Controlled Mechanical Wounding Applied on Leaves during Preharvest As an Innovative Way to Increase the Levels of Bioactive Phytochemical in Fruits

Biotic and abiotic stresses like wounding and herbivores induce changes in plant metabolism. Wounded tissues induce the production of phenylpropanoid secondary metabolites as a local response, and also as a systemic response in the same organ type (e.g. leaves). The importance of phytochemicals for human health has lead the study of pre and post-harvest factors that influence the production of bioactive phenylpropanoids. In this study, a preharvest leaf wounding was applied to measure the effects on production of bioactive compounds on fruits. The experiment was conducted on strawberry (advanced selection LBM10.3) subjected to two levels of mechanical wounding applied on completely developed leaves, 7-12 days before harvest time. The fruits were evaluated after harvest for quality parameters (color, soluble solids, firmness, and fresh weight), total phenolics (TP), vitamin C, and specific phenylpropanoids. No differences with the control were detected (p>0.05) for color, soluble solids, fresh weight, firmness and vitamin C. However, the level of TP in fruits of treated plants increased significantly > 20% over the control. Moreover, significant increase (p≤0.05) in the level of specific phenylpropanoids was observed: epicatechin (+186%), quercetin (+194%) and rutin (+190%) and the ellagitannins derivatives, ellagic acid and gallic acid (+128% and +17%, respectively). These results support the idea that higher levels of phytochemicals reported previously in organically grown fruits and vegetables could be due to the wounding component of the biotic stress attributed to insects to which the plant are exposed. In addition, the controlled mechanical wounding applied during preharvest in leaves could be used as an innovative way to increase phytochemical levels in fruits and the basis for a novel use of plants as biofactories of nutraceuticals.