Dispersal of Transgenes through Maize Seed Systems in Mexico (original) (raw)
Related papers
Environmental Biosafety Research, 2005
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 N e /n (effective /census population size), (3) minimizing variance at all levels sampled, and (4) using N e 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, Nature 414: 541-543; 2002, Nature 416: 602) or "detectable transgenes" are absent (Ortiz-García et al., 2005, Proc. Natl. Acad. Sci. USA 102: 12338-12343 and 18242). We analyzed these papers using information on Oaxacan maize seed systems and estimates of N e . 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 N e . Using estimates of N e 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. et al. 198 Environ. Biosafety Res. 4, 4 (2005) (Quist y Chapela, 2001, Nature 414: 541-543; 2002, Nature 416: 602) o no hay "transgénicos detectables" (Ortiz-García et al., 2005, Proc. Natl. Acad. Sci. USA 102: 12338-12343 y 18242). Nosotros hemos analizado estos artículos usando información de los sistemas de semilla de Oaxaca y cálculos de N e . Concluimos que si los resultados de Quist y Chapela mostrando la presencia de transgénicos son aceptados, las conclusiones de Ortiz-García et al. de que no existen transgénicos detectables en los maíces de la Sierra Juárez de Oaxaca no se justifican científicamente. Esto se debe a que los tamaños de muestra usados por Ortiz-García no son representativos y su análisis estadístico no es concluyente por que usaron n en lugar de N e . Usando estimadores de N e basado en el n de Ortiz-García et al., nosotros estimamos que transgénicos pueden ser presente en las razas de maíz de la región de Sierra Juárez en frecuencias de ~1-4%, además es posible que estén presentes en el 90% del área sembrado con maíz criollo que se encuentra en las zonas no montañosas de Oaxaca. Por lo tanto no hay evidencias científicas de la presencia o ausencia de maíz transgénico en años recientes en México, o en el estado de Oaxaca, o en la región de la Sierra Juárez.
Plants
Mexico harbors over 50% of maize’s genetic diversity in the Americas. Native maize varieties are actively managed by small-scale producers within a diverse array of cultivation systems. Seed lot use, exchange and admixture has consequences for the in situ conservation of such varieties. Here we analyze native maize seed management dynamics from 906 small-scale producers surveyed in three Mexican states: Mexico City, Oaxaca and Chiapas. Furthermore, we analyze how their management practices can relate to transgene presence, which was experimentally documented for maize samples associated with the applied surveys. Through a data mining approach, we investigated which practices might be related with a higher probability of transgene presence. The variables found to have a strong spatial association with transgene presence were: for Mexico City, maize producers with larger parcels; for Oaxaca, producer’s age (43–46 years) and the sale of seed; for Chiapas, the use of agricultural machin...
Ecology and evolution, 2017
The flow of transgenes into landraces and wild relatives is an important biosafety concern. The case of transgene flow into local maize varieties in Mexico (the center of origin of maize) has been intensively debated over the past 15 years, including legal, political, and environmental disputes fanned by the existence of a significant scientific controversy over the methods used for the detection of transgenes. The use of diverse approaches and a lack of harmonized methods specific to the detection and monitoring of transgenes in landraces have generated both positive and negative results regarding contamination of Mexican maize with genetically modified material over the years. In this paper, we revisit the case of transgene contamination in Mexican maize and present a novel research approach based on socio-biological analysis of contrasting communities and seed management systems. Two communities were used to investigate how different social and biological factors can affect trans...
Gene flow scenarios with transgenic maize in Mexico
Environmental …, 2004
Maize diversity is widespread in Mexico and it has been stewarded by campesinos in small communities until the present. With the arrival of transgenic maize, the objective of this study is to analyze possible scenarios that could result if genetically modified maize were not regulated and openly available in Mexico. By applying a simple logistic model based on the conditions of maize production in Mexico, the dispersion of transgenic maize in different situations within fields of farmers is described. In traditional open systems of freely exchanged seed within communities it is concluded that the most likely outcome of GM maize release is the incorporation of transgenes in the genome of Mexican germplasm and possibly in that of teosinte.
Absence of detectable transgenes in local landraces of maize in Oaxaca, Mexico (2003-2004)
Proceedings of The National Academy of Sciences, 2005
In 2000, transgenes were detected in local maize varieties (landraces) in the mountains of Oaxaca, Mexico [Quist, D. & Chapela, I. H. (2001) Nature 414, 541-543]. This region is part of the Mesoamerican center of origin for maize (Zea mays L.), and the genetic diversity that is maintained in open-pollinated landraces is recognized as an important genetic resource of great cultural value. The presence of transgenes in landraces was significant because transgenic maize has never been approved for cultivation in Mexico. Here we provide a systematic survey of the frequency of transgenes in currently grown landraces. We sampled maize seeds from 870 plants in 125 fields and 18 localities in the state of Oaxaca during 2003 and 2004. We then screened 153,746 sampled seeds for the presence of two transgene elements from the 35S promoter of the cauliflower mosaic virus and the nopaline synthase gene (nopaline synthase terminator) from Agrobacterium tumefaciens.
Gene flow between maize commercialized by Diconsa and native populatios at the Mixteca of Puebla
2011
Respecto a la primera hipótesis, Soleri et al. (2006) exponen que desde la implementación del Tratado de Libre Comercio con América del Norte, México ha importado de Estados Unidos de América, un promedio anual de 5.45 millones de toneladas métricas de maíz, que entre los años 2000 y 2003 overlapped with those of the native populations. This shows that, in the Mixteca of Puebla, gene flow between introduced materials and native maize populations is quite possible, representing an effective way to spread transgenes if these are in the pollen grains.
2016
Mexico, the center of origin of maize (Zea mays L.), has taken actions to preserve the identity and diversity of maize landraces and wild relatives. Historically, spatial isolation has been used in seed production to maintain seed purity. Spatial isolation can also be a key component for a strategy to minimize pollen-mediated gene flow in Mexico between transgenic maize and sexually compatible plants of maize conventional hybrids, landraces, and wild relatives. The objective of this research was to generate field maize-to-maize outcrossing data to help guide coexistence discussions in Mexico. In this study, outcrossing rates were determined and modeled from eight locations in six northern states, which represent the most economically important areas for the cultivation of hybrid maize in Mexico. At each site, pollen source plots were planted with a yellow-kernel maize hybrid and surrounded by plots with a white-kernel conventional maize hybrid (pollen recipient) of the same maturity. Outcrossing rates were then quantified by assessing the number of yellow kernels harvested from white-kernel hybrid plots. The highest outcrossing values were observed near the pollen source (12.9% at 1 m distance). The outcrossing levels declined sharply to 4.6, 2.7, 1.4, 1.0, 0.9, 0.5, and 0.5% as the distance from the pollen source increased to 2, 4, 8, 12, 16, 20, and 25 m, respectively. At distances beyond 20 m outcrossing values at all locations were below 1%. These trends are consistent with studies conducted in other world PLOS ONE |
PLOS ONE, 2015
Mexico, the center of origin of maize (Zea mays L.), has taken actions to preserve the identity and diversity of maize landraces and wild relatives. Historically, spatial isolation has been used in seed production to maintain seed purity. Spatial isolation can also be a key component for a strategy to minimize pollen-mediated gene flow in Mexico between transgenic maize and sexually compatible plants of maize conventional hybrids, landraces, and wild relatives. The objective of this research was to generate field maize-to-maize outcrossing data to help guide coexistence discussions in Mexico. In this study, outcrossing rates were determined and modeled from eight locations in six northern states, which represent the most economically important areas for the cultivation of hybrid maize in Mexico. At each site, pollen source plots were planted with a yellow-kernel maize hybrid and surrounded by plots with a white-kernel conventional maize hybrid (pollen recipient) of the same maturity. Outcrossing rates were then quantified by assessing the number of yellow kernels harvested from white-kernel hybrid plots. The highest outcrossing values were observed near the pollen source (12.9% at 1 m distance). The outcrossing levels declined sharply to 4.6, 2.7, 1.4, 1.0, 0.9, 0.5, and 0.5% as the distance from the pollen source increased to 2, 4, 8, 12, 16, 20, and 25 m, respectively. At distances beyond 20 m outcrossing values at all locations were below 1%. These trends are consistent with studies conducted in other world PLOS ONE |