Effects Of Low Temperature Stress On Growth,photosynthesis And Chlorophyll Fluorescence Characteristics Of Cotton At Bud Stage

[Objective]As a worldwide cash crop,cotton plays a very important role in the development of China’s national economy.Cotton likes temperature and light,and is a cold sensitive crop;Bud stage is the initial stage of cotton growth and development from vegetative growth to reproductive growth.The growth environment of bud stage plays an important role in cotton yield and quality.However,there are few reports on low temperature stress in bud stage.This experiment aims to analyze the effects of low temperature stress on cotton growth and development index,photosynthesis and chlorophyll fluorescence characteristics in bud stage,and explore the response law of cotton to low temperature stress in bud stage,so as to provide theoretical basis and technical guidance for identification of cold resistant resources,breeding of new varieties and Application of cultivation and management measures in bud stage.[method]Three main cotton varieties Xinluzao 10,Xinluzao 36 and Xinluzao 61 in Northern Xinjiang were used as experimental materials,and low temperature stress was simulated in indoor artificial climate chamber.The potted seedlings of all tested cotton varieties were tested at bud stage based on different stress intensity(mild T1（20/15℃,day/night）,moderate T2（15/10℃）,severe T3（10/5℃）、CK（28/25℃）and duration（short-term 5D,medium-term 10d,long-term 15d）were used to observe and analyze the response changes of seedling phenotype,main growth and development indexes,photosynthesis and chlorophyll fluorescence characteristics of cotton varieties under different low temperature stress at bud stage.[result]1.Under low temperature stress in bud stage,cotton leaves gradually turned yellow,wilted,the tightness of leaf tissue structure decreased,and the looseness of leaf tissue structure increased.The main growth and development indexes of cotton,such as plant height,stem diameter,leaf area,number of buds and single bud weight,were affected.The lower the stress temperature and the longer the stress time,the more obvious the inhibition degree of cotton growth.The damage of different stress intensity to cotton showed T3>T2>T1.The growth and development index values of the stress group were less than those of the control group,but compared with the control group,the difference significance and variety change rate under different stress were different:under the low temperature stress of T1 for 15 days,the growth and development index（bud number,single bud size,plant height）of cotton showed only slight differences,while after the treatment of T3 for 15 days,the fresh and dry matter accumulation,leaf area,plant height of each cotton showed no significant difference Compared with CK group,the stem diameter showed significant difference.Cotton plants almost stopped growing and tended to die.Compared with the control group,under T3 stress for 15 days,the single bud weight,plant height,dry and fresh weight of roots,stems and leaves of all varieties decreased to more than 30%,and the decrease range of fresh weight of leaves was Xinluzao 10>Xinluzao 36>Xinluzao 61,which decreased by 44.3%,42.4%and 32.1%respectively;The number of buds decreased by 63.0%,64.4%and 93.4%respectively for Xinluzao 10,Xinluzao 36 and Xinluzao 61.2.Under low temperature stress,Pn,Gs,Tr and ls of cotton leaves at bud stage were significantly decreased.The Pn of Xinluzao 10,Xinluzao 36 and Xinluzao 61 decreased by 52.8%,61.4%and 53.9%respectively on the 15th day of T1 low temperature stress.The Pn of Xinluzao 10,Xinluzao 36 and Xinluzao 61decreased by 75.1%,62.1%and 66.7%respectively on the 10th day of T2 low temperature stress.The Pn of Xinluzao 10,Xinluzao 36 and Xinluzao 61 decreased by 93.9%,76.4%and 86.2%respectively on the5th day of T3 low temperature stress.In the same period,the Ci of WUE showed a significant increase.Under T1 and T2 stress,WUE of Xinluzao 36 increased the most,while Xinluzao 10 increased the least.Under T3 stress,WUE of Xinluzao 10 decreased the most,followed by Xinluzao 36,and Xinluzao 61changed the least.Under T2 and T3 stress,the Ls of Xinluzao 10 decreased the most,and Xinluzao 36decreased the least.Ci decreased first and then increased with the increase of stress intensity and stress time.Ci decreased and WUE increased under low temperature above 20/15℃and 15/10℃for 5 days;Ci increased and WUE decreased under low temperature stress below 10/5℃and 15/10℃for more than 15days.Compared with CK,T1,T2 and T3 increased LCP and AQY（E）,and decreased LSP,Rp,A_max,V_C,max,J_maxand TPU,indicating that low temperature reduced photosynthetic capacity and CO₂ utilization range of cotton leaves at bud stage.3.After 15 days of low temperature treatment,Fo increased significantly and q P decreased significantly;There were significant differences among treatments,but no significant differences among varieties.The effects of T1 and T2 stress on FM,Fv/Fo and Fv were not significant.Under T3 stress,Fm,Fv/Fo and Fv decreased sharply,and the difference was extremely significant;Fm,Fv/Fo and FV of Xinluzao 61decreased the least,followed by Xinluzao 10 and Xinluzao 36.Fv/Fm increased significantly under T1and T2 stress.The Fv/Fm of Xinluzao 10,Xinluzao 36 and Xinluzao 61 decreased significantly by 49.0%,72.2%and 61.8%,respectively,compared with CK group.The increase of Fv/Fm of Xinluzao 36 was the smallest under T1 and T2 stress,and the decrease of Fv/Fm of Xinluzao 36 was the smallest under T3stress.The same treatment duration and different low temperature treatments showed differences.[Conclusion]The lower temperature stress in bud stage can significantly inhibit the growth and development of cotton,and make the photosynthetic performance of cotton decrease,and the yield of photochemical efficiency will be reduced.The higher the intensity and time of low temperature stress,the greater the impact on cotton.Under low temperature stress,the plant height,stomatal limit value ls and the maximum photochemical efficiency Fv/Fm were significantly different in different stress treatments and varieties,which could be used as the index factors for cold resistant resources identification and new variety selection of cotton in bud stage.The results show that the cold resistance of Xinlu zao10 in Lei period is poor,and that of Xinluzao61 is stronger.