INSTYTUT DENDROLOGII

Abstract: The study was carried out in three Scots pine (Pinus sylvestris L.) single tree plot half-sib progeny tests planted in 1984–86. Phenotypic selection was done in two ways: F about 0.5% to 1% of the total number of trees were chosen by the author on the basis of their appearance only, and Fbis on the basis of diameters at breast height and heights measurements and observations scored for individual trees. The best trees were selected on the basis of the index value weighing traits by their economic value. Genetic selection was performed based on both family index value (Wf) and tree index value (WT), weighing traits by heritability and economic value. This was done in four different ways: (A) The best trees were selected only on the basis of their index value (WT) with no attention paid to the family; (B) About 10 to 12 trees were selected in the best families, (both (Wf) and (WT) were taken into consideration); (C) The best 30% of the families (Wf) were selected and then equal numbers of best trees were selected (WT); (D) The same number families (Wf) as in the phenotypic selection were selected and within these families equal numbers of best trees (WT). The number of trees that were genetically selected was always the same as the number of phenotypically selected ones (selection type F). The selections were compared using a calculated expected genetic gain and the relative loss of effective population size. As expected, phenotypic selection resulted in the lowest genetic gain. Phenotypic selection generally conserved genetic variability, while genetic selection reduced it, especially when genetic gain was maximised. Phenotypic selection type F generally identifies the good families. The agreement of genetic selection with the phenotypic selection is low (0% to 19%) at the individual tree level. This is slightly better with phenotypic selections using measurements data (Fbis). Phenotypic selection is recommended only where information concerning pedigrees is not available. It can provide a simple and cheap way of obtaining material for future selection. Genetic selection method (A) where best trees were selected without any restrictions provided highest genetic gain and cause the greatest loss of genetic diversity.

Additional key words: selection index, heritability, genetic gain, genetic diversity, phenotypic and genotypic selection.