Maize (Zea mays L.) is a major staple crop in West Africa and has the potential to mitigate the food insecurity in the subregion. However, maize grain yield is severely constrained by drought. A study was conducted at 13 locations in West Africa for 2 yr to determine genetic gains in yield of cultivars developed during three eras, 1988 to 2000 (first‐generation cultivars), 2001 to 2006 (second‐generation cultivars), and 2007 to 2010 (third‐generation cultivars) under drought and optimal conditions. Under drought, yield ranged from 1346 kg ha⁻1 for first‐generation cultivars to 1613 kg ha⁻1 for third‐generation cultivars with a genetic gain of 1.1% yr−1. Under optimal conditions, yield gain ranged from 3363 kg ha⁻1 for first‐generation cultivars to 3956 kg ha⁻1 for third‐generation cultivars with genetic gain of 1.3%. The average rate of increase in yield was 14 and 40 kg ha⁻1 yr⁻1 under drought and optimum conditions. Genetic gains in yield from first‐ to third‐generation cultivars under drought was associated with improved plant aspect and husk cover, whereas under optimum conditions it was associated with plant and ear aspects, increased ears per plant, plant and ear heights, and improved husk cover. Cultivars TZE‐W DT C2 STR, DTE‐W STR Syn C1, DT‐W STR Synthetic, 2009 DTE‐W STR Syn, and EV DT‐W 2008 STR were high yielding and stable across drought environments. Substantial progress has been made in breeding for drought tolerance during the last three decades.

Maize (Zea mays L.), an important staple crop in West and Central Africa (WCA), has enormous potential to reduce food insecurity in this subregion. Research covering three periods or eras of breeding has been conducted to develop cultivars resistant/tolerant to three maize stress factors: Striga parasitism, drought, and low soil nitrogen. A study was conducted under optimal or natural growing environments at 35 locations in WCA for 2 yr to determine genetic improvement in grain yield of the maize cultivars developed during the three breeding periods: 1988–2000 (period 1), 2001–2006 (period 2), and 2007–2010 (period 3). The average rate of increase in grain yield under optimum growing conditions was 40 kg ha−1 yr−1 with a genetic gain of 1.3% yr−1, which was slightly higher than the gain of 30 kg ha−1 yr−1, an annual genetic gain of 1.2% across 16 stress environments. It was concluded that substantial improvement in the yield potential of early maize under relatively nonstress environmental conditions has been made in this subregion by breeding for stress tolerance during the past three decades. The varieties EV DT‐W 2008 STR, 2009 DTE‐Y STR Syn, and TZE‐W DT C2 STR, all from the latest era of improvement, were identified as the highest yielding and most stable cultivars and should be promoted to contribute to food security in this subregion.

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Identification of outstanding maize (Zea mays L.) hybrids for target environments is complicated by genotype × environment interactions. Thirty‐two early‐maturity maize hybrids were evaluated at eight locations in Nigeria and six locations in Ghana for 2 yr to (i) identify high‐yielding, stable hybrids across locations and/or hybrids specifically adapted to different locations, and (ii) identify ideal test sites for selection of superior hybrids in the two countries. Genotype, country, year, location (country), and their interactive effects were significant (P < 0·01) for grain yield, days to anthesis and silking, anthesis‐silking interval, plant and ear aspects, and ears per plant. Mean grain yield of the hybrids ranged from 3177 kg ha−1 for EWH‐5 to 4596 kg ha−1 for EWH‐29. The genotype main effects plus genotype × environment interaction (GGE) biplot analysis revealed that EWH‐29, EWH‐8, and EWH‐30 did not differ significantly in grain yield and were the most stable hybrids in both countries, whereas EWH‐26 and EWH‐32 were the most stable hybrids only in Ghana. The GGE biplot analysis identified Samaru, Kafin Soli, and Minjibir in Nigeria and Nyankpala, Damongo, and Fumesua in Ghana as the most discriminating locations. Minjibir (Nigeria) and Nyankpala (Ghana), being most discriminating and representative locations, were considered the ideal testing sites for the respective countries. The type of cultivars evaluated determined the most suitable locations for multilocation testing within Ghana and Nigeria. Whereas hybrids EWH‐29, EWH‐8, and EWH‐30 should be suitable for production in Nigeria, EWH‐26 and EWH‐32 should be promoted for production in Ghana.

Genotype × environment interactions complicate selection of superior genotypes for narrow and wide adaptation. Eighteen tropically-adapted maize cultivars were evaluated at six locations in Nigeria for 2 yrs to (i) identify superior and stable cultivars across environments and (ii) assess relationships among test environments. Environment and genotype × environment interactions (GEI) were significant (P < 0·05) for grain yield. Environments accounted for 63.5% of the total variation in the sum of squares for grain yield, whereas the genotype accounted for 3.5% and GEI for 32.8%. Grain yield of the cultivars ranged from 2292 kg ha -1 for DTSTR-W SYN2 to 2892 kg ha -1 for TZL COMP4 C3 DT C2 with an average of 2555 kg ha -1 . Cultivar DT SYN2-Y had the least additive main effect and multiplicative interaction (AMMI) stability value of 7.4 and hence the most stable but low-yielding across environments. AMMI biplot explained 90.5% and classified cultivars and environments into four groups each. IWD C3 SYN F3 was identified as the high-yielding and stable cultivar across environments. ZA15, ZA14, BK14, BK15 and IL15 had environment mean above the grand mean, while BG14, BG15, LE14, LE15, IL14, LA14 and LA15 had mean below the grand mean. ZA, BK, BG, LE and LA were found to be consistent in ranking the maize cultivars. However, Zaria, Birnin Kudu, and Ilorin were identified as the best test locations and could be used for selecting the superior maize cultivars. The identified high-yielding and stable cultivar could be further tested and promoted for adoption to contribute to food insecurity in Nigeria.

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Maize (Zea mays L.) grain yield is severely constrained by drought and this study was conducted to assess gains in grain yield and other traits of released maize cultivars. Twenty-three maize cultivars plus a check were evaluated under drought and well-watered conditions at Zaria and Kadawa during 2015/2016 and 2016/2017 dry seasons. The 24 cultivars were evaluated using 6 x 4 lattice design with three replications. Genotypes differed significantly for all measured traits except anthesis-silking interval (ASI), husk cover, and number of ears per plant under drought, and ASI, husk cover, and ear aspect under well-watered conditions. Under drought, grain yield ranged from 2251 kg ha−1 for SAMMAZ 31 to 4938 kg ha−1 for SAMMAZ 19, with a genetic gain of 1.93% yr−1. Under well-watered conditions, grain yield varied from 3082 kg ha−1 for SAMMAZ 37 to 5689 kg ha−1 for SAMMAZ 51, with the same genetic gain found under drought conditions. Grain yield reduction as a result of drought was 28.4% and performance under drought predicted performance under well-watered conditions better than vice versa with regression coefficient value of 0.8. Grain yield had significant correlations with all measured traits under both water conditions, except for husk cover, plant and ear heights under drought. Our data revealed that substantial genetic gains have been made in breeding for high grain yield cultivars under drought and well-watered conditions over a period of 16 years in Nigeria.

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