Registration of tropical populations of maize selected in parallel for early flowering time across the United States

Authors: WELDEKIDAN, TECLEMARIAM - University Of Delaware; MANCHING, HEATHER - University Of Delaware; CHOQUETTE, NICOLE - North Carolina State University; DE LEON, NATALIA - University Of Wisconsin; Flint-Garcia, Sherry; Holland, Jim - Jim; Lauter, Nicholas; MURRAY, SETH - Texas A&M University; XU, WENWEI - Texas A&M Agrilife; GOODMAN, MAJOR - North Carolina State University; WISSER, RANDALL - University Of Delaware

Submitted to: Journal of Plant Registrations
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2021
Publication Date: 1/8/2022
Citation: Weldekidan, T., Manching, H., Choquette, N., de Leon, N., Flint-Garcia, S.A., Holland, J.B., Lauter, N.C., Murray, S.C., Xu, W., Goodman, M., Wisser, R.J. 2022. Registration of tropical populations of maize selected in parallel for early flowering time across the United States. Journal of Plant Registrations. 16(1):100-108. https://doi.org/10.1002/plr2.20181.
DOI: https://doi.org/10.1002/plr2.20181

Interpretive Summary: Tropical corn is unadapted to temperate growing regions of the US and tends to flower very late in comparison to commercial hybrids. Other problems manifest themselves in unadapted corn, such as tall plants with high ear heights which makes the plants sensitive to wind damage, poor root structures leading to plants falling over prior to harvest, and poor coordination between male and female flowering resulting in reduced yield. This unadaptedness prevents the use of genetic diversity in tropical corn for broadening and improving the genetic base of the US corn crop. In order to study adaptation of tropical corn to temperate regions, we crossed seven tropical corn varieties together and intermated the progeny for multiple generations, resulting in a new population called TropicS. We then grew the TropicS population for two years each at eight locations with differing latitudes and therefore differing daylengths, the primary driver of adaptation to tropic versus temperate environments. At each location, only the earliest plants were selected for advancement, resulting in a locally adapted version of TropicS for each location (Wisconsin, Iowa, Delaware, North Carolina, north Texas, central Texas, Florida, and Puerto Rico). This germplasm resource will be of interest to geneticists and breeders seeking to investigate adaptation and integration of genetic diversity from tropical germplasm into temperate breeding programs.

Technical Abstract: Tropical strains of maize (Zea mays subsp. mays L.) flower very late in temperate environments. This is a barrier to maize diversification and improvement in regions where a large share of the world's corn production takes place. For investigating early flowering time adaptation, a tightly controlled parallel selection experiment spanning a 28° latitudinal range (~3,100 km) across the United States was conducted. First, a tropical synthetic population (TropicS-G0) (Reg. no. GP-605, PI 698625) of maize was created from seven inbred parents. The molecular genetic diversity in TropicS-G0 is representative of tropical inbreds that are differentiated from the prevailing germplasm used for hybrid production in the United States. Admixture analysis and genome simulation showed that breeding of TropicS-G0 captured the parental genomes mostly at random, as intended prior to selection. With TropicS-G0 as a common base population, a standardized protocol was used to recurrently select for early flowering time at eight locations for two generations, giving rise to location-specific lineages (TropicS-G1-PR, Reg. no. GP-621, PI 698641; TropicS-G2-PR, Reg. no. GP-622, PI 698642; TropicS-G2-FL, Reg. no. GP-620, PI 698640; TropicS-G1-cTX, Reg. no. GP-618, PI 698638; TropicS-G2-cTX, Reg. no. GP-619, PI 698639; TropicS-G1-nTX, Reg. no. GP-616, PI 698636; TropicS-G2-nTX, Reg. no. GP-617, PI 698637; TropicS-G1-NC, Reg. no. GP-614, PI 698634; TropicS-G2-NC, Reg. no. GP-615, PI 698635; TropicS-G1-DE, Reg. no. GP-610, PI 698630; TropicS-G1-IA, Reg. no. GP-608, PI 698628; TropicS-G2-IA, Reg. no. GP-609, PI 698629; TropicS-G1-WI, Reg. no. GP-606, PI 698626; TropicS-G2-WI, Reg. no. GP-607, PI 698627). Additional generations of selection were performed for the DE lineage (TropicS-G3-DE, Reg. no. GP-611, PI 698631; TropicS-G4-DE, Reg. no. GP-612, PI 698632; TropicS-G5-DE, Reg. no. GP-613, PI 698633). The parallel-selected maize population is a novel resource for breeders and those seeking to investigate adaptation.