Food insecurity and malnutrition are major challenges facing rural populations in sub‐Saharan Africa. A total of 150 quality protein maize (Zea mays L.) (QPM) hybrids generated from 30 early‐maturing QPM inbreds plus six checks were evaluated under drought, low soil N, and Striga [Striga hermonthica (Delile) Benth.]‐infested environments in Nigeria for 2 yr. The objectives were to (i) examine the gene action conditioning the traits in the inbreds, (ii) classify them into heterotic groups using two methods, (iii) identify the best QPM inbred testers across environments, and (iv) identify stable and high‐yielding hybrids. General and specific combining ability (GCA and SCA, respectively) mean squares were significant (P < 0.01) for grain yield and other traits across environments, indicating that additive and nonadditive gene actions were important in the inheritance of most traits of the inbreds. Preponderance of SCA sum of squares over GCA for most measured traits across environments indicated that nonadditive gene action largely modulated inbred trait inheritance. The GCA effects of multiple traits (HGCAMT) method classified the inbreds into three heterotic groups each under drought and across environments and four groups under low N and Striga‐infested environments. Single nucleotide polymorphism (SNP)‐based method placed the inbreds into three groups across environments and was more efficient. TZEQI 6 and TZEQI 55 were identified as testers across environments. TZEQI 44 × TZEQI 4, TZEQI 35 × TZEQI 39, TZEQI 35 × TZEQI 59, TZEQI 6 × TZEQI 35, and TZEQI 45 × TZEQI 33 were the most stable and highest‐yielding hybrids across environments and should be commercialized for improved nutrition and food security in sub‐Saharan Africa.

a b s t r a c tFood insecurity and malnutrition are two major challenges facing rural populations in sub-Saharan Africa (SSA). Hybrids of quality protein maize (QPM) have a crucial role here to play because QPM contains increased lysine and tryptophan concentrations and has a higher biological value than the normal maize. Information on the combining ability and heterotic patterns of QPM inbreds is crucial for the success of hybrid programs in the sub-region. Ninety-one diallel crosses derived from 14 early maturing yellowendosperm QPM inbreds were evaluated from 2010 to 2012 under Striga infested, drought, low-N and optimal environments in Nigeria. The objectives were to (i) examine the combining ability of the set of early yellow QPM inbreds, (ii) classify the inbreds into heterotic groups and identify the best testers (iii) compare the efficiencies of the heterotic grouping methods in classifying the inbreds and (iv) determine the grain yield and stability of the inbreds in hybrid combinations under the research environments. General (GCA) and specific (SCA) combining ability effects were important in the inheritance of grain yield and other traits of the inbreds. However, GCA was more important than SCA under each contrasting environment and across environments suggesting that the additive gene action was more important than the non-additive in the set of inbreds. The SCA effects of grain yield and the heterotic group's SCA and GCA of grain yield (HSGCA) methods classified the inbreds into three groups each, while the heterotic grouping based on GCA of multiple traits (HGCAMT) and the SNP-based genetic distance (GD) methods had two groups each across research environments. There was close correspondence among the classifications of all the grouping methods in terms of placement of inbreds into the same heterotic groups. The SNP-based method was the most efficient and was used to identify TZEQI 87 and TZEQI 91 as the best testers for the SNP-based heterotic groups 1 and 2. The hybrids, TZEQI 87 × TZEQI 93, TZEQI 77 × TZEQI 91 and TZEQI 80 × TZEQI 91 were identified as the most stable and high yielding across research environments and should be commercialized.

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Two major constraints militating against the achievement of food security in West Africa (WA) are recurrent drought and poor soil fertility. Seventeen early maturing maize inbreds from IITA and CIMMYT were used as parents to produce 136 diallel crosses which were evaluated along with four checks in contrasting environments at four locations for 2 year in Nigeria. The objectives of the study were to (i) examine the combining ability of the lines under drought, low soil nitrogen (low N), optimal and across environments; (ii) classify the inbreds into heterotic groups using the specific combining ability (SCA) effects of grain yield, heterotic group's specific and general combining ability (HSGCA), the heterotic grouping based on general combining ability (GCA) of multiple traits (HGCAMT) and the molecular-based genetic distance methods; (iii) compare the efficiencies of the four heterotic grouping methods in classifying the inbreds and identifying the best testers; and (iv) examine the performance of the inbreds in hybrid combinations across environments. Sum of squares for GCA of inbreds for grain yield and other measured traits were larger than those of the SCA in all environments. The relative importance of GCA to SCA effects for grain yield and other traits increased from stress to nonstress environments with the additive genetic effects accounting for the major portion of the total genetic variation under all research environments. The HSGCA method classified the lines into three groups and was the most efficient because it had the highest breeding efficiency (40 %) in the test environments followed by the HGCAMT, SNP marker-based and the SCA effects of grain yield methods. Inbred TZEI 19 was identified as the best tester across research environments based on HSGCA method. Hybrids ENT 11 9 TZEI 19 and TZEI 1 9 TZEI 19 were the most outstanding and should be tested extensively in on-farm trials and commercialized.

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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.

Early-maturing provitamin A (PVA) quality protein maize (QPM) hybrids with combined drought and low soil nitrogen (low-N) tolerance are needed to address malnutrition and food security problems in sub-Saharan Africa (SSA). The current study's objectives were to (i) examine combining ability of selected early maturing PVA-QPM inbreds for grain yield and other agronomic traits under drought, low-N, optimal environments and across environments, (ii) determine gene action conditioning PVA accumulation under optimal environments, (iii) classify inbreds into heterotic groups and identify testers and (iv) assess yield and stability of hybrids across environments. Ninety-six hybrids generated from 24 inbred lines using the North Carolina Design II together with four commercial hybrid controls were evaluated under drought, low-N and optimal environments in Nigeria in 2016 and 2017. Fifty-four selected hybrids were assayed for PVA carotenoid and tryptophan content. Additive genetic effects were greater than non-additive effects for grain yield and most agronomic traits under each and across environments. The gene action conditioning accumulation of PVA carotenoids under optimal growing conditions followed a pattern similar to that of grain yield and other yield-related traits. The inbred lines were categorized into four heterotic groups consistent with the pedigree records and with TZEIORQ 29 identified as the best male and female tester for heterotic group IV. No tester was found for the other groups. Hybrid TZEIORQ 24 × TZEIORQ 41 was the highest yielding and most stable across environments and should be further tested for consistent performance for commercialization in SSA.

Availability of multiple-stress tolerant maize is critical for improvement in maize production in West and Central Africa (WCA). A study was carried out to (i) assess a set of inbred lines for combining ability under stressed and optimal conditions, (ii) determine the performance of the testcrosses under different conditions, and (iii) identify outstanding hybrids across the conditions. Two hundred and five testcrosses were planted with five hybrid checks under Striga-infested, low soil nitrogen, drought and optimal conditions between 2015 and 2016 in Nigeria. The grain yield inheritance under optimal condition was largely regulated by additive gene effect whereas non-additive gene effects largely regulated grain yield under the three stresses. Four of the inbreds had significant positive general combining ability effects each under low N and drought, and three under Striga infestation for grain yield. The inbreds could be vital sources of beneficial alleles for development and improvement of tropical yellow maize hybrids and populations. Hybrids TZEI 443 x ENT 13 and TZEI 462 x TZEI 10 were high yielding and stable; they out-performed the three early maturing released hybrids in WCA. The new hybrids should be extensively assessed and released in the sub-region to improve food security.