Full sibling material has fully identifiable hereditary genetics i.e. both parents are clones from material traceable to either two original plus trees or to identifiable progeny of two original “plus trees”. The “plus trees” have desired growth and quality traits that have through progeny trials proven to be heritable.
With full sibling material there is a very high probability that each individual tree from the full sibling family grown in a forest plantation will conform to the stated predicted gains.
When a forest nursery purchases seed from a Sitka stand or seed orchard it is purchased by the Kg with 350,000 seeds per Kg- prices varying from circa £350 per Kg to £1300. When buying full sibling Sitka seed the price is between circa £4 to £10 for each individual seed! Hence the reason full sibling material is not grown by forest nurseries in the traditional way.
For full sibling production, clone banks are established and maintained. The grafting of clones involves the taking of scions from clones of plus trees and then grafting them on to young root stock.
The production of basic full sibling material (embryonic seed or fully developed seed) is created by direct pollination.
Direct pollination techniques involve the isolation of male flowers and female cones on identified clones in the clone bank.
Male flowers from identifiable clones are removed prior to pollen being released. The flowers are isolated and the pollen extracted. The pollen is then stored in laboratory conditions for future use.
Female cones are isolated prior to their full development. Isolation is by either a specially designed bag or transparent container being secured around the clone. The container is fully sealed to prevent cross contamination from air borne pollen. The container sealing the cone is then pierced by a syringe containing pollen collected from an identified clone (as above). As the seed develops within the cone the sealed container is eventually removed to allow full development. The cones are then harvested and the embryonic seed or fully developed seed is extracted.
Currently full sibling material is grown on forest nurseries using one of three techniques:-
Growing from seed using traditional vegetative propagation (VP)
Micro propagation using somatic embryogenesis and then using the somatic emblings as a source of cutting material for VP. Alternatively somatic emblings can be grown on and directly planted into the forest, however this method is currently far too expensive to be commercially viable
There are systems in place in other parts of the world where the direct pollination and harvesting of full sibling material is partly automated allowing the “bulk” production of full sibling seed with planting stock reared directly from the resultant seed. Such systems have not been developed in the UK to date due to the prohibitive cost.