Contents - Faperta

422 Biotechnological Approaches for Pest Management and Ecological Sustainability
Gene Flow and Aquatic Environments
Transgenic crops are intended to reduce the types and quantities of pesticides necessary
for production of food, feed, and fi ber. Because of decreased reliance on chemical pesticides,
extensive cultivation of transgenic crops may result in improved water quality and
related ecosystems (Estes et al., 2001). A simple model has been proposed to examine the
displacement of insecticides by growing Bt cotton and Bt maize, and assess the impact on
drinking water quality. Based on this module, all the transgenic cropping systems resulted
in signifi cantly lower pesticide concentrations in ground and surface waters, thereby
reducing whatever impacts these products have on drinking water quality and the aquatic
environments.
Management of Gene Flow
There are many ways to prevent transgene introgression from crops to other varieties or to
related weeds or wild species (containment strategies), as well as to preclude the impact
should containment fail (mitigation strategies) (Gressel and Al Ahmad, 2003). The needs are
most acute with rice and sunfl owers, which have conspecifi c weeds, and with oilseed rape,
sorghum, and barley, which have closely related weeds. Containment and mitigation are
critical for pharmaceutical crops, where gene fl ow from the crop to edible varieties must be
precluded. Some gene fl ow (leakage) is inevitable with all containment mechanisms, and
once leaked, could then move through populations of undesired species, unless their spread
is mitigated. Leakage even occurs with chloroplast-encoded genes. A mechanism for mitigation
has been proposed where the primary transgene (herbicide resistance, etc.) is tandemly
coupled with fl anking genes that could be desirable or neutral to the crop, but unfi t
for the rare weed into which the gene introgresses. Mitigator traits include dwarfi ng, nonbolting,
no secondary dormancy, no seed shattering, and poor seed viability, depending on
the crop. Hybrids with the tandem construct are unable to reach maturity when grown
interspersed with the wild type. Such mitigation should greatly decrease the risk of transgene
movement when coupled with containment technologies, allowing cultivation of
transgenic crops having related weeds. As the number of transgenic crops being released for
cultivation is increasing, the problem of monitoring such genes also increases geometrically.
There is a need for a uniform system, where a small piece of noncoding DNA carrying
an assigned variable region is used to mark transgenic crops, allowing monitoring.
Use of Taxonomic Information
Systematic studies can be used for managing gene fl ow as they provide important information
on breeding system and sexual compatibility of related species, likelihood of such
crosses, and the factors affecting the successful production and survival of hybrid progeny
(Warwick, 1997). They also provide information on the distribution of crop and wild relatives,
their ecological requirements, status in natural environments, and if weedy, the areas
of infestation and patterns of spread. This information is needed on a case-by-case basis
for evaluation of both the likelihood of escape of a transgenic trait and the environmental
impact, if such an escape occurs.