Use of composted agro-energy co-products and agricultural residues against soil-borne pathogens in horticultural soil-less systems

One feedstock of composted agro-energy co-products and agricultural residues was physically-chemically-microbiologically characterized and investigated for the phytotoxic property and the disease suppression for finding next-generation "green composts" suitable for use in horticultural soil-less systems. The suppression of three composts made of crude steam-explosion liquid-waste of miscanthus (SELWM), giant reed (SELWA) and wheat straw (SELWWS) mixed with the agro-waste mostly available in Southern Italy [C-WS (SELWWS + woodchip + tomato-waste), C-M (SELWM + coffee-ground + artichoke-waste) and C-A (SELWA + defatted olive marc + fennel-waste)] was tested by the in vitro and in vivo experiments against seven horticultural pathosystems (Phytium ultimum/Cucumber, Phytophthora nicotianae/Tomato, Rhizoctonia solani/Bean, Sclerotinia sclerotiorum/Lettuce, Fusarium oxysporum f. sp. melonis/Melon, Fusarium oxysporum f. sp. lycopersici/romato, and Verticillium dahliae/Eggplant). One compost (C-c) sourced from the differentiated municipal bio-waste with pathogen-specific property was employed as reference. The phytotoxicity of composts was assessed on lettuce and cress. In vitro bioas-says carried out on pure colonies showed that raw compost water extracts (CWEs) were able to inhibit all of pathogens adopting a pouring technique, and that a well-cut diffusion method allowed the block of growth of the pathogens without physical interaction with compost microflora. The sterile-filtration of CWEs annulled inhibition of the pathogens, but S. sclerotiorum and V. dahliae were inhibited by sterile CWEs using a pouring procedure. In vivo tests performed under greenhouse conditions using peat-based plant growing media amended with each compost at dosage of 20% (v/v) showed multi-suppressive activity: C-WS suppressed most efficiently P. ultimum, R solani, P. nicotianae, F. oxysporum f. sp. melonis, F. oxysporum f. sp. lycopersici, V. dahliae; C-M was capable to suppress P. ultimum, R. solani, P. nicotianae, S. sclerotiorum, V. dahliae; C-A was suppressive against R. solani, P. nicotianae, V. dahliae. The microbiological inactivation of composts by heating treatment reduced suppression in all of pathosystems, but for S. sclerotiorum/Lettuce and V. dahliae/Eggplant the loss of suppressivity was smaller in C-A, C-M and C-c. The predictive parameters to suppression were different: total fungal biomass for P. nicotianae; FDAH for P. ultimum; Trichoderma for R. solani; Aspergillus, Pseudomonas and Streptomyces for F. oxysporum. Instead, the parameters that drive suppression of S. sclerotiorum and V. dahliae were not well cleared. The use of composted agro-waste seems to be an efficient alternative to peat-based substrates for controlling diseases on a broad range of horticultural crops with inappreciable phytotoxic effects if added in moderate dose. (C) 2016 Elsevier B.V. All rights reserved.