Study On Improvement Measures Of Upper Tobacco Leaf Of Premature Senescence

The upper leaves make great contribution to the yield and quality of flue-cured tobacco,playing an important role in the formulation of low-tar cigarette leaf group.Flue-cured tobacco field in the southern tobacco area often suffers high temperatures and drought in the late stage,resulting in premature senescence of roots and false maturation of tobacco leaves,which seriously affects the quality of upper tobacco leaves.In order to improve the availability of upper tobacco leaves,the differences of physiological and biochemical indexes between different qualities of upper fresh tobacco leaves and roots have been investigated,and the effects of planting methods and microbial fungicides on the physiological characteristics of flue-cured tobacco and the growth of upper tobacco leaves in the later stage of the field have been studied,so as to improve the root growth environment of flue-cured tobacco,improve the physiological function of tobacco leaves,and reduce the occurrence of upper leaves of premature senescence.The main conclusions are as follows:(1)The root activity,root dry and fresh weight of pale tobacco leaves which are under premature senescence are lower than those of normal tobacco leaves or hyper-trophic tobacco leaves.The content of MDA increases while the activity of SOD decreases in pale tobacco leaves that are premature and senescent.The activities of chlorophyll enzyme and amylase in premature senescent and pale tobacco leaves have lowered than those in normal and overactive tobacco leaves.The trace elements content in premature senescent and pale tobacco leaves is lower than that in normal tobacco leaves and energetic tobacco leaves.The contents of starch,total sugar,reducing sugar and potassium in normal tobacco leaves are higher than those in hypertrophic tobacco leaves and premature senescent and pale tobacco leaves.The indexes of premature senescent and pale tobacco leaves are all poor and not in the suitable range.(2)Compared with single ridge planting without mulching cultivation,the total length of root,the average diameter of root and the total volume of roots of concave double ridges uncoated and concave double ridges with side mulching cultures could be increased by 11.67% to 37.62%,15.87% to 34.92% and 31.53% to 69.18% respectively,and the root activity could be increased by 7.39% to 10.85%.The area of upper tobacco leaf increased by 103.11% to 153.91%.The rate of photosynthesis increased by 9.89% to 27.47%.The proportion and output value of the upper class smoke have increased by 7.47% to 11.01% and 3.53% to 7.27% respectively.The availability indices of physical characteristics and chemical components have increased by 1.76% to 2.69% and 6.79% to 10.53% respectively.The planting pattern of concave double ridges with side mulching benefits most.(3)Compared with the control group,the total length of root,the average diameter of root and the total volume of roots have increased by 5.45%,9.25% and 25.80% respectively,and the root activity has increased by 3.57%.The maximum leaf area of upper tobacco has increased by 1.36 times.The degradation rate of SPAD value is slower by 5.16%.The rate of photosynthesis has increased by 12.62% to 35.39%.The proportion and output value of the upper class smoke have increased by 7.03% and 5.34% respectively.The availability index of physical characteristics and chemical components have increased by 2.33% and 19.80% respectively.Spraying microbial bacteria can promote the growth of tobacco leaves,improve the photosynthetic ability of tobacco leaves,increase the yield and quality of upper tobacco leaves,and enhance the availability of upper tobacco leaves.(4)The premature senescent and pale of upper tobacco leaves is related to the premature senescence of roots and the decline of physiological function of tobacco leaves.Therefore,in order to prevent premature senescence of upper tobacco leaves,some solutions are going to be adopted: Firstly,to improve the root growth environment of flue-cured tobacco in the middle and late stage and the activity of root so as to meet the water and nutrient requirements for healthy growth of upper tobacco leaves.Secondly,to enhance the physiological function of the leaves and the photosynthesis ability of the upper tobacco leaves so as to promote the healthy growth of the upper tobacco leaves.