DIGITALNA ARHIVA ŠUMARSKOG LISTA
prilagođeno pretraživanje po punom tekstu
| ŠUMARSKI LIST 1-2/1966 str. 62 <-- 62 --> PDF |
(2) collect the seed from trees selected as representatives of all degrees of the variation series in proportion to their frequencies if it is desired to preserve the natural variability of the population, otherwise only from plus trees. For the already mentioned reasons we recommend the first-named criterion; (3) collect the seed from a sufficient number of trees retained for the preservation of population variability in the progenies. We lack concrete data for drawing a conclusion about the minimum number of trees. In view of the heterozygous character of the most genotypes of forest tree populations, we might conclude that the gene pool of individual trees is large, that great variability appears already in the progenies of the individual trees of the population, and that the population gene pool could be preserved ammong in the progenies of a relatively small number of parent trees. Falconer´ s data (1960) indicated that in half-sib families the degree of inbreeding attains the value of F= l only within twenty generations and that the greatest decrease in variability occurs in the first generations (10—12,5%). Yet, lacking concrete experimental data, it is necessary to observe the practice of collecting seed from at least 10—15 selected representatives of a population. We should mention that for the study of provenances the seed should be collected from 10—25 trees of a population (C a 11 a h a m 1964). Two methods could be used for the selection of seedlings germinated from the seed collected in a population: (1) select the best seedlings; (2) select the individuals by random sampling. The first method should enable us to preserve the »better« portion of the population. Such a principle is usually applied in provenance tests. In the selection of young plans this is very unsafe. Using to the second method, one should select the seedlings at random in the needed number from all the variability degrees in proportion to their frequencies. We make these recommendations for preservation of as complete a range of genetic variability of the population as possible. We consider this the only correct method, especially if we deal with the selection of very young plants. The selection of individuals or groups as representatives of the gene pool of natural forest tree populations would be possible after a knowledge of the genetic variability (races) on the basis of the phenotypic expression of genetically related and economically important characters. Although botanical- systematical studies of varieties and genetic studies of races offer insight into the variability of some more important forest tree species, available data on variability of most forest tree species are still too limited to enable one to select genetic material of the more significant races. A complete knowledge of the genetic variability of the populations of individual forest tree species which would render possible a separation of the geographical and ecological races would take so long to attain that selection of the hereditary material of the natural forests is an urgent task, especially if we consider how rapidly they are destroyed by man. The only possible solution to the problem of how to select is therefore to use the results of previous investigations of botanical varieties, population variabilities, provenance studies, and to avail oneself of forest inventory data |