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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 ,
Daniela Soleri ,
Flavio Aragón Cuevas ,
José Crossa  and
Paul Gepts
David A. Cleveland
Affiliation:
 Environmental Studies Program, University of California, Santa Barbara, CA 93106-4160, USA
Daniela Soleri
Affiliation:
 Environmental Studies Program, University of California, Santa Barbara, CA 93106-4160, USA
Flavio Aragón Cuevas
Affiliation:
 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
Affiliation:
 Biometrics and Statistics Unit, International Maize and Wheat Improvement Center (CIMMYT), Apdo. Postal 6-641, México D.F., México
Paul Gepts
Affiliation:
 Department of Plant Sciences/MS1, Section of Crop and Ecosystem Sciences, University of California, Davis, CA 95616-8780, USA

Abstract

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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.

Keywords

effective population sizesamplinggene flowMexicomaizetransgenesgenetically engineered cropslandracestraditional agriculturethird worldOaxacaresearch design
Type
Research Article
Information
Environmental Biosafety Research , Volume 4 , Issue 4 , October 2005 , pp. 197 - 208
Copyright
© ISBR, EDP Sciences, 2006

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