The original plus trees
- The genetic improvement of Sitka spruce started in the late 1960s when superior trees (‘Plus’ Trees) were selected in forests all over Britain. But were these trees really better genetically or were they just growing on a favourable site? If genetically superior, they ought to pass an element of that superiority on to their progeny. By collecting wind-pollinated seed from these trees – 2,000 of them – and growing them in comparative replicated trials on a number of sites for around 15-years, breeders determined the very best.
- In this way a breeding population has been composed of around 300 individuals superior for one of more characteristics of growth rate, stem straightness, branching quality, wood density and increasingly, acoustic velocity (wood stiffness).
- The next stage became securing an improved planting stock. Seed generating areas (seed orchards) containing the best parents were planted in the mid-1980s but proved slow in yielding commercial qualities of seed. To fill the gap, control pollination was carried out between the best parents and the seed bulked up using vegetative propagation (VP)
- As time went on the gains available from VP has increased. Now the best available families and new seed orchards are only available from The Conifer Breeding Co-operative which holds the exclusive rights to the Sitka spruce IP from Forest Research.
Establishment and security of clone banks by Co-op
- Working in partnership with Forest Research, The Conifer Breeding Co-operative has access to existing Sitka spruce clone banks and is also establishing it’s own new ones for future breeding work. The clone banks contain grafted copies of the original Plus Trees. These trees form the basis of our breeding work. Here we can combine parents to re-create superior full-sibling families identified in field-trial or take scion material for the new grafting required to create a new seed orchard.
- The Co-op now has 2 new clone banks containing around 275 clones with the most important genetics selected according to a weighted trait index developed by Forest Research.
- Recently the index has been amended to increase the weighting of clones with good timber density and wood stiffness values in response to industry feedback.
Gain statistics
- Tree improvement is only successful if it identifies the best in the population for the traits under selection – often growth rate and stem quality – and then gets that material out to the forests as quickly as possible.
- So that managers can make value judgements regarding the range of improved planting stocks available, and which is best for them, breeders have attached gain statistics to individual Plus Trees, seed orchards and full-sibling families. In the Sitka spruce programme everything is compared to the standard control of unimproved Sitka imported from the Queen Charlotte Islands, BC, Canada.
2024 Resilience & Climate Matching Field Trial
- Later this year (autumn/winter 2024/25) the Co-op will be setting up its most ambitious field trial yet. With the help of match funding from DEFRA, we will be planting a large scale trial to test 100 families of full-sibling (both parents known) offspring across 5 UK sites.
- The trial is intended to test the improved material to verify predicted gains (see above).
- Due to the nature of the materials being used (full-sibling, clonal) the experiment will also allow us to look for resilience traits.
- The trial sites are being selected to cover a wide geographic range (Scotland England and Wales) and will include one marginal site specifically selected to test for drought resilience.
- In this way we hope to gather information which in future will allow SS breeding cohorts to be developed to match UK climate zones.