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

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 degrees latitudinal range (similar to 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.