify the correlation between the variables and compost suppressiveness. Samples taken from the rhizosphere of plants grown in suppressive media had highest total enzymatic activity and highest concentration of total fungi. The comparison of DGGE profiles of microbial populations revealed greater diversity in the fungal community than that of bacteria. Pseudomonas sp., among bacteria, and Simplicillum lamellicola, among Deuteromycetes, were detected only in the rhizosphere of plants treated with 1% compost, indicating that they may play an active role in disease suppressiveness.