Impact of Drought and Biostimulant in Greenhouse Tomato: Agronomic and Metabolomic Insights

Widespread drought conditions have increasingly affected agricultural productivity, requiring the exploration of alternative approaches for improving crop resilience, yield and quality, since plants adopt many physiological strategies to cope with challenging environments. This study evaluated the effects of a vegetal-derived protein hydrolysate (PH) applied via foliar spray or root drench on tomato plants under two irrigation levels (well-watered and stressed). Dry biomass accumulation, fruit yield, quality traits (°Brix, pH, titratable acidity, firmness, sugars), and metabolic alterations were investigated as a result of irrigation and PH treatments. Overall, sub-optimal irrigation significantly decreased plant dry biomass (-55.3 %) and fruit production (-68.8% marketable yield), and enhanced fruit quality in terms of sugar concentration and antioxidant levels. PH treatments, regardless of the application method, did not notably influence above-ground dry biomass, yield, or fruit quality, suggesting that the intensity of drought might have limited PH effectiveness. Metabolomic analysis showed higher concentrations of stress- and quality-related metabolites in tomato fruits from plants under stress, with PH not exerting significant metabolic changes in the fruits. These findings revealed the diminished effectiveness of PHs under severe drought conditions, suggesting that drought stress level needs to be taken into consideration for optimizing biostimulant efficacy.