Postharvest ASM or Harpin Treatment Induce Resistance of Muskmelons Against Trichothecium roseum

Induced resistance was studied in muskmelons (cv. Yindi) inoculated Trichothecium roseum with postharvest 1,2,3- benzothiadiazole-7-carbothioic acid S-methyl ester (ASM) (100 mg L-1) or harpin (50 mg L-1) treatment. Both ASM and harpin significantly reduced lesion diameter in inoculated fruit. Lesion diameter was limited in the treated and untreated halves of the same fruit, indicating that the local and systemic resistance was induced. Inhibiting efficacy of elicitors lasted 7 and 5 days in the treated and untreated halves. The resistance increased by the chemicals was associated with the activation of peroxidase (POD) and chitinase (CHT). The elicitors induced a significantly and progressively increasing activity of POD and CHT in the treated and untreated halves, and the activation lasted at least 5 days. The activities of POD isoenzymes increased in the treated fruit. However, no new enzyme band was found in the treated and untreated halves.