Food Safety - The Oxford Topic of Food, Politics, and Society - page 590

With the development of modern plant breeding over the last 200 years a number
of methods were introduced that were intended to increase the rate of mutation and
expand the spectrum of changes that were possible (Chrispeels and Sadava, 2003).
Radiation and chemicals that could induce alterations in the genomic DNA sequence
such as point mutations, frame shift mutations, duplications, insertions, and deletions
were introduced (Parrott, 2005; Weber et al., 2012). Mutagenesis accelerated the pro-
duction of improved varieties and allowed the creation of new varieties and species.
Methods for making wide-crosses that allowed interspecific gene exchange between
species that would not normally mate productively were also introduced.
It is worth noting that these and other methods used for breeding plants all depend on
the production of unknown and uncharacterized changes in DNA. To restate the obvi-
ous, all plant breeding depends on genetic modification. . Until recently, methods did not
exist with which the nature of the mutations that lead to changes in phenotype could be
assessed. Over the millennia, breeding has greatly increased the variety and productiv-
ity of crops as well as their resistance to various pests and diseases. Plant breeding also
has proven to be quite safe, although a handful of examples of new varieties that pro-
duced adverse effects have been identified (Cellini et al., 2004). A potato variety that
produced unacceptably high levels of toxic glycoalkaloids and a celery variety that pro-
duced high levels of toxic furanocoumarins are two examples.
Successful as traditional methods of plant breeding using passive selection, muta-
genesis, and crossing have been, the methods suffer from a number of shortcomings
and challenges. The methods are time consuming, labor intensive, and can be expensive
over time as years of crossing, back-crossing, and selection may be required to intro-
duce a new variety. Owing to the percentage of progeny that contain unintended and
undesirable effects, or which lack desired phenotypes, tens of thousands of candidate
plants may need to be cultured and evaluated (Cellini et al., 2004; König et al., 2004).
Traditional breeding and breeding using biotechnology are alike in that they rely on
crossing and selection to sort out unintended changes. Traditional breeders can spend
many years searching for a sexually compatible plant that has a desired trait or on muta-
genesis protocols designed to produce desired novel traits. Some targeted phenotypes
have proven to be thus far impossible to achieve by conventional breeding methods,
despite the introduction of sophisticated screening methods designed to accelerate the
process and increase the chances of success (e.g., marker assisted selection, identifica-
tion of quality trait loci, and various automated screening systems). The critical need for
development of crops enabled to withstand the biotic and abiotic stresses that are being
imposed by rapid climate change is a task to find which of the rapid, precise, and reliable
breeding methods made available using modern biotechnology are well-suited (Newell
McGloughlin, this volume).
Methods for the transformation of plants in vitro using rDNA emerged in the 1980s.
These methods are, in principle, relatively simple (Chrispeels and Sadava, 2003). A target
gene that encodes a desired trait is isolated. Any living organism can be used as a source
since all living cells use DNA as their genetic code and the code is processed in exactly
the same way in all organisms. Although most species may be sexually incompatible,