Differentiated Leaf Characteristics and Fruit Quality of Developing Fruits on Different Branches of a Longan Tree

Differences in the characteristics of leaves and quality of fruits on different branches of two longan cultivars in fruit developmental stages were observed.

Method The surrounding temperature, humidity, and light intensity as well as the leaf photosynthetic characteristics and fruit quality indicators on different branches on a longan tree were monitored during the fruit developmental stages.

Result (1) From 100 to 155 days after flowering (DAF), the temperature around Longsui plants was 0.43 ℃ to 3.46 ℃ higher than around Husui cultivar, while the light intensity around the former significantly 1.75 to 4.10 times and the humidity 2.03% to 36.91% higher than the latter. (2) From 100 to 145 DAF, the net photosynthetic rate, transpiration rate, water use efficiency (WUE), and ratio of net photosynthetic rate/transpiration rate of Longsui leaves were lower to varied extents than those of Husui leaves. But on 155 DAF, Longsui was consistently higher than those of Husui. The intercellular CO₂ concentration was opposite to the net photosynthetic rate and other changes. The stomatal conductance of Longsui was significantly higher than that of Husui on 155 DAF. The chlorophyll content in Longsui was higher than that in Husui as the fruits were developing. (3) From 115 to 155 DAF, the single weight and longitudinal, transverse, and lateral diameters of Longsui fruits were 0.67 to 1.81g, 0.82 to 2.54 mm, 0.95 to 2.48 mm, and 0.28 to 2.31 mm, respectively, smaller than those of Husui fruits. The total soluble solids (TSS) of Longsui fruit juice was significantly 1.78% to 4.02% lower than that in Husui fruits. During the fruit development period, except for 130 DAF, the edible portion of a Longsui fruit was 1.24% to 2.00% lower than that of a Husui fruit. (4) Peaked in 130 DAF, the total sugar, sucrose, fructose, and glucose contents as well as the sucrose/hexose ratio of Longsui fruits were 175.55 mg·g⁻¹, 130.20 mg·g⁻¹, 30.52 mg·g⁻¹, 30.08 mg·g⁻¹, and 2.15, respectively. In 115 to 155 DAF, the total sugar and sucrose contents and sucrose/hexose ratio of Longsui fruits were 15.69 mg·g⁻¹ to 56.39 mg·g⁻¹, 5.06 mg·g⁻¹ to 49.24 mg·g⁻¹, and 0.91 to 1.21, respectively, lower than those of Husui fruits. Especially during the fruit ripening period (i.e., 145-155 DAF), the total sugar and sucrose contents and sucrose/hexose ratio of Husui fruits were significantly higher than those of Longsui fruits.

Conclusion When Zuixiang longans reached maturity in 148-155 DAF, the single fruit weight, flesh growth rate as measured in longitudinal, transverse, and lateral diameters, TSS, edible rate, total sugar, sucrose, and sucrose/hexose ratio of Husui fruits were all higher than those of Longsui fruits. The information obtained by this study was of value for optimizing cultivation through branch regulation to improve longan fruit quality.