Methyl p-coumarate inhibits black spot rot on jujube fruit through membrane damage and oxidative stress against Alternaria alternata

Black spot rot caused by Alternaria alternata is one of the main postharvest diseases on jujube fruit. The aim of this study was to investigate the antifungal activity of methyl p-coumarate (MpCA) against A. alternata, and to elucidate the underlying mechanism involved. MpCA treatments significantly inhibited the development of black spot rot on the jujube fruit inoculated with A. alternata. Moreover, MpCA exhibited pronounced antifungal activity against mycelial growth and spore germination of A. alternata, with half-inhibition concentration of 242.5 mg L−1. MpCA treatments caused a great leakage of intercellular electrolytes, soluble proteins, sugars and nucleotides of A. alternata during incubation, indicating that MpCA is targeted to plasma membranes of the pathogen. Furthermore, count of cells dyed with propidium iodide by flow cytometer suggested that MpCA treatments destroyed the plasma membrane integrity of spores of A. alternata. Ultrastructural observations evidenced MpCA damaged the plasma membranes and impeded the morphogenesis and growth of A. alternata, which resulted in distortion, shriveling and lysis of spores and mycelia of the pathogen. In addition, observations by confocal laser scanning microscopy and quantitative determinations confirmed that the MpCA treatments induced the formation of intercellular endogenous reactive oxygen species in the spores of A. alternata, which would lead to oxidative stress to cellular membranes and organelles. These results indicated that MpCA exerts antifungal activity through membrane damage and oxidative stress against A. alternata, and MpCA is a promising candidate for the control of postharvest diseases of jujube fruit.