Revealing the mode of action of Phenylalanine application in inducing fruit resistance to fungal pathogens

Pathogenic fungi cause most postharvest decay. Phenylalanine (Phe) is an eco-friendly treatment that increased fruit resistance to various pathogenic fungi including Colletotrichum gloeosporioides, the main postharvest pathogen of mango fruit. The mode of action of Phe-induced fruit tolerance against C. gloeosporioides was examined after harvest, post-treatment, and post-inoculation by transcriptome, metabolome, and biochemical assays. Phe treatment induced defense response-related genes including Ca2+ signaling, MAP kinase, WRKY transcription factors, and activation of the phenylpropanoid pathway, which lead to an accumulation of flavonols and anthocyanins. In addition, after Phe application and C. gloeosporioides inoculation, the levels of the antioxidant, total phenolic, and flavonoid were induced. The increase in antioxidants in Phe-treated fruit was correlated with reduced lipid peroxidation. Phenolic extract of mango peel treated with Phe reduced conidia germination and hyphal growth of various pathogenic fungi including C. gloeosporioides, Botrytis cinerea, Alternaria alternata, and Lasiodiplodia theobromae. Furthermore, the application of peel extracts from fruit treated with Phe reduced decay against C. gloeosporioides and A. alternata in mango fruit. Overall, the novelity of this study show that postharvest Phe treatment induces the fruit defense response and the biosynthesis of antioxidant and antifungal flavonoids, which can effectively control fungal growth and disease development, indicating its applicative potential as postharvest control against fungal pathogens.