Ronald Nigh, Charles Benbrook, Stephen Brush , Luis Garcia-Barrios,
Rafael Ortega-Paczka, and Hugo R. Perales
In their letter (25 Feb., p. 1399), J. P. R. Martínez-Soriano and D. S. Leal-Klevezas say that there "should be no need for concern" that the introduction of transgenic maize varieties in Mexico may pose a risk to landraces or wild relatives of maize in its ancestral home. However, it would be a mistake to dismiss such concerns given the limited state of our current knowledge. Indeed, what little evidence is available seems worrisome.
Martínez-Soriano and Leal-Klevezas mention that there is only one wild relative of maize, annual teosinte, but there are several subspecies of teosinte (which is conspecific with maize itself) as well as a perennial teosinte, a separate species endemic to Jalisco, Mexico. Other less closely related species are found throughout Mexico and Central America. The possibility of gene flow from the teosintes to maize is well established and has been deliberately induced by Mexican farmers. The possibility of gene flow and introgression (incorporation of genes) from maize to teosintes is less studied, but the work of J. Doebley and M. Goodman and of B. Benz et al. confirm this possibility (1). Reviews on the issue (2) also make it clear that reciprocal gene flow between maize and the teosintes is possible. Thus, the available evidence does not support the authors' comment that "transgenes cannot be established in a natural population of teosinte." The concern expressed by some scientists that such gene flow could create aggressive strains of weeds cannot be dismissed on the basis of the reasoning presented in their letter.
Martínez-Soriano and Leal-Klevezas also say, "Any transgene transferred inadvertently to native maizes can be removed from the progeny by selecting against the incorporated trait." But "gene" and "trait" are not synonymous; selection by farmers for a trait is not 100% efficient in eliminating a gene from a breeding population.
Although perhaps technologically feasible, there is no practical way for farmers or breeders to select out genes for Bt or glyphosate resistance, for example, given the scale at which landraces are grown in Mexico. Furthermore, maize farmers actively increase infraspecific diversity by interplanting varieties to generate hybrids (3). Any transgenic trait that is introduced can therefore be expected to diffuse into other maize races--especially if the trait is dominant. Martínez-Soriano and Leal-Klevezas say that transgenic maize is opposed because people think maize is "genetically fragile." However, the issue is not fragility, but the irreversible insertion of a new trait that may become common in Mexican maize landraces or wild relatives.
We believe that the genetic and ecological risks of introducing transgenic crops into the centers of origin of agronomic crops are largely unknown. We must not get beyond the science. The effects may prove, in most cases, of little consequence, but we should not find out by default or accident. Regulatory decisions involving the introduction of transgenic plants should be based on thorough scientific research, which in the case of maize, at least, has not yet been conducted.
Hugo R. Perales
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Last Updated on 3/27/00
By Rachel C. Benbrook