Skógræktarritið - 15.12.1991, Page 55

Biotechnology in forestry
Propagation of forest trees by tissue culture.
The article discusses in general terms micropropagation of trees and its potential appli-
cations to forestry in Iceland. The different propagation techniques, i.e. axillary bud
brake, adventitious organogenesis and somatic embryogenesis are explained with the
aid of a schematic drawing, and using examples from research done by the author and
others at The Botanic Garden, Copenhagen University. The „state of the art" of micro-
propagation research in some of the most important tree species grown in Iceland, is
summarized in a table format with selected references.
By clonal propagation it is possible to directly exploit elite genotypes of trees. The ad-
vantages of micropropagation, as compared to other clonal strategies, are the successfui
multiplication of species or genotypes recalcitrant to conventional methods and the
high multiplication rates obtainable. Both of these advantages Iie in the small size of the
explant, making controlled chemical and physical manipulations possible. The most
serious limitations of this technology are the presently high costs, potential genetic
change in culture and the sharp decline in response with age in conifers.
Axillary bud brake is the major route for commercial propagation of mature
hardwoods, such as birch, alder and poplars. Adventitious organogenesis is used for
large scale propagation of a few mature conifers (Pinus radiata, Sequoia). But for con-
ifers in general, the newly developed technique of somatic embryogenesis is the most
promising one. Presently, however, only very juvenile material can be induced to un-
dergo embryogenesis. This necessitates a cryopreservation unit for conservation of lines
until field tests have been conducted.
in spite of the current limitations, micropropagation will be a useful tool for refores-
tation programmes in lceland. The most immediate application is the direct propagation
of selected genotypes of the heterogenous native birch (Betula pubescens) and moun-
tain ash (Sorbus aucuparia), as well as the exotic hardwoods. Another potential appli-
cation is the propagation of seeds/seedlings from elite trees of Russian and Siberian
larch (Larix sukaczewi and L. sibirica), as seed procuration for these species is difficult
and expensive.
FIGURE L-EGENDS:
Fig 1. A schematic drawing explaining the different micropropagation methods: axillary
bud brake (brumræktun), direct and indirect adventitious organogenesis („bein" and
„óbein" Iíffæranýmyndun") and somatic embryogenesis (kynlaus kímmyndun).
Fig 2, A-F. Axillary bud brake in mountain birch (Betula pubescens).
Fig 3, A-E. Adventitious organogenesis in male strobili from mature (33 years old) euro-
pean larch (Larix decidua).
Fig 4, A-H. Somatic embryogenesis in sitka spruce (Picea sitchensis). With permission
of Dr. Peter Krogstrup, Botanic Garden, University of Copenhagen.
Table 1. An overview of micropropagation methods developed in tree species currently
used for reforestation purposes in lceland.
Abbreviations used:
Micropropagation methods (örfjölgunarkerfi): B = axillary bud brake, L = adventitious
organogenesis, K = somatic embryogenesis.
Age of mother tree (aldur móðurtrés): K = zygotic embryo, FR = seedling (1-12 weeks),
U = young plant (not sexually mature), F = adult tree.
1) For most species only one reference mentioned out of many possible.
2) No references found.
SKÓGRÆKTARRITIÐ 1991
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