Genetic parameters in diallel-crossed Scots pine favor heartwood formation breeding objectives

After 25 years, full-sibs of Scots pine (Pinus sylvestris L.) in a north Swedish progeny test showed an estimated heritability of 0.30 for heartwood diameter at 80 cm above ground. This was equal to the heritability estimate for tree height, although accompanied by a much larger additive genetic coefficient of variation (0.20 compared with 0.06). The heritability estimate for diameter at breast height was about half that for tree height. Strong and positive phenotypic and environmental correlations were assessed between heartwood and the following traits: diameter at breast height, tree height, and branch diameter. The genetic correlation was low and positive at 0.02 between heartwood and diameter at breast height in contrast with 0.27 between heartwood and tree height. The assessed genetic correlations between heartwood and branch diameter and between heartwood and crown length were very weak compared with the phenotypic and, particularly, environmental correlations. This indicates that the association between crown length and heartwood is significant with regard to environmental factors, no matter to what extent they are independently modified by genes. However, crown limit was the trait that showed the strongest genetic correlation with heartwood (0.49). Since no correlations with production traits were unfavorable, we conclude that including heartwood formation capacity in a breeding programmay be done without drawbacks and with good prospects for success.