Comparison of Heterozygosity and Genetic Diversity Between Wild and Domesticated Macadamia

Macadamia is a diploid rainforest tree native to Australia. A total of 349 samples, including wild and domesticated accessions, were subjected to whole-genome sequencing, identifying 4.2 to 7.7 million, 2.4 to 7.4 million, 2.8 to 4.4 million, 1.6 to 3.2 million and 3.1 to 9.6 million single-nucleotide polymorphism (SNP) positions for M. integrifolia, M. tetraphylla, M. ternifolia, M. jansenii and the domesticated cultivars and breeding selections respectively. Overall diversity for wild M. integrifolia, M. tetraphylla, M. ternifolia and M. jansenii was 4.43%, 4.33%, 1.80% and 1.1%, respectively. Domesticated M. integrifolia showed an overall diversity of 3.4%, which was 1.03 percentage points lower than that of wild M. integrifolia. Among breeding groups, Australian breeding selections had the highest diversity, whereas Hawaiian cultivars had the lowest. Wild M. integrifolia, M. tetraphylla, M. ternifolia and M. jansenii exhibited heterozygosity ranging from 0.36% to 0.71%, 0.30% to 0.71%, 0.29% to 0.42%, and 0.19% to 0.34 respectively. Heterozygosity showed weak correlation with yield efficiency, cumulative kernel yield, and cumulative nut-in-shell yield, with a weak trend suggesting that performance may be the greatest at intermediate levels of heterozygosity. Overall, substantial genetic variation exists among the different macadamia accessions, with wild germplasm showing the greatest diversity.