Physiological Responses Of Different Tobacco Varieties To Low Temperature Stress In Seedling Stage And Comprehensive Evaluation Of Cold Tolerance

In order to clarify the cold resistance mechanism of tobacco,three flue-cured tobacco varieties and three sun-cured tobacco varieties were selected as test materials.by analyzing in the relative electrical conductivity,semi-lethal temperature,antioxidant enzyme activity and malondialdehyde(MDA)content of tobacco leaves under low temperature gradients,comparing the cold resistance of six tobacco varieties.In addition,by studying the physiological responses of six tobacco varieties under low temperature lasting days,a comprehensive evaluation of the cold-resistance of the tested physiological and biochemical indexes was performed using the membership function method.The main results were as follows:With the increase of low-temperature gradient stress,the relative conductivity increases gradually,the semi-lethal temperatures of six tobacco varieties were ranked as follows:Yunyan 87(5.17?),NC95(3.08?),Jianping Large Human Head(2.64?),Jiyan No.9(1.89?),Laohe No.1(1.5?)and Yanshang No.7(0.86?).With the decrease of temperature,the activity of antioxidant enzymes showed a trend of first increase and then decrease.The order of increase from big to small is Yanshang No.7,Piaohe No.1,Jiyan No.9,Jianping Large Human Head,NC95 and Yunyan 87.The MDA content began to rise rapidly with increasing cold gradients and days,whereas the control group tended to be gentle.Among them,the Yunyan 87 reached the peak at 8?and the growth amplitude was the largest,Both NC95 and Jianping Large Human Head reached the peak at 6?and the growth rate was second,while Yanshang No.7,Piaohe No.1 and Jiyan No.9 were relatively late,and reached the peak value at 4? and the growth rate was lower.Under low temperature stress,the content of proline and soluble sugar increased obviously,Yanshang No.7 had the highest increase in proline content and soluble sugar content at each treatment stage,Piaohe No.1,Jiyan No.9 and Jianping Large Human Head was second,NC95 and Yunyan 87 the growth rate was lower.The various tobacco varieties were kept at low temperatures for a few days.Chlorophy content,soluble protein content,dry matter weight and root activity showed a gradual downward trend.The decrease of Yanshai N07 is the least,NC95 and Yunyan 87 are the largest.The comprehensive analysis of physiological and biochemical indexes of 6 tobacco varieties from strong to weak was:Yanshai No.7(0.57)>Piaohe No.1(0.52)>Jiyan No.9(0.48))>Large Human Head(0.44))>NC95(0.41))>Yunyan 87(0.37).Under low temperature stress,the cold resistance of local varieties(Yanshai No.7,Jiyan No.9)was stronger than that of other varieties.