Open field assessment of kiwifruit waste-derived biostimulants on Tomato quality under water stress

This study evaluated the effects of innovative bio-based biostimulants obtained from discarded kiwifruits (fermented juice with Lactiplantibacillus plantarum (T3), non-fermented juice (T4), fermented juice with Companilactobacillus farciminis (T5), and seed protein hydrolysate (T6) compared to controls (T1: no biostimulants added), and selenium-based biostimulant (T2) on the yield, nutritional value, aroma, and antioxidant properties of open-field tomatoes grown under three irrigation regimes: water deficit (WD), water optimum (WO), and water excess (WE). Under WD, biostimulants (T3, T5, and T6) maintained total and marketable yields similar to optimal irrigation control (T1+WO), with T3 preserving fruit weight. From a nutritional point of view, T4 and T5 increased protein content to 16-17 % dw (T1+WD=<15 % dw), while T6 enhanced dietary fibres by 48 %. T3 increased glucose under WO (+20 % of T1), whereas T5 and T6 resulted in the highest hexose levels under WD and WE, respectively. Under WE, T3 also promoted the accumulation of free amino acids like Lys, Asp and Glu, while under WD, T2 increased Pro, an osmotic stress marker associated with protein degradation. At all irrigation levels, T3, T5 and T6 enhanced lycopene and mitigated aromatic loss observed especially under WE, by increasing key volatiles (e.g., aldehydes and 2-isobutylthiazole). The Principal Component Analysis (PCA) supported these findings, suggesting that tomatoes from WD or WE and treated with new tested biostimulants (T3-T6) clustered near WO samples. In conclusion, kiwifruit waste-derived biostimulants effectively mitigate the adverse effects of water stress on tomato production, enhancing crop performance in a climate change context.