Effects of Girdling at Different Stages on Growth and Development and Quality of Upper Tobacco Leaves

To study the effect of girding on growth and development, and quality of upper tobacco leaves of flue-cured tobacco, Yunyan 87 was used as the test material, and girdling after topping (T1), girdling after harvesting the lower leaves (T2), and girdling after harvesting the middle leaves (T3) were used as test treatments, with ungirdling plants as controls to determine and analyze the agronomic traits, photosynthetic parameters, sugar metabolism indexes, key enzymes of carbon and nitrogen metabolism, oxidative stress indexes, chemical routines, and sensory quality of the upper tobacco leaves. The results showed that girdling after harvesting the lower leaves (T2) promoted the opening of tobacco leaves, reduced the aspect ratio by 7.90%, increased the leaf area by 6.53%, inhibited photosynthesis, promoted intercellular CO₂ concentration by 16.48%, and reduced transpiration rate by 20.26%. Girdling treatments inhibited the activities of SOD, POD and CAT, increased the content of MDA and H₂O₂, and promoted leaf aging in varying degrees. T1 and T2 significantly promoted the activities of alapha amylase, beta amylase, total amylase and NI, but reduced the NR activity as well as the content of nicotine and proteins, improved the aroma quality, aroma amount, the aftertaste and sensory quality. Girdling after harvesting the lower leaves had the best effect on the upper leaves.