The Process Of Flower Bud Differentiation And The Changes Of Physiological And Biochemical Indexes Of Cold Tolerance In Different Tobacco Varieties Under Low Temperature Stress

Early flowering induced by low temperature is a common abnormal phenomenon in flue-cured tobacco production at home and abroad,especially in Yanbian tobacco area,early flowering occurs every two or three years due to short frost free period and low temperature in spring,which seriously affects the yield,quality and economic benefits of local tobacco.In order to select low temperature resistant and early flowering tobacco varieties,six tobacco varieties were used as test materials in this experiment.The 7-8-leaf-old tobacco plants were treated with low temperature in an artificial climate box.The process of flower bud differentiation at the shoot tip was observed and analyzed by the method of paraffin section and stereomicroscope.Secondly,the half lethal temperature,protective enzyme activity and MDA content at the seedling stage of tobacco were measured under the low temperature gradient,Then,the sensitivity of different tobacco varieties to low temperature was evaluated.Thirdly,the changes of physiological and biochemical indexes,such as dry matter weight,protective enzyme activity and osmoregulation substance,were studied in the process of low temperature stress.Through the analysis of the correlation between the physiological and biochemical indexes and the relative growth rate,and the cold tolerance of different tobacco varieties was comprehensively ranked by principal component analysis.It also laid a foundation for the discovery of genes of low temperature tolerance and early flowering and the study of molecular mechanism.The main conclusions are as follows:1.After 54 days of transplanting,the relative leaf number reduction indexes of Longjiang 981,CV91 and Yanshai No.9 were all less than 10%,while the relative leaf number reduction indexes of NC89,NC82 and Dalanhua were all about 20%;Longjiang 981 under low temperature treatment reached the budding stage 2 days earlier than the control,and the relative early flowering index(RE)was the smallest,4.08%,while the budding stage of NC89 and NC82 under low temperature treatment was earlier than the control 5 d.RE was 12.24%and 12.64%respectively.2.The order of the half lethal temperature of different tobacco varieties from high to low was Dalanhua,NC82,NC89,Qianchengta,Yanshai No.9,Longjiang 9813.With the decrease of temperature,the activity of SOD,CAT and POD of different tobacco varieties increased first and then decreased.During this period,Longjiang 981 had the highest increase of protective enzyme activity,and the Dalanhua had the lowest increase4.After 9 days of low temperature treatment,the dry matter accumulation of the control treatment was greater than that of the low temperature treatment,and the lowest dry matter decrease was Longjiang 981,and the largest one was Dalanhua.The chlorophyll content of different tobacco varieties showed a downward trend with the extension of stress time,the smallest decline was Longjiang 981,and the largest decline was Dalanhua.5.With the extension of low temperature stress time,the activities of protective enzymes(SOD,POD,CAT)of all tobacco varieties increased first and then decreased.Compared with the control group,the increase of protective enzyme activity of Longjiang 981 was always the highest,while that of Dalanhua was always the lowest.In the process of low temperature stress,the increase of MDA content in Dalanhua has always been the highest,while that in Longjiang 981,Yanshai No.9 and Qianlangta are smaller.6.The content of soluble sugar and proline in different tobacco varieties increased gradually with the extension of low temperature stress time,while the content of soluble protein decreased gradually;compared with the control,the content of soluble sugar and proline in Longjiang 981 increased the most in each period,while that of magnolia flower was the least;the content of soluble protein in Longjiang 981 and Yanshai No.9 decreased the least,while that of Dalanhua was the same Larger.7.The correlation analysis of physiological and biochemical indexes and relative growth rate showed that the correlation degree was Dry weight>CAT activity>soluble protein content>chlorophyll content>SOD activity>POD activity>soluble sugar content>Pro content>MDA content.8.The order of comprehensive evaluation of cold tolerance based on principal component analysis was the same as that of semi lethal temperature,that is,the order of cold tolerance of six tobacco varieties was Longjiang 981,Yanshai No.9,Qianlangta,NC89,NC82 and Dalanhua.In conclusion,Longjiang 981 has the strongest cold tolerance and early flowering resistance,while Magnolia has the weakest cold tolerance and is sensitive to low temperature.