Effects Of Combined Application Of Boron,Zinc And Molybdenum On Polyphenol Metabolism,Nutrient Utilization And Quality Of Flue-Cured Tobacco In Southern Shaanxi

Tobacco（Nicotiana tabacum L.）,as one of southern Shaanxi’s key cash crops,is crucial to the local economic development.Continuous cropping of flue-cured tobacco,rain washing and large amount of chemical fertilizer application are easy to cause soil nutrient imbalance,leading to serious plant deficiency disease,and then affect the growth and development of flue-cured tobacco,resulting in the quality decline.The scarcity of trace elements The lack of trace elements is becoming one of the factors restricting the high-quality development of tobacco leaves in southern Shaanxi.Therefore,based on the abundance and deficiency of trace elements in tobacco-growing soil in Luonan,Shaanxi province,this study investigated the effects of microfertilizer with different proportions(CK:H2O 750 kg·hm^-2;T1:H3BO3 0.260+Zn SO4·7H2O 0.800+Na2Mo O4 0.110,kg·hm^-2;T2:H3BO3 0.520+Zn SO4·7H2O 0.400+Na2Mo O4 0.082,kg·hm^-2;T3:H3BO3 0.780+Zn SO4·7H2O 1.600+Na2Mo O4 0.055,kg·hm^-2;T4:H3BO3 1.040+Zn SO4·7H2O 1.200+Na2Mo O4 0.027,kg·hm^-2;T5:H3BO3 1.300+Zn SO4·7H2O 2.000+Na2Mo O4 0.137,kg·hm^-2)on polyphenol metabolism,nutrient utilization and quality of cured tobacco leaves.The main results are as follows:1.Combined application of appropriate amount of boron,zinc and molybdenum fertilizer can greatly boost polyphenol metabolism in flue-cured tobacco.Compared with the control,the contents of flavonoids,anthocyanins and other phenolic compounds in different parts of tobacco leaves were increased to different degrees,and T5 treatment had better effect.The activities of phenylalanine ammoniase（PAL）,cinnamate 4-hydroxylase（C4H）and 4-coumaric acid coenzyme A ligase（4CL）in the leaves were increased by 49.33%,78.48%and29.34%,respectively.The contents of flavonoids,anthocyanins and total phenols in different parts were increased by 54.03%,39.74%and 30.79%on average,which increased the amount of polyphenols accumulated.Meanwhile,the content of ascorbic acid in middle leaves increased by 56.64%,and the activity of polyphenol oxidase（PPO）in different tobacco leaves decreased by 20.73%on average,which reduced the loss of polyphenols.2.Combined application of appropriate amount of boron,zinc and molybdenum fertilizer can improve dry matter accumulation and nutrient utilization efficiency of tobacco plant.After spraying micro fertilizer,the accumulation of boron,zinc and molybdenum in tobacco leaves increased significantly,and the accumulation of nitrogen,phosphorus and potassium also increased to a certain extent.Compared with the control,T5 treatment had better effect,and the accumulation of nitrogen,phosphorus and potassium in tobacco plant increased by 7.0%,15.86%and 10.78%,respectively.3.Combined application of appropriate amount of boron,zinc and molybdenum fertilizer can effectively improve chemical composition and quality of tobacco leaves.After spraying microfertilizer,the contents of potassium and chlorine in upper leaves（B2F）,total nitrogen and potassium in middle leaves（C3F）and potassium in lower leaves（X2F）were significantly increased,which improved the comprehensive score of chemical composition.The contents of organic acids in upper leaf（B2F）,trace elements,total phenols,organic acids and aroma substances in middle leaf（C3F）and trace elements and total phenols in lower leaf（X2F）were significantly increased,which improved the quality of tobacco leaves.Comprehensive comparison showed that T5 treatment had better effect,and the comprehensive score of conventional chemical quality of tobacco leaves in different parts was better than the control.The content of boron,zinc and molybdenum increased by 3.19,1.27and 2.33 times on average,the content of total phenols and organic acids increased by 8.63%and 11.40%on average,and the aroma content of middle leaves（C3F）increased by 100.76%.The output value increased by 21.29%,and the incidence of flue-cured tobacco climatic spot and tobacco Mosaic decreased significantly.In general,the combination of boron,zinc and molybdenum fertilizer with appropriate concentration can increase the nutrient accumulation of tobacco plants in flourishing period,improve the activities of key enzymes in polyphenol metabolism of tobacco leaves,and promote the synthesis of polyphenol metabolites such as chlorogenic acid and anthocyanin,and increase the total phenol content.At the same time,micro fertilizer could prevent excessive oxidation and browning of polyphenols by raising ascorbic acid（As A）content and decreasing polyphenol oxidase（PPO）activity.Therefore,it can improve the quality of tobacco color and aroma,and enhance the economic value of tobacco.The above research results can give a scientific foundation and technological support for improving flue-cured tobacco quality in southern Shaanxi.