Juan Pablo Ricardo Martinez-Soriano of the Unidad de Biotecnologia e Ingenieria Genetica de Plantas, Centro de Investigacion y Estudios Avanzados del Instituto Politecnico Nacional,Apartado Postal 629, 36500 Irapuato, Gto, Mexico, writes that according to pre-Hispanic traditions, gods gave native Mexicans the first maize seeds and from then on, and for thousands of years, maize has been a vital element to the Latin American cultures. Biologically, Martinez-Soriano says maize is an orphan plant and has only one relative, the annual teosinte (1).

Morphologically the two are similar, but they differ strikingly in the pistillate inflorescence (what becomes the cob). For our discussion, the most notable difference is that the maize cob is solid, whereas the teosinte cob is brittle and comes apart at maturity. Molecular analysis, says Martinez-Soriano, has shown that maize was domesticated in the Balsas River drainage (Mexico) 6000 years ago (2). Primitive cobs found in caves and other archaeological sites share the same characteristics: they are of small size and are, invariably, solid.

This is of major importance--viable seeds can only be released by mechanical means (basically by humans). Maize does not disperse itself and therefore does not exist as a free species in nature.

Recently, some biotechnology companies have requested authorization to plant and market transgenic maize in Mexico. Several ecological groups have raised concerns about the potential risks of introducing such plants to Mexico, where maize originated. The main concern regarding the possible effects on the native maizes and relatives has little if any scientific basis; it is more related to cultural factors rather than biological ones. Arguments stating that maize is genetically fragile are weak. It seems paradoxical to argue that it is necessary to protect the genetic background of corn when, for 6000 years of traditional breeding, Martinez-Soriano says we have protected only alleles important for humankind. Even if we decide to protect the actual genotypes, there should be no need for concern. Any transgene transferred inadvertently to native maizes can be removed from the progeny by selecting against the incorporated trait. Maize is always under strong artificial selection, and therefore natural selection has no practical meaning for the species.

On the other hand, transgenes cannot be established in a natural population of teosintes. Any teosinte recipient of maize pollen is at risk of transmitting to its progeny the trait of not being able to release its seeds, just as in maize. The transference of an allele from teosinte to maize is, says Martinez-Soriano, a natural process. The opposite can only happen if the hybrid seeds are mechanically released. Still, fixation of a (trans)gene or allele in a teosinte population would be impossible if it did not confer an evolutionary advantage to the species.

The bt gene, for example, would most likely not confer any advantage to teosinte because pests are not a natural selection factor in the wild. The transgene would be lost like the thousands that never conferred adaptative advantages to the recipient plants. References

1. W. C. Galinat, Maydica 30, 137 (1985).
2. R.-L. Wang et al., Nature 398, 236 (1999).