2023-12-07 07:00:10
A corn field, in France, in 2005. CLAUDIUS THIRIET/BIOSPHOTO
Yellow, red, black, blue, purple, orange, green or white grains; horny, toothed or pearly, floury or oily, vitreous or waxy varieties; capable of growing from equatorial zones to the north of temperate regions, from sea level to more than 3,000 meters above sea level… The diversity of corn, the first cultivated plant in the world, is truly astonishing.
“Corn grown in northern Canada looks as much like corn grown in Mexico as a Chihuahua does to a Saint Bernard”s’amuse Alain Charcosset, from Inrae (Paris-Saclay University, CNRS, AgroParisTech). The plant, in fact, has been able to adjust its life cycle to the length of the seasons, the daily light and the temperature of the varied latitudes where it is cultivated, in nearly one hundred and fifty countries.
“From its center of origin, the Mexican highlands, the expansion of corn was accompanied by a spectacular adaptation to varied environmental conditions”summary Serge Bahuchetfrom the National Museum of Natural History (MNHN), in The Earth, the living, humans (MNHN/La Découverte, 2022).
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But how can we explain this tremendous adaptive success? The answer lies in the saga of the domestication of corn, a new episode of which has just been traced in the review Science from November 30.
Teosinte, ancestor of corn
First curiosity: unlike rice or wheat, there is no wild plant in nature that resembles cultivated corn, Zea mays mays. From what wild plant was the latter domesticated? After long debates, we now accept that the ancestor of corn is teosinte, a small, rather ordinary-looking wild grass.
Difficult, however, to have a more contrasting morphology than teosinte and corn! The first is bushy and very branched, with small ears with tough grains; the second has only one stem, has developed larger ears and edible grains. How did the metamorphosis take place?
Let’s go back to the roots of this fabulous saga, nine to ten millennia ago. In the southwest of Mexico, in the lowlands of the Rio Balsas valley, the first Native American civilizations began to cultivate teosinte, Zea mays parviglumis. For what uses? Mystery. Perhaps for its green ears, eaten as vegetables; or for its stems rich in sugar which, once fermented, can produce an alcohol, chicha. Whatever the case, these people had just invented, without realizing it, a form of agriculture.
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