Effects Of Silicon On The Growth And Quality Of Flue-Cured Tobacco And The Population Structure Of Endophytic Fungi

Tobacco(Nicotiana tabacum)is an important economic crop for leaf use in China,which plays a key role in improving the national tax revenue and the poverty alleviation.In recent years,due to the influence of soil conditions and cultivation measures,the contents of aroma components of tobacco leaves are getting insufficient and quantity of it is not good.And there is still a certain gap between the quality of tobacco leaves and the demand for raw materials of China Tobacco Corporation.At present,in the actual production,many major elements such as nitrogen,phosphorus and potassium are applied to improve the quality of tobacco leaves,but there is little research on the beneficial element silicon to control the quality of tobacco leaves.Although more attention has been paid to silicon fertilizer due to its characteristics of promoting the growth of crops and improving the resistance of plants against natural adversities,the comparative study on the application effect of common silicon and nano-silicon on the tobacco has not yet been reported.In order to provide theoretical basis and technical measures for improving the quality of the tobacco,the effects of silicon fertilizer on the growth status,endophytic fungi population structure and quality of the tobacco have been studied by the investigation of main cultivar Yunyan 99.The main results are as following:1. Common silicon and nano-silicon could effectively improve the growth and physiological characteristics of the flue-cured tobacco.Compared with CK(spraying water),the content of carotenoids in immature tobacco leaves increased by 6.44%?29.61%with the application of common silicon and nano-silicon in different degree,and the content of carotenoids in immature and mature tobacco leaves increased by 13.9%and17.6%,respectively with T8 treatment(0.32 kg/hm~2nano-silicon).At the same time,T8treatment increased the activities of invertase,acid invertase and alkaline invertase,respectively by an average of 13.2%,11.49%and 23.75%higher than CK treatment.Compared with CK,nicotine and total potassium contents in immature and mature tobacco leaves were also significantly increased,among which the nicotine content of T3(0.32kg/hm~2common silicon)and T8 increased by an average of 14.81%and 14.87%,and the total potassium contents of T3 and T8 increased by an average of 50.32%and 14.93%,respectively.The expression of QPT gene,a key gene involving in the nicotine synthesis,in T7 treatment(0.56 kg/hm~2nano-silicon)was significantly increased by 42.53%as compared to CK,while the expression of SPS gene and SPP gene,two key genes in sucrose synthesis,in T5(0.17 kg/hm~2common silicon)and T8 treatments were significantly increased by 46.23%and 64.72%over CK.T2(0.56 kg/hm~2common silicon)and T8treatments increased the total contents of aroma matter by 24.45%and 26.63%,respectively as compared with CK.Comprehensive analysis showed that T8 treatment(0.32 kg/hm~2nano-silicon)had the best effect on the growth and physiological characteristics of flue-cured tobacco.2. Common silicon and nano-silicon could improve the quality,the yield and the antibiotic property of flue-cured tobacco.Compared with CK(spraying water),with common silicon and nano-silicon treatments,the potassium content of middle leaves was increased by 2.13%?42.75%,nicotine content was increased by 7.14%?57.14%,the ratio of potassium to chloride and total nitrogen content were increased in varying degrees.The tobacco with T8 treatment(0.32 kg/hm~2nano-silicon)had the highest content of aroma quality and quantity,the most after-taste,the highest score(75),and the highest quality level(better~-).Compared with CK,T9 treatment(0.23 kg/hm~2nano-silicon)had a maximum amplification in the yield per mu(7.05%),and T6 treatment(2.25 kg/hm~2nano-silicon)had a maximum amplification in the output per mu(5.29%).In addition,nano-silicon could also enhance the resistances of tobacco to the diseases.Compared with CK,the incidence rate of mosaic disease with T7,T8,T9 and T10 treatments(nano-silicon0.17 kg/hm~2)were 52.8%,60.4%,56.6%and 54.7%lower than the CK treatment,respectively,and the disease index of mosaic disease were 50%,62.5%,62.5%and 68.8%lower than the CK treatment,respectively.Among them,the disease index of weather fleck of T8 treatment was 54.5%lower than the CK treatment.Based on the correlation analysis of the chemical composition and sensory quality of flue-cured tobacco leaves,it is concluded that the total sugar,nicotine,the content of potassium and chlorine,sensory strength and impurities could be used as the evaluation indices of comprehensive quality of tobacco leaves.The cumulative contribution rate of the three main components extracted after the principal component analysis of the selected evaluation indices was 84.90%,which is further based on the contribution of each main component,the comprehensive score function was obtained,and the comprehensive quality of tobacco treated with common silicon and nano-silicon was evaluated.Comprehensive analysis showed that T8treatment(0.32 kg/hm~2nano-silicon)had the highest score.3. Common silicon and nano-silicon had significant effects on the population structure of endophytic fungi in tobacco leaves.Compared with CK(spraying water),T5(common silicon 0.17 kg/hm~2)and T8(nano-silicon 0.32 kg/hm~2)treatments could effectively improve the community diversity of endophytic fungi,community composition of endophytic fungi,community structure of endophytic fungi and ecological function of the community.Compared with CK,the diversity of endophytic fungi increased in T8treatment and decreased in T5 treatment.Compared with CK,the relative abundance of Basidiomycota increased by 58.14%and 37.35%,respectively.At the same time,the relative abundance of Flobasidium increased by 113.17%and 417.07%,respectively.Among them,T8 treatment increased the species of endophytic fungi,with 31 species more than CK treatment.Compared with CK,T5 and T8 treatments changed the number of unique ecological functional communities,T5 treatment decreased 2 than CK,T8 treatment increased 13 than CK.At the same time,the relative abundance of pathogens in T5 and T8tobacco leaves decreased by 16.84%and 22.22%,respectively compared with CK.Through the correlation analysis of chemical components and aroma substances of tobacco leaves with the community composition of endophytic fungi,the content of nicotine and soluble protein,the content of maillard reaction products of aroma substances of tobacco leaves were significantly correlated with the community composition of endophytic fungi.In conclusion,common silicon and nano-silicon could improve the growth status and physiological characteristics of flue-cured Tobacco by increasing the abundance of basidiomycetes,by means of improving the diversity of community structure and ecological functional community,and reducing the relative abundance of pathogenic fungi,so as to improve the quality of flue-cured tobacco.Among all treatments,the comprehensive improvement effect of T8 treatment(0.32 kg/hm~2nano-silicon)was better.