Hostname: page-component-797576ffbb-jhnrh Total loading time: 0 Render date: 2023-12-02T02:54:26.027Z Has data issue: false Feature Flags: { "corePageComponentGetUserInfoFromSharedSession": true, "coreDisableEcommerce": false, "useRatesEcommerce": true } hasContentIssue false

Detecting (trans)gene flow to landraces in centers of crop origin: lessons from the case of maize in Mexico

Published online by Cambridge University Press:  22 June 2006

David A. Cleveland
 Environmental Studies Program, University of California, Santa Barbara, CA 93106-4160, USA
Daniela Soleri
 Environmental Studies Program, University of California, Santa Barbara, CA 93106-4160, USA
Flavio Aragón Cuevas
 Instituto Nacional de Investigaciones Forestales y Agropecuarias (INIFAP), Campo Experimental Valles Centrales, Melchor Ocampo No. 7, Santo Domingo Barrio Bajo, Etla, Oaxaca, México
José Crossa
 Biometrics and Statistics Unit, International Maize and Wheat Improvement Center (CIMMYT), Apdo. Postal 6-641, México D.F., México
Paul Gepts
 Department of Plant Sciences/MS1, Section of Crop and Ecosystem Sciences, University of California, Davis, CA 95616-8780, USA


Core share and HTML view are not possible as this article does not have html content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

There is much discussion of the probability of transgene flow from transgenic crop varieties to landraces and wild relatives in centers of origin or diversity, and its genetic, ecological, and social consequences. Without costly research on the variables determining gene flow, research on transgene frequencies in landrace (or wild relative) populations can be valuable for understanding transgene flow and its effects. Minimal research requirements include (1) understanding how farmer practices and seed systems affect landrace populations, (2) sampling to optimize Ne/n (effective /census population size), (3) minimizing variance at all levels sampled, and (4) using Ne to calculate binomial probabilities for transgene frequencies. A key case is maize in Mexico. Two peer-reviewed papers, based on landrace samples from the Sierra Juárez region of Oaxaca, Mexico, reached seemingly conflicting conclusions: transgenes are present (Quist and Chapela, 2001, Nature414: 541–543; 2002, Nature416: 602) or “detectable transgenes” are absent (Ortiz-García et al., 2005, Proc. Natl. Acad. Sci. USA102: 12338–12343 and 18242). We analyzed these papers using information on Oaxacan maize seed systems and estimates of Ne. We conclude that if Quist and Chapela’s results showing presence are accepted, Ortiz-García et al.’s conclusions of no evidence of transgenes at detectable levels or for their introgression into maize landraces in the Sierra de Juárez of Oaxaca are not scientifically justified. This is because their samples are not representative, and their statistical analysis is inconclusive due to using n instead of Ne. Using estimates of Ne based on Ortiz-García et al.’s n, we estimate that transgenes could be present in maize landraces in the Sierra Juárez region at frequencies of ~1–4%, and are more likely to be present in the 90% of Oaxacan landrace area that is not mountainous. Thus, we have no scientific evidence of maize transgene presence or absence in recent years in Mexico, Oaxaca State, or the Sierra Juárez region.

Research Article
© ISBR, EDP Sciences, 2006


Altman, D, Bland, JM (1995) Absence of evidence is not evidence of absence. Brit. Med. J. 311: 485 CrossRef
Alvarez-Morales A (2000) Mexico: Ensuring environmental safety while benefiting from biotechnology. In Persley GJ and Lantin MM, eds, Agricultural biotechnology and the poor: proceedings of an international conference, Washington, D.C., 21-22 October 1999. Consultative Group on International Agricultural Research, Washington, DC
Alvarez-Morales A (2002) Transgenes in maize landraces in Oaxaca: official report on the extent and implications. (posted 2002 Oct 10-16; verified 2006 Jan 24)
Andow, DA (2003) Negative and positive data, statistical power, and confidence intervals. Environ. Biosafety Res. 2: 16 CrossRef
Aragón Cuevas F, Taba S, Castro-García FH, Hernández-Casillas JM, Cabrera-Toledo JM, Alcalá LO, Ramírez ND (2005) In situ conservation and use of local maize races in Oaxaca, Mexico: a participatory and decentralized approach. In Taba S ed, Latin American maize germplasm conservation: regeneration, in situ conservation, core subsets, and prebreeding; proceedings of a workshop held at CIMMYT, April 7-10, 2003. CIMMYT, Mexico
Ballinas V, Becerril A (2005) Aprueba el senado la ley de bioseguirdad, pese a deficiencias, La Jornada, México
Baltazar, BM, Sanchez-Gonzalez, JD, de la Cruz-Larios, L, Schoper, JB (2005) Pollination between maize and teosinte: an important determinant of gene flow in Mexico. Theor. Appl. Genet. 110: 519526 CrossRef
Baltazar BM, Schoper JB (2002) Crop-to-crop gene flow: dispersal of transgenes in maize during field tests and commercialization. Paper presented at the 7th International Symposium on the Biosafety of Genetically Modified Organisms, Oct 10-16, 2002, Beijing, China. (posted 2002 Oct 10-16; verified 2006 Jan 24)
Berthaud J, Gepts P (2004) Chapter three: Assessment of effects on genetic diversity. In: Maize and biodiversity: The effects of transgenic maize in Mexico. Commission for Environmental Cooperation of North America (verified 2006 Jan 7)
CEC (2004) Maize and biodiversity: the effects of transgenic maize in Mexico. Key findings and recommendations. Secretariat article 13 report. CEC. (verified 2004 Nov 10)
Cleveland DA, Soleri D (2005) Rethinking the risk management process for GE crops in Third World agriculture. Ecol. Soc. 10: Article 9.
Crossa, J, Vencovsky, R (1994) Implication of the variance in effective population size on the genetic conservation of monoecious species. Theor. Appl. Genet. 89: 936942 CrossRef
Crossa, J, Hernandez, CM, Bretting, P, Eberhart, SA, Taba, S (1993) Statistical genetic considerations for maintaining germ plasm collections. Theor. Appl. Genet. 86: 673678 CrossRef
Crow JF, Kimura M (1970) An introduction to population genetics theory. Harper and Row, New York
Ellstrand NC (2003) Dangerous liaisons? When cultivated plants mate with their wild relatives. Johns Hopkins University Press, Baltimore
Esteva G, Marielle C, eds (2003) Sin maíz no hay país. Consejo Nacional para la Cultura y las Artes, Dirección General de Culturas Populares e Indígenas, México
Gepts, P, Papa, R (2003) Possible effects of (trans)gene flow from crops on the genetic diversity from landraces and wild relatives. Environ. Biosafety Res. 2: 89103 CrossRef
Hall, L, Topinka, K, Huffman, J, Davis, L (2000) Pollen flow between herbicide-resistant Brassica napus is the cause of multiple-resistant B. napus volunteers. Weed Sci. 48: 688694 CrossRef
Hartl DL, Clark AG (1989) Principles of population genetics. Sinauer Associates, Sunderland, Massachusetts
Hernandez, CM, Crossa, J (1993) A program for estimating the optimum sample-size for germplasm conservation. J. Hered. 84: 8586
Huang, JK, Hu, RF, Rozelle, S, Pray, C (2005) Insect-resistant GM rice in farmers’ fields: Assessing productivity and health effects in China. Science 308: 688690 CrossRef
INEGI (1996) Anuario Estadístico del Estado de Oaxaca, Edición 1996. INEGI, Aguascalientes, Mexico
INEGI (2004) Sistema para la consulta del anuario estadístico de Oaxaca, Edicion 2004. (verified 2005 Oct 8)
Jarosz, N, Loubet, B, Durand, B, McCartney, A, Foueillassar, X, Huber, L (2003) Field measurements of airborne concentration and deposition rate of maize pollen. Agr. Forest Meteorol. 119: 3751 CrossRef
Kaiser, J (2005) Calming fears, no foreign genes found in Mexico's maize. Science 309: 1000 CrossRefPubMed
Kaplinsky, N, Braun, D, Lisch, D, Hay, A, Hake, S, Freeling, M (2002) Maize transgenic results in Mexico are artefacts. Nature 416: 601 CrossRef
Louette, D, Charrier, A, Berthaud, J (1997) In situ conservation of maize in Mexico: genetic diversity and maize seed management in a traditional community. Econ. Bot. 51: 2038 CrossRef
Lu, BR, Snow, AA (2005) Gene flow from genetically modified rice and its environmental consequences. Bioscience 55: 669678 CrossRef
Ma, BL, Subedi, KD, Reid, LM (2004) Extent of cross-fertilization in maize by pollen from neighboring transgenic hybrids. Crop Sci. 44: 12731282 CrossRef
Marris, E (2005) Four years on, no transgenes in Mexican maize. Nature 436: 760 CrossRef
Marshall DR, Brown AHD (1975) Optimum sampling strategies in genetic conservation. In Frankel OH and Hawkes JG eds, Crop genetic resources for today and tomorrow, Cambridge University Press, Cambridge, U.K., pp 53–80
Matsuoka, Y, Vigouroux, Y, Goodman, MM, Sanchez, GJ, Buckler, E, Doebley, J (2002) A single domestication for maize shown by multilocus microsatellite genotyping. Proc. Natl. Acad. Sci. USA 99: 60806084 CrossRef
Metz, M, Fütterer, J (2002) Suspect evidence of transgenic contamination. Nature 416: 600601 CrossRef
Nature Biotechnology (2002) Editorial: Going with the flow. Nat. Biotechnol. 20: 527
NRC (2002) Environmental effects of transgenic plants: the scope and adequacy of regulation. National Academy Press, Washington, DC
NRC (2004) Biological confinement of genetically engineered organisms, Washington, DC
Ortiz-García, S, Ezcurra, E, Schoel, B, Acevedo, F, Soberón, J, Snow, AA (2005a) Absence of detectable transgenes in local landraces of maize in Oaxaca, Mexico (2003-2004). Proc. Natl. Acad. Sci. USA 102: 1233812343 CrossRef
Ortiz-García, S, Ezcurra, E, Schoel, B, Acevedo, F, Soberón, J, Snow, AA (2005b) Correction. Proc. Natl. Acad. Sci. USA 102: 18242 CrossRef
Papa, R, Acosta, J, Delgado-Salinas, A, Gepts, P (2006) A genome-wide analysis of differentiation between wild and domesticated Phaseolus vulgaris from Mesoamerica. Theor. Appl. Genet. 111: 11471158 CrossRef
Paulson KM (2005) Found-and-lost: transgenic maize in Oaxaca, Mexico. Information Systems for Biotechnology (verified 2005 Nov 07)
Peregrina K, Crúz J (2005) Mexico approves planting and sale of GM crops. Source: SciDev.Net. (verified 2006 Jan 24)
Prakash CS (2005) Duh.... No GM genes in Mexican corn. AgBioWorld. (verified 2005 Aug 25)
Pressoir, G, Berthaud, J (2004) Population structure and strong divergent selection shape phenotypic diversification in maize landraces. Heredity 92: 95101 CrossRef
Quist, D, Chapela, IH (2001) Transgenic DNA introgressed into traditional maize landraces in Oaxaca, Mexico. Nature 414: 541543 CrossRef
Quist, D, Chapela, IH (2002) Quist and Chapela reply. Nature 416: 602 CrossRef
Raven, PH (2005) Transgenes in Mexican maize: desirability or inevitability? Proc. Natl. Acad. Sci. 102: 1300313004 CrossRef
Raynor, GS, Ogden, EC, Hayes, JV (1972) Dispersion and deposition of corn pollen from experimental sources. Agron. J. 64: 420 CrossRef
Savidan A (2002) Tritrophic interactions in maize storage systems. Institute of Zoology, Laboratory of Animal Ecology and Entymology, University of Neuchâtel, Neuchâtel, p 225
Serratos JA, Willcox MC, Castillo-González F, eds (1997) Gene flow among maize landraces, improved maize varieties and teosinte: implications for transgenic maize. CIMMYT, Mexico
Snow, AA, Andersen, B, Jorgensen, RB (1999) Costs of transgenic herbicide resistance introgressed from Brassica napus into weedy B-rapa. Mol. Ecol. 8: 605615 CrossRef
Snow, AA, Pilson, D, Rieseberg, LH, Paulsen, MJ, Pleskac, N, Reagon, MR, Wolf, DE, Selbo, SM (2003) A Bt transgene reduces herbivory and enhances fecundity in wild sunflowers. Ecol. Appl. 13: 279286 CrossRef
Soleri, D, Smith, SE, Cleveland, DA (2000) Evaluating the potential for farmer and plant breeder collaboration: a case study of farmer maize selection in Oaxaca, Mexico. Euphytica 116: 4157 CrossRef
Soleri, D, Cleveland, DA, Aragón Cuevas, F, Ríos Labrada, H, Fuentes Lopez, MR, Sweeney, SH (2005) Understanding the potential impact of transgenic crops in traditional agriculture: maize farmers' perspectives in Cuba, Guatemala & Mexico. Environ. Biosafety Res. 4: 141166 CrossRef
Soleri, D, Cleveland, DA, Aragón Cuevas F (2006) Transgenic crop varieties and varietal diversity in traditionally based agriculture: the case of maize in Mexico. Bioscience 56: 503513 CrossRef
Uitenbroek DG (1997) “SISA-Binomial”. (verified 2006 Jan 09)
Velasco CE (2005) El maíz criollo de Oaxaca, libre de contaminación genética: cientificos, La Jornada, México
Vencovsky, R, Crossa, J (1999) Variance effective population size under mixed self and random mating with applications to genetic conservation of species. Crop Sci. 39: 1282– 1294 CrossRef
Vencovsky, R, Crossa, J (2003) Measurements of representativeness used in genetic resources conservation and plant breeding. Crop Sci. 43: 19121921 CrossRef
Wright, S (1931) Evolution in Mendelian populations. Genetics 16: 97159
Zi, X (2005) GM rice forges ahead in China amid concerns over illegal planting. Nat. Biotechnol. 23: 637 CrossRef