Induction of antifungal resorcinols in flesh of unripe mango fruits and its relation to latent infection by Alternaria alternata

Abstract

A mixture of antifungal compounds, consisting primarily of 5-(12- cis-hepta decenyl)-resorcinol and 5-penta decylresorcinol was found at fungitoxic concentrations in the peel, but not in the flesh of unripe mango fruit. The unpeeled fruits were resistant to Alternaria alternata, but freshly peeled fruits were susceptible. The flesh of peeled mango fruits became resistant to A. alternata infections within 24 h after peeling. During this period the concentration of the 5-substituted resorcinols increased from 30 to 80 μ g −1 fresh weight and continued to increase to reach a concentration of 160 μ g −1 fresh weight 96 h after peeling. A browning reaction, accompanied by increased activity of the enzyme phenylalanine ammonia lyase (PAL), also occurred in the flesh as a result of peeling. Cycloheximide inhibited browning and PAL activity in the fruit flesh, but not the synthesis of 5-substituted resorcinols and the development of resistance to A. alternata. Anaerobiosis prevented flesh browning, the development of resistance in peeled fruits, and the increase in concentration of the antifungal 5-substituted resorcinols. This work provides further evidence for the involvement of antifungal resorcinols in the latency of A. alternata in unripe mango fruits.