Genetic Gains From Selection for Grain Yield and Striga Resistance In Early-Maturing Maize Cultivars of Three Breeding Eras In Striga-Infested and Striga-Free Environments.

Maize is the most important staple cereal crop in sub-Saharan Africa (SSA) and has great prospect to rectify the food insecurity in the sub-region. However, maize grain yield is severely constrained by Striga hermonthica parasitism in the savanna of SSA which has the greatest potential for maize production due to reduced disease and pest pressure, low night temparatures and high incoming solar radiation. To combat the threat posed by Striga, the International Institute of Tropical Agriculture (IITA) has during the past three decades developed early-maturing Striga resistant/tolerant maize cultivars. A study was conducted at two locations each in Nigeria and Benin in 2010 and 2011 to determine the rate of genetic improvement in grain yield of the cultivars developed during three breeding eras (1988-2000, 2001-2006 and 2007-2010)  under Striga-infested and Striga-free conditions. Environment (E), Genotype (Era),  Era, E × Genotype (Era), and  E × Era interactions mean squares were significant for grain yield under both Striga-infested and Striga-free conditions except E × Genotype (Era) and E × Era interactions when Striga-free. Under Striga infestation, mean grain yield ranged from 2537.4 kg ha^–1 for cultivars bred during 1988-2000 to 3121.8 kg ha^–1 for those developed during 2007-2010 with a corresponding genetic gain of 1.93% per year. When Striga-free, grain yield ranged from 3646.1 kg ha^–1 for cultivars bred during 1988-2000 to 4226.9 kg ha^–1 for those developed during 2007-2010 with annual genetic gain of 1.0%. The average rate of increase in grain yield was 41.4 kg ha^–1 per year when Striga-infested and 33.9 kg ha^–1 per year when Striga-free. The increase in grain yield under Striga infestation was associated with significant decrease in the Striga damage rating and the number of emerged Striga plants at 8 and 10 WAP, improvement in ear aspect and increase in the number of ears per plant from old to modern era cultivars. The Striga damage rating at 8 WAP decreased from 3.3 for the old cultivars to 2.9 for the modern cultivars with genetic gain of -0.85% while the Striga damage at 10 WAP decreased from 4.6 to 4.1 with genetic gain of -0.80%. For the number of emerged Striga plants, the annual genetic gain of -0.63% for 8 WAP and -0.57% for 10 WAP were obtained for cultivars of the three breeding eras. The increase in genetic gains was 0.70% for the number of ears per plant and -0.65% for ear aspect. Cultivars DTE-Y STR Syn C₁, EV DT-Y 2000 STR, and 2009 DTE-Y STR Syn were the highest yielding and most stable across Striga-infested environments. Substantial progress has been made in breeding for high yielding, Striga resistant / tolerant cultivars during the past three decades.