Macadamia (Macadamia spp.) Breeding

Macadamia breeding is in its infancy with most cultivars only two generations removed from their wild progenitors. Two active breeding programs have released cultivars in the past decade and several others are in progress. Until recently, the majority of cultivars have been selected from commercial seedling orchards. Breeders are hindered by the large size of the trees which can grow to 15 m, long juvenile phases (fruiting after 5-7 years), and a poor correlation (r = 0.1) between annual nut-in-shell yield at 4 and 10 years. Current programs involve controlled cross-pollination to produce biparental families, progeny trials planted in randomized replicated designs, prediction of clonal and breeding values and use of a multi-trait weighted selection index. Strategies that allow rapid phenotyping are being examined. Selection for small trees and reduced juvenility will accelerate breeding by improving trait prediction accuracy through replication and reducing selection cycle periods, respectively. We discuss the potential to improve breeding efficiency and reduce cultivar release time by incorporation of genomic selection methods. There may be genetic variation in wild germplasm for dwarfing, resistance to major pests and diseases and adaptation to a wider range of climates. Genomic and phenotypic characterization of wild germplasm to identify material of highest conservation value and to identify useful traits has commenced on an ex situ collection of over 300 accessions of the 4 species.