Formation of Adventitious Buds in Stem Internodes of Populus spp. Cultured in vitro on Basal Medium: Influence of Endogenous Properties of Explants.

Stem-internodes of the following poplar species formed adventitious buds when cultured in vivo on basal medium in the absence of exogenous growth regulators: Populus nigra, P. deltoides, P. tacamahaca, P. trichocarpa, P. alba, P. wilsonii and Populus hybrid TT32 (P. trichocarpa × P. tacamahaca). The number of buds formed per internodal explant varied with each genotype. Adventitious buds differentiated in tissue produced by cambium and phloem cells. Capacity for bud formation was highest at the physiological apical end of explants. Morphogenesis was reduced in explants cultured with an axillary bud. Formation of adventitious buds was greatest during the initial period of explant culture; bud-formation was reduced or absent in re-cultured explants. Bud-forming capacity was related to length of explant; explants 2mm in length were unresponsive whereas a mean of eight buds were obtained per 8mm explant. Internodes close to the shoot apex failed to produce buds and morphogenic competence increased with increasing distance from the apex.