Study Of Defoliants Spraying Time On Cotton Physiological Mechanism

Chemical dehydration of cotton is an essential technology of mechanized cotton picking and quick manual cotton picking. It is significant for guarantying the Machinery Picking Cotton in Xinjiang, reduction the cost of cotton production and improvement the efficiency of the cotton. Since there are little studies on the physiological basis of leaf removal at present, it has important theoretical and practical significance to clarify the effect of leaf removal agent on cotton yield and quality, and its relationship with meteorological factors. This study adopting split plot design, defoliants sprayed with time as the main area, controlling the boll opening rate of 10%,30%,50%. Dropp ultra 300 g/hm2, B2:Thidiazuron 2700ml/hm2, B3:water (CK). The effects of leaf removal agents on chlorophyll fluorescence parameters, antioxidant enzyme system, yield and fiber quality of cotton were studied, and the aim is to find the proven removal effects on the physiological effects of cotton leaf agent, elucidate climate and defoliation rate and the rate of boll opening and to screen suitable off leaf agent spraying time and defoliation effect better off leaf agent, for the production of defoliants promotion to provide a scientific basis. The main findings reported as below:1. Effect of defoliations spraying time on cotton defoliation percentage, yield and fiber qualityCotton defoliation rate, boll opening rate, yield and fiber quality showed 50% of boll opening process> boll opening rate of 30% processing> processing boll opening rate of 10%. Boll opening rate of 10% of cotton defoliant spraying boll weight, lint percentage, lint yield on the P<0.05 level was significantly lower than the control. When compared boll opening rate of 30% with boll opening rate of 50%, there are no significant difference in boll opening rate, lint yield and fiber quality of cotton. When the boll opening rate reached 10%, there are no difference in cotton fiber length treating with defoliants and water. Different time and spraying defoliants defoliants cotton fiber breakage strength and micronaire influence difference was not significant. In the cotton boll opening rate of 50% (5 days before spraying defoliants≥10℃ effective accumulated temperature above 55℃. Defoliant spraying when the minimum temperature is 11.2℃, the average daily temperature is 17.6℃) spraying defoliants more conducive to play field defoliant ripening effect.2. Effect of Defoliants spraying time on photosynthetic indices and Chlorophyll Fluorescence of the cotton leavesCotton defoliants cause stomatal conductance (Gs), net photosynthetic rate (Pn), transpiration rate (Tr) decreased CO2 assimilation capacity decreased, so that intercellular CO2 concentration (Ci) increased. The initial fluorescence (Fo) increased, PS Ⅱ potential activity (Fv/Fo), maximum photochemical efficiency (Fv/Fm) and the ratio of the open portion of the reaction center PS Ⅱ, transfer rate and apparent quantum PS Ⅱ overall quantum yield is reduced. Improved the non-photochemical quenching, PS Ⅱ complex damaged along with the photosynthetic electron transport blocked. Spaying the defoliants when the boll opening rate reached 50% is benefit to speed up the cotton leaf senescence. Dropp ultra of cotton leaf damage greater than Thidiazuron.3. Effect of Defoliants spraying time on endogenous hormone contents and antioxidative enzyme activities of the cotton leavesAfter the defoliants sprayed, the IAA content of cotton leaf decreased, ABA content increased in order to turn on the aging process, then ABA decreased. Under defoliants processing antioxidant enzyme activities were higher than the control. SOD, POD, CAT activities were first increased and then decreased. Cotton leaf SOD, POD and CAT activity increased, scavenging reactive oxygen species has increased, and when the active oxygen accumulated more than the normal level, and seriously damage the cell membrane, it will lead to the cotton leaf SOD, POD and CAT activity decreased, and cotton leaf senescence accelerated. Within the cotton boll opening rate of 50% spraying defoliants defoliation best, more advantageously accelerated senescence of cotton leaves, defoliation rate increase.