Epsilon Open Archive

Abstract

The objective of this thesis was to gain more knowledge related to flowering, and to assess its implications for the Swedish Pirns sylvestris L. and Picea abies (L.) Karst, breeding programmes.
Scions of young trees can be induced to flower by grafting them into the crown of reproductively older trees (topgrafting). The effects of the interstock clone and gibberellin (GA4/7) application on topgrafting were studied in P. sylvestris. The interstock clone significantly influenced topgraft flowering and survival, and interacted significantly with the topgraft for female flowering. GA4/7 treatment significantly increased female flowering. The results show that topgrafting can be used to induce early flowering and accelerate generation turnover in P. sylvestris breeding programmes.
The effects of the timing of GA4/7 applications on flower production were studied in P. sylvestris using stem injections. Maximal female flowering was obtained from the latest applications in both of the two years examined. The treatment had no effect on male flowering. The characters shoot and needle elongation were poor indicators of optimal application time. However, heat sums (degree-day summation), can be used to determine the optimal time for treatment, which occurs at about 700 degree-days (threshold +5°C) for female flowering.
In breeding, trees are often selected for height. Strong genotypic correlations between height growth and reproductive traits could, if present, adversely affect genetic gain and diversity. So, genotypic correlations between early cone-set and height growth traits were studied in P. abies clonal trials. Only weak, non-significant genotypic correlations were found, implying that selection for growth traits should not affect fecundity in the species. Strong genotypic correlations (0.7 - 1.0) for cone-set were found between trials, indicating low GxE interactions for early flower initiation.
The rooting ability of cuttings decreases and flowering competence increases with age of the tree. Rooting success and cutting performance of flowering and non-flowering clones of P. abies were studied. No significant differences in rooting or cutting performance was found between clones with and without cone-set, indicating that genetic selection for rooting success or cone-set will not cause unwanted correlated responses in the other trait.