Bioactive compounds for crop stress mitigation: mechanisms and scientific evidence

Background. Abiotic stress accounts for 66% to 82% of the gap between record and average yields of the major field crops, compared with 5–10% attributable to pests and diseases (Bray et al., 2000). Management strategies based on plant- and microbe-derived compounds, combined with micronutrients, aim to keep the plant physiologically active during stress and to reduce pressure from harmful organisms without adding a phytotoxic load.Objective. To review the available scientific evidence on the groups of compounds underpinning this strategy, to describe their modes of action in the plant and in the target organism, and to quantify, where the literature allows, the magnitude of their effects.Methods. Narrative review of peer-reviewed literature, doctoral theses, technical documents from public bodies and patents, with extraction of quantitative data and classification of the level of evidence for each effect as high, moderate or low.Results. Ten functional groups are identified: citrus flavonoids, phenolic monoterpenes and phenylpropanoids, isothiocyanates, pyroligneous extract, piperamides and ginger sesquiterpenes, d-limonene, yeast polysaccharides and nucleotides, protein hydrolysates and osmoprotectants, organic amendments (lignosulfonates, humic substances and cellulose hydrogels) and micronutrients with an enzymatic function. Carvacrol and thymol completely inhibited the mycelial growth of Botrytis cinerea at 150–200 µg/mL (Sempere-Ferre et al., 2021). Pyroligneous extract caused 72–78% juvenile mortality in four Meloidogyne species (Li et al., 2009). Nickel fertilisation increased urease activity 3.9-fold and nitrogenase activity 1.4-fold in soybean, with yield gains of up to 1161 kg/ha (Rodak et al., 2024). When applied as salts, micronutrients reached the sap of the lower half of the plant in amounts 37–91% lower than when complexed with organic molecules, and only the complexed form increased soybean yield, by 11.8% (Nascente et al., 2023). Conclusions. The evidence is high for antioxidant, antimicrobial, nematicidal, elicitor and nutritional mechanisms in vitro and under controlled conditions, and moderate or variable in the field, where formulation, soil and timing of application determine the response. Some common claims (gene regulation by applied RNA, activation ofinvertases by essential oils, foliar “vasodilation”) currently lack experimental support. Micronutrient effects must be separated from extract effects in validation trials.Keywords: abiotic stress; reactive oxygen species; biostimulants; essential oils; allyl isothiocyanate; elicitors; biological nitrogen fixation; foliar fertilisation.