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ŠUMARSKI LIST 1-2/1966 str. 9     <-- 9 -->        PDF

SELECTION OF PLUS TREES*
(Introductory paper)
by


MIRKO VIDAKOVIĆ


Forestry Faculty, Zagreb and Institute for Conifers, Jastrebarsko, Yugoslavia.


INTRODUCTION


Plus trees are used as stated by Schreine r (36) for: (1) the establishment
of seed orchards, (2) direct silvicultural purposes, if a clonal propagation by
means of cuttings is possible, and (3) use in hybridization, i.e. in tree breeding
work. In consequence it is understandable that great attention is paid to the
selection of plus trees. Both the success of further work in tree improvement
and the final result depend in many ways on the choice of the initial material.
With the development of forest genetics, methods of plus tree selection have
also been developed. In the initial stages of forest genetics, when work was
done with great enthusiasm but perhaps less knowledge about the heritability
of characters in forest trees, the choice of plus trees was performed mainly
by means of visual estimate. It was believed that such a selection is completely
sastisfactory, and that further use of the material selected in this manner will
yield desirable results. With an ever intensified development of forest genetics
new conceptions were formed. As theortical knowledge and experience with
forest tress, increased it was realized that a good phenotype need not always
be a good genotype. It was established the majority of commercially important
properties is of a quantitative character. It was likewise found that the habit
of a tree is influenced by the site, the silvicultural system, and the environment
under which a tree grows. All this contributed to a more serious approach to
the problem of plus tree selection. If we take into consideration the object of
tree improvement as well as the search for the safest possible criteria for the
selection of trees, we notice all the difficulties with which investigators are
confronted in the solution of these problems. It should be stressed that in this
direction much has already been done.


In this report we are going to treat a number of problems and individual
views about plus tree selection in order to provide a basis for discussion and
explanation of the individual view points. We consider that the following
questions are important:


1.
Intensity (criterion) of selection.
2.
Development and use of mathematical indices in the selection of plus
trees.
3.
Selection for one, two or more characters.
* The author wishes to express his thanks to Professor Howard B. Kriebel who
has read and corrected the manuscript.