Evaluation On Resistance Of Zucchini-Cucumber Grafts To Cotton Aphid

Cotton aphid(Aphis gossypii Glover)is a typical stinging and sucking pest,which can cause a wide range of zucchini and cucumber crop loss.At present,chemical control methods are mainly used to control cotton aphid,but the resistance of cotton aphid is developing rapidly,and the problem of resistance in production is obvious.Therefore,it is urgent to find and develop new and efficient control methods to replace chemical pesticides.Grafting is an important horticultural technique,which has great application value in the control of various plant diseases.However,there are no relevant conclusions about the effect of grafting on insect resistance.Hapl type cotton aphid survived well on zucchini(Cucurbita pepo)and in Cucumber(Cucumis sativus).In this paper,we took zucchini and cucumber as the research objects,evaluated the indoor and external resistance performance of them before and after grafting by bioassay technology,and analyzed the symbiotic bacteria in cotton aphid,trying to explore the mechanism of zucchini cucumber grafting affecting the resistance to cotton aphid.The main results are as follows:1.The number of cotton aphids on melon hosts in the field from mid to late May to early June was systematically investigated.The results showed that from mid to late May to the end of May,the number of cotton aphid in the field increased rapidly,and from early June,the number of insects began to decline sharply.The cotton aphid basically disappeared in the field until early June.Molecular identification showed that Hapl type cotton aphid could occur in zucchini,but not in cucumber.2.By constructing the life table of Hapl cotton aphid on various cucurbit crops,the adaptation of Hap1 cotton aphid on various host plants was investigated.The results showed that the adult stage of Hapl type cotton aphid was shorter on watermelon(citrullus lanatus),zucchini,loofa(Luffa cylindrica)and gourd(Lagenaria siceraria).In squash(Cucurbita moschata),muskmelon(Cucumis melo)and cucumber.The intrinsic growth rate and net proliferation rate of Hapl type cotton aphid feeding on zucchini were significantly higher than those of other melons.The survival rate and life span of cotton aphid feeding on cucumber were generally shorter and their size was generally smaller than those feeding on other cucurbit crops.These results indicated that Hapl type cotton aphid could not establish population on cucumber,but could establish population on zucchini.3.The leaves of zucchini and cucumber grafted with each other were used to determine the adaptation of Hap1 type cotton aphid.The results showed that the total prereproductive period of cotton aphid fed on zucchini leaves(4.81 d)was significantly lower than that fed on grafted zucchini(5.14 d),and the total prereproductive period of Hap1 type cotton aphid fed on cucumber was higher than that fed on grafted cucumber.The net breeding rate of cotton aphid fed on grafted zucchini(12.69)was significantly lower than that fed on ungrafted calabash(24.11),while the net breeding rate of cotton aphid fed on grafted cucumber(21.29)was significantly higher than that fed on ungrafted cucumber(5.86).This indicated that grafting had a significant effect on the insect resistance of zucchini and cucumber.After grafting,zucchini changed from an adaptive host to an unsuitable host,while cucumber changed from an unsuitable host to an adaptive host.4.16S rRNA high-throughput technique was used to analyze the changes in the diversity and composition of symbiotic bacteria community of Hapl type cotton aphid in zucchini and cucumber before and after feeding and grafting.The diversity and composition of symbiotic bacteria community in the cotton aphid of zucchini before feeding on grafting had a great change compared with the cotton aphid of zucchini after feeding on grafting,and the relative abundance of Acinetobacter had a significant change.The structure and abundance of symbiotic bacteria in cucumber aphid before and after grafting were also significantly changed.The relative abundance of Rhodococcus was significantly decreased in the aphids living on the grafted zucchini for a long time,but significantly increased on the grafted cucumber.In addition,the relative abundance of Actinobacteria in Hapl type goaphid fed on grafted cucumber increased slowly from generation to generation within three generations,while Proteobacteria in Hapl type goaphid fed on grafted zucchini decreased at T2 and returned to T1 at T3.