Many genetically modified plants are currently used in agriculture. These plants fall can be divided into different categories based on the type of advantage conveyed by the modification.
Insect resistance is a highly desirable trait for agriculture. Damage to crops from pests lowers yields and increases the cost of production. Pesticides are commonly used to protect plants by killing the insects. While pesticides can be very effective, some can be toxic to non-pest insect species or other animals, including humans. The manufacturing, transportation and application of pesticides costs money and contributes significantly to the cost of production. To reduce or eliminate the need for application of pesticide, some plants have been genetically engineered to produce proteins that are selectively harmful to insect pests. An example is Bt plants, which contain a gene from the bacteria Bacillus thuringiensis which leads to the production of a protein which selectively kills caterpillars.
Herbicides are chemicals which kill weed species that compete with planted crops for water, sun, space and nutrients. If not controlled, weed species can significantly reduce the agricultural yields. Herbicides must kill weed species but have no effect on the crop or other organisms. They must also be cheap to manufacture in order to be economical. Because weed species share many biological processes with crop species, it can be difficult to identify a herbicide which has all of these characteristics. To help with this problem, genetic engineering has been used to provide crop species with resistance to specific chemical herbicides. An example is crops identified as "Roundup Ready". Roundup Ready crops have a gene that allows them to grow in the presence of the herbicide Roundup.
Improved Nutrition Content
Humans are incapable of producing certain vitamins which are essential for metabolic function. These vitamins must be consumed in the diet. Fruits and leafy vegetables which often contain many of these vitamins can be difficult to grow and are consequently more expensive. Key cereal crops, such as rice, which support a significant percentage of the worlds population lack some of these key vitamins. The lack of these vitamins in diets composed primarily of cereal grains causes serious disease and disability. To remedy this, genetic engineering has been used to improve the nutritional content of cereal grains. An example is Golden Rice. Several genes have been introduced into Golden Rice that cause it to accumulate significant amounts of vitamin A, giving the grains a yellow/orange appearance. While not currently in widespread use, Golden Rice offers the potential to reduce disease caused by vitamin A deficiency which is a serious problem for people whom depend upon rice for much of their diets.
Plants face diseases just as animals do. These diseases can be difficult to control and inflect widespread damage to crops. Modern agricultural systems which involve very large fields and low genetic diversity of crops can be particularly vulnerable. Traditional breeding approaches can be used to incorporate disease resistant genes into crop cultivars. However, traditional breeding can take several years or more to produce resistant and agriculturally viable plants. Genetic engineering can be used to allow the direct insertion of disease resistance genes into the crop genome, potentially allowing for faster production of resistant plants. Furthermore, while breeding approaches rely upon the disease resistant allele being present somewhere in the species genetic diversity, genetic engineering approaches allow for any gene to be used.
Storage and distribution are major challenges for some crop species. Some crops need to be transported far from where they are grown or stored for prolonged periods of time to ensure supply the entire year. Crops that are damaged easily or ripen quickly are difficult (and therefore expensive) to store and transport. Refrigeration, careful handling procedures, and/or chemicals are sometimes used to slow ripening and protect produce during storage and transport. These add economic and environment costs to food production and have a major impact on the price, availability, and quality of produce. Ripening, firmness, bruising, browning, and size are all under biological control. Genetic engineering offers a tool to help understand these processes and to alter existing crops to improve the post-harvest characteristics of the fruit. The Flavr Savr tomato and the Arctic Apple are both examples in which enzymes involved in ripening and browning, respectively, have been reduced to create a fruit with more desirable characteristics.