Apple Sunburn: Physiological Mechanisms, Influencing Factors, and Advances in Sustainable Management Strategies

Apple (Malus domestica Borkh.) is one of the most widely cultivated fruit crops globally. However, fruit sunburn, induced by excessive heat and intense solar radiation, poses a significant threat to apple production and fruit quality. Although numerous studies have investigated individual mitigation strategies, a comprehensive synthesis of sustainable management approaches and their practical applicability remains limited. This review provides an overview of advances in apple sunburn management, encompassing cultural practices such as canopy management and irrigation, physical protection methods including shade nets and evaporative cooling, protective treatments such as reflective sprays and particle films, and emerging approaches such as nanocoatings and gene editing. The review compares the reported effectiveness, physiological mechanisms, limitations, and practical considerations of these strategies. The evidence indicates that integrating complementary approaches may improve sunburn management, although their effectiveness varies with cultivar characteristics, climatic conditions, orchard practices, and resource availability. Accordingly, a practical framework is presented to guide strategy selection according to local sunburn risk, cultivar susceptibility, and economic feasibility. Future research priorities include improved risk-prediction models, standardized field trials, precision monitoring, and functional validation of candidate genes. This synthesis provides a basis for developing site-specific, economically feasible, and sustainable strategies to mitigate apple sunburn under changing climatic conditions.