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Abstract Background Using a desirable tester is considered one method used to maximise genetic differences among test crosses derived from new inbred lines and improves the overall performance of maize. Thus, this study aimed to evaluate the potency of the tester with varying levels of resistance to Striga hermonthica in determining the testcross performance of the hybrids for Striga resistance and yield-related traits. Method The experiment was conducted with these test crosses and two standard checks (susceptible and tolerant) for different Striga resistance and agronomic traits during the 2018 cropping season in Abuja and Mokwa, Nigeria. The experiment was laid out in a 23 × 4 alpha-lattice design with two replications in each location. Field evaluation data was collected from Striga resistance and yield-related traits to estimate the performance of test crosses. Analysis of variance was conducted to determine the variance of the testcross performance. Results There were significant differences among test crosses for days to silking, days to pollen shedding, ear at harvest, ear aspect, ear per plant, grain yield, Striga damage rating at 8 and 10 weeks after planting (WAP), and Striga count at 8 and 10 WAP. Variations among test crosses were always higher than the corresponding variations due to the interaction between test crosses and the environment for all traits. Conclusion The inbred lines with low yield reduction crossed with different testers under Striga infested were recorded. These inbreds should be used to develop high-yielding hybrids and synthetics with elevated levels of Striga resistance to improve the maize breeding program.

Vitamin A deficiency and its associated disorders are pervasive in sub‐Saharan Africa (SSA) including many middle‐ and low‐income countries across the world. Provitamin A‐enriched maize (Zea mays L.) inbred lines with desirable agronomic and adaptive traits have been developed and used to generate and commercialize maize varieties with medium to high levels of provitamin A in a few countries to curb vitamin A deficiency. Nonetheless, these inbred lines have not been made widely available to the public and private sector breeders in many countries. The main purpose for releasing the 21 provitamin A‐enriched tropical maize inbred lines (PI 705424–PI 705444, Reg. nos. GP‐624–GP‐644) is to supply maize breeders with elite source germplasm for increasing provitamin A and other carotenoids to much higher levels to offset losses during storage, natural degradation, and processing. These inbred lines were developed at the International Institute of Tropical Agriculture (IITA) from backcrosses of high β‐carotene temperate lines as donors and elite tropical lines as recipients. These inbred lines were developed through repeated self‐pollination with rigorous visual selection among and within lines for plant vigor, synchronous silk emergence and pollen shedding, low ear placement, and resistance to lodging and major tropical diseases, followed by selection for bright yellow to orange kernel color with semi flint to flint kernel texture after harvest. The released maize inbred lines will be diverse sources of favorable alleles to accelerate genetic gain in provitamin A and other beneficial carotenoid enrichment for human health. Core Ideas: Vitamin A deficiency and its associated disorders are pervasive in sub‐Saharan Africa and other developing countries.Provitamin A‐enriched inbred lines are important for developing and commercializing maize varieties to curb Vitamin A deficiencies.Supplying tropical elite inbred lines to breeders will facilitate increasing provitamin A and other beneficial carotenoids to human health.Releasing diverse elite inbred lines promotes access to favorable alleles for further enrichment of beneficial carotenoids. [ABSTRACT FROM AUTHOR]

Maize is an important food and industrial cereal crop that serves as the main source of energy for millions of low-income people in sub-Saharan Africa (SSA), but its production and productivity are constrained by many constraints, among which the fall armyworm (FAW) is the major one. The use of insecticides is the most effective control measure for the FAW. However, excessive use of chemical insecticides has environmental and health implications, and it can be expensive for resource-poor farmers. The objective of this study was to evaluate the extent of variation in yield losses due to the FAW among some elite maize open-pollinated varieties (OPVs) under two levels of insecticide application and control (0 application). In a two-year field study, 10 elite maize OPVs were evaluated under two levels of emamectin benzoate (5% WDG) applications and the control: 75 and 150 mL of spray solution per 20 L of water. The experimental design was a randomized complete block with three replications. The data were collected on grain yield (GY) and FAW leaf damage rating (LDR). The LDR was conducted on a 1–9 scale and used to categorize the maize varieties as resistant (1–4), moderately resistant (4–6), and susceptible (6–9). Significant varietal differences were obtained for GY and LDRs. The GY of the varieties under control (0 mL), 75 and 150 mL insecticide applications ranged from 3.3 t ha−1 (DTSTR-Y SYN-13) to 4.6 t ha−1 (PVA SYN-3), from 4.5 t ha−1 (DTSTR-Y SYN-13) to 6.4 t ha−1 (PVA SYN-13), and from 4.2 t ha−1 (DTSTR-Y SYN-13) to 6 t ha−1 (DTSTR-Y SYN-14), respectively. No significant differences in GY were found between the application of 75 and 150 mL of insecticide application. The relative loss in GY among the varieties under control (0 mL) differed with an increase in the level of insecticide application. The relative GY loss at the 75 mL insecticide application ranged from 18% (PVA SYN-3) to 38% (DTSTR-Y SYN-15) with a mean of 27%, whereas at the 150 mL insecticide application, it varied from 13% (PVA SYN-3) to 42% (DTSTR-Y SYN-15), with a mean of 26%. All the varieties exhibited moderate resistance to FAW, except DTSTR-Y SYN-14, which was susceptible. The varieties PVA SYN-3 and PVA SYN-13 were the most consistent in GY across the three insecticide treatment levels. The mean performance of the varieties for FAW leaf damage ranged from 4.0 (SAMMAZ-15) to 6.2 (DTSTR-Y SYN-14), from 4.5 (SAMMAZ-15) to 6.3 (PVA SYN-6), from 4.5 (SAMMAZ-15) to 6.3 (DTSTR-Y SYN-14), and from 3.5 (SAMMAZ-15) to 5 (DTSTR-Y SYN-14) for LDR 1, LDR 2, LDR 3, and LDR 4, respectively. The use of moderately resistant varieties, combined with timely spraying of emamectin benzoate at 75 mL provided adequate management for the FAW infestation and sustained high maize grain yield. [ABSTRACT FROM AUTHOR]

Breeding maize with high contents of zinc, iron and provitamin A (PVA) could be effective in mitigating micronutrient deficiency in developing countries with a high reliance on maize-based diets. Information on the mode of inheritance of zinc, iron, PVA and grain yield (GY) would facilitate the development of varieties with enhanced contents of these nutrients. Twenty-four yellow to orange maize inbred lines and their 96 F1 hybrids generated using North Carolina Design II, were evaluated alongside four checks for two years at two locations in Nigeria. The effects of environment, hybrid and inbred line were significant for GY and contents of zinc, iron and PVA. The GY, and contents of zinc, iron and PVA of the hybrids ranged from 1.49 to 6.05 t ha−1, 22.51 to 33.33 mg kg−1, 20.04 to 29.65 mg kg−1 and 3.55 to 15.28 µg g−1, respectively. Additive gene effects controlled the accumulation of PVA and Fe, whereas both additive and non-additive gene effects controlled the inheritance of Zn and GY. Inbred lines with high general combining ability for GY and single or multiple micronutrients were identified, and could be used to develop hybrids and synthetics that combine high GY with high micronutrient content. Six hybrids combined high GY with high contents of all three micronutrients, and are recommended for further evaluation and possible release. Our study revealed the feasibility of enriching maize with multiple micronutrients without compromising grain yield. [ABSTRACT FROM AUTHOR]

Identifying efficient testers for separating maize (Zea mays L.) inbred lines into heterotic groups can facilitate the development of superior hybrids. Striga-resistant yellow-maize inbred lines developed at the International Institute of Tropical Agriculture (IITA) do not have well established heterotic groups. This study was conducted to identify efficient testers for classifying yellow-maize inbred lines into heterotic groups. Thirty Striga-resistant inbred lines were crossed with three testers having varying levels of resistance to Striga. A trial comprising 90 testcrosses and two hybrid checks was conducted at two locations in Nigeria for 2 years under Striga-infested and non-infested conditions. The approach that involved specific combining ability (SCA) effects and mean grain yields was found to be more efficient than the heterotic group's specific and general combining ability (HSGCA) grouping method in separating the 30 inbred lines into three heterotic groups. The tolerant and resistant testers were highly efficient in grouping the inbred lines into heterotic groups under Striga-infested and non-infested conditions using the two approaches. Striga-resistant yellow inbred lines assigned to two of the three major heterotic groups could be used as parents for developing superior hybrids and/or synthetics and for generating source populations for developing new maize inbred lines. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Striga hermonthica and drought are the major stresses limiting maize yields in sub-Saharan Africa. The search for diverse maize lines' tolerance to drought and resistance to S. hermonthica ( DTSTHR) is very crucial for yield improvement in areas affected by the two stresses. Understanding the genetic diversity among the lines is important to develop cultivars resistant to S. hermonthica and tolerant to drought. The lines were developed from biparental crosses of drought-tolerant and Striga-resistant lines. A total of 128 DTSTHR maize lines were characterized using single-nucleotide polymorphism ( SNP) markers. Results of the cluster analysis based on 3297 SNP markers showed four distinct groups consistent with the pedigrees of the lines. Furthermore, model-based analysis also formed the same groups of the DTSTHR lines. Integrating the pedigree information with combining ability and the SNP analyses may provide defined heterotic groups for maize improvement work in West and Central Africa. These results also help breeders to utilize DTSTHR lines present at IITA for developing biparental crosses without disrupting the heterotic groups they have established in their breeding programmes. [ABSTRACT FROM AUTHOR]