Photoperiod Sensitivity in Tropical Maize Accessions, Early Inbreds, and Their Crosses

One factor causing lack of adaptation of tropical and subtropical maize (Zea mays L.) to the U.S. Corn Belt is its photoperiod sensitivity. Six tropical maize populations (‘Caingang-BOV 78’, ‘Negro de Tierra Caliente-GUA146’, ‘Lenha-RGS XX’, ‘Negro de Tierra Caliente-GUA159’, ‘Negrito’, and ‘Costeño-VEN 453’) and five testers (‘Zapalote Chico’ PI 217413, ‘BI4A’, ‘Oh43’, ‘CM105’, and ‘A654HT’) were used to determine which tester most effectively reduced time to flowering when crossed with tropical populations and to determine whether there was a population ✕ tester interaction for genes controlling photoperiod sensitivity. Evaluations were carried out in 1987 and 1988 under decreasing photoperiod (18-9 h of light) in the growth chamber for the populations, testers, and testcrosses and also in the field for the testcrosses. Three field environments, two in Iowa and one in Puerto Rico, were utilized. In the growth chamber, days to tassel emergence differed among populations and testers per se and among testcrosses. Tassel emergence for populations and testers occurred from the 12-h to the 9-h photoperiod. The tropical population least sensitive to photoperiod was Negro de Tierra Caliente-GUA146, while CM105 was the least sensitive tester. There were significant differences among testcrosses in the combined analysis for days to pollen shed for the field environments. Two testers, CM105 and A654HT, produced the earliest testcrosses over all environments. There were significant differences in the contribution testers made toward earliness in tropical population testcrosses in temperate environments. Joint contribution of the USDA-ARS and Journal Paper no. J-13868 of the Iowa Agric. and Home Econ. Exp. Stn.; Project 2778. Part of the senior author's Ph.D. research.