Characterization of composted olive mill wastes to predict potential plant disease suppressiveness

Despite its proven agronomic value, the plant disease suppressive effect of composts from olive waste has not been adequately investigated. In the present study, the disease suppressive potential of two olive waste (OW) composts against soil-borne plant pathogens was investigated. Both OW composts showed sizeable, active microbial populations, which were able to grow actively on chitin and cellulose. In plate inhibition trials, OW compost water extracts (CWEs) exerted a significant inhibitory effect on the growth of the pathogens Fusarium oxysporum f.sp. lycopersici (Fol), Pythium ultimum, Phytophtora infestans, Sclerotina sclerotiorum and Verticillium dahliae; and in pot experiments, the OW composts significantly reduced P. ultimum damping-off and Fol wilt diseases on tomato seedlings. The disease suppressive effect of OW composts seems to be due to the combined effects of suppression phenomena caused by the presence of microorganisms competing for both nutrients and space as well as by the activity of specific antagonistic microorganisms.

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► In vitro suppressive effect of olive waste compost water extracts on five soil-borne fungal and two Oomycete plant pathogens.
► Potting mix amended with olive waste compost reduces severity of Fusarium wilt and Pythium damping-off of tomato seedlings.
► Microbial population of olive waste compost grows on chitin and cellulose and shows specific enzymatic activity.
► Suppressive effect possibly due to coexistence of both general and specific suppression phenomena.