© 1994 Heron Publishing—Victoria, Canada
Induction and stability of somaclonal variation in growth, leaf phenotype and gas exchange characteristics of poplar regenerated
from callus culture
N. Th. Saieed (1, 2), G. C. Douglas (3) and D. J. Fry (1, 4)
1. Department of Environmental Resource Management, University College, Dublin, Ireland / 2. On leave of absence from the Forestry Department, Mosul University, Iraq / 3. Agriculture and Food Development Authority, Kinsealy Research Centre, Malahide Road, Dublin 17, Ireland / 4. Author to whom correspondence should be addressed / Received December 20, 1991
Summary
Populus trichocarpa Torr. and Grey × P. balsamifera L. TT32 lines were regenerated from calli that had been maintained under differing in vitro conditions for sixteen months.
In the final months, calli were maintained with one of six concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D, 0.1, 0.2,
0.3, 0.4, 0.5 or 0.6 mg l–1)and regenerated with 0.25, 0.50 or 1.0 mg l–1 benzylaminopurine (BA). Regenerant lines were obtained from 15 of these 18 treatments. The spectrum of variation in several
morphological, physiological and leaf gas exchange traits was evaluated in the primary regenerants in 1986, and in their secondary
vegetative propagules in the two subsequent years, in relation to differences in the original culture conditions. The results
indicate that somoclonal variation was induced largely as a result of prolonged culture in the presence of 2,4-D, but that
the terminal maintenance and regeneration phases also induced changes in the regenerants. Qualitative differences among the
regenerant lines were detected by the end of 1986. For most traits, these differences were statistically confirmed within
the 3-year period. The treatment lines ultimately diverged sufficiently to produce lines showing general performance that
was either above or below that of the original TT32 clone. An early visible indicator of this divergence was variation in
leaf shape (leaf length/width ratio), which could be related to 2,4-D–BA interactions in the final stages of culture. Graphic
illustration of the independent effects of either 2,4-D or BA on stem height and gas exchange parameters suggested an inverse
relationship with BA concentration and a complex interaction with 2,4-D. Significant correlations were detected between gas
exchange parameters and morphological characteristics representing leaf form and stem development. Overall, the results indicate
the presence of somaclonal lines that offer potential for the selective improvement of growth using morphological and gas
exchange parameters as screening tools.
Keywords:
benzylaminopurine, 2,4-dichlorophenoxyacetic acid, hybrid poplar, leaf morphology, Populus, somaclones.
