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ŠUMARSKI LIST 1-2/1966 str. 25     <-- 25 -->        PDF

genes, and 3) selection can be effective in changing the genetic constitution
of a population or of a group of individuals, if the genetic differences of the
group arc expressed in phenotypes.


In Sweden, during recent decades the supply of forest tree seed has been
especially actualized (see, e.g. two publications by the National Board of Private
Forestry, 1945 and 1950, L i n d q u i s t, 1948, Jensen, 1954, A r n b o r g, 1960,
Arnborg & Johnsson, 1963, and Plym Forshell, 1963). Knowledge
of the biological aspects of heredity has increased. There is general agreement
that, from the point of view of heredity the best possible seed material should
be used for forest reproduction. Consequently, a national programme for the
production of forest seed in plantations has been worked out (Johnsson ,
Andersson and Stefansson, 1950, and Andersson, 1958 and 1960).
The country has been divided into 16 zones — or climate area (Fig. 1) for
Scots pine, and 10 for Norway spruce (Fig. 2). For each climate area, forest
seed will be produced by tree species in specially laid out clonal seed orchards
and, in certain cases in north Sweden, in seedling seed orchards (Andersson ,
1965). As a rule, each polyclonal seed orchard contains 30 to 60 plus trees,
which are vegetatively propagated by grafting. Great demands are made in
respect of these plus trees. They must be markedly superior to other comparable
trees in the stand in question, with regard to a number of valuable characters
from an economic point of view, such as: resistance to diseases and unfavourable
environmental factors, wood quality, growth rate, stem form, branching habit,
good seed production capacity, and high seed germination ability, especially at
altitudes above 300 m in northern Sweden (see, e.g. Andersson , 1948, 1958,

1960, 1962, and 1963, Lind qui s t, 1948, Ericson, 1959. 1960 a and b, and
1961, and B j ö r k m a n, 1963). In order, among other things, to obtain the
requisite material for breeding and plantation work intensive and comprehensive
selection has been carried out for several years and is being continued in
certain regions or provenance areas. The plus trees selected are carefully
measured and assessed in respect of wood specific gravity, growth rate, stem
form, and branch characters — a so-called phenotype control (see e.g. Plym
Forshell , 1963). In this connection, all the selected trees in the entire
country are assessed by the same person. The best phenotypic trees in each
area are selected for direct or indirect inclusion (after evaluating the average
value of the trees as female parent trees, when mated at random, by (one parent)
progeny tests, or after observing the reaction of the genotypes by clonal tests)
in different types of seed orchards (Gustafsso n, 1949, Stern, 1960, and
Johnsson , 1964). The selected plus trees are registered centrally.

Thus, the seed orchards can be regarded as a means of improving the
material for seeding and planting through breeding, as well as an attempt to
rationalize forest seed production. Both the genetical constitution of the seed
(see, e.g. Eklund h Ehrenberg , 1963) and its physiological characters
(Ehrenberg, Gustafsso n, Plym Forshell and Si mak 1955, and
Gustafsson , 1962) can be improved by breeding. The question of seed is
particularly precarious in the extremely high altitudes in the north of Sweden
(Andersson , 1965). The unfavourable climatic conditions in these high
altitudes has always made it more difficult to obtain Scots pine and Norway