Differences in the Induction of Defence Responses in Resistant and Susceptible Muskmelon Plants Infected with C olletotrichum lagenarium

Defence reactions occurring in resistant (cv. Gankezaomi) and susceptible (cv. Ganmibao) muskmelon leaves were investigated after inoculating with C olletotrichum lagenarium . Lesion restriction in resistant cultivars was associated with the accumulation of hydrogen peroxide (H 2 O 2 ). The activity of antioxidants catalase ( CAT ) and peroxidase ( POD ) significantly increased in both cultivars after inoculation, while levels of both CAT and POD activity were significantly higher in the resistant cultivar. Ascorbate peroxidase ( APX ) increased in both cultivars after inoculation, and level of APX activity was significantly higher in the resistant cultivar. Glutathione reductase ( GR ) activity significantly increased in both cultivars following inoculation, but was higher in the resistant cultivar, resulting in higher levels of ascorbic acid (AsA) and reduced glutathione ( GSH ). Phenylalanine ammonia lyase ( PAL ) significantly increased in inoculated leaves of both cultivars, resulting in higher levels of total phenolic compounds and flavonoids. The pathogenesis‐related proteins chitinase ( CHT ) and β‐1, 3‐glucanase ( GLU ) significantly increased following inoculation with higher activity in the resistant cultivar. These findings show that resistance of muskmelon plants against C. lagenarium is associated with the rapid accumulation of H 2 O 2 , resulting in altered cellular redox status, accumulation of pathogenesis‐related proteins, activation of phenylpropanoid pathway to accumulation of phenolic compounds and flavonoids.