Research PaperFoliar applications of a legume-derived protein hydrolysate elicit dose-dependent increases of growth, leaf mineral composition, yield and fruit quality in two greenhouse tomato cultivars

- Biostimulant application rate effect on two tomato cultivars was explored.
- Application of biostimulant at high dose (5 ml L−1) improved marketable yield.
- Biostimulant at high dose enhanced photosynthesis and leaf nutritional status.
- Key quality attributes of fresh tomato were improved by biostimulant application.

The use of natural plant biostimulants is proposed as a promising and innovative approach to ensure improved and sustainable yields and product quality. A greenhouse experiment was performed to assess the yield performance, leaf net assimilation of CO2, mineral composition of leaves and fruits, and fruit physicochemical quality attributes of two tomato cultivars (Akyra and Sir Elyan) in relation to biostimulant treatments (control or two different concentrations of the legume-derived protein hydrolysate Trainer®). Treated tomato plants were sprayed every 10 days with a solution containing 2.5 and 5.0 ml L−1 of biostimulant. Akyra was found to be richest in K, Ca, Mg, lipophilic and hydrophilic antioxidant activities (LAA and HAA), lycopene, total phenolic and total ascorbic acid. Foliar applications of legume-derived protein hydrolysate at 5.0 ml L−1 increased marketable yield of Akyra and Sir Elyan by modulating yield components differently depending on cultivars: higher number of fruits in Akyra and increase of fruit mean weight in Sir Elyan. Improved yield performance with biostimulant foliar applications at the highest rate was related to improved leaf nutritional status (higher K and Mg) and higher net assimilation of CO2. The application of legume-derived protein hydrolysate at 5.0 ml L−1, and to a lesser degree at 2.5 ml L−1, elicited an increase in antioxidant activities, total soluble solids, mineral composition (K and Mg) as well as bioactive molecules such as lycopene and ascorbic acid, thereby increasing the nutritional and functional quality of the fruits. These findings can assist tomato growers in selecting cultivars and application dose for protein hydrolysate to complement high crop productivity with optimal fruit quality.