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GENE FLOW, CONTAMINATION & FIELD TRIALS’ RISK22. Legere A (2005) : Riks and consequences of gene flow from herbicideresistantcrops: canola (Brassica napus L) as a case study. Pest Manag.Sci. 61 (3) : 292-300.Data from the literature and recent experiments with herbicide-resistant (HR)canola (Brassica napus L) repeatedly confirm that genes and transgenes willflow and hybrids will form if certain conditions are met. These include sympatrywith a compatible relative (weedy, wild or crop), synchrony of flowering, successfulfertilization and viable offspring. The chance of these events occurring is real;however, it is generally low and varies with species and circumstances. Plants ofthe same species (non-transgenic or with a different HR transgene) inneighbouring fields may inherit the new HR gene, potentially generating plantswith single and multiple HR. For canola, seed losses at harvest and secondarydormancy ensures the persistence over time of the HR trait(s) in the seed bank,and the potential presence of crop volunteers in subsequent crops. Althoughcanola has many wild/weedy relatives, the risk of gene flow is quite low for mostof these species, except with Brassica rapa L. Introgression of genes andtransgenes in B rapa populations occurs with apparently little or no fitness costs.Consequences of HR canola gene flow for the agro-ecosystem includecontamination of seed lots, potentially more complex and costly control strategy,and limitations in cropping system design. Consequences for non-agriculturalhabitats may be minor but appear largely undocumented.http://www.ncbi.nlm.nih.gov/pubmed/1559329123. Cleveland DA, Soleri D, Cuevas FA, Crossa J, Gepts P. (2005) : Detecting(trans)gene flow to landraces in centers of crop origin: lessons from thecase of maize in Mexico. Environ Biosafety Res. 4(4) :197-208; discussion209-15.There is much discussion of the probability of transgene flow from transgeniccrop varieties to landraces and wild relatives in centers of origin or diversity, andits genetic, ecological, and social consequences. Without costly research on thevariables determining gene flow, research on transgene frequencies in landrace(or wild relative) populations can be valuable for understanding transgene flowand its effects. Minimal research requirements include (1) understanding howfarmer practices and seed systems affect landrace populations, (2) sampling tooptimize Ne/n (effective/census population size), (3) minimizing variance at alllevels sampled, and (4) using Ne to calculate binomial probabilities for transgenefrequencies. A key case is maize in Mexico. Two peer-reviewed papers, based onlandrace samples from the Sierra Juarez region of Oaxaca, Mexico, reachedseemingly conflicting conclusions: transgenes are present (Quist and Chapela,2001, Nature 414: 541-543; 2002, Nature 416: 602) or “detectable transgenes”are absent (Ortiz-García et al., 2005, Proc. Natl. Acad. Sci. USA 102: 12338-12343and 18242). We analyzed these papers using information on Oaxacan maizeseed systems and estimates of Ne. We conclude that if Quist and Chapela’sresults showing presence are accepted, Ortiz-García et al.’s conclusions of noevidence of transgenes at detectable levels or for their introgression into maize(207)