Genetic improvement of Leucaena spp and Acacia koa Gray as high-value hardwoods

• Main Author: Shi, Xuebo
• Other Authors: Brewbaker, James L
• Published: University of Hawaii at Manoa 2009
• Online Access: http://hdl.handle.net/10125/6908

Studies on genetic improvement of Leucaena and Acacia koa Gray were undertaken in Hawaiʻi from 1999-2003. There studies were described in two sections. The first section focused on research of Leucaena hybrids, which included vegetative propagation of Leucaena hybrids, hybrid yield trials, and chromosome doubling of diploid Leucaena species. Different hybrids rooted differently. Cuttings with more leaf presence had higher rooting frequency, better root qualities, and quicker root initiations. Leafless cuttings did not root under a mist system. One-node cuttings rooted as well as bi-nodal cuttings. Cuttings from younger (25-45 days old) regrown shoots rooted better than cuttings from older shoots (>45 days old). All hybrids rooted poorly in winter. Difficult-to-root hybrids rooted well after the treatments of etiolation. Three hybrid yield trials using clones of hybrids were carried out at three locations, Waimanalo of O'ahu, and Hamakua and Kona of Hawaiʻi Island. Seedless hybrid K1000 grew best at warm areas of Waimanalo and Kona, but grew poorly at cool area of Hamakua in terms of DBH, height, and wood volume. Two tetraploid hybrids, KX3 cl2 (L. leucocephala xL. diversifolia) and K156 x K376 (L. diversifolia x L. pallida) were among the fastest-growing hybrids at Waimanalo and Hamakua. The method (0.1% colchicine treatments on seedlings) to induce tetraploid Leucaena species was effective. Larger, thicker and darker leaflets, and larger flower heads of induced tetraploids were observed. The second section focused on studies of koa, which included cytological study of koa, vegetative propagation, koa mortality and tolerance to wilt disease, and prediction of breeding values of koa. No variations in chromosome number were found among three koa types and populations. The chromosome number of koa was identified as 2n=52 among all populations examined. Koa vegetative propagation was feasible at juvenile stage. Rooting ability of cuttings declined quickly with the increase of the age of cuttings. Cuttings of most families did not root at transitional and mature stages, and they did not respond to the treatments of growth regulators. Only cuttings of two families from Hawaiʻi Island responded to auxins well with a moderate increase in rooting percentage at transitional and mature stages. Etiolation treatments appeared to have some effects on rooting at transitional stage. Koa survival rates in progeny trials declined steadily over the years. The mortality appeared to be mainly caused by koa wilt disease. The survival rates of koa families were analyzed and used to assess family tolerance to the disease. Great variation in survival rate was found among the families. Family selection based on survival rate was conducted. To rank the growth performance of koa families in progeny trials, breeding values of DBH at the age of 4 years were predicted in 4 progeny trials using BLP (Best Linear Prediction) method. Family ranking and selection based on predicted breeding values were conducted. Genetic gains of selection were calculated based on family selection. === xiv, 192 leaves