Abstract: In order to investigate the effect of NO fumigation on cell wall metabolism and disease resistance in postharvest melons, “Xizhoumi 25” melons (Cucumis melo L. var. saccharinus cv. Xizhoumi) were fumigated with 60 μL/L nitric oxide gas for 3 h and then kept at room temperature for 12 h. The fumigated fruit were inoculated with Alternaria alternata and stored at room temperature. Disease incidence, hardness, cell membrane permeability, the contents of protopectin, soluble pectin and cellulose, and the activities of polygalacturonase (PG), pectin methyl esterase (PME) and cellulase (Cx) were regularly measured during storage, and changes in the surface structure of melon rinds was observed by scanning electron microscopy (SEM). The results showed that NO fumigation treatment could effectively reduce the lesion diameter, lesion depth and disease incidence of postharvest melons, maintain high fruit hardness and high contents of protopectin and cellulose, suppress the increase in cell membrane permeability and soluble pectin content, and reduce the activities of PG, PME and Cx. In addition, SEM results exhibited that NO treatment could inhibit the growth of mycelium in surface stomata and cracks and maintain the integrity of the stomatal structure of melon fruit. Therefore, exogenous NO fumigation treatment at appropriate concentration can delay the cell wall degradation process and enhance disease resistance in postharvest melons.

Key words: melon, cell wall, nitric oxide, black spot, metabolism