Genetic structure of growth and phenological traits in Salix viminalis

The genetic structure of Salix viminalis L. for different growth traits and bud flush has been studied. The aim was also to study differences in the genetic structure due to geographic origin and type of trait. Two incomplete factorial crossings with parental clones originating from Poland and Sweden were used. Growth traits showed a high amount of dominance genetic variance independent of parental origin. It is suggested that inbreeding depression found in S. viminalis could be a biological cause of the high levels of dominance as an alternative to overestimation due to epistasis. There were significant differences in amount of dominance genetic variance between the two origins for three of the nine growth traits. The higher number of characters influenced by dominance in the pedigree with Swedish origin can possibly be explained by linkage disequilibrium, since S. viminalis in Sweden has been introduced from Germany and Poland, and no sexual propagation of the species in Sweden has been reported. Bud flush showed high additive genetic variance in contrast to the growth traits. In the breeding for biomass production of S. viminalis, the high amount of dominance has to be taken into consideration.