Potential suppressiveness and effect on Photinia fraseri growth by a composted amendment from olive mill wastes

Olive mill wastes (OMW)from two-phase extraction system have become problematic to be managedand represent a serious environmental problem.SAN-SOIL is a composted amendment from OMW potentially useful as a peat surrogate in the preparation of growing media for potted plants. The aim of this work was to test the potential in suppressiveness of such compost by the characterization of population of antagonistic fungi and bacteria and the suitability for nursery production of the ornamental Photinia fraseri cv. "Red Robin",grown in substrate with different composition,substituting peat with 33%, 66%, 100% SAN-SOILwith or without chemical fertilization; fungi and bacteria belonging to the genus Aspergillus, Penicillium, Bacillus, Pseudomonas, were isolated and identified morphologically and molecularly. A number of fungal species hadantagonistic properties in vitrotoward the Photinia soil-borne pathogens Sclerotinia sclerotiorum and Phytophthoracactorum. Sterilised "tea compost" was also obtained from the different substrates and assayed against the two pathogens to test potential antimicrobial activity of their abiotic components. Theirin vitroeffect on pathogensgrowth depended on the substrate composition ranging from weak inhibition to weak promotion.Potting mix amended with the highest proportions of compost (66 % and 100 % of peat replaced) and in absence of chemical fertilization, was able to support an optimal growth of Photinia plants produced over theperiod, with no phytotoxicityeffects. Based on these observations,SAN-SOIL compostis confirmed as an effective substitute of peat in potting mix, due to its potential suppressiveness and nutritional support of plant growth.