DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 1-2/1966 str. 23 <-- 23 --> PDF |
THE SELECTION OF PLUS TREES IN SWEDEN (Invited paper) by ENAR ANDERSSON* The Royal College of Forestry and 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. |