Bt Brinjal The scope and adequacy of the GEAC environmental risk assessment

24 Bt Brinjal: The GEAC environmental risk assessmentadaptation or introgression can occur after a weak F1 generation (Mikkelsen et al. 1996, Warwick et al. 2007).Even if Bt brinjal cannot revert to feral forms, gene flow from Bt brinjal to wild populations of S. melongena could resultin significant risks. EC-II reported published outcrossing estimates of 0.2-48% for brinjal in various environments. Thusgene flow from brinjal can be low or high, and the factors determining these rates are poorly known. The Dossier presentsinformation from one (or possibly two; the details were not clear) outcrossing experiment with Bt brinjal conducted during2002-3 (Volume 5). The Supplemental Materials present the results of an additional gene flow experiment conducted during2009 conducted at two sites (IIVR 2009).The level of gene flow from Bt brinjal that was measured was probably close to 1% or less in the 2002-3 experiment (theactual value is not reported). During 2009, it was 0.43% or 0.85% at the two sites. EC-II used these low measured rates inits assessment and ignored the higher rates from the published literature. Gene flow can vary substantially from experimentto experiment, depending on a number of factors (Box 3), so these data provide only weak support for low gene flow from Btbrinjal. Thus, it is possible that the rate of gene flow from Bt brinjal will be low, but it is also possible that the rate of gene flowwill be substantially higher under normal conditions of cultivation.Indeed, based on the sampling design and published literature, it is likely that the gene flow distance was underestimated inthe experiments described in the Dossier and Supplemental Materials. Gene flow up to 30 meters was reported in the Dossier(Vol. 5), but the farthest distance examined was 50 meters during 2002-3. The 2009 experiments made observations up to 300meters away, but sampling was intensive only in the first 30 meters (1200 plants per site = 400 plants per 10 meters of distancefrom Bt brinjal). After 30 meters, fewer plants were sampled per location with a much lower density of sampling. Previousstudies on bee-pollinated plants demonstrate that gene flow distances can be hundreds of meters and even several kilometers(St. Amand et al. 2000, Rieger et al. 2002, Pasquet et al. 2008). Thus, it is possible that the distance of gene flow is farther thanconsidered.What are significant and insignificant levels of gene flow? Although this is a challenging problem, rates as low as 0.5% canbe biologically significant. If the trait has an advantage in the recipient population and/or the trait is recurrently introduced(Haygood et al. 2003), such “low” rates of gene flow could result in rapid introgression in the recipient population. Thus, eventhe experimentally measured rates of gene flow could be biologically significant, and EC-II is incorrect to assert that “low” ratesof gene flow are sufficient by themselves to conclude that there are low gene flow risks.Needed Experiments and ObservationsIt could be useful to conduct additional outcrossing experiments to establish that gene flow does occur at evolutionarysignificant rates. These outcrossing experiments should be conducted under conditions facilitating gene flow, examiningdistances farther than 30 meters with larger sample sizes or alternate methodologies (see St. Amand et al. 2000, Rieger et al.2002, Pasquet et al. 2008). The densities of wild bees that are capable of pollinating brinjal, the occurrence of bee visitationbetween source and recipient brinjal, and the overlap of flowering times between source and recipient brinjal should bemonitored during these experiments.However, conducting these additional gene flow experiments could be a waste of time, unless it is possible to estimate thetrue mean gene flow rate and its variance. Such work would take a considerable amount of time and effort, because there aremany experimental factors that bias estimates downward. A simpler alternative might be to estimate a reasonable worst-casevalue for gene flow and evaluate the consequences stemming from such a worst-case estimate. It is a standard method of riskassessment to evaluate worst-case scenarios because they provide considerable support to a risk assessment when the risks andeffects are found to be low even under the worst-case assumptions.A more productive experimental approach for risk assessment would be to assume that intraspecific gene flow is sufficientlyhigh that risks could possibly occur, and focus efforts on evaluating the consequences of gene flow. As noted above, rathersmall amounts of gene flow can be significant, and the present data are insufficient to conclude that the rates of gene flow are solow that there are no significant risks. In addition, the extant scientific literature on gene flow (Ellstrand 2003) also suggests thatit might be reasonable to conclude that intraspecific gene flow occurs at evolutionarily significant rates.1) Fitness of intraspecific hybrids and backcrosses. Risk assessment research should shift to investigate the consequences of