Reductive catalytic fractionation-derived lignin as a novel elicitor of induced resistance in tomato for biological control of plant pathogens and pests

Abstract: The negative impacts of chemical plant protection products on human and
environmental health, combined with resistance development in pests and pathogens,
necessitate sustainable alternatives in crop protection. Within Integrated Pest Management
(IPM), biocontrol agents that activate induced resistance (IR) in plants offer a promising
strategy to enhance crop resilience while reducing reliance on chemical pesticides. We
evaluated a spruce-derived lignin oil (RCF-lignin) produced by reductive catalytic fractionation (RCF) for its capacity to elicit IR (RCF-lignin-IR) in tomato (Solanum lycopersicum) against both a major plant disease and an insect pest. First, we tested a RCF-lignin fraction, at a concentration without direct antifungal activity in vitro, against the necrotrophic fungus Botrytis cinerea. Relative to a mock treatment, foliar application of RCF-lignin three days prior to inoculation significantly reduced lesion area development and fungal proliferation by 52.7 % and 58.3 %, respectively. Next, we evaluated RCF-lignin application against the zoophytophagous mirid bug Nesidiocoris tenuis. RCF-lignin applied on tomato leaves three days before infestation, significantly reduced feeding damage from on average 1.5 to 0.4 necrotic rings per plant seven days post-infestation. Insect mortality did not differ significantly from control plants, indicating the absence of insecticidal effects. Altogether, in this study we prove that RCF-lignin, derived from a natural source, can act as an elicitor of IR in tomato for biological control of both a major pathogen (B. cinerea) and pest insect (N. tenuis).