Koa:A Decade of Growth ~ Isozyme Studies of Genetic Variability

Little is known about genetic variation and geographic patterns of diversity of Acacia koa. We analyzed diversity using laboratory studies of enzymes. Wide samples of koa possess significant variation in six enzyme genes; several genes have alleles in intermediate frequencies. The variable genes have average expected heterozygosity of 0.41; this indicates that koa has significant levels of genetic diversity to adapt to varied natural environments, and it provides evidence that tree improvement can operate on a rich genetic base. Samples from trees on Kaua'i, O'ahu, and Maui appear closely related; all share about the same profiles for the variable enzyme genes. It is noteworthy that two populations on the Island of Hawai'i, one above Kailua and the other in Hawai 'i Volcanoes National Park, have enzyme profiles that are similar to one another, but both differ substantially from the profiles of populations on Kaua' i,0'ahu, and Maui. This islandto-island differentiation indicates that it is important for foresters to plant with seedlings from local seed sources until more is known about the adaptations and growth of koa geographic races. The introduced and naturalized Passiflora vine (banana poka) has potential to over-top and smother forests; it is adapted to elevations and conditions characteristic of native koa forests. Banana poka seed samples from Kaua'i, O'ahu, Maui, and the Kailua and Hawai'i Volcanoes National Park areas on Hawai'i all were found to lack genetic variation: enzyme patterns were identical throughout Hawaii, there was no evidence of allelic variation for 14 genes, there was no evidence of genetic diversity, and the observed heterozygosity was zero. The Hawaiian banana poka enzyme gene profile exactly matches the profile of Passiflora tripartita var. tripartita from Ecuador, Colombia, and Venezuela. The latter species, a common domesticated juice plant of the high Andes, is also genetically uniform and homozygous, with a single allele type at each enzymegene. The other Andean candidate progenitor species, Passiflora tripartita var.mollissima, has distinctly different enzyme profiles. Researchers can collect Passiflora biological control organisms in South America for tests on Passiflora tripartita var. tripartita with knowledge that significant genetic differences exist between the two Andean species, and with knowledge that var. tripartita and banana poka have identical and homozygous genetic constitutions. Isozyme studies of koa genetic variability Little is known about the relative amounts of genetic variation of the geographic patterns of genetic diversity of Acacia koa, Hawai'i's signature wood and major forest tree species. While some workers collected seeds, planted common garden trials, and evaluated growth adaptations, we analyzed genes using laboratory studies of enzymes. Enzyme genes disclose levels of diverstiy and help to reveal geographic races. Fresh seeds were collected from the Waimea Canyon, Koke'e, Alaka'i forest of Kaua'i (60 trees in the sample); Wai' anae Range (24), and also northern [Pupukea (44)], and southern Honolulu (32) forests of the Ko'olau Range, O'ahu; forest near the Hosmer Grove, Haleakala, East Maui (6); and forests on the island of Hawai'i: Hualalei above Kailua-Kona (18), and Mauna Loa Strip Road, Hawai'i Volcanoes National Park (28). Our laboratory analyzed enzyme genes from the embryos of germinating seeds. Koa is a tetraploid, 4N plant that presents numerous isozyme band patterns. Initial analyses of seeds from individual pods, each being a full-sib family, helped to characterize the gel band patterns from six polymorphic genes (6PG2, IDH, MDH2, PGI2, GOTI, GDH). Our species analysis used one seed per tree to avoid seed parent bias and to provide wide evaluation of diversity within the respective forests. Koa population samples possess relatively large numbers of alleles per gene, from three alleles for IDH, up to seven for MDH2. Several of the genes have alleles in intermediate frequencies. Overall, the variable genes have average expected heterozygosity of 0.4l.