Genetic Analysis And QTL Location Of Tobacco Leaf Stem Conten

Tobacco is a cash crop with leaves as the harvest,the leaves are composed of smoke stems and leaf flesh,and the processing of cigarette stems into cigarettes will produce a large number of hot and rough smoke and stinging odors,which seriously affect the sensory quality of cigarettes,often burned or discarded as waste,causing pollution to the environment and increasing the processing costs and benefits of cigarettes.Therefore,reducing the infarct rate of tobacco leaves is of great significance to improve the quality and efficiency of cigarette production and processing.In the early stage,this research group found that there were obvious differences in the infarel rate of tobacco leaves between different varieties,and variety breeding was an effective way to improve the infarel rate of tobacco leaves,but the genetics of tobacco leaf stalk rate needed to be elucidated.Therefore,in this study,the genetic research populations of F₁,F₂,BC₁ and BC₂ were constructed based on the flue-cured tobacco cultivar NC82 with low stem inflower rate and Jiuchiping2 of the flue-cured tobacco cult with high stem content,and the genetic mapping of tobacco leaf infarction rate was carried out by Bulked Segregant Analysis（BSA）combined with resequencing technology and KASP labeling technology.The main findings are as follows:1.The stem rate of flue-cured tobacco NC82 and Jiucaiping 2 were 17.97%and 23.97%,respectively.The difference was very significant,which was suitable for genetic analysis of tobacco stem rate.The stem content of positive and negative F1 was 21.43%and 20.71%,respectively,with no significant difference.The average leaf stem content of F₂ segregation population>median>majority,kurtosis>0,skewness>0,showing a right-biased normal continuous distribution.The results showed that the stem content of tobacco was a quantitative trait controlled by nuclear genes,which might be jointly controlled by major genes and minor polygenes.2.The results of genetic model showed that the stem content of tobacco was controlled by two pairs of additive-dominance major genes+additive-dominance polygenes.The heritability of two pairs of major genes was 56.8477%,which was mainly additive effect,and the additive effect was equal（d_a=d_b>0）.The stem content of tobacco was partially dominant to the low stem content（0<h_a/d_a<1、0<h_b/d_b<1）.The inheritance of BC₁ was dominated by major genes(σ²_mg)=52.6879%、σ²_pg)=0%),and BC₂ was dominated by polygenes(σ²_mg)=4.3478%、σ²_pg)=58.8661%).The results showed that the stem rate of tobacco was mainly affected by two pairs of equivalent major genes.The high stem rate was partially dominant to the low stem rate,and the major genes of low stem rate varieties had greater genetic efficiency.3.The hybrid pool with high and low stem content was constructed by screening 30 tobacco plants with the highest and lowest stem content,respectively.The whole genome resequencing of the two parents and the hybrid pool was carried out by BSA and resequencing.The results showed that the gene of stem content in tobacco leaf was most likely to exist in the 17.75-27.06 Mb interval of chromosome 9,with a size of9.31Mb.There were 220 genes and 84 nonsynonymous mutant genes.4.Five KASP markers were used to detect the individual plants of 1528F2 populations,and the correlation between stem content traits and marker Nt900034 reached significant aboriginality（p=0.041）.The interval was narrowed between markers Nt900033-Nt900035,and the size was 3.34 Mb.In this interval,new markers were developed to detect the recombinant plants.The candidate interval was narrowed between markers Nt900044-Nt900045,with the interval of 24.00-24.70 Mb and the size of 703 kb.Three genes and two non-synonymous mutation genes were obtained.5.Three genes were analyzed.Nitab4.5＿0008208g0010 and Nitab4.5＿0011464g0010 were related to the synthesis of auxin,which is a signal substance formed by vascular bundles and may affect the development of leaf veins.Therefore,it is speculated that these two genes may affect the stem content of tobacco leaves by regulating leaf veins.In summary,tobacco stem content is a quantitative trait controlled by nuclear genes,which is controlled by two pairs of additive-dominant major genes+additive-dominant polygenes.The gene is located in the interval of 24.00 Mb–24.70 Mb on chromosome 9,with a size of 703 kb.It is speculated that Nitab4.5＿0008208g0010 and Nitab4.5＿0011464g0010 are candidate genes for regulating tobacco stem content.