Drench Application of Soy Protein Hydrolysates Increases Tomato Plant Fitness, Fruit Yield, and Resistance to a Hemibiotrophic Pathogen

At a time when growers have to increase food production, while facing many environmental challenges, biostimulants and plant defence stimulators (PDS) may help reduce the use of chemical fertilizers and pesticides and to promote agriculture that is more respectful of the environment. For organic farming, they may contribute to increasing plant resilience and crop productivity. Several studies have shown that plant-derived protein hydrolysates may increase nutrient use efficiency and promote plant resistance to abiotic or biotic stresses. We therefore hypothesized that soy protein hydrolysates increase tomato growth and productivity, while promoting plant disease resistance. Our results showed that one or two drench applications of soy protein hydrolysates (SPH13 and SPH18 at 10 g L−1) to the growing medium increased tomato (‘Micro Tom’) plant growth and fruit production, while one studied hydrolysate enriched in glycine (SPH18) increased the expression levels of PR1 and PR8, two defence-related genes. Although no significant effect was observed on Botrytis cinerea resistance of Micro Tom plants, SPHs significantly increased ‘M82’ plant resistance to foliar inoculation with Pseudomonas syringae pv. tomato DC3000, which further confirmed the systemic activation of plant defence mechanisms by SPHs in tomatoes