Role of non-structural carbohydrates in the sustainable production of apples (Malus domestica)

Consistent yield and production of high-quality fruits are key drivers for sustainable apple industry. Flowering and fruiting in apple (Malus domestica) can be limited by non-structural carbohydrates. Apples flower profusely, and as strong sinks, both flowers and fruits compete with vegetative parts of the tree for carbohydrate allocation. Low sugar availability results in inconsistent blooms and regular cropping disruptions, leading to low yields and substantial economic losses. Various crop thinning strategies are used to reduce crop load and improve carbohydrate allocation for better fruit quality and return bloom. The implementation times of these strategies in the current season can significantly alter the sugar balance, affecting flower formation in the following season. This review examines various roles of non-structural carbohydrates in apple tree physiology, with a focus on flower and fruit development. It appraises the fundamentals of effective carbohydrate management for achieving long-term sustainability in apple production. A dual carbon transport system in apples ensures a more stable and efficient supply of sugars to the sinks and enables carbohydrates to perform essential roles in signalling, structural support during flower formation, floral metabolism, pollination, fruit set, fruit development, fruit metabolism, and fruit quality enhancement. Understanding the vital functions of carbohydrates in tree dormancy, flowering, and fruiting calls for a more efficient implementation of fruit thinning strategies at the earliest possible time during the reproductive phase.