Genetic relationships of macadamia cultivars and species revealed by AFLP markers

World production of macadamia nuts is based on two species, the smooth shell Macadamia integrifolia Maiden and Betche, and the rough shell Macadamia tetraphylla L.A.S. Johnson, and their hybrids. One hundred and five AFLP markers were used to analyze 26 macadamia accessions representing four species: M. integrifolia, M. tetraphylla, M. ternifolia, and M. hildebrandii as well as a wild relative, Hicksbeachia pinnatifolia (rose nut). Each macadamia accession showed distinct AFLP fingerprints indicating a significant level of genetic variation in this macadamia germplasm collection. The four Macadamia species included in this study were clearly separated using cluster analysis with AFLP marker data. Based on a single accession, the separation of M. ternifolia from M. integrifolia suggested the relatively distant genetic relationship between these two species and casts doubts on the notion that the M. ternifolia may be a variant of M. integrifolia. Within the major cluster of M. integrifolia, nine established smooth shell cultivars were separated into two sub-clusters, suggesting the heterozygous nature of the original gene pool that had contributed to macadamia variety improvement programs. M. hildebrandii and H. pinnatifolia formed a distinct cluster and shared dramatically less genetic similarity with the other Macadamia species. Additional data would be needed to clarify the phylogenetic nature and status of M. hildebrandii in the genus Macadamia.