Study on relationship between reducing sugar content and leaf morphological characteristics of flue-cured tobacco in Hubei Province based on grey correlation analysis

【Objective】To explore correlation between reducing sugar content and morphological characteristics of flue-cured tobacco leaves in different parts and to determine the main morphological characteristics of the impact on reducing sugar content，so as to provide a theoretical reference for the production of high-quality tobacco raw materials in Hubei tobacco producing areas.【Method】 Flue-cured tobacco samples（272 upper leaf samples，277 middle leaf samples and 282 lower leaf samples）from three tobacco producing areas（Zaoyang City，Nanzhang County and Baokang County）in Xiangyang City of Hubei Province from 2017 to 2019 were used as experimental materials.Their main leaf morphological characteristics and reducing sugar content were determined.The relationship between reducing sugar content in different parts of leaves and morphological characteristics such as single leaf weight，stem rate，leaf length，leaf width and leaf length-width ratio was analyzed，and the quantitative relationship between reducing sugar content and leaf morphological characteristics was studied.【Result】 The variation coefficient of reducing sugar content in different parts of flue-cured tobacco was about 15.00%.The stem rate of flue-cured tobacco in different parts had an extremely significant negative correlation with reducing sugar content（P<0.01，the same below）.The reducing sugar content of middle and lower leaves had an extremely significant positive correlation with leaf width；and it had an extremely significant negative correlation with leaf length-width ratio.The upper leaves was significantly negatively correlated with leaf length-width ratio（P<0.05，the same below）.The single leaf weight of lower leaves had an extremely significant positive correlation with reducing sugar content.The order of grey correlation between morphological indexes of upper and middle leaves and reducing sugar content was： leaf width>leaf length>leaf length-width ratio>stem rate>single leaf weight.The order of grey correlation between morphological indexes of lower leaves and reducing sugar content was as follows：leaf width>leaf length>single leaf weight>leaf length-width ratio>stem rate.The regression equation of leaf width and reducing sugar content in different parts reached significant level： for the upper leaf，y=0.238x+17.909，R² was 0.720； for the middle leaf，y=2.358x-0.045x²-4.894，R² was 0.831；for the lower leaves，y=3.693x-0.074x²-20.106，R² was 0.946.【Conclusion】The grey correlation degree between reducing sugar content and leaf width of flue-cured tobacco leaves in different parts was the largest，and the wider the leaf width，the higher the reducing sugar content.Leaf width can be used as an important reference index for the production of high quality tobacco materials in Hubei tobacco areas.