One of the earliest methods to help plants survive disease and insect infestation was to cross-breed plants that could survive these assaults with plants that could not in the hopes of passing on the 'resistant' gene (see Limits of Traditional Breeding). While studying a plant disease named crown gall, which is caused by a bacterium, scientists discovered that the disease spread in plants by transference of genetic material from the bacterium into the plant cells (see Taming the Crown Gall). This led to the development of techniques to cut and splice DNA and introduce genes into plants. However, isolating the genes responsible for a specific desired trait was another matter.

Researchers looking for a way to help plants resist pests, began by studying a bacterium called Bacillus thuringiensis (Bt), which killed silkworms. Scientists examined how Bt kills insects and realized that it produced proteins that were toxic to the insects. By the late 1980s, scientists had isolated several genes responsible for producing proteins toxic to specific insects (see The Quest for Desirable Genes). In 1987, an initial attempt to splice Bt genes into plants to make them resistant to insects failed. Scientists quickly realized that they needed to alter the gene slightly to make it useable in the plants. By 1990, Bt cotton plants had been genetically engineered to produce enough Bt toxin to be protective against insects (see Genetic Stumbling Block). Moving on from resistance to pests, scientists were able to pinpoint and clone several genes that made plants resistant to bacterial, viral, and fungal infections (see Viral Resistance). The next step was to develop methods that could kill weeds while leaving the desired crop unaffected (see Herbicide Resistance). The possibilities of bioengineering are many, including creating crop plants that are tastier or more nutritious (see New Possibilities on the Horizon).

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