Traditional breeding and selection methods have been used successfully for years. However, the process is very time-consuming, sometimes requiring up to 20 years to develop a new plant variety. This is because traditional methods are random and imprecise, involving the passing of thousands of genes with each generation. It is difficult to guarantee that the undesirable traits will not be passed along with the desired traits and to screen for all possible trait combinations. This results in the tedious effort of selecting out those varieties that are most desirable and continuing the process until the final plant variety is achieved.
New biotechnology techniques — specifically genetic engineering — are an extension of older techniques and apply the same principles. However, new biotechnology is more precise and direct than traditional breeding and selection and allows for the transfer of genes from one species or genus to another. This is because new biotechnology allows for the transfer of a single genetic trait — rather than thousands as in traditional breeding — in a predictable and controllable manner. A wider range of new traits can be introduced into food without the introduction of extraneous and undesirable genes and in a more timely fashion.
Genetically modified varieties of papaya, potato, squash and tomato have been marketed internationally. The Rainbow variety of papaya from Hawaii was genetically modified to resist a virus that was destroying the crop.
A WHO report on modern food biotechnology can be found here: http://www.who.int/foodsafety/publications/biotech/biotech_en.pdf