Modern Maize Created from Two Teosintes

Broad genetic sampling of maize and its teosinte grass ancestors reveals evidence of wild admixture during the crop's initial domestication and dispersal, according to a new study. The findings clarify the contentious origin of modern maize and raise new questions about the anthropogenic mechanisms underlying its spread throughout the Americas. The domestication of crops transformed human culture. For many crops, the wild plants that modern domesticates are most closely related to can be readily identified by morphological and genetic similarities. Yet, despite its global agricultural importance, the ancestry of modern maize has long been debated. The most widely accepted model suggests that maize was domesticated from a wild grass commonly known as teosinte. However, none of the proposed models for the origin of maize can explain conflicting archaeological, genetic, and geographic evidence. Recent studies have shown a potential genetic contribution from another wild relative, Zea mays spp. mexicana (mexicana). Here, Ning Yang and colleagues present a detailed population genetic analysis of maize origins and propose a new model of domestication and dispersal. Yang et al. examined more than 1000 genomes of domesticated maize and related wild teosinte grasses, including 338 newly sequenced traditional varieties, and found evidence that 4,000 years after initial domestication, introgression from wild mexicana occurred in the highlands of Mexico before the crop spread across the Americas, either replacing or hybridizing with preexisting maize populations. The alleles contributed by mexicana appear to affect plant photoperiodicity and flowering time, suggesting that these traits from this wild relative may have been beneficial during domestication. "These results not only highlight the past importance of crop wild relatives but also point to their potential as a source of adaptative diversity for future breeding," write Yang et al.