The black spot disease caused by Alternaria alternata is one of the major diseases which seriously reduce the commercial value of muskmelon. This study was to investigate the possible effect against black spot disease in postharvest muskmelon (Cucumis melo L. cv. Xizhoumi 25) by fumigation with 60 μL/L nitric oxide (NO). Our results showed that NO decreased the lesion diameters and lesion depths of muskmelon inoculated with A.alternata, while NO maintained the structure and reduced the number of hyphae in tissues surrounding the netting sides. NO not only activated the activities of peroxidase (POD), phenylalanine aminolysis enzyme (PAL), cinnamic acid-4-hydroxylase (C4H) and 4-coumaric acid-CoA ligase (4CL), but also increased the content of total phenols, flavonoids and lignin. Moreover, β-1,3-glucanase (GLU) and chitinase (CHT) activities were promoted by NO. These results suggested that the regulation of phenylpropanoid pathway and pathogenesis-related proteins by NO were a possible mechanism for enhancing muskmelon resistance to black spot disease.
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