The most prominent examples include genes that make the crops resistance to insects, viruses and herbicides.
Herbicide tolerance. The first GM characteristic to be widely adopted was resistance to a herbicide called Roundup (or glyphosate) in soybeans. There are also varieties of herbicide tolerant crops produced by non-GM methods. Resistance to these types of broad herbicide – which would usually kill both weeds and crops – means that efficient weed control is possible because the herbicide can be applied while the crop is growing, without damaging the crop. Without herbicide tolerant crops, a range of different types of herbicides might be needed to clear out all the weeds before planting the crop. Another benefit of herbicide tolerant crops is that they can be planted into a weedy field, because the weeds can be controlled with herbicide. This reduces the need for ploughing, which means less soil erosion. Disadvantages are that the farmer must buy the proprietary herbicide to match the herbicide tolerant crop, and this type of control runs counter to attempts to reduce the dependency of agriculture on chemical inputs.
Insect resistance. The bacterium Bacillus thuringiensis (Bt) produces a group of proteins known as the Bt toxin, which are toxic for certain insects, but do not harm beneficial insects or other animals. Bacillus thuringiensis is used as an insecticide spray in organic farming. Genes for several Bt toxins have been introduced into many crops by GM. For example over 90% of the cotton planted in the USA, India, China, Australia and South Africa are GM varieties containing Bt toxin genes. Over the last 20 years, it is estimated that the application of 450,000 tons of insecticide has been avoided due to the use of Bt toxin genes in crops.
Bacillus thuringiensis is used as an insecticide spray in organic farming. Genes for several Bt toxins have been introduced into many crops by GM.
Virus resistance. GM has been used to resurrect the papaya industry of Hawaii as papaya ringspot virus almost destroyed its plantations in the 1990s. There are no known papaya varieties with natural resistance to this virus but by adding a gene to the papaya from the virus itself, resistant papaya strains were created. Today 77% of Hawaiian papaya farmers grow GM papaya.
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