Effects of bagging on rind pigmentation of ‘Sanhongmiyou’ fruit

Abstract：【Objective】Citrus maxima (Brum.) Merr.‘Sanhongmiyou’originated from Pinghe county, Fujian province and is a mutant from‘Guanximiyou’. Different from‘Guanximiyou’,‘Sanhongmiyou’is with red flesh and albedo. The natural color of its flavedo is orange yellow in mature fruit, and the red color appears under bagging treatment. The mechanism of effect of bagging on peel coloration is still unknown. To optimize the bagging scheme, guide production and provide a basis for further research on the mechanism of fruit color formation, the study examined the effects of different bagging treatments on the accumulation of pigment in the flavedo.【Methods】The experiment was carried out in a pummelo orchard in Pinghe county from June 6th to October 6th in 2018. There were 4 treatments in this study. Six trees were employed for each treatment. 40 fruit were chosen for bagging treatments, and 10 fruit from them without bagging served as the control. The rest fruit were bagged by 1 layer-, 2 layer- or 3 layer-paper bags. Starting from the date of bagging treatment, 18 bagged fruit were randomly collected at intervals of 20 days till harvest (190 days after blooming). The color of flavedo, luster and pigments including lycopene, β-caroten, zeaxanthine, chlorophyll a, b and carotenoids were immediately detected.【Results】The result showed that the values of L*, a* and CCI of bagged fruit showed an increasing trend and were higher than those of the control. The L* value in treatment B (75.60) was higher than in the other treatments, and the value was the second high treatment A. The results showed that the bagging treatments improved the brightness of the flavedo significantly. The a* in treatment A (12.06) was the highest among all the bagging treatments, followed by that in treatment B. The a* value of bagged fruit was significantly higher than that of the control fruit. The CCI value of flavedo in bagged fruit had a similar pattern to a* value. With the maturation of fruit, the CCI value in treatment A (5.14) was the highest among the 3 bagging treatments, and the CCI value of bagged fruit was significantly higher than that of the control fruit. The results show that the bagging treatments significantly improved the proportion of red in the peel and increased the Citrus Color Index of the peel effectively. The chlorophyll a of the bagged fruit showed a decreasing trend, specially from 70 and 110 days after blooming, when the chlorophyll a content in the bagged fruits decreased rapidly. At the same time, the chlorophyll a content in the control fruit was significantly higher than the bagged fruits. It showed that the bagging treatment reduced the green component in the of the peel. The treatment B had the lowest chlorophyll a content. The content of chlorophyll b was lower than that of chlorophyll a, but the trend was consistent with that of chlorophyll a. Lycopene in fruit peel was low in the early stage of fruit development and increased gradually from the 150th day after flowering. The lycopene content of bagged fruit increased rapidly from 170 day after flowering. The content of lycopene in the peel of fruit was significant different among treatments. The highest content of lycopene was found in treatment A with 21.03 mg·kg^-1 , and the second highest was seen in treatment B. At 190th day after flowering, the lycopene content in all the bagging treatments reached a peak with the highest content in treatment A (44.54 mg·kg-1 ) followed by treatment B. The content of lycopene in the control was lower than 20 mg·kg^-1 in mature fruit. The results indicated that the higher accumulation of lycopene during the late stage of fruit development was an important factor causing the redness of ‘Sanhongmiyou’ fruit. The β-carotenoid and zeaxanthin in‘Sanhongmiyou’flavedo were low in the early stage of fruit development and increased gradually from 70th days after flowering. At 110 days after flowering, β-carotenoid and zeaxanthin contents in the bagging treatments reached their highest values, and were highest in treatment C, with a content of 12.34 mg·kg^-1 and 29.37 mg·kg^-1 , respectively. However, β-carotenoid and zeaxanthin contents of the control fruit were significantly higher than those in the bagged fruit during fruit development. It showed that the bagging treatment reduces the contents of β-carotenoid and zeaxanthin in‘Sanhongmiyou’fruit flavedo.【Conclusion】It was concluded that fruit bagging could improve the pigmentation of ‘Sanhongmiyou’fruit flavedo effectively, reduce chlorophyll content, promote degreening of the flavedo and increase the lycopene content and thus the red color in the flavedo in‘Sanhongmiyou’fruit. The results also showed that double-layer bag was the best for‘Sanhongmiyou’fruit.