Effect of Shade Strength on the Fruit Quality of Different Blueberry Cultivars

Blueberry fruit is famous for its anthocyanin abundance and has high nutritional, medicinal, and economic value. The adaptability of different source cultivars to high temperature in summer has not been systematically explored. The objective of this study was to evaluate the suitability of different blueberry cultivars under different shading environments and explore the effects of different shading intensities on fruit quality and antioxidant substances. In this study, three cultivars respectively belonging to three types (rabbiteye, southern highbush, and northern highbush) of blueberries were shaded, and the fruit size, shape, hardness, nutritional quality index, and antioxidant substances were determined. The results show that excessive shading affects flower bud differentiation, leading to abnormal flowering and fruiting of the blueberry cultivar 'Chandler'. The fruit firmness of highbush blueberries ('Primadonna' and 'Chandler') in the one-layer black shading (T1) group was significantly higher than that in the total light (CK) group. Total phenols, flavonoids, anthocyanins, and protein reached the highest values in the T1 treatment for cultivar 'Brightwell'. Moreover, the malondialdehyde and H2O2 contents and peroxidase activity in the T1 group were significantly lower than those in the two-layer black shading (T2) group, but the catalase and polyphenol oxidase activities in the T1 group were significantly higher than those in the T2 group. There was a correlation between the main antioxidant substances, and different blueberry cultivars had different tolerances to shading. This study provides a practical reference for improving fruit quality and the efficient utilization of antioxidant substances in blueberry production.