Plant biostimulants: New tool for enhancing agronomic performance and fruit quality of cucurbits

Plant biostimulants are substances (i.e., humic and fulvic acids, protein hydrolysates and seaweed extracts) and microbial inoculants (i.e., mycorrhizal fungi and plant growth promoting rhizobacteria-PGPR) that have been introduced as an efficient, safe and sustainable tool to optimize root system thus boosting crop performance, and nutrient use efficiency as well as enhancing tolerance to environmental stressors in vegetable crop production. The stimulation of biomass production in response to biostimulant application has been often associated to the action of specific signaling molecules on plant metabolism and physiology. Several trials have shown that Cucurbit crops can also benefit from the application of biostimulants. Early application at transplanting or in nursery of arbuscular mycorrhizal fungi (Rhizoglomus irregulare and Funneliformis mosseae) or vegetal biopolymer-based biostimulant on several Cucurbit crops (e.g., cucumber, melon, zucchini) were able to boost root growth and to activate defense mechanisms against environmental stresses (e.g., salinity, soil acidty and alkalinity). Moreover, foliar applications of biostimulant substances during the growing cycle were also effective in promoting crop productivity and increasing nutritional and functional quality in Cucurbit crops. Several examples will be presented and discussed together with possible mechanisms involved.