Suppressive effect of cured compost from olive oil by-products towards Verticillium dahliae and other fungal pathogens

After oil extraction from olives, large amounts of by-products are generated every year. If subjected to advanced biotechnologies of composting they can be re-used in agriculture as eco-compatible amenders, fertilizers and/or natural pesticide. In this regard, olive oil by-products composted in a pilot scale olive plant were characterized and assayed for suppressive activity against fungal plant pathogens. Some cured composts consistently reduced the growth in vitro of Verticillium dahliae and other important fungal pathogens. The efficacy of composts decreased or disappeared when the composts were autoclaved before using. The inhibitory activity seems due to the beneficial residual microbial population selected during the composting process. In experiments performed on young olive plants grown on soil artificially contaminated by V. dahliae microsclerotia (MC), the incorporation of 15% (w/w) of a selected cured compost or the antagonistic fungus Trichoderma viridae as well as 15% (w/w) of cured compost and T. viridae applied together significantly reduced the density of V. dahliae MC in the soil. The results of this investigation indicate that composted olive by-products are very promising to control fungal pathogens of olive and other crops in organic and integrated agriculture systems. Monitoring of V. dahliae MC in the soil by a semi-selective media was compared to a molecular method based on Real-Time Scorpion PCR. The latter technique, which enables V. dahliae detection by a specific increase of fluorescence during amplification, drastically reduced the time required for the assessment of V. dahliae MC in the soil, as compared to the microbiological cultural techniques