|TEIXEIRA, JULIANA - University Of Delaware|
|WELDEKIDAN, TECLEMARIAN - University Of Delaware|
|DE LEON, NATALIA - University Of Wisconsin|
|Holland, Jim - Jim|
|MURRAY, SETH - Texas A&M University|
|XU, WENWEI - Texas A&M University|
|HESSEL, DAVID - Iowa State University|
|KLEINTOP, ADRIENNE - University Of Delaware|
|HAWK, JIM - University Of Delaware|
|HALLAUER, ARNEL - Iowa State University|
|WISSER, RANDALL - University Of Delaware|
Submitted to: Heredity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2014
Publication Date: 2/1/2015
Publication URL: http://handle.nal.usda.gov/10113/61127
Citation: Teixeira, J.E., Weldekidan, T., de Leon, N., Flint Garcia, S.A., Holland, J.B., Lauter, N.C., Murray, S.C., Xu, W., Hessel, D., Kleintop, A.E., Hawk, J., Hallauer, A.R., Wisser, R. 2015. Hallauer’s Tusón: a decade of selection for tropical-to-temperate phenological adaptation in maize. Heredity. 114:229-240.
Interpretive Summary: Tropical maize germplasm (inbred lines, populations, landraces) is a potential source for genetic diversity essential for continued corn improvement in today’s changing environments. Yet very little tropical germplasm is used in temperate breeding programs as they are generally maladapted to temperate environments, primarily because of late flowering. Two main mechanisms contribute to adaptation of the lines for decreasing time to flowering: response to daylength (photoperiod) and response to temperature. The subject of our study was a tropical maize population that had gradually been adapted to central Iowa over the course of ten years by selection for early flowering. We evaluated samples of the original unadapted population, the final adapted population, and four intermediate generations in nine field locations ranging in latitude from Wisconsin to Puerto Rico. These locations differ in their photoperiod and temperatures, allowing us to differentiate between these mechanisms of adaptation. First, we observed a clear decrease in flowering time across generations at each location. Second, we determined that adaptation to longer daylength was the primary process in the early generations of selection, followed by other mechanisms, such as temperature, that were responsible for adaptation in the later generations. Finally, we also found that other maladaptive traits associated with the tropical germplasm, such as excessive ear and plant heights, were also improved by selection for early flowering. Our results indicate that selection for flowering time alone may be enough to alleviate many of the effects of the maladaptive syndrome. This information will be useful to corn breeders and geneticists as they incorporate useful genetic variation from unadapted tropical and other germplasm stocks.
Technical Abstract: 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.