Contents - Faperta

420 Biotechnological Approaches for Pest Management and Ecological Sustainability
diffi cult-to-control insect pests and diseases than that experienced by traditional breeding
in the past.
Gene Flow and Genetic Purity of Crops
One of the concerns about the use of transgenic crops involves the possibility that the
transgene will move to the nontransgenic crops, resulting in situations that are either
undesirable, for example, presence of Starlink maize (cry9C) gene in nontransgenic maize
(Dorey, 2000). Inadvertent mixing of transgenic and nontransgenic crops through pollen
dispersal and seed is of particular concern for the organic farming, for both economic and
emotional reasons (Dale, 1994; Moyes and Dale, 1999). In such cases, liability can become
a major issue (Moeller, 2001). Genetic modifi cation does not change the frequency with
which admixture of genetic material occurs. However, modern molecular techniques can
detect low levels of genetic mixing. Maintenance of seed quality is an important issue in
modern agriculture. For commercial cultivars of both nontransgenic and transgenic crops,
the genetic purity of seed represents the homogeneity of a single recognized cultivar or its
trueness to type (Briggs and Knowles, 1967). Strict management guidelines have been
imposed to allow multiplication of suffi cient amounts of seed for sowing large areas with
commercial crops (Condon, 2001). Without imposing seed production guidelines to maintain
the genetic purity of certifi ed seed, a cultivar may quickly deteriorate and become
unrecognizable due to factors such as mechanical admixtures, gene fl ow through natural
crossing, mutations, random genetic drift, or selection pressure.
Monitoring of genetic purity and seed certifi cation is based on the phenotype of the plants,
and on observing the plant characteristics and ensuring that they match the standards in
the cultivar descriptions. The international seed purity standards require the incidence of
admixture and genetic instability of cultivars to be maintained above a minimal threshold
value that depends on the reproductive characteristics of each crop. Tolerance of a low level
of gene transfer by pollen is considered an inherent component of modern day agriculture,
especially when growing commercial crops for food production. International seed certifi
cation standards require genetic purity levels of 98% to 99% (Leask, 2000). These purity
levels represent the compromise between the stringency imposed on seed production, and
the market need for affordable seed, especially for crops grown over large areas.
New molecular and biochemical techniques such as polymerase chain reaction (PCR)
and enzyme-linked immunosorbent assay (ELISA) allow for more precise testing. Such
diagnostic tests allow the testing of a particular gene (or allele) or products of a particular
gene (or allele) to be measured. Consequently, cultivar purity can now be estimated on the
basis of genotype, rather than on phenotype. An additional advantage is that the environment
can substantially infl uence the latter. Sophisticated diagnostic tests based on genotype
reveal higher frequencies of occurrence of adventitious genetic material in commercial
seed than previously anticipated. Existing cultivars that are widely used and traded, and
thought to be homogeneous, pure, and stable at the phenotypic level, may actually contain
considerable variability at the genotypic level. This will present new challenges for commercial
seed production, and will require a thorough reassessment of existing quality
control paradigms, given the new opportunities to measure genetic purity.
If adventitious genetic content in commercial seed of nontransgenic crops is common,
given current seed certifi cation schemes, the appearance of transgenic material in