Powdery mildew-resistant enzyme activities induced with BTH in melon seedlings.

The effects of benzothiadiazole(BTH) spraying and infection of Erysiphe cucurbitacearum on defensive enzyme system to melon powdery mildew were investigated in two melon(Cucumis melo) cultivars with different disease resistance,via determination of leaf POD,PPO and PAL activities.The results showed that POD,PPO and PAL activities in melon leaves were significantly increased after BTH spraying and Erysiphaceae cucurbitacearum inoculation.The effect of BTH on PPO activity in the disease-resistant cultivar was earlier in time and higher in intensity than that in the susceptible one.No significant difference in leaf PAL activity was found between the cultivars after BTH spraying and Erysiphe cucurbitacearum inoculation,but the response of the disease-resistant cultivar was far earlier in time than in the susceptible one.The results suggested that the effect of BTH spraying may transfer to untreated tissues via plant transduction system to increase melon resistance and defensive enzyme activity systematically.