TRANSGENIC PLANTS AND THE ENVIRONMENT
Modern agriculture is intrinsically destructive of the environment. It is particularly destructive of biological diversity, notably when practiced in a very resource-inefficient way, or when it applies technologies that are not adapted to environmental features (soils, slopes, climatic regions) of a particular area. This is true of both small-scale and large-scale agriculture. The widespread application of conventional agricultural technologies such as herbicides, pesticides, fertilizers and tillage has resulted in severe environmental damage in many parts of the world. Thus the environmental risks of new GM technologies need to be considered in the light of the risks of continuing to use conventional technologies and other commonly used farming techniques.
Some agricultural practices in parts of the developing world maintain biological diversity. This is achieved by simultaneously cultivating several varieties of a crop and mixing them with other secondary crops, thus maintaining a highly diverse community of plants (Toledo et al. 1995; Nations and Nigh 1981; Whitmore and Turner 1992).
Most of the environmental concerns about GM technology in plants have derived from the possibility of gene flow to close relatives of the transgenic plant, the possible undesirable effects of the exotic genes or traits (e.g., insect resistance or herbicide tolerance), and the possible effect on non-target organisms.
As with the development of any new technology, a careful approach is warranted before development of a commercial product.
It must be shown that the potential impact of a transgenic plant has been carefully analyzed and that if it is not neutral or innocuous, it is preferable to the impact of the conventional agricultural technologies that it is designed to replace (Campbell and Cooke 1993; May 1999; Toledo et al. 1995).
Given the limited use of transgenic plants worldwide and the relatively constrained geographic and ecological conditions of their release, concrete information about their actual effects on the environment and on biological diversity is still very sparse. As a consequence there is no consensus as to the seriousness, or even the existence, of any potential environmental harm from GM technology. There is therefore a need for a thorough risk assessment of likely consequences at an early stage in the development of all transgenic plant varieties, as well as for a monitoring system to evaluate these risks in subsequent field tests and releases.
Risk assessments need base line information, including the biology of the species, its ecology and the identification of related species, the new traits resulting from GM technology, and relevant ecological data about the site(s) in which the transgenic plant is intended to be released. This information can be very difficult to obtain in highly diverse environments. Centers of origin or diversity of cultivated plants should receive careful consideration because there will be many wild relatives to which the new traits could be transferred (Ellstrand et al. 1999; Mikkelsen et al. 1996; Scheffler et al. 1993; Van Raamsdonk and Schouten 1997). For special environments, transgenic plants can be developed using technologies that minimise the possibilities of gene flow via pollen and its effects on wild relatives, through the use of male sterility methods or maternal inheritance resulting from chloroplast transformation (Daniell 1999; Daniell et al. 1998; Scott and Wilkinson 1999).
Studies of gene transfer from conventional and transgenic plants to wild relatives and other plants in the ecosystem have so far concentrated on species of economic importance such as wheat, oilseed rape and barley. A virtual absence of data, particularly for
species like maize, imposes the need to carefully and continuously monitor any possible effects of novel transgenic plants in the field (Hokanson et al. 1997; Daniell et al. 1998). In addition there is a continued need for research on the rates of gene transfer from traditional crops to indigenous species (Ellstrand et al. 1999).
When monitoring a small-scale pilot release of a transgenic crop the following issues should be considered in addition to any concerns specific to a particular local environment:
Does the existence of a transgenic plant with resistance for a particular pest or disease exacerbate the emergence of new resistant pests or diseases, and is this problem worse than that with the traditional alternative? (Riddick and Barbosa 1998; Hillbeck et al. 1998; Birch et al. 1999).
If traits (e.g., salt tolerance, disease resistance, etc.) are transferred to wild varieties, is there an expansion in the niche of these species that may result in the suppression of biological diversity in the surrounding areas?
Would the widespread adoption of stress-tolerant plants promote a considerable increase in the use of land where formerly agriculture could not be practiced in a way that destroys valuable natural ecosystems?
The risk assessments performed should be standardized for plants new to an environment. Most nations already have procedures for the approval and local release of new varieties of crop plants. Although these assessments are based primarily on the agronomic performance of the new variety compared with existing varieties, this approval process could serve as the beginning or model for a more formal risk assessment process to investigate the potential environmental impact of the new varieties, including those with transgenes.
Historically, both poverty and structural change in rural areas have resulted in severe environmental deterioration. The
adoption of modern biotechnology should not accelerate this deterioration. It should instead be used in a way that reduces poverty and its deleterious effects on the environment.
We recommend that: (i) coordinated efforts be undertaken to investigate the potential environmental effects, both positive and negative, of transgenic plant technologies in their specific applications; (ii) all environmental effects should be assessed against the background of effects from conventional agricultural practices currently in use in places for which the transgenic crop has been developed or grown; and (iii) in situ and ex situ conservation of genetic resources for agriculture should be promoted that will guarantee the widespread availability of both conventional and transgenic varieties as germplasm for future plant breeding.