Abstract: Based on the climatic characteristics of Danjiangkou City, Hubei Province, chuxue 26（CX-026） was taken as the research material, the agronomic traits and internal physiological indexes of the middle and upper tobacco leaves harvested at different growth periods （59~101 d after transplanting） were analyzed, and the changing rules of tobacco maturity were explored to clarify the optimal harvesting time. The results of agronomic character analysis showed that with the delay of harvesting time, the middle and upper tobacco leaves gradually became longer and wider, and the identity became thicker to a constant level; the color of the leaves changed from green to dark, and then yellow-brown markings appeared; the angle between the stem and leaf increased, and the tensile force decreased, which indicated that the maturity of the leaves was gradually improved. The analysis of physiological indexes showed that the pigment indexes （SPAD, chlorophyll a, etc.） and photosynthetic characteristics （net photosynthetic rate, stomatal conductance, etc.） decreased with the growth, which led to an increase in the color value of tobacco leaves （LAB）. The entropy weight analysis revealed the important role of photosynthetic indexes and pigment indexes in the evaluation of tobacco maturity, which not only had high weight, but also had a significant correlation, providing a key reference for the identification of tobacco maturity. According to the analysis results of photosynthetic indexes and pigment indexes, the changes of the middle leaves tended to be stable at 66~73 days after transplanting, and the upper leaves tended to be stable at 87~94 days after transplanting, indicating that the maturity stage might be at this time, which could be selected as the appropriate time for harvesting.

Key words: tobacco, wrapper, maturity, transplanting time, physiological indexes, agronomic character