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