Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2003
Publication Date: 7/15/2003
Citation: Steiger, D.L., Moore, P.H., Zee, F.T., Liu, Z., Ming, R. 2003. Assessment of genetic diversity in macadamia by AFPL markers. Euphytica 132/2:269-277.2003. Interpretive Summary: The efficiency of tree crop improvement and germplasm conservation can be severely hampered by the lack of information about the DNA diversity among accessions, especially for tropical and subtropical species. A collaborative study, conducted by scientists of ARS and the Hawaii Agriculture Research Center, analyzed the genetic diversity among macadamia species and cultivars maintained in the Hilo, Hawaii ARS germplasm repository and in production in the Hawaiian macadamia nut industry. A genetic similarity analysis based on 105 differential DNA markers showed two distinctive clusters of cultivars of M. integrefolia that were significantly different from the other macadamia species and hybrids. These results will be used by germplasm curators to manage the collections for maintaining maximum diversity at lowest cost and by macadamia breeders to plan crosses that avoid inbreeding depression.
Technical Abstract: Macadamia is a high value nut tree native to Australia, but its development as a significant crop has occurred primarily in Hawaii. World production of macadamia nuts is based on two species, the smooth shell Macadamia integrefolia Maiden and Betche and the rough shell Macadamia tetraphylla L.A.S. Johnson, and their hybrids. The smooth shell M. integrefolia produces higher quality nuts. All Hawaiian cultivars are the smooth shell type. AFLP markers were used to analyze twenty-six macadamia accessions representing four species: M. integrefolia, M. tetraphylla, M. ternifolia, and M. hildebrandii as well as wild relative, Hicksbeachia pinnatifolia. Six primer pairs generated a total of 105 polymorphic AFLP markers. Pair-wise simple matching coefficients were used to construct a similarity matrix. The average genetic similarity among the eighteen M. integrefolia accessions was 0.839 and ranged from 0.697 to 0.985, while the average genetic similarity among the nine established M. integrefolia cultivars was 0.881 and ranged from 0.826 to 0.985. The average genetic similarity among all twenty-seven accessions was 0.742. Cluster analysis revealed four main clusters with all four macadamia species clustered independently. Within the major cluster of M. integrefolia, nine cultivars were separated into two distinctive sub-clusters, suggesting two diverse gene pools may have been major contributors to macadamia variety improvement programs.