Biowaste-derived hydrolysates as plant disease suppressants for oilseed rape

Water soluble substances, obtained by aqueous alkaline hydrolysis of fermented urban kitchen and garden waste, have been reported enhancing the productivity of several food and ornamental plants. The present work reports unknown new property of these substances as plant disease suppressants. It describes a case study where oilseed rape cotyledons were protected by pre-treatment with two different types of soluble substances against a fungal pathogen Leptosphaeria maculans. One type was isolated from the digestate of a biogas production reactor fed with kitchen wastes. The second type was obtained from a compost made from a mix of biogas digestate, gardening residues and sewage sludge. The results demonstrate that the alkaline hydrolysate exhibited the following effects: (i) decreased the necrosis development by L. maculans by 42–56% when applied to leaves and by 31–37% when applied to roots; (ii) reduced cotyledon leaf area by 13–17%; (iii) increased biomass dry weight by 9% compared to the distilled-water-treated control. The soluble substances induced a plant defence involving an ethylene-dependent signalling pathway, which was assessed through the expression of marker genes involved in the main plant defence signalling pathways. Considering the performance, cost and origin of the alkaline hydrolysates they seem a promising alternative to commercial synthetic fungicides. The benefits for the agriculture and waste management sectors, which may potentially derive from the market allocation of the alkaline hydrolysates for use in agriculture, environmental technology, and in the chemical industry for manufacturing consumer goods and products, are discussed.