| Six tropical maize populations and five testers were used to characterize critical daylengths, to determine which tester reduced time to flowering when crossed to tropical populations, and to determine whether there was a population x tester interaction for genes controlling photoperiod. The six populations were: (1) Caingang (BOV 78) from Brazil; (2) Negro de Tierra Caliente (GUA 146) (NDTC-146) from Guatemala; (3) Lenha (RGS XX) from Brazil; (4) Negrito from Colombia; (5) Costeno (VEN 453) from Venezuela; and (6) Negro de Tierra Caliente (GUA 159) (NDTC-159) from Boliva. The testers were: (1) Zapalote Chico (Z. Chico), a population from Mexico; (2) B14A, an inbred of Iowa Stiff Stalk Synthetic background; (3) Oh43, an inbred of Lancaster Sure Crop background; (4) CM105, an inbred of Iowa Stiff Stalk Synthetic background; and (5) A654HT, an inbred of Reid Yellow Dent background. These plant materials were evaluated as populations and testers per se and also as testcrosses under decreasing periods of light in the growth chamber. The testcrosses were also evaluated in three field environments.;Significant differences were found among populations and testers per se and among testcrosses for days to tassel emergence in the growth chamber evaluations. Days to tassel emergence for populations and testers occurred during four photoperiods, while in the testcrosses they occurred during two photoperiods. Among the tropical populations, the least photoperiod sensitive was NDTC-146, followed by Caingang, Costeno, Lenha, Negrito, and NDTC-159. The least photoperiod sensitive tester was CM105, followed by OH43, Z. Chico, B14A, and A654HT. There were significant differences among testcrosses, and populations in the combined analysis for days to pollen shed for the field environments. The testers and populations x testers interaction mean squares were not significant. Populations, therefore, performed in a similar manner in their crosses with different testers. Two testers, CM105 and A654HT, produced the earliest population crosses over all environments.;Crossing tropical populations to adapted Corn Belt testers can bring the population cross to a maturity level where is can be evaluated for agronomic traits in Iowa. It was, however, not possible to determine which tester would reduce the time to flowering the most. |
