A bio-based approach to produce inducers of plant defense responses through fermentation of agri-food waste biomass with white rot fungi

• A bio-based elicitor complex (PhaOP) was produced by fermenting orange peels with the white rot fungus Phanerochaete chrysosporium . • PhaOP induces strong defense responses in Arabidopsis thaliana , including PAD3 and PDF1.2 expression and callose deposition. • The resistance conferred by PhaOP is dependent on jasmonate signaling and indole compound biosynthesis but independent of ethylene and camalexin. • PhaOP reduces Botrytis cinerea infection in economically important Solanaceae crops and does not affect tomato yield. • The study demonstrates the potential of fermentation of agri-food byproducts with white rot fungi for sustainable crop protection strategies. To protect crops against microbial diseases, intensive agriculture heavily relies on pesticides, that can have a negative impact on human health and on the environment and can lead to the emergence of resistant pathogen strains. There is therefore an urgent need of novel products for crop protection, that are safe, eco-friendly, inexpensive and effective. Elicitors, plant- and microbe-derived compounds able to induce plant defense responses, represent a promising strategy towards achieving a sustainable agriculture. We developed a protocol to produce a heat stable elicitor complex by fermentation of agro-industrial byproducts with the white rot fungus Phanerochaete chrysosporium . A pasteurized culture filtrate of the fungus grown on orange peel waste as the sole carbon source (PhaOP) induces defense responses and increased resistance to the fungal pathogen Botrytis cinerea in the model plant Arabidopsis thaliana . PhaOP-induced resistance to Botrytis is dependent on jasmonate-mediated signalling and on indole compounds but is largely independent of camalexin production and of ethylene-mediated responses. Notably, PhaOP can reduce B. cinerea symptoms also in different Solanaceae crop species and does not significantly affect fruit production in tomato plants, suggesting that it could be employed for crop protection without yield penalty.