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| Figure 1. Cassava plantlet produced through micropropogation. |
Plant tissue culture is a form of biotechnology with great potential to aid agriculture in developing countries. It is based on the ability to grow plants in vitro, by culturing sterilized tissues or seeds in test-tubes or Petri dishes. Nutrients, vitamins and sugar are supplied in specially designed media incorporated into a gel which supports the plant tissues. Originally developed to multiply orchids, it is now possible for every major crop plant to be handled in this way. The great value of plant tissue culture is that it allows the developmental fate of the plant tissues to be manipulated towards desired ends by inclusion of growth regulators (plant hormones) and other chemicals in the medium. The ability to culture plant tissues forms the basis for several biotechnologies and is a central component of crop genetic engineering programs. However there are also non-transgenic applications including meristem cleaning, micropropagation and embryo rescue.
Meristem cleaning facilitates the production of virus and bacterial free plants by regeneration of plantlets from just a few cells excised from the growing tip of a new shoot. Micropropagation involves the rapid multiplication of small shoots in vitro, to generate 100,000s of pathogen-free plants in a matter of a few months. A combination of these two technologies has, among other successes, recently led to the delivery of improved sweet potato and cooking banana planting material to farmers in China and Kenya respectively. Yield improvements of up to 30% are being reported from this material in China. Both biotechnologies are relatively simple to handle and can be carried out in most developing countries possessing basic laboratory conditions.Embryo rescue is a tool which greatly enhances the power of traditional plant breeding. Achieving successful sexual mating between distantly related species of the same crop, for example African and Asian rice varieties, is problematic, often leading to abortion of the resulting embryo. Embryo rescue involves removal of the young embryo from the developing seed before abortion occurs and culturing it to maturity. One example of this capability is the new Nerica rice variety that combines the best of Asian and African traits; it has been released recently in West Africa and appears to potentially offer up to 50% increases in yields over local varieties. Conventional breeding, without the embryo rescue biotechnology component, could not have delivered this product.