Effect Of Aphid Infection On Secondary Metabolism And Related Enzyme Activity In Cucumber Seedling Leaves

Melon aphid is one of the main pests of cucumber. Chemical control is a major measure on production, it not only increases the cost of production and product residue, but also pollutes the environment , so it is very important to breed new cultivar which can resist to aphid.Glabrous cucumber and their hybrid were used to compare their different resistant abilities to aphid. The relationship between the secondary metabolites and several correlative enzymes of leaves were studied. This study will lay a foundation for the further study and provide information for the selection and breeding of new cultivar. It also can provide a theory for studying resistance to aphids. The main results were as follows:1 A natural field survey was carried out on three cucumber materials to compare their resistance to aphid. Glabrous cucumber was a high aphid-resistant material, normal cucumber was a susceptible material, the capacity of F1 to aphid–resistance was between its parents.2 During the process of invasion by aphid, the activities of metabolism related enzymes increased by in different degrees. Compared with normal cucumber, the activity of aphid-resistance types increased rapidly, and had high peak, its response was rapid too. The strength of induced resistance to aphid was different between the different genotypes. Before infected by aphid, enzymes activity was not significantly different. Enzyme activity was all increased after infected by aphids, and aphid-resistance material had high level of resistance to aphid than susceptible material. The changes of SOD and CAT activity indicated that they had influence on resistance to aphid. PPO and PAL activities on glabrous and F1 were always higher than normal cucumber, and POD, PPO and PAL activity in cucumber seedling leaves increased first and then showed a downward trend. Thus, in the process of melon aphid damage, PAL and PPO activity in the cucumber were closed related to the aphid-resistance of cucumber, so they can be identified as the chemical indicators.3 Induced by the melon aphid, the metabolite content increased in different levels. The content of lignin and flavonoids increased first and then showed a downward trend. Tannin and total phenol content expressed as alternating rise and fall. After inoculation of melon aphid, the content of lignin in glabrous cucumber was 14.3%, 128.5% higher than that of F1 cucumber and normal cucumber. The accumulation of total phenols in glabrous cucumber was 24.2%, 4.9% higher than that of normal cucumber and F1 cucumber. The accumulation of flavonoids and tannins in F1 cucumber was higher than the other two materials, while the accumulation of tannins was closer among the three materials. Thus, in the process of melon aphid damage, lignin and total phenols content in cucumber were closely related to aphid-resistant ability. The content of flavonoids and tannin had little relationship with resistance to aphid.4 Induced by the melon aphid, the metabolite content increased in different levels of F2 plants. The content of tannin, total phenol and flavonoids increased first and then showed a downward trend, which shows the similar rule as glabrous and normal cucumber. After inoculation of melon aphid, the accumulation of total phenol, flavonoids and tannin in glabrous cucumber of F2 was 42.82%, 30.3%, 11.1%higher than that of normal in F2. Thus, in the process of melon aphid damage, lignin and total phenols content in the cucumber was closely related to aphid-resistant ability. The content of flavonoids and tannin had little relationship with resistance to aphid.