DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 1-2/1966 str. 61     <-- 61 -->        PDF

and economically important characters (plus trees), or (b) among individuals
which have a phenotype (and genotype) close to the mean of the group with
respect to these same characters. Selections made under (a) have the advantage
of representing the best portion of the population with respect to the characters
under consideration. However, the individual thus selected (from the extreme
values of frequency series of quantitative characters) will probably be to a greater
extent of homozygous constitution, and it will represent to a smaller extent
the variability of the gene pool of the population. In so far as our main
objective is to preserve the variability of the gene pool, it would be more
desirable to select a representative which by its characters would be near the
mean value of the frequency series, for there is high probability that such a
genotype is of heterozygous constitution. The progenies of the representative
thus selected will reflect to a greater extent the gene pool of the parent
population.


For the selection of individual representatives of the gene pool of natural
forests we recommed the following procedure. If only one representative is
to be selected from the population, let us take it from the better portion
(positive according to the characters) or from the middle of the frequency
series. If two representatives are selected from one population, then choose
them from the extreme positive or middle portion of the frequency series.
Jf three representatives are selected, the third one should be chosen from the
negative portion of the frequency series. We would recommed such a criterion
of selection aiming at the preservation of the population gene pool. Otherwise,
selection should be directed as for a plus tree, i.e. al the three representatives
should be selected from the extreme positive portion of the frequency series.


To preserve the natural variability of the gene pool, we would recommend
a similar procedure for selection of representatives of the populations. Individuals
should be chosen from the entire range of natural variation in proportion
to their frequencies, and not only from the portion rated best according to its
characters. In selecting representatives for provenance studies, however, it is
recomended to be chosen dominant and codominant trees (Callaha m 1934).
The selection of a group of trees of the best phenotype could also be considered
in selection of the gene pool for preservation, if preference is not given to the
variability of the population. According to Ster n (1960) the fear of loss of
the natural gene pool because of artificial selection and of taking only certain
representatives is not justified. By reasonable selection one obtains a new gene
pool which be assessed in the same way as one which has passed trough natural
selection. We consider that any artificial selection guided by definite criteria
can improve the genetic composition of the population, even though it may
be to the detriment of natural variability important for potential needs.


The problem of how and what to choose also arises in the selection of
group representatives if there is no apparent need to reproduce the gene pool
found in nature. In selection of individual representatives, vegetative propagation
represents no problem. However, vegetative propagation of a greater
number of individuals of a population is more difficult, because of difficulties
occurring in the collection of scions, grafting, etc. If group representatives are
to be sexually propagated the seed should be collected by observing the
following principles:


(1) collect the seed from trees which most probably were fertilized by
trees of the same population;