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 SSBC 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 SSBC 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.
- 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.