Effects And Mechanism Of Grafting On Potassium Absorption And Utilization Of Flue-cured Tobacco

The potassium content is closely related to the quality of flue-cured tobacco.The potassium content of Chinese tobacco leaves is low,which is generally lower than the requirement of international high-quality tobacco leaf potassium content of 25g/kg or more.This has become a difficult problem restricting the development of high-quality cigarettes in China.China has a large area of tobacco cultivation and is rich in variety resources in various tobacco areas.Screening potassium-efficient high-yield tobacco varieties and grafting them with high-quality scion,it has important theoretical and practical significance in dealing with the low potassium content of flue-cured tobacco leaves in China.In this paper,25 tobacco materials were screened to obtain the high-efficiency flue-cured tobacco variety Wufeng No.2.Through hydroponic culture and field experiment,it is studied whether Wufeng No.2 can be used as grafting rootstock to increase the content of potassium in Yunyan87 leaves,and the difference of K+absorption and utilization of flue-cured tobacco in different grafting combinations and the quality of flue-cured tobacco leaves are analyzed,and the effect of grafting on potassium content of flue-cured tobacco is discussed.the main results are as follows:1.25 parts of tobacco resources were used as test materials?2 Maryland tobacco,3 burley tobacco and 20 flue-cured tobacco?under normal potassium supply?300kgK/hm²?and potassium starvation?30kgK/hm²?.The potassium efficiency evaluation of tobacco varieties resources was carried out in the form of field experiment,and it was classified by the potassium efficiency of each variety.Through cluster analysis,five potassium efficient varieties,eight potassium-effective varieties and 12 potassium-inefficient varieties were identified.Among them,Wufeng No.2,regardless of the potassium level,its potassium content,KUI,KUE and KS showed good performance,especially the potassium content of tobacco leaves reached 5.13%,which was the highest value of each tested variety.We selected it as the grafting material of potassium efficient rootstock and carried out the mutual marriage test together with the main variety Yunyan 87 to verify the effectiveness of grafting to improve the potassium efficiency of flue-cured tobacco.2.The grafting of Wufeng No.2 as a rootstock significantly increased the growth,potassium absorption and K⁺utilization efficiency of Yunyan 87.Compared with the ungrafted self-rooted seedlings,the K⁺uptake and K⁺utilization efficiency of Y/W were improved respectively.89.5%and 13.6%.The hydroponic test results of different potassium levels(normal potassium supply5mmol L^-1 and potassium starvation 0.5mmol L^-1)showed that the physiological mechanism of grafting to improve the performance of flue-cured tobacco seedlings can be attributed to:?1?enhances the K⁺absorption potential,affinity and nutrient flow rate into the root system,while the minimum absorption threshold is lower;?2?The roots of flue-cured tobacco were pretreated with CsCl?potassium channel inhibitor?and Na₃VO₄?plasma membrane H⁺-ATPase inhibitor?,respectively,and found under low potassium stress.The K⁺absorption pattern of roots of Y-type flue-cured tobacco is mainly high-affinity system?HATS?which is dependent on potassium transporter,while the K⁺absorption mode of W variety plays a role together with high-affinity system?HATS?and low-affinity system?LATS?.This indicates that grafting can cope with low potassium stress by changing the K⁺absorption pattern of flue-cured tobacco roots;?3?enhance the inward current intensity of root K⁺channel;?4?by observing the energy spectrum of K⁺distribution in roots of cross-section,we found that different grafting combinations The difference in lateral transport efficiency of K⁺in flue-cured tobacco roots was independent of its ability to enter the epidermis and cortex,but was related to the loading capacity through the endoderm to the parenchyma cells.Under the condition of+K,the presence of K⁺enrichment loop in Y and W/Y treatments indicates the presence of K⁺transport barrier in endoderm cells,and grafting can eliminate the effect of this barrier and increase the transport efficiency of K⁺from outer root tissue to the middle column;?5?The time required for the net K⁺flow rate at the hypocotyl of the grafting combination with W as the rootstock to fall to a steady state is 5 minutes,while the Y is required to be a rootstock for 16 minutes,which indicates that the W genotype flue-cured tobacco can be under low potassium stress.The potassium distribution pattern in plants was changed more rapidly,and the relatively higher potassium level in the above-ground parts was maintained by reducing the K+cycle in the lower part.;?6?The results of transcriptional regulation analysis indicated that the expression of NHA1,NVP1,SKOR and AKT2 was up-regulated under low potassium stress.This indicates that flue-cured tobacco reduces the growth of flue-cured tobacco by changing the energy supply distribution and activating the transport efficiency of the above-ground K⁺channel.Regardless of the level of potassium supply,the expression level of K⁺uptake and utilization genes in the grafting combination with W as rootstock was significantly higher than that of grafting with Y as the rootstock,which explained the genetics of these two genotypes in the potassium.The results of this study also show that the low potassium tolerance of W rootstock can be utilized by scion Y by grafting techniques.In addition,in the indicators of plant growth,K⁺absorption and transport,there is a feedback regulation between the scion W and the rootstock Y,so that the potassium efficiency of the W/Y treatment shows a tendency to shift to the scion,indicating grafting.There is a signal substance transfer in the process,but specifically miRNAor hormone needs further research.3.The grafting of Wufeng No.2 as a rootstock significantly improved the light contracting power of Yunyan 87.Through the study of photosynthetic pigments,gas exchange parameters,chlorophyll fluorescence parameters and Rubisco initial enzyme activity of flue-cured tobacco,the photosynthesis efficiency of flue-cured tobacco grafting was changed because:?1?there was no difference in the photosynthetic pigment content of each treatment during normal potassium supply,and grafting Significantly reduced the decrease of photosynthetic pigments under low potassium stress;?2?potassium deficiency caused a significant decrease in net photosynthetic rate?P_N?,transpiration rate?E?and stomatal conductance?g_s?of tobacco leaves,while the intercellular CO₂content increased significantly?C_i?,there is a stomatal limitation.This problem can be effectively alleviated by grafting.Compared with ungrafted self-rooted seedlings,Y/W treated P_N increased by33.6%;?3?chlorophyll fluorescence analysis showed that potassium deficiency caused the efficiency of PSII reaction center to decrease,the proportion of open reaction center decreased,and heat dissipation increased.Grafting can effectively improve the electron transfer efficiency of PSII in flue-cured tobacco leaves under low potassium stress and reduce non-radiative energy dissipation.?4?Low potassium stress can significantly reduce the initial activity of Rubisco in each grafted tobacco leaf,and W is the grafting of rootstock.The initial activity of Rubisco in combination is significantly higher than that of grafting with Y as rootstock,which is important for carbon fixation of flue-cured tobacco;?5?non-stomatal limitation under low potassium stress,decreased efficiency of PSII reaction center and Biochemical factor barrier is the main reason for the decline of photosynthetic rate in flue-cured tobacco leaves.Combined with the previous research results,it can be considered that the improvement of photosynthesis of tobacco leaves is due to the improvement of K+absorption and utilization efficiency of rootstocks..4.The grafting of Wufeng No.2 as a rootstock not only significantly increased the potassium content in Yunyan87 tobacco leaves,but also the flavor and flavor of Yunyan87 tobacco leaves were retained after grafting.Through field experiment with different potassium application rates?normal potassium supply 270kg K/hm² and potassium starvation 0kg K/hm²?,the biomass and potassium accumulation of grafted tobacco,potassium distribution of tobacco tissues,agronomic traits and chemical constituents of roasted tobacco leaves were studied in the field experiment.The effect of appearance quality and evaluation results,found that grafting improves the potassium efficiency of Yunyan 87:?1?grafted flue-cured tobacco will only grow in the early stage of growth,and it will catch up with the ungrafted self-rooted seedlings from the prolonged period of time.It will not affect the total growth period;?2?potassium application can significantly increase the biomass and potassium accumulation of flue-cured tobacco,but the treatment with W as the rootstock has a smaller increase,while the treatment with Y as the rootstock has a larger increase;?3?Potassium application can prolong the rapid accumulation duration of potassium and biomass of flue-cured tobacco,increase the maximum relative accumulation rate,and delay the occurrence of maximum relative accumulation rate;?4?under low potassium conditions,the proportion of potassium accumulation in tobacco leaves decreases,potassium in roots The proportion of accumulation increased,and the stem did not change significantly.The W-type flue-cured tobacco has stronger ability to maintain the above-ground potassium level.?5?The industrial quality of flue-cured tobacco after grafting is basically between the rootstock and the scion,but it is still dominated by the scion,and some indicators have super-affinity,grafting effect.Good;?6?Nicotine content in the Y/W treated tobacco leaves increased slightly after the grafting,the potassium content increased significantly,and the chemical coordination score was higher.After roasting,the tobacco leaf has a loose structure,bright color and sufficient oil.While maintaining the original flavor of the Y variety,the flammability is improved and the smoking experience is better..Studies have shown that grafted flue-cured tobacco can utilize the characteristics of potassium efficient rootstock for efficient absorption and utilization of potassium,improve the unfavorable potassium nutrition status of the scion itself,thereby improving the potassium content and contracting ability of tobacco leaves,thereby producing a field growth and industrial quality.The influence of the series finally makes the grafted flue-cured tobacco have the high-efficiency absorption of potassium in the underground rootstock and the excellent characteristics of the aboveground scion,which improves the quality of tobacco leaves.