Modern biotechnology has been applied in agriculture to develop varieties of crops with new traits that are bringing benefits for farmers. The first generation of crops developed through modern biotechnology since 1996 and their use has grown from 1.7 ha in a few countries to 181.5 Million hectares in 28 countries in 2015. The technology has found a number of applications in agriculture.
- Production of crops that are resistant to specific insect pests: Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium that produces proteins that show specific toxicity to some insects. Bt has been used as an insecticide spray dust to protect crops from the European corn borer for some time. The use of Bt in the form of a spray has been limited by the fact the bacteria are unable to survive for long on the surface of the crop. Another consideration is that for pests that start their life cycle inside the plant, Bt has limited effectiveness. Scientists are using rDNA technology to insert the gene that codes for these insecticidal proteins into crops to give them resistance to specific pests such as cutworm in maize and bollworms in cotton.
- Bt produces two classes of proteins that show toxicity to specifc insects. Cytolysins (Cyt) are toxic to insect in the orders Coleoptera (i.e. beetles) and Diptera (i.e. flies). Crystal proteins (Cry) are toxic towards insects in the order Lepidoptera (moths and butterflies). Genes that code for various Cry proteins have been inserted into some crops to give them resistance to specific insect pests.
- Production of crops that are tolerant to herbicides: The broad spectrum herbicide glyphosate (Roundup) acts by blocking a step in the synthesis of some amino acids which are required for growth and development of the plant. Roundup acts by binding to the enzyme 5-enolpyruvyl-shikimate synthase (EPSPS) and thus blocks its action. Agrobacterium, another soil bacterium, is not affected by Roundup because it uses a slightly different EPSPS. The gene that codes for EPSPS in Agrobacterium has been inserted into various crops to give them resistance to Roundup. Resistance in this case results from use of an alternative pathway for synthesis of these amino acids.
Liberty (Glufosinate ammonium) is another broad spectrum herbicide that has been used in a similar manner. Liberty acts by binding to the enzyme Glutamine synthetase which is involved in synthesis of some amino acids as well as recycling ammonium. A gene that codes for Phosphinothricin acetyl transferase (PAT) confers resistance to Liberty. This enzyme destroys Liberty thus rendering it inactive.
- Manipulation of the breeding system: Modern biotechnology has also been used to insert genes that cause male sterility. For example, the barnase gene derived from Bacillus amyloliquefaciens has been inserted into plants. The gene codes for the barnase ribonuclease (RNAse) enzyme which interferes with Ribonucleic acid (RNA) in the cells of the anthers causing sterility.
- Modification of product quality: Genetic modification has also been used to alter product quality in some crops. In oil crops, the technology is being used to alter the oil content. An example here is increasing the lauric acid content in rape seed oil.
- Tolerance to specific diseases: Modern biotechnology has been used to develop crops that are resistant to specific diseases. Examples here include:
- Carica papaya (pawpaw) developed for resistance to Papaya ringspot virus;
- Plum (Prunus domestica) developed for resistance to Plum Pox Virus
- Tomato and Sweet pepper developed for resistance to cucumber mosaic cucumovirus (CMV).
- Tolerance to biotic stress: Various projects aimed at developing crops that are tolerant to biotic stress (e.g. drought tolerance) in maize and other crops are ongoing. An example here is DroughtGard™ Maize developed by Monsanto. Efforts aimed at developing drought tolerant maize under the Water Efficient Maize for Africa (WEMA).