Sitka spruce full-sib families with cuttings on Ireland
According to procedures 2008.
Written by Dag Lindgren in contact with David Thompson summer 2008.
Regarding the numbers of rooted cuttings to be produced in Ireland, the original plan was to produce 6 million per year, however, with a reduced overall planting programme this has now been revised downwards to 4 million and at present Ireland produces 2 to 3 million with the object to scaling-up to 4 million in the near future. It is also entirely possible that the programme will be scaled-up to the 6 million in the future as a result of an increased wood supply demand, on the other hand the current land values on Ireland are to high to justify conversion of land to commercial forestry .
An embling (SE plantlet) is transplanted or a seed sown in a 100 cc container in a greenhouse (year 0). The purpose is to multiply genotypes from assumed good cross families vegetatively. At the end of the first growing season (year 1) the seedling (stock plant, donor plant, mother plant) is transplanted to a 3 litre pot and grown a second year in the green house. At the end of the second year (year 2), 5-10 cuttings are collected from each plant.
The stock plants are transplanted to an outdoor nursery bed "hedge orchard" at the end of the second growing season with about 100 000 stock plants/hectare. At the end of the third growing season (year 3) the stock plants produce 20 to 30 cuttings rising to 40-50 cuttings after the fourth to seventh growing season (the stock plant are typically five years in the "hedge orchard". On average the production is around 200 cuttings which yields 150 marketable plants similar to three year old seedlings, but made in two vegetation periods from cutting. The “hedge orchard” is kept five growing seasons in the nursery bed and when “retired” and replaced by a new. 40000 stock plants annually supports a plant production of 6 million cutting plants, some hectares of nursery land is needed for the hedges (1/5 of that is renewed each year), but the plant demand has sunk so now it is 30000 stocks.
Earlier the stock plants were produced from seed, but nowadays it is usually only with emblings.
There would not be time for six years field testing with acceptable maturation for the cutting technology foreseeable, but when cell-lines are cryo-stored and supporting emblings it will be possible to use cell-lines which has been tested in ordinary field trials.
It is possible to harvest cuttings in the hedge orchard a further year (after the seventh growing season), but as plant producers are reluctant, this is only done if needed because of unforeseen circumstances. and the stock plant production is not dimensioned for that. There has seldom been a need to do this.
The added cost compared to seedlings is of the magnitude 15 c, that includes the embling production.
It would be possible (and has been done) to use the first cutting harvest from the stock plants to produce new stock plants from cuttings and increase the multiplication rate from 150 per genotype to a higher figure, maybe 500. In that way a 7-8 year cycle, where after the first two or three growing seasons new stock plants are initated as rooted cuttings and transplanted to the "hedge orchard" producing cuttings after 2+2 growing seasons or so, but usually there is no need to do this.
To get new cell-lines is not that trivial. To compensate for bottlenecks in the SE process it is needed to start with much material. 100 immature zygotic embryos may be needed to establish 30 embryogenic cell lines, of which 10 will be good embryogenic cell lines but of these 5 will be very good embryogenic cell lines useable in commercial production). Only 50% of these very good embryogenic cell lines may recover well after cryogenic storage. Just to be able to multiply some family members hundreds of immature zygotic embryos may be needed.
A similar operation is done in UK, and there is an other organisation on Ireland which plans rooted cuttings of Sitka spruce.