Abstract:

Through the effects of different topping stage and remained leaf number on agronomic and economic traits of flue-cured tobacco, the individual development and population structure of tobacco plants were improved, reasonable plant type was established, and the yield and quality of upper tobacco leaves was improved, and then the quality and industrial availability of upper tobacco leaves of Tongren flue-cured tobacco were improved, providing a theoretical basis for the high-quality production of upper tobacco leaves of Tongren. Through the field experiment, a two-factor and three-level random block design was adopted. The two factors were topping stage and remained leaf number, the topping stage was recorded as A; the three levels were bud stage (A1), initial flowering stage (A2) and full flowering stage (A3), the remained leaf number was recorded as B; the three levels were 18 pieces (B1), 20 pieces (B2) and 22 pieces (B3), and each treatment was repeated 3 times. The results showed that the maximum leaf area, the area of the uppermost leaf area and the area of the third leaf from the top increased first and then decreased with the increase of the remained leaf number in the same topping stage. The topping stage had little effect on the economic properties of flue-cured tobacco, but with the increase of the remained leaf number, the yield, average price, output value and proportion of high-grade tobacco gradually decreased, and the proportion of medium and high-grade tobacco was higher under A2B2 and A2B1 treatment, which were 98.63% and 98.55%, respectively. The appearance quality and sensory quality scores of cured tobacco leaves were the highest, 7.38 and 69.10 points, respectively. With the increase of the remained leaf number, the indices of total sugar content, reducing sugar content, sugar-base ratio and potassium-chlorine ratio all increased first and then decreased at the peak of bud stage, while the nicotinic, total nitrogen, potassium and chlorine all decreased first and then increased, and the ratio of two sugar gradually decreased. At the peak of early flowering, the contents of total sugar and reducing sugar gradually decreased, the contents of nicotine and total nitrogen and the ratio of potassium to chlorine first decreased and then increased, the ratio of potassium, chlorine and the ratio of two sugar gradually increased, and the ratio of sugar-nicotine first increased and then decreased. At the peak of flowering stage, the content of total sugar, reducing sugar, total nitrogen and the ratio of sugar-nicotine increased first and then decreased, the content of nicotine and the ratio of potassium to chlorine decreased first and then increased, and the content of potassium and the ratio of two sugar gradually increased. All in all, topping and leaving 20 leaves at the bud stage can improve the agronomic traits of tobacco plants, improve the appearance quality and sensory quality of tobacco leaves, the chemical composition content is suitable and the coordination is better, and the economic properties are relatively good, which can be demonstrated and applied in Tongren tobacco-growing area.

Key words: structure optimization, topping stage, number of remained leaf, upper tobacco leaf, production quality, tobacco