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Hallauer’s Tusón: a decade of selection for tropical-to-temperate phenological adaptation in maize

J. E. C. Teixeira, T. Weldekidan, N. de Leon, S. Flint-Garcia, J. B. Holland, N. Lauter, S. C. Murray, W. Xu, D. A. Hessel, A. E. Kleintop, J. A. Hawk, A. Hallauer, R. J. Wisser
Heredity 2015 v.114 no.2 pp. 229-240
Zea mays, abnormal development, artificial selection, corn, corn ears, crops, flowering, genotype-environment interaction, germplasm, latitude, phenology, phenotypic variation, photoperiod, plant adaptation, plant breeding, selection response, temperate zones, temperature, tropics, Iowa
Crop species exhibit an astounding capacity for environmental adaptation, but genetic bottlenecks resulting from intense selection for adaptation as well as productivity can lead to a genetically vulnerable crop. Improving the genetic resiliency of temperate maize depends upon the use of tropical germplasm, which harbors a rich source of natural allelic diversity. Here, the adaptation process was studied in a tropical maize population subjected to ten recurrent generations of selection for early flowering in a single temperate environment in Iowa, USA. We evaluated the response to this selection across a geographical range spanning from 43.05° (WI) to 18.00° (PR) latitude. This study reveals the capacity for an all-tropical maize population to become adapted to a temperate environment in dramatic fashion: on average, families from generation 10 (g10) flowered 20 days earlier than families in generation 0 (g0), with a nine day separation between the latest g10 family and the earliest g0 family. Results suggest that adaptation was primarily due to selection on genetic main effects tailored to temperature-dependent plasticity in flowering time. Genotype-by-environment interactions represented a relatively small component of the phenotypic variation in flowering time, but were sufficient to produce a signature of localized adaptation that radiated latitudinally, in partial association with daylength and temperature, from the original location of selection. Furthermore, a maladaptive syndrome including symptoms of excessive ear and plant heights correlated with later flowering observed in the original population was dramatically reduced in frequency by selection on flowering time.