Effects of cytokinins and an auxin on organogenesis in vitro of fraser fir : (Abies Fraseri (Pursh) Poir.)

Abies fraseri (Pursh) Poir., Eraser fir, grows in the southern Appalachian region of the United States and is important in the Christmas tree industry. Natural stands of Fraser fir are rapidly dwindling. This decline has been attributed to the exotic pest balsam woolly adelgid [Adelges piceae (Ratz.)]. In this investigation, Abies fraseri embryos have been cultured in vitro with the main objective of micropropagation through adventitious bud induction. Sucrose concentrations in the medium of 0 to 8% and three medium formulations [Schenk and Hildebrandt (1972), Cheng (1977), and Medium for conifer morphogenesis of Bornman and Jansson (1982)] were tested on the growth of Abies fraseri embryo explants in an attempt to optimize conditions for explant growth. Two to A% sucrose and Cheng medium formulation produced the best growth of explants exhibited by cotyledon length and fresh weight. Induction of adventitious buds was accomplished with the addition of cytokinin to the medium. Basal medium (Cheng with 3% sucrose) was supplemented with N₆-(2-isopentenyl)amino purine (2iP), kinetin (KN), or N₆-benzylaminopurine (BA) at the concentrations of 10^-7M, 10^/-6M, and 10^-5M, respectively. No adventitious buds were formed on explants left on cytokinin-containing medium for six weeks. Adventitious buds were formed on explants cultured on cytokinin-containing medium for two or four weeks then recultured on basal medium without growth regulators. Adventitious buds were produced on explant hypocotyls and varied in number with each treatment. The average number of adventitious buds formed per explant ranged from 0 to 0.52. No greater than 36% of the cultured embryos formed adventitious buds. Data analysis indicated that each cytokinin tested was equally effective in inducing adventitious buds. In general, the explants with a four-week incubation on a medium containing cytokinins had a significantly greater production of adventitious buds as compared to explants with a two-week exposure to cytokinins. Cytokinin levels of 10^-6M and 10^-7M induced significantly more adventitious buds on explants with a four-week exposure to cytokinin-containing medium than did 10 cytokinin. The addition of 10^-9M or 10^-7M to the medium containing KN or BA (at 10^-6M or 10 ^-5M) did not increase the number or improve the form of adventitious buds produced when embryos were cultured on this medium for four weeks then transferred to basal medium without growth regulators.