The double helix architecture of DNA was elucidated in 1953. Twenty
years later, in 1973, the discovery of restriction enzymes helped to
create recombi- nant DNA molecules in vitro. The implications of these
powerful and novel methods of molecular biology, and their potential in
the genetic manipulation and improvement of microbes, plants and
animals, became increasingly evi- dent, and led to the birth of modern
biotechnology. The first transgenic plants in which a bacterial gene had
been stably integrated were produced in 1983, and by 1993 transgenic
plants had been produced in all major crop species, including the
cereals and the legumes. These remarkable achieve- ments have resulted
in the production of crops that are resistant to potent but
environmentally safe herbicides, or to viral pathogens and insect pests.
In other instances genes have been introduced that delay fruit ripening,
or increase starch content, or cause male sterility. Most of these
manipulations are based on the introduction of a single gene - generally
of bacterial origi- that regulates an important monogenic trait, into
the crop of choice. Many of the engineered crops are now under field
trials and are expected to be commercially produced within the next few
years. The early successes in plant biotechnology led to the realization
that further molecular improvement of plants will require a thorough
understanding of the molecular basis of plant development, and the
identification and charac- terization of genes that regulate
agronomically important multi genic traits.