Effects of bagging on fruit development and quality in cross-winter off-season longan

Clusters of cross-winter off-season longan (Dimocarpus longan Lour) cv. Chuliang were bagged with three types of bags: perforated translucent plastic bag (TPB), white adhesive-bonded fabric bag (WAFB) with about 70% light transmittance, and black adhesive-bonded fabric bag (BAFB) with <10% light transmittance. Bagging treatments began at 34 days after anthesis and continued until harvest. The results showed that bagging modified the microenvironment for fruit development. Bagging with TPB was most effective in increasing humidity, and air moisture within TPB maintained above 90% from 2 weeks after bagging. Bagging with BAFB or WAFB increased humidity most of the time, and the effect was more prominent when the weather was very dry (RH < 60%). All bag types tended to increase temperature and promoted fruit development, resulting in larger sized fruit. Bagging tended to promote early fruit drop but reduced late fruit drop, and the final fruit retention rate was not significantly affected by bagging. Bagging with different materials showed differential effects on incidence of fruit cracking. WAFB and BAFB reduced cracking incidence significantly as compared to the control (5.1% and 11.6% vs 32.8%). Sugar content was not significantly affected by bagging but organic acids including vitamin C (Vc) were considerably affected. Concentration of malic acid, the dominant organic acid in longan aril, was 605.6, 830.0, 1161.0 and 1428 μg/g FW in TPB, BAFB, WAFB and the control. Vc in the aril was significantly reduced by BAFB (108.4 μg/g FW), slightly increased by WAFB (183.9 μg/g FW) and significantly increased by TPB (264.5 μg/g FW) as compared with the control (174.7 μg/g FW). Pericarp of fruit bagged with TPB had a slightly higher content of Vc (1337 μg/g FW), while those bagged with BAFB (873.6 μg/g FW) and WAFB (787.4 μg/g FW) had significantly lower Vc contents than the control (1243 μg/g FW). The responses of oxalate and Vc contents in the aril and the pericarp to bagging treatments showed an opposite trend. The results suggested that WAFB increased fruit size and fruit retention rate while significantly reduced fruit cracking incidence and could be a promising practice for cross-winter longan production.