35.7:
Plant Breeding and Biotechnology
Plant breeding is a science that creates crops with desirable traits such as high-yields, improved taste, and increased nutrition.
Such traits often evolve naturally from spontaneous mutations. However, this process is slow, and breeders often want particular combinations of traits that do not occur in nature.
Farmers can identify a desired trait in a wild species, and cross that plant with a domesticated plant variety. In such a cross, however, there is an equal chance that the progeny inherits undesired traits from the wild species.
The use of biotechnology is beneficial for gene transfer in distantly related crops such as rice and daffodils that have many intermediate species and an extinct common ancestor.
Traditionally, plant breeders would need multiple crosses laid over several centuries to transfer the necessary traits in the progeny. In contrast, modern biotechnologists can bypass multiple crosses to transfer the desired gene between these plants.
Biotechnology facilitates gene transfer between two different species, resulting in a unique phenotype.
For example, the broad-spectrum herbicide glyphosate inhibits a critical enzyme called EPSPS in plants.
Scientists created herbicide-tolerant maize by directly transferring a gene from the soil bacteria Agrobacterium to maize plants.
Crops that contain the bacterial gene for this enzyme are immune to the inhibitory effect of the herbicide.
This genetic modification allows farmers to spray their fields with herbicide, killing competitor weeds that reduce yield while leaving the crop unaffected.
35.7:
Plant Breeding and Biotechnology
Crop cultivation has a long history in human civilization, with records showing the cultivation of cereal plants beginning at around 8000 BC. This early plant breeding was developed primarily to provide a steady supply of food.
As humans' understanding of genetics advanced, improved crop varieties could be achieved more quickly. Artificial selection could be more directed, and crop varieties enhanced for favorable traits more quickly to produce better, more robust, or more palatable plants.
However, traditional techniques for breeding plants are slow and do not always produce the desired crop varieties. Later, biotechnological tools made it easier to engineer desired traits into plants that are otherwise difficult to breed using traditional methods. For example, improving nutritional deficiency in plants is difficult via artificial selection, and particularly challenging for vitamin A and iron. Rice, for example, does not contain genes for beta carotene, which is a vitamin A precursor. However, it does contain genes for the compound geranylgeranyl pyrophosphate, which can be sequentially converted to beta carotene using four enzymes. Rice was engineered using genes for two enzymes derived from daffodils, and the remaining two enzymes from the bacteria Erwinia uredovora. The resulting crop is known as golden rice. Because rice is the staple food of more than half of the world, bioengineered crops such as these could potentially play a role in preventing blindness among children caused by vitamin A deficiency, or improving the health of rice-reliant countries.
Many commonly grown crop plants now have some degree of genetic modification introduced using biotechnology. For example, maize, papaya, and many potato varieties have been modified for herbicide, disease, or pest resistance. Genetic modification can even be carried out to reduce allergen production, which is the case in soybeans.
Suggested Reading
Jauhar, P. P. (2006). Modern biotechnology as an integral supplement to conventional plant breeding: the prospects and challenges. Crop science. 46 (4), 1841-1859. [Source]