Abstract
Crop landraces are managed populations that evolve in response to gene flow and selection. Cross-pollination among fields, seed sharing by farmers, and selection by management and environmental conditions play roles in shaping crop characteristics. We used common gardens to explore the local adaptation of maize (Zea mays ssp. mays) landrace populations from Chiapas, Mexico to altitude. We sowed seeds of 21 populations from three altitudinal ranges in two common gardens and measured two characteristics that estimate fitness: likelihood of producing good quality seed and the total mass of good quality seed per plant. The probability of lowland plants producing good quality seed was invariably high regardless of garden, while highland landraces were especially sensitive to altitude. Their likelihood of producing good seed quadrupled in the highland site. The mass of good quality seed showed a different pattern, with lowland landraces producing 25% less seed mass than the other types at high elevations. Combining these two measures of fitness revealed that the highland landraces were clearly adapted to highland sites, while lowland and midland landraces appear more adapted to the midland site. We discuss this asymmetry in local adaptation in light of climate change and in situ conservation of crop genetic resources.
Highlights
Maize, originally domesticated in central Mexico up to 9000 years ago (Matsuoka et al 2002), is grown globally as open-pollinated landraces, or populations of traditional varieties (Aquino et al 2001)
In this article we offer preliminary insights into the ways that natural selection may have played a role in organizing the present maize diversity in Chiapas, Mexico
Lowland landraces had the greatest proportion of plants that produced good quality seed regardless of environment (88%; Fig. 2A)
Summary
Originally domesticated in central Mexico up to 9000 years ago (Matsuoka et al 2002), is grown globally as open-pollinated landraces, or populations of traditional varieties (Aquino et al 2001). More than 75% of Mexico’s maize farmers still sow their own seeds of landrace populations rather than, or in addition to, improved varieties (Aquino et al 2001). Repeated seed selection within a given environment could contribute to local adaptation of maize populations. Gene flow between landrace populations and selection by the growers and the environment for adaptive characteristics that increase fitness can play, at times, contradictory roles (Slatkin 1987; Lenormand 2002)
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