Ustilago and the accidental domestication of maize

Abstract

Maize is the essential crop of the Americas. Maize appeared suddenly about 8,500 years ago as domesticated teosinte; however, there is no evidence (genetical, archaeological, linguistic or ethnobotanical) able to support a gradual transformation from the teosinte ear into the corn ear. Teosinte has never been cultivated by Americans, nor did they ever attempt to domesticate it. Its grains were not used as food, making unrealistic the assumption that prehispanics created something edible from seeds that were not so. Plant domestication is a slow process in almost every known crop but maize evolution might not be the case. Teosinte has a brittle cob, whereas maize forms solid ones that do not release their seeds 2. The latter are soft, while in teosinte they are enclosed in hard inedible cases. Why would the prehispanic natives even think of modifying those hard seeds, if they were not used as food in the first place?. The switch from teosinte to maize were due to important mutations, occurring in a relatively short period so that natives immediately noticed if they were well aware of the importance of teosinte (or its parasites) and rescued the resultant newborn maize.Teosinte-maize hybrids were highly susceptible to the fungus Ustilago maydis (known in Mexico as huitlacoche) under natural conditions. Consequently, this parasite was found to infect every part of the hybrid plant.Huitlacoche is well known as a food delicacy and it has been important to Mexicans since prehispanic times and it might have been very likely used as food taken from infected teosinte at the same time it was changing into maize. Ustilago maydis probably played a vital role on the domestication process of maize, since the change from teosinte to maize was noticed by humans, who then rescued it from nature