The importance of secondary metabolites (SM) in plant defense mechanisms against environmental stresses as well as their benefits in human health have led to the study of how pre-harvest factors enhance their biosynthesis in fruits and vegetables. Plant secondary metabolites are regulated by signal transduction pathways that can be triggered and regulated by abiotic and biotic stress factors, e.g. the wounding produced by chewing insects induce changes in plant secondary metabolism rate. Several authors speculate that higher levels of phytochemicals, particularly phenolic compounds, are related to higher levels of biotic stress when plants are grown without the application of synthetic chemicals in the field (pesticide-free or organic production). Organic agriculture claims that under this method of production, plants suffer more biotic stress and accumulate more SM in fruits. Phytochemicals are especially relevant for human health since they may play a role in the treatment and prevention of chronic cardiovascular and inflammatory diseases or cancer. Regarding the higher levels of phytochemicals, several studies supported that organic fruit and vegetables contain higher levels of secondary metabolites related to plant defenses. In this review biotic stresses are discussed in two plant models (strawberries and pecans), with focus on changes in the ellagitannin accumulation and the importance for human consumption.
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