Genetics, Breeding, and Genomics of Apple Rootstocks

Abstract

AbstractThe ability to graft genetically diverse apple cultivars onto diverse root systems (rootstocks) has increased the breeding efficiency of the whole apple system by dividing the combinatorial complexity into two systems—one focused on scion traits (e.g., fruit color, acidity, and crispness, among others) and the other one on rootstock traits (e.g., productivity, disease resistance, and growth habit, among others). While apple rootstocks may have originated to facilitate the propagation of desired fruit, this has since transitioned to the selection of superior root systems that fit certain needs of apple growers. Efforts to identify and improve traits associated with whole apple tree performance by purposeful hybridization are relatively recent compared with the initial selection of apple rootstocks. Several breeding programs have developed breeding protocols depending on the regional needs (cold hardiness in both Canada and Russia, fire blight resistance in the U.S.A., and drought tolerance in China, among others) resulting in the development of diverse new apple rootstocks and complex traits that go well beyond the initial dwarfing growth habit for which several of the founding ‘Malling’ generation of rootstocks are known for. Advances in apple genetics, phenomics, and genomics are increasing the ability to customize the performance of apple rootstocks to specific cultivation requirements, including scion cultivar, soil type, water availability, disease pressure, and tree training system, thus contributing to significant gains in sustainable yield of the final product; i.e., high-quality and nutritious apples that customers will purchase recurrently.