Fermentation-derived biostimulant BiH2-B enhances abiotic stress tolerance in horticultural crops

Abiotic stresses such as transplant shock and low-temperature events represent major constraints to early crop establishment and productivity in horticultural systems. This study evaluated the effect of the fermentation-derived biostimulant BiH2-B obtained from the exhausted fermentation broth of dark biohydrogen production (BiH2 technology, Biorenova S.p.A.) in mitigating transplant and chilling related stress in tomato (Solanum lycopersicum L.) and pepper (Capsicum annuum L.) grown in climatic chambers conditions. In tomatoes, five BiH2-B doses (10–25 L ha-1) were applied via fertigation at and after transplanting; growth and physiological parameters were monitored during early vegetative development. BiH2-B significantly increased leaf chlorophyll (SPAD) and leaf area up to 15 L ha-1 with a maximum leaf area increase of 7.5% and higher aerial fresh biomass at intermediate doses, without affecting the root biomass or inducing phytotoxicity. In peppers, the same application rates (10–25 L ha-1) were foliar-applied as foliar sprays before and after an imposed chilling event (6 °C for 48 h). Intermediate rates (12–15 L ha-1) enhanced SPAD (+10.3%) and plant height (7.4%) and markedly reduced chilling injury compared with the untreated control, while higher rates did not provide additional benefits. Overall, these results identify an optimal application range for BiH2-B between 12 and 15 L ha-1 and support the use of fermentation-derived biostimulants as sustainable tools to enhance physiological resilience to abiotic stress in horticultural crops, without exerting a fertilizing effect and in line with the European Union (EU) definition of plant biostimulants.