The Mechanism Of Cucumber Resistance To Aphis Gossypii

Aphis gossypii Glover is one of the main pests on cucumber in the w6orld. Its nymph and adult gathered at the back of the leaves, young-shoot, young-stalks, sucks plant juices, excretes honeydew, that serve as media for sooty mold. Sooty mold could interfere with plant photosynthesis. In addition, aphis can also transmission of virus diseases, which bring about great economic loss.The prevention methods of Aphis gossypii mainly uses chemical pesticide over a long period of time, not only pollutes the environment, but also results in Aphis gossypii become resistant, lead aphids harm get worse. Breed and chose cucumber varieties, which can resist to aphids, can make cucumber escape of aphids by its own mechanism. It is the best measure of pest control through change the characteristic of plant-self, it’s also an important part of pest management system. Therefore, through breeding resistance varieties against aphids has become an effective way to control the hazards.In this study, use different cucumber varieties as test materials, aphis as bio-stimulating factor, combined with greenhouse experiments, on the basis of in-house testing, the mechanism of aphid selection and antibiosis to different varieties of cucumber has been systematically researched, for further breeding cucumber resistant varieties and provides some basic theoretical for aphid resistance identification. The main findings are as follows:1. The dynamic trend of aphids populations on different resistant varieties of cucumber are basically the same, but resistant varieties has smaller damage than the susceptible varieties. The population trend index method was used to evaluate the resistance of13cucumber varieties. The result shows that, the growth of aphids on resistant varieties is longer than that on sensitive varieties, the nymph duration of aphids on resistant varieties number4is the longest (8.71±0.64d), on susceptible cucumber varieties number9is the shortest (5.67±0.14d), the former is1.54times of the latter, and the survival rate and bearing capacity of aphids on resistant varieties is significantly lower that of sensitive varieties; The density of blade hairy of resistant varieties is lower than sensitive species, but the wax content of resistant varieties is higher than sensitive species, and the vascular bundle depth of resistant varieties more deeper; Correlation analysis and multivariate stepwise regression showed that the aphid population and hair density has a very significant positive correlation. The density of blade hairy increase by one unit, aphid population trend index increased by0.8114; Signs that the density of blade hairy is one of the main physical character of cucumber aphid-resistance。2. In color selective experiment, the host selection of aphids to different varieties of cucumber leaf is not significant. Olfactory selective experiment signified that the selective of resistant varieties is significant lower than the susceptible varieties; Soluble sugar, free amino in resistant varieties is significant lower than the susceptible varieties, chlorophyll, phenolic compounds, flavonoids is higher than the susceptible varieties, but soluble protein content in the resistant and susceptible varieties has not regularity. Correlation analysis showed that, aphid population trend index and phenolic compounds, chlorophyll has a significantly negative related, the flavonoid compounds showed a significant negative related, under the condition of soluble sugar, phenolic compounds, chlorophyll and soluble protein content unchangeable, flavonoids content increase by one unit aphid population trend index decreased by0.0165. No significant correlation relationship with the free proline, and has a significantly positive correlation with soluble sugar. As the condition of phenolic compounds, flavonoids content unchangeable, soluble sugar content increase by one unit aphid population trend index decreased by0.1574.3. Before and after aphis vaccination, the determination of peroxidase isozyme (POD), Polyhenoloxidase (PPO), Phenyalanine ammonialyase (PAL) activity has been test. The results show that, compared with the susceptible varieties, the cholinesterase activity of resistant varieties rise faster, peak higher, more timely and effective. For example, PPO enzyme activity of variety number6and8reached73.09U/(g.min) and57.74U/(g.min), compared with the control, increased of1.89times and2.69times separately, after aphid infestation24hours. POD activity increasing with time after the infestation during the test period, and the level of the resistant varieties is always higher than the susceptible varieties; PPO activity of susceptible varieties is went up with the time increasing at first and then decline, the rise time of resistant varieties continues longer; PAL activity trend rebounded slightly increased and then decreased, and the day after the infestation reached maximum in resistant and susceptible varieties. Thus, in the process of aphis sucking period, POD, PPO and PAL activity changes with cucumber resistance is closely related to physiological indicators, which can be used as an identification of cucumber resistance to aphid.4. By the infestation of aphid, the content of secondary metabolites showed varying degrees of change in resistant and susceptible varieties. Free proline, phenolic compounds and flavonoids content in resistant varieties is always higher than the susceptible varieties, and each compound content is first increased and then decreased, with the time increasing, the higher the density, the trend more obvious. For example,200heads/leaf inoculated aphids, after48h, free proline content of the two species are increased by0.34times and0.32times compared with the control, the content of flavonoids, increased of0.34times and0.14times compared with the control respectively; Soluble sugar content, susceptible varieties is higher than resistant varieties, after the infection, the sense of anti-soluble sugar shows a trend of increased and then decreased, on the third day reaches maximum value. Thus, in the process of aphis sucking period, proline, phenolic compounds, flavonoids and soluble sugar content have a close related with cucumber resistance to aphids.