Apple Bitter Pit: Symptoms, Physiological Mechanisms and Integrated Management Strategies

Apple bitter pit is a widespread and destructive physiological disorder in global apple production, which is mainly correlated with fruit calcium deficiency and brings huge economic losses to the apple industry. This review systematically summarizes the typical symptom characteristics of apple bitter pit, and expounds the physiological mechanisms from five key dimensions: decreased calcium content and local calcium deficiency, imbalance between calcium and other mineral elements, reactive oxygen species (ROS) accumulation and oxidative damage, hormone regulation imbalance, and xylem vessel destruction and function loss. Other influencing factors of bitter pit are comprehensively clarified, including cultivar and rootstock differences, soil physicochemical properties, environmental conditions, cultivation strategies and storage parameters. In addition, the integrated management system for apple bitter pit is summarized, involving agricultural management, physical auxiliary strategies, chemical regulation and biotechnology. Finally, the existing deficiencies in the current research are put forward, and the future research directions are envisioned, such as in-depth analysis of molecular regulation mechanisms, breeding of less-susceptible cultivars, and development of green and efficient management technologies. This review provides a systematic theoretical reference for in-depth research and precise management of apple bitter pit and hopes to boost the healthy and sustainable development of the apple industry.