Reconstructing the Domestication Pathway of Macadamia, from Australia via Hawaii and California

Macadamia F. Muell is an iconic Australian plant as is the only international food crop developed from the Australian flora. The genus is a member of the ancient Gondwandic family, Proteaceae, and is endemic to the lowland rainforests of the sub-tropical rainforest of eastern Australia. This paper reviews historical records and current international collaborative research efforts to better define the pathway and wild origin of the domesticated germplasm. The first recorded ex-situ planting of  Macadamia F. Muell. was in 1858 in the Brisbane Botanical Gardens and over the subsequent decades macadamia became a popular backyard tree in subtropical Australia. In the late 19^th century, macadamia seed were introduced into California and Hawaii. There are two recorded introductions into Hawaii of M. integrifolia, the preferred commercial species; by William Purvis to the big island in 1881 and by Robert Jordan to Oahu in 1892. There is strong evidence linking the Jordan introduction to a remnant tree on the Gold Coast hinterland of SE Queensland, Australia, but the wild origin of the Purvis introduction is unknown. By 1920, commercial interest in macadamia had developed in Hawaii and several large and other small orchards were established using seed reportedly collected from the Purvis and Jordan introductions. Following the successful development in Hawaii of grafting in the mid-1930s, a selection program was initiated by surveying the seedling orchards for elite performing individuals from which the initial cultivars of the Hawaiian breeding program were selected. It is estimated that 70% of the current world’s commercial macadamia orchards are planted with cultivars originating in Hawaii. Macadamias were also introduced into California in the late 19^th century, but much less is known of the origin of this germplasm. A subsequent selection program in California produced cultivars that were commercially planted in California and South Africa. With the expanding opportunities offered through molecular technology it is now possible to better define the wild origins of the commercial cultivars. The results from this study will be used to highlight the heritage importance of this unique plant and assist focus current breeding programs.