Diallel crossing in Pinus cembra : IV. Age trends in genetic parameters and genetic gain for growth and branching traits

This paper reports results from a complete 10 x 10 diallel carried out in a natural population of Swiss stone pine (Pinus cembra L.) from the southern Carpathian Mountains. At age six, after nursery testing, the material was field planted on one site, using a completely randomized block design with 100 families, fourreplicates and 15 tree row-plots per replication, spaced 2.5 x 2.5m. Total and annual height growth, root collar diameter, number of branches per whorl and survival were assessed at successive ages between ages eight and 14 after seed. In addition, severaltraits that were assessed during the nursery test were used in correlation and some other analysis. Plot means of the measured traits were analyzed using the general least-squares method by means of the computer DIALL programme prepared by Schaffer and Usanis (1969). Across the field testing periods, significant (p<0.05) andhighly significant (p<0.01; p<0.001) differences occurred in total height growth and root collar diameter for general and specific combining ability as well for maternalinteraction effects. These results suggest that the traits are controlled by nuclear(additive and non-additive) and by nuclear x extra-nuclear gene interactions. In an ascendant trend, the additive variance, as a percent of the total genetic variance, ranged from 35% at age eight to 66% at age 14 for total height growth, while that for root collar diameter trend varied less between 16% and 34%. In a descendant trend,the dominance ratios σ2SCA/ σ2GCA for total height growth ranged from 0.9 at age eight to 0.3 at age 14, suggesting that the additive variance should be used in the breeding programme. Parents with significant general combining effects for all but one trait were found. For total height growth, the narrow-sense family mean heritability estimates varied in an ascendant trend between 0.45 and 0.65 while the narrow-sense individual tree heritability varied irregularly from year to year between 0.31 and 0.37. By selecting the best 20 families and the best 20% of individuals within families, a genetic gain in total height growth of 9.7% and 10.9%, respectively,could be achieved at age 14. The improvement of growth and branching by using both family and individual selections could be applied. The very high age-age and trait-trait genetic correlations suggest that both early and indirect selection could be applied effectively.