| Nicotine is a specific alkaloid in tobacco plant,and its content is a key index to evaluate the quality of tobacco in tobacco production and cigarette manufacturing.The agronomic measures such as topping and fertilization and ecological environment have significant effects on nicotine content in tobacco leaves.The tobacco leaf nicotine content has obvious heterosis,the research shows that the genes involved in nicotine synthesis,metabolism and transportation play a key role in the formation of heterosis of nicotine content,however,it is not clear whether the agronomic measures such as topping and fertilization and ecological environment have an effect on the formation of Heterosis of nicotine,which is not conducive to the improvement of heterosis evaluation efficiency.In order to clarify the effects of ecological conditions and topping measures on Heterosis,three crosses and their parents with different heterosis of nicotine content in tobacco leaves were selected randomly on the basis of previous studies,different ecological environment tre atments,topping and non-topping treatments with different ecological conditions were established.The effects of ecological environment and topping on nicotine content and heterosis were analyzed by measuring nicotine content in different treatments,and the relative expression of related genes(PMT,AO,QS)was measured by fluorescence quantitative PCR,the heterosis of nicotine content and nicotine content in tobacco leaves under different ecological environment and topping measures was analyzed from the level of gene differential expression.The main findings are as follows:1.The ecological environment has a significant effect on nicotine content in tobacco leaves.The content of nicotine in leaves of different varieties Was significantly different.The content of nicotine in leaves of Cynanchum paniculatum was the highest(1.2336%),and that in leaves of Cynanchum paniculatum the lowest(0.5 181%).The content of nicotine in leaves of Cynanchum paniculaum was 2.38 times higher than that in leaves of Cynanchum paniculatum,it shows that the content of nicotine in the materials chosen iii this study is quite different and has strong representativeness.The content of nicotine in the leaves of the same material was signficantly different among the test sites.The content of nicotine in the leaves of the Dejiang Test Site the highest,followed by the Weining Yi,Hui,and Miao Autonomous Counnty test site,and the Yangwu test site the lowest,the high content of nicotine in the tobacco leaves of the test sites in Dejiang and Weining Yi,Hui,and Miao Autonomous County may be caused by drought,and the average content of nicotine in the leaves of the eight test materials of the three test sites were 0.9149%,0.6980%and 0.532%,respectively,the results showed that ecological environment had a significant effect on nicotine content in tobacco leaves,and the regulation of nicotine content varied with the environment of tobacco growing areas.2.Topping can obviously regulate the content of nicotine in tobacco leaves.7 days after topping treatment,the nicotine content of tobacco leaves increased rapidly.The average value of nicotine content in topping treatment was 0.9727 for 8 materials,0.7050 for no topping treatment,and 37.97%higher than that in no topping treatment.The effect of topping treatment on increasing nicotine content of tobacco leaves varied with varieties,the biggest increase range vas VA116,the increase range was 52.31%,the smallest increase range was Qinggeng,the increase range was 21.68%.Therefore,when suitable topping time was used to control nicotine content in tobacco leaves,the topping time should be determined reasonably according to variety characteristics,in addition to the nutritional status.3.Effect of ecological environment on Heterosis of nicotine content.The relationship between heterosis and ecological environment varied with the difference of Heterosis Index,but the difference of heterosis among the three test sites not significant,the mean values of Heterosis of the three crosses in Dejiang,Yangwu and Weining Yi,Hui,and Miao Autonomous Counnty were-4.7332%,-4.6823%and-4.2210%,respectively,with no significant difference The difference of super-high,super-low and super-high heterosis of the same combination was significant among the three test sites.The results showed that the mid-parent heterosis did not change obviously with the change of ecological environment,while the super-parent heterosis and super-standard heterosis varied with the change of ecological environment.Therefore,it is representative to identify the Heterosis at a test site wtliout considering the influence of environment on the heterosis value in the study of heterosis genetic theory and formation mechanism When the heterosis and Heterosis were used to evaluate the utilization potential and value of hybrid combinations,more attention should be paid to the effect of ecological environment on heterosis,while evaluating the utilization potential and value of hybrid combinations,the adaptive regions of hybrid combinations were screened.4.Effect of topping on Heterosis of nicotine content.The effect of topping on heterosis varies with different heterosis metrics.After 7 days of topping treatment,there no significant difference in the content of nicotine between topping and non-topping treatments in the same combination,the mean values of mid-parent heterosis of nicotine content in tobacco leaves of three crosses were-3.9978%and-4.4002%respectively,and the difference was not significant.There were significant differences between topping and non-topping treatments in super-high,super-low and super-high relative heterosis of nicotine content in the same combination.The results showed that there was no significant difference between the top-cutting and no-top-cutting measures,and that the top-cutting and no-top-cutting measures were related to the super-parent and super-standard advantages.There fore,the genetic theory of Heterosis and the mechanism of heterosis can be studied by selecting Middle Parent Heterosis,and the effect of topping and no topping on heterosis can be ignored When selecting heterosis and Heterosis to evaluate the utilization value of hybrid combination,we should adopt the local tobacco production technical scheme to set the test conditions and adopt the top-cuutting treatment to identify and screen.5.Differences in expression of genes related to heterosis of nicotine in different ecological environments.The correlation coefficients between the Mesophilic dominance of PMT,AO,QS and the Mesophilic dominance of nicotine content were 0.92,0.85 and 0.874,respectively,the results showed that PMT,AO and QS genes were the key genes for the formation of parent dominance in nicotine content of tobacco leaves.There was no significant difference in the relative expression of the same gene in the same combination,the mean expression of PMT gene was 2.6022,2.5828 and 2.5345 in the three combinations in Weining Yi,Hui,and Miao Autonomous County,Yangwu and Dejiang,respectively,the average values of Ao gene relative expression were 0.6809,0.6497 and 0.6640,respectively.The average values of QS gene relative expression were 1.2493,1.2530 and 1.2575,respectively.The results showed that ecological environment had no significant effect on relative expression of heterotic genes related to nicotine content in tobacco leaves,the results from the gene expression level confirmed that the envronment had no significant effect on the parental dominance of nicotine content in tobacco leaves.6.There was no significant difference in the expression of genes related to heterosis between topping and no topping.After 7 days of topping treatment,there was no significant difference in the relative expression of the same gene between topping treatment and no topping treatment,and the mean expression of PMT gene in the three treatments was 2.5676 and 2.4015,respectively,the average values of Ao gene relative expression were 0.8180 and 0.7475 respectively,and the average values of QS gene relative expression were 1.4889 and 1.3513 respectively.The results showed that topping treatment had no significant effect on the expression of relative genes of nicotine content in tobacco leaves,results from the level of gene expression,it was proved that topping had no significant effect on the parental dominance of nicotine content. |
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