Correlation between tobacco leaf chemical compositionsand latitude in Sichuan Tobacco Region

The growth, development and quality of flue-cured tobacco are influenced by main geographic factor of latitude. The correlations of tobacco leaf chemical content and latitude in the Sichuan Tobacco Region (STR) were analyzed in this study. The aim of the study was to determine the best latitude range for tobacco cultivation, provide a reference for tobacco production layout and allocation in the region. Partial least squares (PLS) regression, for dealing with 7 chemical indicators with internal linear correlation, and grey relational analysis were used to determine the relationships between leaf chemical compositions of flue-cured tobacco and latitude in the STR. The study analyzed 243 cured leaf samples collected respectively from the upper (14~16 leaf-position), middle (8~12 leaf-position) and lower (4~6 leaf-position) tobacco leaf positions at 153 monitoring points in four latitude regions (Panzhihua, Liangshan, Luzhou and Dazhou) of the STR in 2010. The results showed that Sichuan tobacco performed best in the latitude range of N26°02′~N31°20′. The overall chemical compositions of STR tobacco leaf showed that total sugar and reducing sugar were marginally in the highest amount, followed by starch and chlorine. The contents of nicotine, total nitrogen and potassium were in suitable range with higher variation coefficient of nicotine, chlorine and starch. PLS regression model of chemical composition in relation to upper tobacco leaf and latitude was latitude=28.762 0.146x1 0.214x2 0.005 23x3 0.172x4+0.316x5 0.232x6 0.046 4x7; that for middle tobacco leaf was latitude=28.762 0.117x1 0.088x2+0.009 9x3 0.127x4+0.288x5 0.328x6 0.041 3x7; and that for lower tobacco leaf was latitude = 28.762 0.026x1 0.123x2+0.25x3+0.010 3x4+0.271x5 0.237x6 0.136x7. x1~x7 respectively denoted total sugar, reducing sugar, nicotine, total nitrogen, potassium, chlorine and starch contents. Correlation analysis showed that for the same position leaves, latitude was positively correlated with potassium, but negatively correlated with total sugar, reducing sugar and chlorine contents. It meant that increment of latitude across Sichuan form south to north increased tobacco leaf potassium content and decreased total sugar, reducing sugar and chlorine contents. For different position leaves, however, correlations between latitude and nicotine, total nitrogen and starch were inconsistent. The correlation sequence for chemical compositions and latitude was as follows: reducing sugar > total sugar > total nitrogen > potassium > starch > nicotine > chlorine.