Appearance Quality Characteristics and Causes Analysis of Cigar Tobacco Leaves Cultivated in Greenhouses

In order to explore the characteristics and underlying causes of the appearance quality of cigar tobacco leaves cultivated in greenhouses, the leaf traits and field microclimate characteristics of cigar tobacco leaves cultivated in greenhouse and open field were analyzed. The results showed that greenhouse cultivation could significantly improve the appearance quality of cigar tobacco leaves, which was reflected in the fact that the scores of leaf structure, length and width, branch thickness and branch flatness were significantly or extremely significantly higher than those in open field cultivation. At 70 days after transplanting, leaf length increased by 15%, leaf width by 13%, and leaf area by 30%. Furthermore, the thickness of the 9th branch in middle leaves decreased by 29.81%, while branch flatness improved by 4.98 percentage points. The palisade and sponge tissues exhibited lower density and thickness with larger intercellular spaces. Correlation analysis and stepwise regression identified the causes: compared to open field cultivation, the greenhouse environment provided a higher average temperature (+1.28°C) and relative humidity (+0.60 percentage points), which promoted increases in cigar tobacco leaf length, width, and area. Meanwhile, the daily average photosynthetically active radiation decreases by 41.82%. This reduction in radiation, combined with the aforementioned increase in average humidity, leads to a reduction in leaf tissue thickness, making cigar tobacco leaves thinner, reducing the thickness of primary veins at the leaf base, improving vein flatness, and resulting in a looser leaf structure. Therefore, this study suggests that greenhouse cultivation can be adopted in China to improve the appearance quality of cigar tobacco leaves, thereby producing more high-quality cigar wrapper tobacco leaves.