Tissue culture propagation (also called micropropagation) is a method of propagating a plant from a piece of the plant. A cutting (explant) is taken from a stock plant and grown in a sterile medium. This explant can be from almost any part of the plant. It is important that the stock plant is disease-free and a good quality plant. Tissue culture propagation must be done in a very clean environment to avoid contaminating the plants.
The explant is cleaned and transferred to a sterile medium. This medium is composed of nutrients and growth regulators optimized for the specific plant that is being propagated. The explants require very little care while in the medium because the medium provides all the explants' needed nutrients. Once the explant has grown into a number of plantlets, the plantlets can be further divided into more explants. When the desired number of plants is reached, the plants can be moved into another medium which promotes root growth. When the plants reach the desired size, they can be replanted in to soil and gradually acclimated to the outside world.
There are a number of advantages that tissue culture propagation has over other propagation methods. The tissue culture propagated plants are clones of the stock plant. The plants are uniform and true to type because they are identical to the parent plant. The plants are grown in sterile condition so they are healthier. They are disease and pest free.
Another advantage is that less of the stock plant is needed for propagation. Therefore, new cultivars can be propagated more rapidly than with traditional methods. This results in faster time for the grower to field test the new cultivar and to get the plants to market.
In the initial stages, the explants require less care compared to seedling or cuttings. There is no need to water or fertilize the plants because the growth medium provides all the plants' requirements.
Micropropagation has the potential to help save endangered species. Such a small amount of plant material is needed, that there is less fear of destroying the mother plant. Also, an almost infinite number of plants can be propagated from the initial explant.
The disadvantages of tissue culture propagation are few and can be reduced by careful plant selection and good procedures. The original stock plant must be free of diseases. The careful preparation of the explant by cleaning can remove most pests and diseases. If a disease-free stock plant is unavailable, It might be possible to use the apical meristem tissue found at the tip of the shoot. This tissue is often disease-free because it is not yet attached to the plant's vascular system.
The stock plant should also be a good quality plant to avoid propagating an inferior plant. The plant should be thoroughly field tested under different conditions to weed out poor plants.
A micropropagation facility is more expensive to set up than a traditional greenhouse. However, the resulting plants are healthier and better quality so there is less waste from disease and pests.
The orchid industry was the first to adopt tissue culture propagation. Orchids had been difficult to propagate because of poor seed quality and diseased plants. Micropropagation allowed the growers to eliminate the viruses and successful propagate orchids. Orchids are now cheaper and healthier thanks to micropropagation.
Tissue culture propagation is now used to propagate a wide variety of plants all over the world. Many plants have benefited from tissue culture propagation including hostas and heucheras. Many new cultivars have been introduced to the market faster and of better quality as a result of micropropagation. In addition, some new mutations that have developed into beautiful new cultivars have been discovered during the process of tissue culture propagation.
There are a number of websites that discuss tissue culture propagation. Some people have even successfully set up propagation labs in their home.
Here's a good video on conservation using micropropagation.
A great book on the subject is: “Plants from Test Tubes: An Introduction to Micropropagation” by Lydiane Kyte & John Kleyn.