Defense Responses, Induced by p-Coumaric Acid and Methyl p-Coumarate, of Jujube (Ziziphus jujuba Mill.) Fruit against Black Spot Rot Caused by Alternaria alternata

The esterified fraction of jujube ( Ziziphus jujuba Mill.) peel extract showed strong antifungal activity on Alternaria alternata. p-Coumaric acid (pCA) was found to be the most predominant individual phenolic acid that was correlated highly with the antifungal activity of the esterified fraction. Thus, effects of postharvest treatments with pCA and its simplest esterified derivative methyl p-coumarate (MeCA) against black spot rot on jujube fruit caused by A. alternata were investigated. pCA and MeCA strongly suppressed in vitro growth of the fungus and significantly reduced postharvest Alternaria rot on fresh jujubes. Biochemical and transcriptional analysis revealed that pCA and MeCA regulated the expression of some genes encoding antioxidant enzymes and their enzymatic activities, enhanced the phenylpropanoid pathway metabolism, and activated the expression of genes encoding pathogenesis-related proteins. These results suggested that, apart from its direct antifungal activity, pCA and MeCA induced defense responses in jujube fruit against postharvest Alternaria rot.