Abstract: 【Objective】The aim of this study is to explore the effect of different color of fruit bags on the fruit quality of Ruixue apple (Malus × domestica Ruixue), providing theoretical guidance and technical support for the production of high-quality Ruixue apples.【Method】The experimental materials were five-year-old trees of Ruixue using M26 as rootstock, bagged with red, orange, yellow, green, blue, indigo and purple single-layer fruit bags at 70 days after full bloom, white bags as control. And fruits were harvested at 190 days after full bloom.

The transmitted light spectrum of bags was measured by spectrometer. The indicators of fruit quality were determined, such as peel chlorophyll, ascorbic acid, soluble sugar and aroma compounds contents. To explore the effect of different light quality on fruit quality, the relationship between light and fruit quality was analyzed by correlation analysis. 【Results】The difference in the color of the fruit bags changed the composition of the light quality and had a positive correlations between light quality and fruit bags. Compared with white bag control, the transmittances of purple in purple bag were the highest, which were 1.15 times than white bag, meanwhile, the transmittances of red in red bag were the highest (1.13 times). The external quality of fruits was significantly improved after the treatment of different color fruit bags. Among the indicators, the L* and b* values of the peel were higher than white bag control, while the a* value, fruit point index and coloration index were lower. Compared with other color fruit bags, some indicators of purple fruit bags were significantly improved (P < 0.05), such as chlorophyll (0.0548 mg·g^-1), total phenolic (1.325 mg·g^-1), total flavonoid content of fruits (1.361 mg·g^-1). Under different light quality environments, there were significant differences in fruit firmness, and the fruit firmness of the red fruit bag was significantly lower, which was 16.1% lower than white bag control. In addition, other internal quality measurements showed that the indigo fruit bags significantly improve the flavor of the fruits, which improved mainly soluble solids, sugar components and sweetness value. The detection of aroma compounds showed that the blue fruit bag significantly increases the total amount of fruit aroma compounds, which was significantly increased by 2.89 times compared with white bag control. Based on the above indicators, we conducted a correlation analysis between light quality and various quality indicators, and found that there was a close correlation between fruit external quality and light quality. The correlation coefficients between the purple/indigo, orange, and purple/blue values and the L*, a*, and b* values of the peel were 0.901, 0.810, and 0.854, respectively. The internal quality of fruit, such as chlorophyll, total flavonoid, total phenolic and total aroma compounds, were most closely related to blue light. The correlation coefficients were 0.947, 0.822, 0.851 and 0.757, respectively. 【Conclusion】According to the comprehensive analysis, purple and blue light were beneficial to improve the external and internal quality of Ruixue apple. Therefore, the transmission amount of purple and blue light can be appropriately increased in the fruit bag during Ruixue bagging cultivation to further improve fruit quality.

Key words: apple, Ruixue, light quality, fruit bags, fruit quality