Plant breeding
An introduction to plant breeding.
Simple articles that explain what plant breeding is and why it is necessary, the underlying principles of plant breeding and a number of important modern techniques that have contributed to the crops we have today.
Pushing the boundaries
As our knowledge about plants and DNA has increased a number of techniques have been developed to complement the basic techniques of plant breeding outlined above.
Two examples below show how plant breeders have tried to increase the variety of traits they can introduce into crop plants by different forms.
1) Embryo rescue (Widening the net)
Frustratingly for plant breeders the large majority of potentially useful traits found in nature cannot be bred into crop plants as they exist in plants not sufficiently closely related to allow successful breeding.
Although (unlike the large majority of animals) plants are often able to breed with other species, the more distantly related the plants the more unlikely it is that any breeding attempt will be successful. In some cases although fertilisation is successful the embryo created is unable to develop into a viable seed.
Embryo rescue is the use of carefully controlled lab conditions to enable plant embryos that might otherwise die to develop fully. This increases the diversity of plants that a breeder can cross a particular plant with and so increases the potential new traits that could be bred in to it.
Plant culturing in the laboratory. By carefully controlling conditions plant breeders can get embryos to develop that might otherwise die.
Photographer: Seb951. Copyright: GFDL
The procedure
Essentially the embryo is removed from the plant and placed in a tissue culture that matches its nutritional requirements, in this way the development of the embryo is encouraged and an embryo that might not have survived in a wild environment can germinate successfully.
The results
A variety of rice called New Rice for Africa was developed in the 90s using Embryo Rescue. The technique allowed scientists to breed a high yielding Asian species of rice with a native rice species that was suited to African conditions, combining the benefits of both.
In general Embryo Rescue is a vital component of much modern plant breeding.
2) Mutagenesis (New variety)
Mutagenesis is a way of introducing new variability into crop plants by encouraging mutation of the DNA - this may result in beneficial traits.
What are mutations?
Our DNA is a long code that acts as a set of instructions for making proteins. Changes in this DNA code are called mutations. Mutations are normally bad for an organism (it is mutations for example that cause cancer). Occasionally however, they can be beneficial. Mutations are a natural occurrence; they are the origin of all variation in life. If DNA was not susceptible to mutation, life as we know it would never have evolved.
How do mutations occur?
Mutations occur naturally all the time, mainly as a result of errors in copying DNA. A mutagen is something that increases the rate of mutation (the rate of mutation is how often a mutation will occur in a certain amount of time). A mutagen can be: chemical, for example smoke. This is why smoking increases your chance of developing lung cancer. physical, such as UV rays. This is why sunbathing increases your chance of developing skin cancer.
X-rays increase the rate of DNA mutation. That is why you are often protected by lead sheets when you have an X-ray at the hospital. X-rays can't penetrate through lead so these shield you from the harmful effects.
Photographer: W. Conrad. Copyright: free
Mutations and plant breeding
As we said above mutations are usually bad for an organism but sometimes they can be beneficial. New mutations can result in a plant having properties that weren't previously found anywhere in nature. This makes them very valuable to plant breeders.
Researchers had discovered back in the 1920s that blasting plants with X-rays increased the number of mutations that occurred.
After the Second World War 'mutation breeding' played an important role in developing new varieties of crops. Researchers used radiation and chemicals to encourage mutation in the DNA of plant cells and, as these cells grew into plants, looked for new traits that would be useful to farmers.
