Friday, May 23, 2003

John M. Burke and Loren H. Rieseberg, "Fitness Effects of Transgenic Disease Resistance in Sunflowers," Science 300 (2003), p. 1250:
Fears about transgene escape have focused attention on the potential for hybridization between crops and their wild relatives. Although transgenes will often escape from cultivation (1), their rate of spread will be mainly governed by their fitness effects, not the migration rate (2). Thus, only highly advantageous transgenes will spread rapidly enough to have a substantial ecological impact. Therefore, research on the risks associated with transgene escape should focus on the fitness effects of the gene(s) in question....

Presence or absence of the OxOx transgene had no effect on seed output (P = 0.25), indicating that there was no cost of resistance in the absence of a pathogen challenge. In terms of infection rates, the OxOx transgene did provide protection against white mold (P = 0.002). The transgene did not, however, have any effect on seed output after inoculation (P = 0.84). Though the transgene provided protection against white mold infection, it had no effect on reproductive output. This result has a simple explanation: Variation in the likelihood of infection was offset by variation in the severity of infection. In California, where the transgene provided the most protection against infection, disease onset had no effect on seed output. In contrast, white mold infection caused a severe decline in seed output in Indiana, but infection rates were unaffected by the transgene. Thus, the transgene had a significant effect on the likelihood of infection, and infection had a negative effect on seed output (P 0.0001), but the disease effect varied across locations (P = 0.001), nullifying any advantage of the transgene....

Our results suggest that the OxOx transgene will do little more than diffuse neutrally after its escape....

Future studies assessing the environmental impact of transgenes should not only be replicated over space and time, but should also examine the effects of genetic background and environmental stresses. Regardless of the form of future research, an informed judgment of the risks and benefits of genetic modification on a case-by-case basis is preferable to either the dismissal of transgenic approaches entirely, or the introduction of transgenic crops in the absence of appropriate scientific scrutiny.


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