Macadamia Breeding for Reduced Plant Vigor: Progress and Prospects for Profitable and Sustainable Orchard Systems

Vigor control in tree crops plays an important role in increasing orchard efficiency and sustainability. It has enabled high-density plantations to maximize yield efficiency while reducing production costs. Although traditional methods such as frequent hedging and pruning are still used, dwarfing rootstocks and low-vigor cultivars are the most effective and sustainable means of vigor control, as these methods reduce labor and management costs while maintaining yield efficiency. Considerable variation among cultivars and rootstocks for vigor has been identified; however, mechanisms by which rootstocks affect scion vigor in slow-maturing tree crops remain unclear. With the lack of adequate information required for early and rapid selection, breeding programs in tree crops such as macadamia still utilize manual phenotyping, which is laborious, time-consuming, and expensive. Providing insights on emerging technologies that enhance breeding programs via rapid selection, this review summarizes the current state of vigor management and underlying mechanisms of vigor control in tree crops. It provides further understanding of the prospects of applying those techniques in rootstock and scion breeding for low-vigor and yield-efficient cultivars in tree crops, with specific reference to macadamia.