The use micropropagation (tissue culture) for the production of plant species and cultivars in horticulture is nothing new, the technique has been widely used for decades. Traditionally many of our trees have been propagated by grafting and for most species this is still the more cost effective option. But for some species such as those of Betula and Alnus grafting can be unreliable and variable, which is why we use micropropgation.
The process by which we produce our micropropagated trees can be split into three stages:
Initiation
The first stage introduces the plant we want to propagate into sterile culture.
We first harvest the part of the plant we want to propagate from (called the explant), this can be apical or axillary buds, stem segments, leaves or roots. The explant is then sterilised in a solutions of bleach and alcohol before being placed on the initiation media. This media consists of a nutrient salt mixture, sugar and plant hormones which is set with agar.
The example to the right is a nodal cutting explant of Betula Youngii
Multiplication
This is the stage where the magic happens.
Every four to eight weeks the trees are removed from the culture vessels and then cut into stem segments of one or two buds or nodal tip cuttings before being placed onto new growth media.
This allows for very fast multiplication and production of large numbers in a very small area.
We repeat this process and continue to multiply until we reach the quantity desired before moving on to stage 3.
Rooting and Acclimatisation
The final stage returns to more traditional horticulture. We again remove the trees from the culture vessels and harvest the shoot tips, all other material being returned to the multiplication phase. From the shoot tips we take nodal cuttings which are rooted on a special agar mix for two weeks before being pricked out into cell trays of regular seed and cutting compost. Another week is spent weaning the plants down in a warm and humid cuttings tunnel before they are ready for growing on.
After a month of growing on they are ready for potting up and growing on further like the tree to the right.
