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ŠUMARSKI LIST 1-2/1966 str. 65     <-- 65 -->        PDF

of genotypes of parent trees (20—30) (V i d a k o v i ć 1960). Seed orchards are
usually planted in a statistical design. We can conclude that seed orchards may
serve primarily for preservation of single tree population samples and also
for preservation of multiple-tree population samples of the gene pool of natural
populations. The founder of these plantings will normally aim at introducing
into the seed orchards those genotypes that were selected as plus trees and
were superior in progeny tests. Therefore in plantations of this type it will
be more difficult to preserve the natural variability of the gene pool.

Provenance tests are established primarily with the objective of studying
the genetic variability of the forest-tree populations, or in a more practical
sense to determine the most suitable seed sources for the afforestation of
individual areas (B o u v a r e 1 1958: C a 11 a h am 1964). Provenance test
plantings are laid out on a statistical basis. For the time being this form of
planting may also serve to preserve the gene pool of natural forest populations,
especially when population samples are groups of trees rather than single trees.
When determining the required number of gene-pool representatives in the
individual provenance test plots, it is important to consider the unavoidable
reduction in the number of stems due to thinning. The problem arises whether
to preserve the natural variability of the gene pool, or only of the material
of the best phenotypical expression. Provenance tests represent a very significant
way to preserve the gene pool of the natural forest while making possible
a study of genetic variability and racial differentiation.

Progeny tests are plantings, established for the purpose of studying the
genetic value of the parent trees by evaluating their progenies and investigating
the degree of inheritance of economically-important characters. Progeny tests
are always established using statistical designs. Populations in the progeny
tests represent half-sib or full-sib families whose genetic variability is lower by
12—25% than the variability of randommating populations (Fa 1 c o n e r 1960).
This reduced variability, coupled with displacement of the natural range of
variation due to use of a particular parental selection index, would be expected
to yield an improvement of the germplasm which is preserved in the plantation.
This improvement however, is detrimental to the preservation of natural
variability in the progeny tests.

Clonal tests are comparative plantings of selected genotypes established
with vegetatively propagated material in order to test for productive capacity
statistical design is necessary. Clonal tests also provide valuable information
on the nature of inheritance in trees. They make possible the detection of
great individual differences, thus providing a basis for improvement. In
plantings of this type the possibility of preserving the gene pool is limited.
Reasons for this limitation are:

(1) are population samples consist of individual genotypes;
(2) only the best phenotypes are selected;
(3) the
test is only preserved for a limited period of time, namely the
economic rotation.
Because it is imperative to preserve the gene pool of our natural forests
for breeding and as a source of valuable genetic material for future progenies,
we consider it necessary to begin to protect and conserve it. We recommend
that as great a number of trees and groups of trees as possible be protected.