Stem borer (SB) and more recently, fall armyworm (FAW) are serious economic pests in maize production in sub-Saharan Africa. It is hypothesized that SB-resistant germplasm may confer resistance against FAW. However, the performance of SB-resistant lines in hybrid combinations and the inheritance of FAW-resistant traits under variable FAW infestations have not been reported. This study was conducted to (i) obtain information on the inheritance of agronomic and FAW-resistant traits under variable FAW infestations; (ii) identify hybrids combining high grain yield (GYLD) and stability under FAW infestations; and (iii) determine the effects of FAW damage on GYLD. Three SB-resistant lines (1393, CKSBL10060 and CML 331) as testers and six open-pollinated varieties (OPVs) as lines were crossed in a line tester scheme to generate eighteen test crosses. The test crosses together with two tester × tester crosses and two checks were evaluated under artificial FAW infestation (AI), natural infestation (NI) and pesticide-protected condition (PC) in Nigeria. Additive and non-additive effects were significant for GYLD, most agronomic and FAW-resistant traits under AI and NI, except ear damage (EDAM) scores under NI, whereas only the non-additive effect was significant for GYLD under PC. Two testers (1393 and CKSBL10060) combined significant and positive GCA effects for GYLD with desirable GCA effects for FAW-resistant traits under AI and NI, whereas CML 331 combined significant and negative GCA effects of GYLD with undesirable GCA effects of FAW resistance under the test conditions. Three OPVs (AWR SYN-W2, AMATZBR-WC4 and TZB-SR) had a significantly positive GCA effect for GYLD and a desirable GCA effect for either leaf damage (LDAM) or EDAM score under AI. The FAW LDAM and EDAM significantly reduced GYLD under AI but not under NI. Three test crosses (AMATZBR-WC4 x CKSBL10060, TZB-SR x CKSBL10060 and TZBR Comp 1-WC2 × 1393) combined high yield with stability and FAW tolerance across the test conditions and thus were recommended for further testing.

Vitamin A deficiency (VAD) is a serious problem in sub‐Saharan Africa (SSA) and other parts of the world. Understanding the effect of marker‐based improvement (MARS) of two maize synthetics (HGA and HGB) representing different heterotic groups on their agronomic performance, carotenoid content, and combining abilities could help identify suitable sources to develop divergent inbred lines for optimizing heterosis. This study involved three selection cycles each of the two synthetics and their nine varietal‐cross hybrids together with a released check variety was conducted across four diverse locations in Nigeria in 2018 and 2019. Environment and hybrid effects were significant on grain yield and other agronomic traits as well as provitamin A content and other carotenoids. Genetic improvement per cycle of MARS in the parental synthetics was 15% for provitamin A, 25% for β‐carotene and 26% for lutein in HGA and 4% for grain yield, 3% for zeaxanthin and 5% for α‐carotene in HGB. Grain yield and agronomic traits of the two maize synthetics were controlled by additive and non‐additive gene effects, while provitamin A content and other carotenoids were mainly controlled by additive gene effects. Some selection cycles which were high in grain yield and provitamin A content were identified as potential sources of new and divergent maize inbred lines in maize breeding programs. Some varietal‐cross hybrids expressed significant mid‐parent heterosis for grain yield and moderate mid‐parent heterosis for provitamin A, β‐carotene and xanthophylls. These hybrids could be commercialized at reasonable prices to small‐scale farmers in rural areas that are most affected by vitamin A deficiency.

Maize is a major staple food in Sub-Saharan Africa (SSA). Vitamin A deficiency index is high in Africa and could be reduced through the consumption of provitamin-A-enriched maize. However, foliar diseases such as maize streak virus, northern corn leaf blight and common rust constrain maize production in SSA. The cultivation of host-resistant varieties is the most effective approach to mitigate their effects. Therefore, maize synthetics improved for PVA carotenoids, their selection cycles and crosses as well as a commercial disease-resistant check were assessed for resistance to maize streak virus, northern corn leaf blight and common rust at hotspots in Nigeria. The foliar diseases’ effects on the agronomic performance and carotenoid content of the maize genotypes were assessed. The Genotypes differed for most agronomic traits and foliar disease resistance. Stepwise regression revealed that, although the agronomic traits determined 93% of the grain yield, each foliar disease had effect on the yield. A unit increase in maize streak virus score increased plant aspect and husk cover scores by 0.6 and 0.4, respectively, whereas an increase in common rust score decreased plant height by 16.2 cm and increased plant aspect score by 0.7. Maize streak virus and common rust decreased genotypic variability for lutein by 36.7 and 18.7%, respectively, while northern corn leaf blight decreased genotypic variability for provitamin A by 27.1%. Most of the genotypes exhibited moderate susceptibility to northern corn leaf blight. However, three selection cycles and three crosses exhibited high tolerance to maize streak virus and moderate tolerance to common rust, thus can serve as sources of PVA-enriched, maize streak virus and common rust tolerant lines.

Provitamin A-enriched maize (Zea mays L.) is an important complementary food staple for combating vitamin A deficiency (VAD) in high maize-producing and maize-consuming countries of sub-Saharan Africa (SSA). However, frequent drought is a major abiotic factor that retards maize growth, resulting in yearly fluctuations in grain yield. Development of provitamin A-enriched maize varieties resilient to recurrent drought stress could enhance and stabilize maize grain yield. This study was conducted to assess the effects of managed drought stress (MDS) on the performance and heterosis of some marker-based improved provitamin A maize synthetics and their varietal-cross hybrids. The maize synthetics and their varietal-cross hybrids, along with a drought-tolerant check (PVASYN13), were evaluated under MDS and well-watered (WW) conditions at Ikenne, Nigeria, for two years. Genotype and year effects were significant for grain yield and some agronomic traits under MDS and WW conditions. Grain yield was reduced by 56% under MDS. Grain yield was significantly correlated with days to anthesis, days to silking and anthesis-silking-interval under MDS but not under WW condition. Under MDS, three varietal-cross hybrids (PVASYNHGBC0/PVASYNHGAC0, PVASYNHGBC2/PVASYNHGAC0, PVASYNHGBC0/ PVASYNHGAC1) had similar grain yields and tolerance indices as the drought-tolerant check, whereas PVASYNHGBC1/PVASYNHGAC2 produced 12.5% more grain yield than the check. Three of the varietal-cross hybrids (PVASYNHGBC0/PVASYNHGAC0, PVASYNHGBC0/PVASYNHGAC1 and PVASYNHGBC1/PVASYNHGAC2) had significant mid-parent heterosis for grain yield under the two test conditions, and were recommended for developing drought-tolerant varieties to combat VAD in drought-prone environments of SSA.

Maize is one of the most important cereal crops used as source of food and feed. Identification of suitable maize inbred lines and testers for the development of stable maize hybrids can be challenging. The assessments of the combining ability of selected maize inbred lines and testers, agronomic performance and yield stability of the resultant topcross hybrids would provide useful information that would guide the breeding program for optimum yield. Nine yellow maize inbred lines and two open-pollinated varieties (Early LN-Y and TZE-31DMRSRLNSYN) were crossed in a line × tester mating scheme. The resultant eighteen topcross hybrids together with two commercial hybrids and two candidate hybrids as checks were evaluated across eight locations in Nigeria. Significant differences were detected among the genotypes, lines, testers, line × tester and their interactions with the environment for most traits studied. Four inbred lines (TZEEIOR-197, TZEI-13, TZEI-17 and TZEIORQ-44) had significant General Combining Ability (GCA) effects for grain yield (GY), whereas TZEIORQ-44, TZEI-8 and TZEI-17 had significant GCA effects for earliness. Five topcrosses (TZE-31DMRSRLNSYN × TZEEIOR-197, TZE-31DMRSRLNSYN × TZEI-129, Early LN-Y × TZEI-13, TZE-31DMRSRLNSYN × TZEI-17 and Early LN-Y × TZEI-8) had significant specific combining ability effects for GY. The best eight topcross hybrids had comparable GY with the commercial checks. Four each of the eight hybrids were of either tester. Based on the GGE-biplot, TZE-31DMRSRLNSYN × ENT 13 was the most stable genotype across the test environments. The inbred lines with significant GCA effects and superior testcrosses were identified for future breeding programs. Key words: Grain yield, inbred lines, line × tester, testers, topcross maize hybrids. Maize is one of the most important cereal crops used as source of food and feed. Identification of suitable maize inbred lines and testers for the development of stable maize hybrids can be challenging. The assessments of the combining ability of selected maize inbred lines and testers, agronomic performance and yield stability of the resultant topcross hybrids would provide useful information that would guide the breeding program for optimum yield. Nine yellow maize inbred lines and two open-pollinated varieties (Early LN-Y and TZE-31DMRSRLNSYN) were crossed in a line × tester mating scheme. The resultant eighteen topcross hybrids together with two commercial hybrids and two candidate hybrids as checks were evaluated across eight locations in Nigeria. Significant differences were detected among the genotypes, lines, testers, line × tester and their interactions with the environment for most traits studied. Four inbred lines (TZEEIOR-197, TZEI-13, TZEI-17 and TZEIORQ-44) had significant General Combining Ability (GCA) effects for grain yield (GY), whereas TZEIORQ-44, TZEI-8 and TZEI-17 had significant GCA effects for earliness. Five topcrosses (TZE-31DMRSRLNSYN × TZEEIOR-197, TZE-31DMRSRLNSYN × TZEI-129, Early LN-Y × TZEI-13, TZE-31DMRSRLNSYN × TZEI-17 and Early LN-Y × TZEI-8) had significant specific combining ability effects for GY. The best eight topcross hybrids had comparable GY with the commercial checks. Four each of the eight hybrids were of either tester. Based on the GGE-biplot, TZE-31DMRSRLNSYN × ENT 13 was the most stable genotype across the test environments. The inbred lines with significant GCA effects and superior testcrosses were identified for future breeding programs. Key words: Grain yield, inbred lines, line × tester, testers, topcross maize hybrids.

Maize (Zea mays L.) is the foremost cereal consumed in Benin but its production is constrained by the lack of access to high-quality seeds for intensification of the crop; hence, the continued cultivation of disease-susceptible, low-yielding, and open-pollinated varieties (OPVs). The study (i) evaluated the agronomic performance and heterosis of topcross hybrids (THs) developed from a cross between new streak-resistant inbred lines and Benin-adapted OPVs, (ii) estimated the combining ability of the parental materials for grain yield (GY), and (iii) assessed the relationship between GY and other agronomic traits. Eleven OPVs were crossed to two inbred lines in a line × tester mating design to generate 22 THs. The THs were evaluated across four environments in Benin. The environment had a significant effect on GY and agronomic traits. General and specific combining ability effects were significant for GY and other traits indicating the presence of additive and non-additive gene effects. Four THs exhibited positive mid- and better-parent heterosis for GY and DMR ESR W × TZIL07A01322, which is the highest yielding TH, at 5.1 tons per hectare, had 29.1 and 13.3% yield advantages over its mid-parent and better-parent mean yields, respectively, with the potential for commercialization by indigenous seed enterprises. GY was positively associated with 100-seed weight enabling indirect selection. Four OPVs contributed favorably to observed heterosis and could serve as potential genotypes for inbred line extraction.