Improvement of yield and other traits of extra-early maize under stress and nonstress environments
Striga, drought, and low soil fertility constrain maize (Zea mays L.) productivity in West and Central Africa (WCA). Two Striga-resistant extra-early populations, TZEE-W Pop STR (white) and TZEE-Y Pop STR (yellow) were improved by four cycles of S1 recurrent selection, and the products were evaluated in field trials in Nigeria from 2005 to 2007. The objective was to assess progress in improvements for grain yield, Striga resistance, and other traits when Striga-free, Striga-infested, and under low- and high-N management. Under Striga infestation, yield gain from C0 to C4 was 136 kg ha–1 for the yellow population and 71 kg ha–1 cycle–1 for the white. The yield gain in advanced cycles of selection in the yellow population was associated with decreases in Striga emergence at 8 and 10 wk after planting (WAP) and Striga damage at 8 WAP, while that of the white was accompanied by increased days to silking (DS) and ears per plant (EPP) as well as a decrease in Striga emergence at 8 WAP. Under Striga-free conditions, yield gain from C0 to C4 was 164 kg ha–1 cycle–1 for the white and 221 kg ha–1 cycle–1 for the yellow. The yield gain in advanced cycles of selection was more pronounced under high-N (157 kg ha–1 cycle–1) than low-N conditions (144 kg ha–1 cycle–1) in the yellow, and higher under low N than high-N conditions in the white. Selection in the yellow was accompanied by increased days to anthesis (DA) and DS, plant and ear heights under low N and increased DS under high N. In the white, selection induced increased DA, ear height, and decreased anthesis–silking interval (ASI).