Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 19, 2003
Publication Date: August 20, 2003
Citation: STEIGER, D., MOORE, P., ZEE, F.T., LIU, Z., MING, R. GENETIC RELATIONSHIPS OF MACADAMIA CULTIVARS AND SPECIES REVEALED BY AFLP MARKERS. EUPHYTICA. 132:269-277, 2003.
Interpretive Summary: Macadamia nut production 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. intrgrifolia, 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 germplsm collection. The four Macadamia species included in this study were clearly spearated 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 questions whether M. ternifolia may be a variant of M. integrifolia. Within the major cluster of M. integrifolia, nine established smooth shell cultivars were spearated 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 claify the phylogenetic nature and status of M. hildebrandii in the genus Macadamia.
Genetic diversity of twenty-seven accessions including M. integrifolia, M. tetraphylla, M. ternifolia, M. hildebrandii and a wild relative Hicksbeachia pinnatifolia were assayed using 105 AFLP markers. The average genetic similarity among all accessions evaluated was 0.742 with a range of 0.326 to 0.985. The average genetic similarity within the 18 M. integrifolia accessions was 0.839 and ranged from 0.697 to 0.985. M. integrifolia was found to be most genetically similar to M. tetraphylla (0.369) and least to Hicksbeachia pinnatifolia (0.369). The extent of genetic variation among macadamia cultivars was much higher than that reported in coffee and papaya. The high degree of genetic variation may be attributed to the heterozygosity that exists in the natural population and the methods used in the macadamia improvement program.