Dispersal of transgenes through maize seed systems in Mexico.

ObjectivesCurrent models of transgene dispersal focus on gene flow via pollen while neglecting seed, a vital vehicle for gene flow in centers of crop origin and diversity. We analyze the dispersal of maize transgenes via seeds in Mexico, the crop's cradle.MethodsWe use immunoassays (ELISA) to screen for the activity of recombinant proteins in a nationwide sample of farmer seed stocks. We estimate critical parameters of seed population dynamics using household survey data and combine these estimates with analytical results to examine presumed sources and mechanisms of dispersal.ResultsRecombinant proteins Cry1Ab/Ac and CP4/EPSPS were found in 3.1% and 1.8% of samples, respectively. They are most abundant in southeast Mexico but also present in the west-central region. Diffusion of seed and grain imported from the United States might explain the frequency and distribution of transgenes in west-central Mexico but not in the southeast.ConclusionsUnderstanding the potential for transgene survival and dispersal should help design methods to regulate the diffusion of germplasm into local seed stocks. Further research is needed on the interactions between formal and informal seed systems and grain markets in centers of crop origin and diversification

Dispersal of transgenes through maize seed systems in Mexico.

ObjectivesCurrent models of transgene dispersal focus on gene flow via pollen while neglecting seed, a vital vehicle for gene flow in centers of crop origin and diversity. We analyze the dispersal of maize transgenes via seeds in Mexico, the crop's cradle.MethodsWe use immunoassays (ELISA) to screen for the activity of recombinant proteins in a nationwide sample of farmer seed stocks. We estimate critical parameters of seed population dynamics using household survey data and combine these estimates with analytical results to examine presumed sources and mechanisms of dispersal.ResultsRecombinant proteins Cry1Ab/Ac and CP4/EPSPS were found in 3.1% and 1.8% of samples, respectively. They are most abundant in southeast Mexico but also present in the west-central region. Diffusion of seed and grain imported from the United States might explain the frequency and distribution of transgenes in west-central Mexico but not in the southeast.ConclusionsUnderstanding the potential for transgene survival and dispersal should help design methods to regulate the diffusion of germplasm into local seed stocks. Further research is needed on the interactions between formal and informal seed systems and grain markets in centers of crop origin and diversification

Source effects on rates of maize seed-lot replacement (<i>1−p</i>) and diffusion (<i>q</i>) in Mexico¹.

<p>Significant at the 0.05 level is indicated by **. G-tests exclude seed from formal seed systems.</p>1<p>Expressed as a ratio, rates vary between 0 and 1. Replacement implies that seed is not saved by a farmer across cycles; diffusion entails the exchange of saved seed among farmers.</p>2<p>The terms “local” and “introduced” refer to the origin of the immediate source of seed; e.g., seed is local if acquired from neighbors, while seed acquired from farmers in another locality is introduced.</p>3<p>Seed acquired during the current cycle is “new;” seed saved by the farmer from a previous cycle is his/her “own.”</p

Expression of transgenic proteins in Mexican maize seed lots in 2002.

1<p>Confidence intervals (in parentheses) were estimated using profile-likelihood and binomial ln(-ln) transformations.</p

Percentage distribution of original sources of maize seed across regions in Mexico in 2002.

*<p>Confidence intervals (in parentheses) were estimated using profile-likelihood and binomial ln(-ln) transformations.</p>1<p>Friends, neighbors and relatives.</p>2<p>Farmers who sell seed openly to the public.</p>3<p>Government agencies and programs, e.g., Kilo por Kilo.</p>4<p>Intermediaries, private firms and banks.</p>5<p>Private seed companies.</p>6<p>Any source outside of Mexico.</p>7<p>Any source of grain other than Diconsa.</p

Altitude and source effects on rates of maize seed-lot replacement (<i>1−p</i>) and diffusion (<i>q</i>) in Mexico¹.

<p>Significant at the 0.05 level is indicated by **; significance at the 0.10 level is indicated by *. G-tests exclude seed from formal seed systems; masl: meters above sea level.</p>1<p>Expressed as a ratio, rates vary between 0 and 1. Replacement implies that seed is not saved by a farmer across cycles; diffusion entails the exchange of saved seed among farmers.</p>2<p>The terms “local” and “introduced” refer to the location of the immediate source of seed; e.g., seed is local if acquired from neighbors, while seed acquired from farmers in another locality is introduced.</p>3<p>Seed acquired during the current cycle is “new;” seed saved by the farmer from a previous cycle is his/her “own.”</p

Distribution of survey sample and maize populations.

<p>ENHRUM localities (blue), including those where transgenic proteins were detected (black circles). Distribution of teosinte (red) and maize landrace (green) according to INIFAP and CIMMYT genebank collections. Geographic data provided by ENHRUM and Campo Experimental Valle de México, Instituto Nacional de Investigaciones Forestales y Agropecuarias (INIFAP) were processed with ArcInfo.</p