Genetic Resources and Improvement in Macadamia

Macadamia is an iconic Australian genus that has undergone recent domestication from the wild with genetic improvement underpinning the development of the crop. Edible kernels are produced by the species Macadamia integrifolia and M. tetraphylla, with the smaller M. ternifolia and M. jansenii kernel having elevated cyanogenic glucosides. Hybrids are generally occurs readily between all 4 species. All four species are listed as 'vulnerable' or 'endangered' and are under threat from land development and fragmentation. Seedling plantations of germplasm collected from nearby wild populations were used to establish the first orchard in Australia. Introduction of limited germplasm from Australia formed the basis of the developing industry in Hawaii. The development of grafting technology for the species stimulated a scion selection program based on M. integrifolia germplasm. Other programs were also initiated in Australia, California, South Africa, and other countries. The structure of the domesticated germplasm is dominated by M. integrifolia sampled from the northern range of the species. The Hawaiian germplasm which is the most common in production orchard world-wide represents on 15% of the diversity available from the wild. There appear to be large opportunities for producing improved and novel cultivars by widening the genetic base of the germplasm to better sample M. integrifolia, and include genetic material form M. tetraphylla, M. ternifoilia and M. jansenii using a satellite breeding strategy.