Closing the loop in agriculture: Evaluation of the effects of fermented tomato-based biostimulant on Solanum lycopersicum (L.) growth and fruit quality

Food waste is a global concern, and its valorization through biostimulant production offers a sustainable and circular approach to agriculture. This study evaluated the effects of a novel fermented tomato-based biostimulant, obtained from unsold green and red tomatoes fermented with Weissella cibaria 4253, on the growth and fruit quality of indeterminate mini plum tomato plants (Solanum lycopersicum L., cv. Solarino) cultivated in a soilless greenhouse system. The biostimulant was applied weekly at three concentrations (100, 200, and 300 mL·L⁻¹) and compared to untreated controls during a 16-week experiment in a commercial greenhouse in Emilia-Romagna, Italy. Vegetative parameters, physiological traits, including chlorophyll content, SPAD, Fv/Fm, and fruit characteristics were monitored. Fruits from different truss positions (lower, medial, upper) were analyzed for morphological, physico-chemical, and biochemical traits, including firmness, total soluble solids, titratable acidity, total polyphenol content, antioxidant activity, and lycopene content. FTB application did not significantly affect vegetative growth, but improved several fruit quality parameters. The 100 mL·L⁻¹ dose increased total yield by 23 % and fruit weight by 8 %, while the 300 mL·L⁻¹ dose enhanced °Brix, sugar/acid ratio, antioxidant activity (up to 20 %), and improved fruit texture, particularly in upper trusses. Lycopene content increased in treated plants over the harvest season, while untreated plants showed a decline. Heatmap and BIOLOG analyses confirmed treatment-specific effects on fruit quality and substrate microbial activity. The potential of an experimental biostimulant derived from fermented unsold tomato fruits to enhance crop performance while reducing food waste was demonstrated, supporting circular agricultural practices.