Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/1997
Publication Date: N/A
Citation: Interpretive Summary: The narrow genetic base on which the Macadamia breeding program in Hawaii is based will likely pose a serious limitation on future achievements. Macadamia presently represents a wholesale value of 56.2 million dollars to Hawaii. This germplasm, in addition to being developed from a narrow genetic base, has been maintained in an isolated island environment potentially leading to genetic vulnerabil- ity. Forty-five accessions representing 4 species (M. integrifolia, M. tetraphylla, M. ternifolia and M. hildebrandii), some interspecific hybrids & a wild relative (Hicksbeachia pinnatifolia) were used. Forty three of the 45 accessions examined could be identified by a unique genotype indicating a high level of genetic variability, far exceeding the level normally observed in a species with such a narrowed range. The isozyme polymorphism strongly suggests the two early introductions to Hawaii were from genetically distinct ancestral populations in Australia, whereas the Australian selections probably represent a different genetic background and selection history. Analyzing genetic variability patterns and relationships among existing cultivars and breeding materials is key not only for understanding deficiencies in collections but also for enriching its genetic diversity and develop- ing a sustainable improvement strategy addressing future needs.
Technical Abstract: A genetic variability analysis involving 45 accessions of Macadamia encompassing four species (M. integrifolia, M. tetraphylla, M. ternifolia and M. hildebrandii) and a wild relative (Hicksbeachia pinnatifolia) was performed. Eight enzyme systems encoded by 16 loci were assayed. Multilocus isozyme genotypes of 43 accessions indicated that each was characterized by an isozyme fingerprint, indicating a high level of genetic variation in this species. Examination of multivariate relationships among accessions with cluster analysis identified four groups, two of which contained one accession each. All Hawaiian cultivars were included in two sub-clusters within the largest cluster, which encompasses all the M. integrifolia and three M. terni- folia accessions, suggesting that: 1) The Hawaiian cultivars must have originated from at least two genetically diverse ancestral populations; and 2) M. ternifolia and M. integrifolia may be conspecific. Macadamia tetraphylla has diverged marginally from the M. integrifolia and M. ternifolia complex suggesting that these taxa represent a species complex. The different measures of genetic variability such as mean number of alleles per locus, polymorphic index, and observed and expected levels of heterozygosity, indicated significant levels of genetic variability in the collection.