The Effect of Different Colors of Film on the Quality and Physiological Characteristics of Mulberry Fruits

The mulberry cultivar Seedless da shi was covered with purple, red, blue, green, white, and yellow films, and quality and physiological characteristics of the mulberry fruits were assessed during the green ripening, pink, full red, purple ripening, and black ripening stages. The results indicated that yellow and white films demonstrated the highest transmittance, at 67.00% and 65.00% of that of uncovered cultivation as the control (CK), respectively, and that red film exhibited the lowest transmittance, at 13.00% of that of CK, as well as a significant main wavelength shift of 109.4 nm more than that of CK. The yellow film increased green light, red light, and the red-to-blue light ratio, which were 5.11%, 16.37%, and 61.31% of that of CK, respectively. The yellow film treatment significantly increased single fruit weight and moisture and achieved peaking during the purple maturity stage, which was 40.97% higher than that that of CK. The green film treatment resulted in the slowest fruit growth rate. The anthocyanin contents of yellow and white film treatments exceeded that of CK by 44.85% and 8.19%, respectively, in the purple maturity stage, while the red film treatment reduced anthocyanin content by 55.99% compared with that of CK; the other treatments showed overall lower anthocyanin levels than that of CK. Purple and red films effectively increased phenylalanine ammonia-lyase (PAL) and catalase (CAT) activities in the fruits. The photosynthetic rate of leaves under all treatments was not significantly different from that of CK. The total nitrogen (N) content of fruits under red film treatment peaked during the green ripening stage, at 12.26% higher than that of CK. After the black ripening stage, red, blue and green films significantly increased the total N and potassium contents in the fruits. It was concluded that white and yellow film treatments accelerated the color conversion process of mulberry fruits. Yellow film treatment had an overall positive impact on fruit quality. Purple and green films significantly delayed ripening, thus producing higher-quality fruit upon maturity. For mulberry production, white/yellow films or purple/green films can be selected for rain avoidance cultivation based on specific production goals to adjust ripening periods and improve fruit quality.