| Flue-cured tobacco is an important economic crop in many poor mountainous areas in China,which is of great significance to the implementation of targeted poverty alleviation.Maturity is an important factor in determining the quality of tobacco leaves after curing,whose criterion is based on empirical appearance at present.In terms of the tobacco-growing areas in Shaanxi,there are few systematic quantitative studies on the maturity of tobacco.Therefore,in this study,field experiments were conducted with the main cultivars of three tobacco-growing areas in southern Shaanxi,namely YN87 of Ankang Xunyang,YN97 of Hanzhong Nanzheng,YN99 of Shangluo Luonan.The physiological characteristics and quality afer curing of different maturities were studied in order to provide a basis for the selection of key indexes for the differences of maturity.The main conclusions are as follows:1.There were significantly linear negative correlations between SPAD value and maturity of flue-cured tobacco in three regions,and the linear regression had higher fitting degree at R2 > 0.95 in middle leaves of Ankang Xunyang,lower and upper leaves of Hanzhong Nanzheng,and lower,middle,upper leaves of Shangluo Luonan,respectively.In Shangluo Luonan,the diffuse reflection spectra of different maturity of tobacco leaves had obvious absorption peak in the wavelength of 500 nm to 600 nm,which gradually shifted backward with the increase of maturity level.And There were significantly linear positive correlations between spectral reflectance and maturity of flue-cured tobacco in each leaf position,among which linear regression had highest fitting degree at R2 = 0.96 in middle leaves.The results show that there is a significant linear correlation between the color characteristics and maturity level.2.Different maturity levels had different effects on the physiological indexes of fresh leaves of flue-cured tobacco in different leaf positions of different areas.The results of principal component analysis showed that the key indexes of maturity in different areas are below: Ankang Xunyang: lower leaves: total chlorophyll content > carotenoid content > water content > reducing sugar content > total nitrogen content;middle leaves: water content > starch content > total nitrogen content > total potassium content > reducing sugar content > total chlorophyll content;upper leaves: total soluble sugar content > total phosphorus content > reducing sugar content > nicotine content > total potassium content.Hanzhong Nanzheng: lower leaves: total nitrogen content > total chlorophyll content > carotenoid content > starch content > total potassium content > total phosphorus content > water content > total soluble sugar content;middle leaves: total nitrogen content > nicotine content > total phosphorus content > total potassium content > total chlorophyll content;upper leaves: carotenoid content > total chlorophyll content > nicotine content > total nitrogen content > water content > starch content > reducing sugar content.Shangluo Luonan: lower leaves: total potassium content > total nitrogen content > total phosphorus content > total chlorophyll content;middle leaves: total nitrogen content > total sugar content > reducing sugar content > starch content > total phosphorus content;upper leaves: water content > total nitrogen content > nicotine content > carotenoid content > reducing sugar content > total chlorophyll content.3.In different leaf positions of different areas,different maturity levels had different effects on the quality of the tobacco leaves after curing.With the improvement of maturity level,the potassium content of tobacco leaves after curing in Ankang Xunyang and Hanzhong Nanzheng showed increased firstly and then decreased,and the starch content of upper leaves after curing also showed increased firstly and then decreased.Other indexs also varied differently in different regions and different leaf positions.4.There were certain correlations between the physiological indexes of fresh leaves and the quality after curing.In addition to the total phosphorus in Ankang Xunyang and the total phosphorus and total nitrogen content in Hanzhong Nanzheng of the fresh leaves,there were significant correlations at P < 0.05 or P < 0.01 between the indexes of the fresh leaves and the chemical components of the tobacco leaves after curing,which could directly or indirectly affect the final quality of flue-cured tobacco.Based on the above analysis,it can be drawn that the physiological indexes of fresh leaves that could measure the different maturity levels in southern Shaanxi are below: Ankang Xunyang: reducing sugar content > total chlorophyll content > carotenoid content;Hanzhong Nanzheng: total chlorophyll content > carotenoid content > starch content;Shangluo Luonan: total nitrogen content > water content.This study verified the linear relationship between tobacco maturity levels and color characteristics.Based on the systematic analysis of the physiological and chemical indexes of tobacco leaves in different areas of southern Shaanxi,this study identified the difference of the physiological indexes and the quality of different maturity levels of tobacco leaves,in order to provide a basis for the selection of key indexes for the differences of maturity and the theoretical support for the maturity judgment of tobacco leaves in southern Shaanxi. |
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