Effects of Enhanced UV-B Radiation Exposure on Fruit-ripening, Photosynthesis, and Leaf-microstructure of Guifei Mango

  Objective  Effects of enhanced UV-B radiation exposure on the ripening and quality of fruit as well as the photosynthesis and microstructure of leaves of Guifei mango were studied.【Methods】Mature Guifei mongo trees of 16-year-old were exposed to 96 kJ·m⁻²·d⁻¹ UV-B radiation (Tr) or natural light (CK). Criteria including ripened fruit percentage on a tree and photosynthetic rate (P_n), stomatal conductance (G_s), and microstructure of leaves were evaluated.

  Result  Under Tr, the tree leaves became 2.29 μm thicker, the upper epidermis and palisade tissue 30.35 μm higher, the cell distribution of palisade tissue and spongy tissue denser, the ratio of palisade tissue and spongy tissue 18% higher, the P_n and G_s greater, and the ripened fruit rates 6.77% higher on April 22, 37.83% higher on April 29, and 17.52% higher on May 7 than CK. The soluble sugar, soluble solids, vitamin C, and sugar/acid and solid/acid ratios of the fruits on the first harvest were significantly higher, while the titratable acid content significantly lower, than those of CK. On the other hand, there was no significant effects exerted by Tr on the thickness of upper and lower cuticle or lower epidermis, nor the size and morphology of stoma of the leaves.

  Conclusion   The photosynthesis of mango trees was promoted by the 96 kJ·m⁻²·d⁻¹ enhanced UV-B radiation-induced microstructural alternation on the tissue of mesophyll and G_s increase in the leaves. The effect on fructescence could be applied to regulate Guifei mango maturation and ripening.