Effect of Powdery Mildew on Physiological and Biochemical Indexes of Different Melon Varieties

Abstract

In order to study the effect of melon powdery mildew on the physiological indexes of different melon varieties, high resistant to melon powdery mildew variety ‘16-6’, medium resistant to melon powdery mildew variety ‘04-38’, and highly susceptible melon powdery mildew variety ‘15B-42’ were used as materials. The activities of antioxidant defense system enzymes, the contents of malondialdehyde (MDA), soluble protein and chlorophyll, and the photosynthetic indicators in leaves of melon seedlings were assayed after inoculated with powdery mildew 1 d, 3 d, 5 d, 7 d and 9 d. The results showed that after inoculation with powdery mildew, except for superoxide dismutase (SOD) activity, the defense enzyme activities, including peroxidase (POD), catalase (CAT), ascorbic acid peroxidase (APX), phenylalanine ammonialyase (PAL) and polyphenol oxidase (PPO) and the MDA content in leaves of the three melon varieties showed a trend of first increase and then decrease, and the increment amplitude of the resistant lines was larger than that of the susceptible lines ; the contents of chlorophyll and soluble protein, and the five photosynthetic indicators, including the net photosynthetic rate (Pn), the stomatal conductance (Gs), the intercellular CO 2  concentration (Ci), the transpiration rate (Tr) and the stomatal limitation (Ls) of leaves of the three melon varieties decreased with different amplitude after inoculation , and the decrement amplitude of the resistant lines was smaller than that of the susceptible lines.