DIGITALNA ARHIVA ŠUMARSKOG LISTA
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|ŠUMARSKI LIST 1-2/1966 str. 23 <-- 23 --> PDF|
THE SELECTION OF PLUS TREES IN SWEDEN
The Royal College of Forestry
The Co-ordination Committee on Forest Tree Breeding and Genetics,
Stockholm 50, Sweden.
The aim in forest tree breeding (irrespective of which of the more or less
advanced forms is applied) may be stated to be: 1) to identify, or 2) to produce
artificially superior genotypes of forest trees for use in practical forestry.
As is well known, the variable genotypical constitution of cross-fertilized
trees can readily be demonstrated by means of vegetative propagation, and,
in certain species, by subjecting the trees to endogamy. These are two out of
a series of methods which, combined with suitable statistical assessments, can
help us to identify the genotype behind the phenotype. A better understanding
of the composition of the genetic variation (participating in a complex expression
or character), and of the breeding value of outbreeding trees, can be obtained
with progenies from complete and incomplete diallel crosses, laid out in well-
designed and repeated experiments. On the basis of such crosses and tests,
estimates can be made of genetic variability, both general and specific combining
ability, environmental effects, and genotype-environmental interactions for
different cross-combinations of selected trees within, and between, populations,
provenances, and, possibly, species.
Although a reliable test of the breeding value of trees and populations
must be based on progeny testing, this method is very expensive and time-
consuming. In all forest tree breeding programmes, the number of trees and
tests must be restricted, at least during the initial stage, to cover only
outstandingly good phenotypes with valuable properties from an economic
point of view, what are known as plus trees.
PHENOTYPE AND GENOTYPE
Thus, artificial selection has a special goal, viz. to select the basic material
for forest tree seed orchards, and for further selection and breeding, or for
collection or raising of forest tree reproductive material. Selection, directed by
man, of domestic animals and cultivated plants was practised long before
Mendelian laws of inheritance were discovered. In spite of this, it seems that
artificial selection, also in the form of mass selection, has led to significant
* The section on wood basic denstity has been written by Dr. Börje Ericson,
The Royal College of Forestry, Sweden.