Salicylic Acid-Medicated Reprogramming of Phenylalanine and Secondary Metabolite Pathways Enhances Anthracnose Resistance in the Mango Fruit (Mangifera indica L.)

The ability of salicylic acid (SA) to control post-harvest fungal disease mango anthracnose caused by plant pathogen Colletotrichum gloeosporioides and the accompanying biochemical and metabolomic changes were studied. In vitro, C. gloeosporioides mycelial growth at 25 °C for 7 days was inhibited by SA at 2 and 5 mM concentrations. In vivo, mango fruits were treated with 2 mM SA for 10 min, then inoculated with C. gloeosporioides. The fruits were then stored at 25 °C and sampled every 2 days after inoculation. The anthracnose severity, infection index, malondialdehyde (MDA), antioxidant capacity (DPPH and FRAP), total phenolics (TPC), total flavonoids (TFC), ascorbic acid, and metabolomic changes in the peel were studied. Six days post inoculation, the SA-treated fruits showed reduced anthracnose severity, and the infection index was significantly reduced by SA (57%) compared to the control (67%). The SA-treated fruits exhibited decreased MDA, enhanced antioxidant capacity, and increased levels of TPC, TFC, and vitamin C in the peel. Compared with the control, SA treatment reduced MDA content by approximately 50% and increased TPC, TFC, and FRAP antioxidant capacity by 77%, 31%, and 29%, respectively. Vitamin C content and DPPH antioxidant activity were also significantly higher in SA-treated fruits. Untargeted metabolomics and a principal component analysis revealed a separation group between the SA-treated and control fruit. The SA treatment induced D-amino acids, phenylalanine pathways, and the biosynthesis of secondary metabolites such as phenolic acid. Together, these findings demonstrate that SA enhances mangoes’ resistance to post-harvest anthracnose through direct antifungal action and the activation of host defense by improving the antioxidant systems and stimulating the accumulation of secondary defense metabolites in mango fruit.