Parent tree selection and evaluation of frost resistance, wood quality, and seed relatedness of Acacia koa.

摘要

This project represents an important effort to develop an improvement program for a valuable native hardwood tree species in Hawai'i, Acacia koa. The ultimate goal of the tree improvement program is to provide improved stock of A. koa through classical breeding, focusing mainly on stem form. In addition, wood quality assessment on young A. koa trees is important to try to develop markets for pre-commercial thinning. This project also clarifies some of the trends related to frost resistance fluctuations over the different seasons in Hawai'i. The main questions that were addressed are: Which are the best families to maintain in order to convert HARC A plantation into a seed orchard? Do heritability estimates change depending on the trees that are taken into account to compute them? Do the selected families show significant differences in frost resistance? Does frost resistance fluctuate between seasons? What are the wood characteristics of young A. koa trees? And finally, how closely related are the seeds within a legume?;The experiments were conducted on the Big Island of Hawai'i at the HARC A stand at Mana Road on the eastern slopes of Mauna Kea. The site it is managed by the Department of Hawaiian Home Lands (DHHL). Half of the originally planted families were selected based on morphological traits. One to four individuals were selected per family. These trees are isolated from pollen of other koa trees by a large population of gorse (Ulex europaeus), so they will only pollinate each other through bees and other insects.;Heritability estimates were determined for morphological traits with normal distributions. In addition, comparisons were made when heritability estimates were computed using all of the trees originally present versus when only the selected trees were considered, and also after a simulated random thinning was performed. When comparing the complete dataset with the after selection treatment, an increase was observed in the heritability estimates of traits that can affect the stem form of koa such as maximum branch angle, stem lean, and height to crown. The heritability of total height decreased, while the heritability of height to first fork and composite DBH remained the same.;Some of the nine year old trees at HARC A had formed heartwood, with sapwood:heartwood ratios ranging from 0.2 to 0.7 with a mean of 0.4. Sapwood tends to have higher modulus of elasticity (MOE), higher density and lower microfibril angle (MFA) than heartwood. In addition, there does not seem to be a direct relationship between wood density and growth rate.;Based on the electrolyte leakage test, frost resistance was assessed for each one of the selected families during winter and during summer. There were no significant differences in frost resistance among the selected families, however their frost resistance significantly fluctuated between seasons, indicating that A. koa goes through a hardening process.;Microsatellites developed for A. koa, and for other closely related species were used to try to determine how closely related are the seeds within a legume. In addition, new microsatellites were developed. However none of them were informative enough to answer the question. Some of them were monomorphic, some did not amplify and some were not polymorphic enough to draw conclusions.