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Maize consumption as human food is high in sub-Saharan Africa (SSA), but the protein quality is low because of deficiencies in two amino acids, lysine and tryptophane, which are not synthesized in the human body and must be consumed daily. In addition, maize is deficient in several micronutrients, resulting in malnourishment of its consumers. Attempts to incorporate high lysine into maize started long ago on opaque-2 to start with, and CIMMYT made efforts to improve tropical maize for the amino acid but met with limited success due to several constraints. Following the conversion of maize germplasm in WCA into streak resistance by IITA, attention was shifted to several other avenues to improve maize productivity, one of which was quality protein maize (QPM). The Ghana Maize Program made a breakthrough in 1992 and released a QPM variety named Obatanpa meaning “good nursing mother.” Since then, several other OPVs and hybrids have been developed, not only in Ghana but also in several other countries in SSA. In the case of provitamin A biofortification, introgression of favorable genes conferring the trait into early and extra-early germplasm in WCA started in 2007, and as a result, several OPVs, inbred lines, and hybrid provitamin A QPM in the two maturity groups are now available.

High-quality seed is of utmost importance in ensuring near-perfect-to-perfect stand when planted in the field, to result in increased agricultural production for sustainable food sufficiency in SSA. Maize seed technology in SSA was neglected for a long time, but the seed business has gradually started to emerge at different times and rates in SSA countries. The demand for seed is high and insatiable in the region; therefore, a high proportion of farmers, primarily small scaled, obtain seed recycled on their farms, from neighbors, or in the open market where grain is sold as seed. National and international maize programs in SSA have developed and distributed improved high-quality seeds of OPV and hybrid maize seeds, conducted research in different aspects of seed technology, supported the establishment of seed companies, developed models that link seed companies with community-based organizations (CBOs) and greatly facilitated public–private partnerships in seed production. The efforts have yielded positive results, and utilization of improved, high-quality maize seeds is on the increase in SSA.

Maize is one of the most important staple crops in sub-Saharan Africa. Its role in the nutrition and food security of the peoples of West and Central Africa (WCA) has increased tremendously during the last four decades. Consequently, research to improve the yield potential has been high in the agricultural agenda in the sub-region, initially on an individual country basis. However, most of the constraints to maize production were too formidable for individual countries to overcome. Because the constraints were crosscutting, there was an opportunity to pool the available resources to tackle the constraints and minimize duplication of efforts. Unfortunately, the different national governments of the sub-region did not really come together as an entity to address this and other agricultural research problems. The establishment of IITA in Nigeria in 1967 provided an avenue and a unique opportunity for establishing such an entity. The Institute’s research efforts were initially limited to Ibadan and environs from where it gradually fanned out to other parts of Nigeria, moved on to other WCA countries and now to much of Africa south of the Sahara desert. Mandatorily, IITA must work in collaboration with NARS thus making it possible for the Institute, within a short time of its existence, to identify the research strengths and weaknesses of the WCA countries in particular. As had been known to the NARS researchers, IITA soon discovered that the savanna agroecology, particularly the Northern Guinea savanna, had the greatest potential for maize production in WCA. IITA’s scientists started maize research in the Nigeria savanna zones in 1980 and clearly targeted maize varieties of different maturities to the agroecology. Intermediate-to-late maturing varieties were available for the lowland savannas, but much of the savannas needed early and extra-early varieties, while the mid-altitude agroecology needed specific varieties all of which, unfortunately, were not available. Therefore, breeding efforts were initiated along these lines, and it became necessary to cover the whole of WCA. In 1977, foreign ministers of WCA met to discuss and proffer solution to the problem of recurrent drought which was plaguing the sub-region. One of the outcomes of the meeting was the establishment of the Semi-Arid Food Grain Research and Development (SAFGRAD) project comprising several commodity networks, including maize. Research on early and extra-early maize was devolved on the maize network of SAFGRAD, and in 1987, the maize network became autonomous and was named West and Central Africa Collaborative Maize Research Network (WECAMAN). The Network served as an effective mechanism for all stakeholders in maize production and productivity to tackle the regional constraints from 1987 to 2007. These included national and international scientists, extension workers, farmers, seed technologists, industrialists, and policymakers.

Genotypes may differ considerably in the magnitude of performance in different environments. When genotypes perform differently in variable environments, genotype x environment interaction (G x E or GEI) has occurred. GEI poses a big challenge to maize breeders when developing varieties for release to farmers in a large geographical area, which is the case in West Africa (WA). Compulsorily, multi-locational environment trials (METs), involving the evaluation of a set of genotypes or varieties in many different environments within agroclimatic zones of WA, are used to identify stable, high-yielding genotypes for registration, release, and commercialization. The test locations used for the different types of Regional Uniform Variety Trials (RUVTs) since the time of WECAMAN (RUVT-early and RUVT extra-early) and now the DTMA/STMA trials for drought-tolerant varieties are not very representative and precisely discriminating. Therefore, there is a need to sample more testing sites in WA, using modern cultivars with high variation in mean performance; varieties developed during the last decade to identify sites which possess high representativeness, discriminating ability, and repeatability. In addition, because WA is large with several distinct agroclimatic zones that cut across the countries of the sub-region, there is a need to identify mega-environments for cultivar evaluation, release, and commercialization across WA. Such sites would be more appropriate for use in evaluating and selecting superior drought-tolerant genotypes as well as for serving as core testing sites within each agroclimatic zone, thereby minimizing human labor and research expenses. Several statistical tools are available for the analysis of data from METs. Among the most powerful tools are the additive main effects and multiplicative interaction (AMMI) and the GGE biplot. Many sets of data obtained during the last three decades were subjected to the statistical tools and the procedures used, results obtained, interpretation of the results, and possible application of the outcome to boost maize production in WA are presented in this Chapter.

Promotion and adoption of early and extra-early maturing normal endosperm and quality protein maize (QPM) developed by IITA, CIMMYT, and partners in SSA have significantly contributed to the rapid spread of maize in the sub-region, making it the most important cereal crop after rice. The availability of the early and extra-early varieties and hybrids has resulted in improvements in the productivity of maize, income, and well-being of people in the sub-region. Apart from being a source of human food and a major component of livestock feed, maize has become an indispensable industrial raw material for the production of grits, flour, breakfast cereals, baby foods, baked foods, alcoholic and nonalcoholic beverages, and other products in SSA. As a result of research undertaken by IITA, CIMMYT, DTMA, WECAMAN, NARS, and other institutions, a large number of improved maize varieties have been developed, and the area planted to these varieties continues to expand. Studies show that in 2005, of the 7 million ha planted to maize in nine WCA countries, over 4 million, representing about 60% of the area, had been planted to improved varieties. Over half of this impact has been attributed to maize research. Since the inception of the DTMA Project in 2007, there have been successes in the development and dissemination of drought-tolerant maize varieties including the multiple stress-tolerant early and extra-early varieties developed under the DTMA/STMA Project. About 160 DTM varieties (DTMVs) have been developed between 2007 and 2014. Most of these varieties have been successfully disseminated to maize farmers in 13 African countries in Western, Central, Eastern, and Southern Africa.

Population improvement is usually done by recurrent selection, a procedure that generally involves three basic stages of field work: development of progenies from the population being improved, evaluation of the progenies in field trials and selection of a certain percentage of the progenies based on their top performance, and recombination of the selected progenies to generate another population from which progenies will again be developed to repeat the cycle of selection. There are two groups of recurrent selection: intrapopulation methods that concentrate on one population per se and interpopulation methods that improve two populations simultaneously. Two populations each of early and extra-early maturing maize were developed in WCA and subjected to recurrent selection for biotic and abiotic stress tolerance/resistance, along with grain yield and some other traits. The selection programs were evaluated and found to be effective after several cycles of recurrent selection. In addition, experimental varieties extracted from the improved cycles were higher yielding and more tolerant/resistant to some specific stresses.

Heterosis, the superior performance of a hybrid over the average of its two parents (known as mid-parent heterosis) or over the better parent (known as heterobeltiosis), is an indispensable concept in maize breeding, especially in the hybrid development programs. The level of expression of heterosis is determined by genetic diversity of the parental lines, type of gene action controlling the trait under consideration, type of testers used to evaluate the parental lines, and environmental factors. At the initial stages of genetic improvement of maize, statistical and quantitative determination of heterosis was established. The concept of combining ability was introduced and used to identify parental lines whose hybrids were highly heterotic. Combining ability estimates have also been used to classify maize germplasm into heterotic groups and heterotic patterns to maximize maize productivity in hybrid combinations. Recently, molecular approaches have been used to refine genetic diversity and combining ability studies and this has resulted in higher hybrid maize productivity at relatively faster and cheaper rates. Presently trending are two efficacious models, one of which was developed by IITA maize breeders and their national scientist collaborators for heterotic classification of inbred lines in hybrid production. Details of the different approaches, along with empirical evidence for classification of early and extra-early maize germplasm into heterotic groups in SSA, are presented in this Chapter.

The maize production environments in sub-Saharan Africa (SSA) are conducive to the development of many disease-causing organisms, which have infected the crop, causing serious reduction in maize production and productivity. Some maize diseases infect maize in all SSA ecologies, while some others are specific to some environments and absent from others. The prominent maize diseases in SSA changed over time, and presently, the most devastating are gray leaf spot (GLS), incited by Cercospora zeae-maydis; northern corn leaf blight, incited by Exserohilum turcicum; southern corn rust (Puccinia polysora); maize streak virus (MSV) disease, transmitted by the leafhopper, Cicadulina mbila; downy mildew, by Peronosclerospora sorghi; ear rots, incited by several fungi, including Aspergillus sp. and Fusarium sp.; and the recently discovered disease that is spreading fast across SSA, the maize lethal necrosis (MLN), a disease incited by the synergistic effect of maize chlorotic mottle virus (MCMV; Tombusviridae: Machlomovirus) and several other potyvirus, such as maize dwarf mosaic virus (MDMV), sugarcane mosaic virus (SCMV), and wheat streak mosaic virus (WSMV). There are several methods used for disease control, but the most effective and economic method is breeding for host plant resistance. In this chapter, four case studies of this breeding approach are presented and their effectiveness in SSA clearly highlighted.

Early knowledge of the weather factors of sub-Saharan Africa (SSA) showed that the agroclimatic zones were characterized by consistent and fairly predictable onset and recession of the rainy season. Although sporadic dry spells could occur during the season, they were exceptions rather than the rule until agrometeorologists started reporting what is now known globally as climate change. Drought occurs at the beginning and towards the end of the season, as well as at any growth stage of the maize crop. Flowering the early part of grain-filling periods are the two most drought-sensitive growth stages of maize. Drought effects can be minimized by using supplemental irrigation, raising the crop in hydromorphic soils, or planting drought-tolerant varieties. The latter is the most durable control method and the cheapest to the farmer. Maize breeders at CIMMYT and IITA, in collaboration with their counterparts in the national programs of SSA countries and with financial support from international donor agencies such as USAID and Bill & Melinda Gates Foundation, have worked out the best screening method for drought tolerance (DT) and developed DT maize varieties in all maturity groups of the crop.

Regional trials involving extra-early (80–85 days) and early (90–95 days) cultivars have been organized annually by IITA and the NARS partners of WCA during the last two decades. The trials serve as the vehicle for dissemination of germplasm and cultivars among the NARS. The trials offer NARS partners the opportunity to select promising and stable cultivars for on-farm testing and release. Usually, a national variety release committee ensures that varieties with outstanding performance are released. Therefore, before a variety is released, it has to be tested in multi-location trials over a number of years on-station and on-farm to verify superior performance and expose the new technologies to farmers. The difficulties with existing variety release systems have resulted in delayed access by farmers to new maize varieties. A protocol on seed signed by the Heads of States of ECOWAS member countries in 2009 and the West African Catalogue of Plant Species and Varieties (COAFEV) have been published. The seed catalogue offers unique opportunity for movement of good quality seed of improved maize varieties and hybrids across borders of WCA countries for production and marketing. As a result, the mega-environments and core testing locations in WCA have been re-assessed for efficient and successful development of maize cultivars with high-yield potential adapted to various agroecologies for increased adoption by farmers. Support is presently provided by DTMA/STMA Project to seed companies to produce seed of available varieties, in order to increase dissemination of seed of improved drought-tolerant maize varieties in WCA.

Drought, Striga, and low-nitrogen, along with several other abiotic and biotic stresses occur simultaneously in the field in sub-Saharan Africa, and the combined effect is drastic reduction in grain yield. Consequently, the current ultimate goal of maize improvement programs in SSA is to breed for biotic and abiotic stress tolerance and high grain yield under the three specific stress factors presently plaguing maize production in SSA. Population improvement and inbred–hybrid methods have been employed with reliable artificial field infestation and screening methods to enhance resistance to the stresses in the breeding materials. The products of the IITA Maize Improvement Program include several source populations, inbred lines, high-yielding OPVs, and hybrids of varying grain types, colors, and maturities with good levels of resistance/tolerance to two or more of the endemic stresses. Early and extra-early maize populations have been improved under controlled drought stress using backcrossing and S1 recurrent selection. This has resulted in new generations of productive open-pollinated and hybrid varieties that combine enhanced levels of drought tolerance with good levels of resistance to Striga and tolerance to low N. The populations and several of the derived varieties have shown superior performance under both Striga-infested and non-infested conditions and have proved to be invaluable sources of Striga-resistant synthetics and inbred lines. Also, several open-pollinated normal endosperm white and yellow varieties, QPM, and pro-vitamin A varieties, hybrids, and inbred lines have been developed in the breeding programs with several of these released for commercialization in the sub-region to contribute to food security and increased incomes in the sub-region.

Maize (Zea mays L.), an important food, feed, and industrial crop in sub-Saharan Africa (SSA), has been researched extensively for genetic enhancement for more than a half century in the subregion. One aspect that received intensified research attention in the last three or four decades is the genetic enhancement of early and extra-early maturing germplasm for resistance or tolerance to drought, Striga, and low soil nitrogen. Improved open-pollinated varieties (OPVs) and hybrids with tolerance/resistance to the stresses and/or high levels of micronutrients such as beta carotene along with elevated levels of lysine and tryptophan are now available in SSA. A brief description of the achievements and the challenges still confronting maize breeders and geneticists is presented in this chapter.

The presence of quantitatively inherited traits in a genotype can make the testing procedure complex, unreliable, and expensive. Under such circumstances, indirect selection using molecular markers becomes an efficient complementary breeding tool. When target traits can be easily identified and linked with one or more markers, the marker loci can be used as a surrogate for the trait, resulting in greatly enhanced breeding efficiency. Marker-assisted selection (MAS) involves the use of DNA markers instead of phenotypic selection to speed up the process of development and release of cultivars. Marker-assisted selection is useful for selecting quantitatively inherited traits that are difficult or expensive to measure, exhibit low heritability, and/or are expressed late during the developmental process. The approaches to MAS include marker-assisted backcrossing (MABC) and marker-assisted recurrent selection (MARS). Marker-assisted selection exploits the tight linkage between QTL and nearby markers and was proposed as easier, faster, and more efficient selection method. However, the use of marker-assisted selection has been limited in complex traits because of low power to detect QTL and bias in the estimated marker effects. The use of markers to track transgenes or pyramid favorable alleles determining a significant proportion of the phenotypic variance is possible for many crops, including maize. It is now generally accepted that the role of MB goes beyond the manipulation of elite alleles at a few loci in biparental segregating populations. There is a need for validation of genetic gain of favorable alleles so that markers could be developed and employed.

Maize, with Mexico of Central America as its center of origin, has been introduced to Africa more than 500 years ago, possibly through two routes: the island of Sao Tome, from where it spread to the West African coast, and by Arab traders crossing the Sahara. Maize anatomy, morphology, and physiology in the temperate environments and SSA are basically similar; however, there are striking differences between the two scenarios in maize phenology. Using the attainment of a specific stage by 50% of the plants under the research condition as the common criterion, maize attains the growth stages at different time periods in the temperate compared with SSA environments. This is caused by some differences in their genetic makeup, effects of the environment, and the genotype x environment interaction effects.

Nitrogen (N) is the most important of the three primary nutrients required for good growth and productivity of the maize plant. Generally, farmers in sub-Saharan Africa (SSA) apply little or no inorganic fertilizer to their maize crop due to nonavailability and/or financial constraints. Inherent soil nutrient is low due to soil structure and texture, heavy, rapid leaching, continuous cultivation of the land, grazing, and/or removal of crop residue to feed livestock. One way out is to develop low-N tolerant varieties for farmers in the region. Therefore, selection under low N has become an important strategy of the IITA maize improvement program for developing low-N tolerant cultivars. For the early and extra-early germplasm, screening for tolerance to low N involves the exposure of the genetic materials to two levels of N fertilizer, 30 and 90 kg N ha−1. Two sites known from soil tests to have been depleted of inherent soil N are used for low-N screening: Ile-Ife in the forest agroecology and Mokwa in Sudan and Guinea savanna (SGS). In addition, Mokwa and Abuja which are the Striga screening sites also serve as indirect screening sites for low N because only 30 kg N ha−1 is applied to the Striga-infested plots, while the non-infested plots that receive optimal recommended N rate (90 kg N ha−1) serve as the control. Several studies have been conducted to determine the most appropriate traits to use as selection criteria for low-N tolerance, its genetics and response to direct and indirect selection, the genotype by N interaction, association of low-N tolerance with tolerance/resistance to other stresses, and performance of low-N varieties in farmers’ fields.

Striga hermonthica(L.) Kuntze, a parasitic weed, is endemic in a large part of the Guinea savanna of West and Central Africa (WCA). Strigaplants do much damage underground before the parasitic plants appear on top of the soil around the maize plant. The weed, which could cause 100% yield loss in the maize crop, has defied all control efforts at the national level of WCA countries thereby forcing farmers to abandon their farmlands. Teaming up with the national research scientists, IITA initiated a massive control effort on Striga. Screening and breeding were done for tolerance, the ability of the host to perform well regardless of the number of Striga plants parasitic on the host plant, as well as resistance, the ability of the host plant to reduce the number of Striga plants surviving on it. An efficacious manual infestation method was established and has been in use since its discovery. Genetics of tolerance/resistance was investigated, along with combining ability of inbred lines in hybrid seed production. Early and extra-early maize populations have been subjected to recurrent selection under Striga infestation, and the response to selection along with correlated responses in other nonselected traits has been evaluated under Striga-infested and Striga-free conditions. Early and extra-early Striga-tolerant/Striga-resistant populations, inbred lines, and hybrids are now available to farmers in the Striga endemic areas of sub-Saharan Africa (SSA). The materials also have value addition of good performance in non-Striga environments.

Apart from the Sahara desert, maize is produced in all agroclimatic zones of sub-Saharan Africa. Rainfall and, to a lesser extent, temperature are the primary climatic factors affecting the cultivation of maize in the sub-region. Intensity, distribution, and duration of rainfall decrease from the coastal areas in the south to the northern areas. High altitudes are absent in WCA, but there is a relatively small portion of the land mass occupied by mid-altitudes. Climate change seems to be negatively impacting maize growth and production in the sub-region. This chapter focuses on the changes in the weather pattern of the agroclimatic zones and how development and deployment of early and extra-early maize varieties have been well justified.

Yield is controlled by many genes, and it is highly influenced by the environment along with often high genotype × environment interaction (GEI), resulting in low heritability estimates. Secondary traits are under the control of fewer genes, have lower GEI, and are characterized by higher heritability estimates. Therefore, traits that show consistent genotypic and phenotypic relationships with yield may be more effective as selection criteria than direct selection for grain yield alone. Breeders commonly use three methods to select for several traits, including tandem selection, independent culling, and index selection. In tandem selection, individual traits are improved successively. In independent culling, individuals must surpass a certain minimum value for each trait to be selected. The plants that are outstanding in certain traits may not be selected if they do not meet the minimum standards for other traits, whereas individuals that are relatively mediocre in some traits are selected as long as they meet the cutoff value in the others. In index selection, each trait is weighted by a score, and the individual scores are summed to give a total score, which is referred to as the index value (I) for the genotype. This is an attempt to correct the weaknesses in tandem selection and independent culling methods. For example, selection for maize grain yield under severe drought stress or low-N has often been considered inefficient because the estimates of heritability of grain yield has been observed to decline with reduced yield levels characteristic of stressed environments. Under these conditions, secondary traits may increase selection efficiency provided they have adaptive value, relatively high heritability, significant genetic correlation with grain yield, and are easy to measure. Based on this, base indices for selecting for Strigaresistance, drought, low-N, and multiple stress tolerance have been developed by IITA and CIMMYT scientists for selecting for tolerance to the individual stresses and/or multiple stress tolerance. Ensuring that greater response to selection is achieved using secondary traits in combination with grain yield in a selection index rather than the primary trait per se is an important strategy in the enhancement of early and extra-early maize in SSA.

Among crops with perfect flowers, maize is unique for hybrid production because of the separation of the staminate and pistillate inflorescences on the same plant, thus making selfing and crossing easier. Although open-pollinated varieties are more popular among farmers in West and Central Africa, there is a growing demand for hybrids to take advantage of heterosis. There are different types of hybrid and different methods for developing inbred lines to produce them. IITA and CIMMYT, in collaboration with national programs and seed companies, work on hybrids adapted to the different agroecologies of SSA. The pedigree method is the most common approach for developing inbred lines in SSA, although backcrossing and elite x elite crosses or recycling of inbred lines have also been extensively utilized in the early and extra-early maize program. The doubled haploid (DH) technology is presently being used in the CIMMYT Maize Program for the development of inbreds at the DH facility established in Kenya with funding from Bill and Melinda Gates Foundation.

In SSA, as in other parts of the world, insect pests live and/or feed on all parts of the maize plant, causing losses that reach millions of dollars annually. In terms of economic importance on maize in SSA, insect pests may be grouped into three: (i) stem and ear borers, armyworms, cutworms, and grain moths, all of which are lepidopterous insects; (ii) weevils, grain borers, rootworms, and white grubs, usually generally referred to as beetles; and (iii) aphids and leafhoppers, which are presently known as virus disease inciting insects. In terms of the damage they cause and available technologies to contain them, insect pests of maize are also grouped into three; that is, field pests (stem and ear borers, armyworms, silkworms, and leafhoppers), field-to-store pests (the most common example is maize weevil, Sitophilus sp.), and the storage pests (including the maize and rice weevils, Sitophilus zeamais Moench, S. oryzae L., and more recently, Prostephanus truncantus Horn). In SSA, genetic studies and breeding for resistance have been focused primarily on the field pests, particularly the stem and ear borers. In the mid-1980s, IITA established a borer rearing facility that made it possible to infest large numbers of lines and populations for screening purposes. Borer rearing facilities are also available at Kenya Agricultural Research Institute (KARI), Katumani, and the International Center for Insect Physiology and Ecology (ICIPE), Nairobi, Kenya. Maize breeders and entomologists have used these facilities to breed for borer resistance and minimize escapes during screening. In 2015, an unprecedented invasion of armyworm occurred in SSA and is presently a challenge to maize breeders and entomologists.