Effects Of Harvesting Time On Yield And Quality Of 6 Upper Leaves Of Flue-Cured Tobacco In Typical Strong-Aroma Style Tobacco-Growing Areas

The harvesting time of tobacco leaves is an important factor affecting the maturity of tobacco leaves.The typical strong-aroma style upper leaves produced in hunan,henan and shaanxi provinces had better comprehensive quality,but there were some problems in the production process.To solve the problem of insufficient maturity of upper tobacco leaf,field experiments were carried out in tobacco-growing areas of Hunan,Henan and Shaanxi provinces from 2018 to 2020 to find the appropriate harvest period.The main results are as follows:1.When we delayed the harvesting time,the mature characteristics of fresh tobacco leaves can be significantly increased,such as the leaf surface became yellow,the main and branch veins of leaves became white,and more mature spots appeared.At the same time,the leaf tissue structure of fresh tobacco leaves was improved.The ratio of palisade tissue to leaf thickness decreased from 0.37 to 0.40.The chlorophyll index of leaves decreased continuously.There were very significant negative correlation between the harvest maturity and SPAD value of tobacco leaves.When we postpone the harvesting time longer,tobacco leaves can be broken easily.By observing the cell structure of tobacco leaves under microscope,it was found that the palisade tissue cells gradually became thinner and shorter from neat long columns,and these cells disintegrated and separated.2.Compared with tobacco leaves harvested at conventional harvest time,some indicators have changed in these typical strong-aroma style tobacco-growing areas.The results showed that the single leaf weight,leaf mass weight,the contenet of reducing sugar and total sugar decreased,while the content of total nirtrogen and nicotine increasd.The chemical composition coordination and leaf tissue structure of flue-cured tobacco were improved,and the leaf color changed to orange.The yield of tobacco leaf decreased,the average value of output value and the proportion of high-quality tobacco leaf increased first and then decreased.The total output value of upper tobacco leaves increased by 3.15%,11.99%and 4.77%when we postpone the harvesting time in Hunan and Henan tobacco-growing areas from 2018 to 2020.Sensory quality scores were first increased and then decreased.Delaying the harvesting time suitably can improve the quality and fullness of smoking.In consideration of tobacco leaf quality,economic benefits and requirements for cigarette raw material,regression analysis indicated that it was appropriate to harvest 6 upper leaves at a time on the 7th day after the conventional harvest time in Hunan tobacco-growing areas,4 days was postponed in Henan,and 17 days was delayed in Shaanxi when the middle tobacco leaves harvest finished.And we may deduce the maturity judgment standard of upper six tobacco leaves in these tobacco-growing areas:during the harvesting period,the 2nd and 4th leaves from top of the tobacco was light yellow,the yellow degree of leaf surface was 80%～100%,the main veins and branches almost become light white and shiny,these tobacco leaves have medium thickness and loose tissue structure,there were many mature spots on the leaf surface,and the SPAD value of fresh leaves was 8.85～10.48 in Hunan,and the SPAD value was 13.66～15.67 in Henan.Meanwhile,the leaf thickness of tobacco leaves was medium,the palisade cells were slightly thinner,and the intercellular space was moderate.