中文摘要：

在温室条件下研究了南瓜不同抗病品种幼苗接种瓜类白粉病后叶片内一些防御酶活性的变化。结果表明,白粉病侵染南瓜幼苗后,南瓜叶片苯丙氨酸解氨酶（PAL）、过氧化物酶（POD）和多酚氧化酶（PPOD）活性增强,中国南瓜（抗病品种）和印度南瓜（感病品种）的3种酶活性曲线均呈现两个峰值。抗病品种酶活性峰值比感病品种酶活性峰值高,增幅大。抗病品种和感病品种,随着病菌侵染的不断深入,酶活性逐渐降低。在未感染情况下,中国南瓜叶片PAL、POD和PPOD活性比感病品种高。

英文摘要：

The infection of Sphaerotheca fuliginea resulted in an increase in activities of phenylalanine ammonialyase, peroxidase and polyphenol oxidase in squash leaves. Activities of the three enzymes showed two peaks in the two tested squash cuhivars. The increase of the enzyme levels in Cucurbita muschata leaves（resistant cultivar） was greater than that in C. maxima （susceptible cultivar）. These results suggested that the early rapid increase of polyphenol oxidase may serve as one of the physiological indices for the selection of C. muschata.