Clonal Propagation of Acacia koa

Introduction Koa (Acacia koa) is currently the most important commercialized hardwood in Hawai'r's forests. A sustainable supply of koa will depend on reforestation with the best adapted seed sources and perhaps with vegetatively propagated cultivars having unique traits. At present, koa forests are in a serious state of decline, and improvement appears warranted if sustainable supply is to be achieved. Vegetative (clonal) propagation provides large numbers of genetically identical plants. Conventional methods include cutting and grafting, while in vitro micropropagation is a more recent approach. These methods would be useful to propagate koa trees selected for superior growth and stem form, disease and insect tolerance, .and desirable wood characteristics such as curly or fiddleback grain. Clonal propagation could provide opportunities for commercial-scale production of koa. Furthermore, clonal koa trees would be useful for breeders in testing for adaptability and developing elite seed sources. Conventional vegetative propagation of A. koa is not presently viable on an operational scale. In vitro propagation (micropropagation), on the other hand, has been used successfully to obtain large numbers of identical trees in various tree species including the genus Acacia. In Acacia, micropropagation through shoot multiplication and somatic embryogenesis (induction of seedlike structures in cultures of somatic cells) has been reported in the past 10 years in A. melanoxylon (Jones and Smith 1989), A. nilotica (Garg et al. 1996), A. auriculiformis (M ittal et al. 1989), A. mangium (Galiana et al. 1991), A. sa ligna (Barakat et al. 1992). In Hawai'i, Skolmen (1977). of the Institute of Pacific Island Forestry, studied clonal propagation of A. koa using both in vitro and conventional methods. Plants were produced through callus culture (Fig. I), air-layering. and mist rooting from young shoots of juvenile trees. However, development of a successful large-scale clonal propagation method is still needed. We studied micropropagation, building upon the