The Study On Defense Aphis Gossypii Glover Of Cotton Induced By Mepiquat Chloride

Mepiquat chloride (DPC), one kind of plant growth retardants, can control the vegetative growth, reduce bollabscission and promote boll development. DPC can also improve the stability of cell membrane and increase plantadverse resistance. Aphid (Aphis gossypii Glover), one of most important pests in Xinjiang, can harm cotton inwhole growth period under suitable climatic conditions. The hazard of aphid can cause crop seedlings wilting anddeformity, and the honeydew secreted by aphid can also affect the photosynthesis and fiber quality of cotton.Littleresearch focused on the physiological response of cotton regulated by DPC to aphid and the toxicity mechanismof DPC on aphid at the present. In this paper, the flower-boll stage cotton was closed to study the toxicitymechanism of DPC on aphid and the effect of DPC on the physiological characteristics of cotton stressed by aphid,aiming at improving cotton resistance ability to aphid by DPC and providing a theoretical basis for delay aphidresistance to pesticides.The results showed that：The soluble protein content, POD and CAT activity in cotton were higher thancontrol after treated with different concentrations of DPC through foliage spray. When the concentration of DPCwas lower than0.1g/L, the SOD activity in cotton was higher than control, but the difference was not significant(p>0.05). The change tends of SOD and CAT activities in cotton were contrast to early ones after treated for15days. The soluble protein content in cotton treated with DPC at a concentration of0.25g/L after treated for20days.The cotton resistance ability could be significantly increased by DPC with the concentration lower than0.25g/Land the effect could last for15days.The change of cotton physiological characteristics and yield traits were significant different after the damageof aphid. In bud stage, the chlorophyll content, soluble protein content and MDA content in cotton treated withdifferent damage degree of aphid were significant higher than control, but the SOD and CAT activities in thesecotton were decreased. However, the change tends of these physiological characteristics were opposite when thedamage of aphid last for13days. Although the single boll weight of cotton treated with the aphid damage degreeof1was lower than control, no significant difference was found (p>0.05). The higher boll number and ginningoutturn from cotton treated with aphid damage degree of1showed that the stress of aphid damage degree of1hada positive effect on cotton. The treatment of other aphid damage degree had a negative stress on cotton, and theresistance of cotton to aphid increased with time prolonged.The changes of aphid detoxification enzyme activities after treated with different concentrations of DPCwere determined under field and indoor conditions. The results showed that: under field conditions, with theincreasing of DPC concentration, the glutathione S-transferase activity in aphid would increase, while thecarboxymethylacid esterase and acetylcholinesterase activities would decreased, however all the detoxification enzyme activities would decrease with time prolonged. Under leaf immersion processing conditions, theglutathione-S-transferase enzyme activity in aphid treated with DPC concentration of0.25g/L was highest(0.11μm/mg pr./min), while the carboxymethylacid esterase and acetylcholinesterase activities were decreasedwith the increasing of DPC concentration. DPC had a toxic effect on aphid when the DPC concentration was lessthan0.5g/L, however excessive DPC concentration would induce the resistance of aphid to pesticides.The effect of DPC on protective enzyme activity of cotton (flower-bolling stage) under the stress of aphidwas studied under field condition. The results showed that: aphid did no damage to cotton after treated for5days,while the soluble protein in cotton increased with time prolonged. Under high aphid population density stress, theSOD activity in cotton was positively correlated with the population density. When cotton were treated with DPCconcentration of0.05g/L or0.1g/L, the SOD activities in cotton under low aphid population density stress werehigher than cotton which was not treated with DPC, however the change trend of SOD activity in high aphidpopulation density stressed cotton was opposite. Compared to cotton untreated with DPC, the POD activity washigher and CAT activity was lower in cotton treated with DPC concentration of0.1g/L.It was concluded thatcotton could tolerate the sap-sucking stress of low aphid population density and high aphid population densitysap-sucking stress had negative effect on cotton. The cotton resistance to aphid could be enhanced by treated withDPC with time prolonged, and the optimal concentration of DPC was0.1g/L.