Genetic Improvement of Extra‐Early Maize Cultivars for Grain Yield and Striga Resistance during Three Breeding Eras
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Maize (Zea mays L.), a food security crop in West Africa (WA) is threatened by Striga hermonthica (Del.) Benth. infestation. A study was conducted at five locations in WA for 2 yr to determine genetic gains in grain yield of 56 extra-early maturing cultivars developed during three breeding eras, 1995 to 2000 (Era 1), 2001 to 2006 (Era 2), and 2007 to 2012 (Era 3) under Striga-infested and Striga-free conditions. Yield ranged from 1827 kg ha(-1) for Era 1 cultivars to 2292 kg ha(-1) for Era 3 cultivars under Striga infestation with average rate of increase in grain yield of 42 kg ha(-1) yr(-1) corresponding to 2.56% annual genetic gain. Under Striga-free conditions, yield ranged from 2939 kg ha(-1) for Era 1 cultivars to 3549 kg ha(-1) for Era 3 cultivars, but the average rate of increase in grain yield of 54 kg ha(-1) yr(-1) corresponding to 1.3% annual genetic gain was not significant. The increase in yield under Striga was associated with increased plant height. Although there was no significant gain in yield under Striga-free conditions, significant increase in plant height and decrease in root lodging were observed. Cultivars 53, 17, and 45 from Era 3 and 23, 21, 34, and 28 from Era 2 were the highest yielding and most stable under Striga infestation. Cultivars 53 and 55 from Era 3 were the most outstanding under Striga-free conditions. Considerable progress has been made in breeding for high yielding and Striga resistant or tolerant extra-early maize cultivars during the last three decades.
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