Effects of Exogenous Melatonin on Growth and Photosynthetic Physiological Characteristics of Different Varieties of Cigar Tobacco

In order to explore the effects of exogenous melatonin on the growth and photosynthetic physiological characteristics of different cigar varieties in this study. CX80 and Dexue No. 5 were used as the experimental material. Two elements including variety and melatonin were conducted to study the effects of exogenous melatonin on photosynthetic pigments, photosynthetic gas exchange parameters, key enzyme activities, root architecture parameters and material accumulation of different varieties. The results showed that exogenous melatonin significantly increased the chlorophyll content, PEPC and Rubisco activity of the leaves of both varieties, and the net photosynthesis rate (P_n) of CX80 and De Xue 5 were 26.39% and 26.19% higher than the control group, respectively. Meanwhile the light energy utilization rate (LUE) was 31.64% and 26.43% higher, the stomatal limitation value (Ls) was 33.70% and 47.79% lower. The total root length, root surface area, root volume, average root diameter, total root tip number, plant height, leaf area, root-to-shoot ratio, and root crown ratio of the melatonin treatment of both varieties were increased to varying degrees. The aboveground and root biomass of CX80 increased by 24.59% and 41.89% compared with the control, respectively. The interaction effect of melatonin and variety on the underground root length, root volume, and root surface area reached a significant level. The results showed that the application of exogenous melatonin can significantly promote the growth and development, as well as photosynthetic physiological characteristics of cigars, especially the growth and configuration of the underground root system. Therefore, exogenous melatonin can be applied to improve the adaptability of cigar to the environment.