The world’s first major macadamia breeding program was initiated by the University of Hawaii (UH) at the Hawaiian Agricultural Research Station (HAES) (Hamilton and Ito, 1982). In 1934, UH commenced surveying of seedling macadamia orchards to select superior genotypes based on tree growth, structure, bearing habits, cracking quality, nut size and shape, kernel size, and kernel recovery (Hamilton and Fukunaga, 1970; Hamilton and Storey, 1956). From more than four decades of evaluation of more than 100,000 seedlings, ≈650 were selected for further evaluation. After successful evaluation and testing in multiple sites, 13 cultivars were named and released for commercial cultivation depending on the adaptation to location and preference of individual growers (Hamilton and Ito, 1982). Although several breeding programs are now continuing around the world, these HAES cultivars still dominate world macadamia production (Aradhya et al., 1998; Hardner, 2016).
‘Keaau’ (‘HAES660’) and ‘Mauka’ (‘HAES741’) are two important varieties from HAES selections, and grafted clones are commercially cultivated worldwide. Cultivar HAES660 was recommended for commercial plantation across a wide range of conditions because it performed well in most of the areas in which it was tested (Hamilton and Ooka, 1966). On the other hand, ‘HAES741’ was recommended mainly for areas at 550 to 670 m altitude, where the performance of most other cultivars was marginal (Hamilton and Ito, 1977). Interestingly, both of them were reported to have a similar upright pattern of growth habit and 43% to 44% kernel recovery (Hamilton and Ito, 1982). A detailed morphological characterization of macadamia varieties identified limited variation between these two cultivars (Bell et al., 1998), despite undocumented reports of morphological variation by the growers. Previous molecular marker studies (Aradhya et al., 1998; Nock et al., 2014; Steiger et al., 2003) identified a very close genetic relationship between the two cultivars.
Aiming to confirm the identity of these two varieties, we reviewed the historical evidence of the development of these two cultivars, investigated the phenotypic differences in a replicated trial, and determined the genetic differences using a large number of high-throughput molecular markers.
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