From physiology to molecular biology: unraveling the mechanisms of fruit cracking

Fruit cracking is a pervasive physiological disorder in horticultural crops that severely compromises fruit appearance and quality, resulting in substantial economic losses. Cracking occurs when internal turgor pressure or external mechanical forces exceed the mechanical resistance of the fruit skin and underlying tissues. Fruit cracking is a complex quantitative trait governed by genes as well as the synergistic interplay between environmental factors and intrinsic physiological attributes, including pericarp mechanical strength, fruit water status, and hormonal homeostasis. The critical swelling pressure model and the zipper model have been proposed as two complementary mechanistic frameworks that explain crack initiation and propagation. Extensive research across diverse species has clarified discrete aspects of fruit cracking, however, an integrative synthesis that reconciles physiological processes with molecular regulatory networks is still lacking. In this review, we summarize the major types and causal factors of fruit cracking, and provide a comprehensive overview of the current knowledge on its multilevel mechanism, including hormonal signaling, cell wall remodeling, water transport and turgor regulation, cuticular wax/cutin biosynthesis, mineral homeostasis, reactive oxygen species dynamics, and transcriptional regulation. By integrating these processes into a cohesive conceptual framework, this review provides mechanistic insights into fruit cracking and highlights potential targets for the precision breeding of crack-resistant cultivars as well as the optimization of cultivation and management practices.