Soil acidity has received less attention than other biophysical stresses such as drought and low N, despite accounting for a considerable reduction in maize (Zea mays L.) productivity in many parts of southern Africa. The line x tester mating design was used to determine the general combining ability (GCA) for grain yield of 14 maize inbred lines and the specific combining ability (SCA) of their corresponding crosses. Thirty-three single-cross hybrids were evaluated under acid and optimum soils across 11 environments over three seasons. Across environments, mean grain yield reduction ranged from 11 to 37% due to low pH. Additive gene action was more important than nonadditive gene action for grain yield under both soil conditions. Tester GCA effects were larger for grain yield than GCA effects of lines and SCA effects of crosses for both soil conditions. Tester GCA effects were less sensitive to environmental fluctuations than line GCA effects and SCA effects of crosses. Cross combinations with desirable SCA effects for grain yield were associated with high per se grain yield, which suggests that SCA was a good predictor of grain yield in this study. These crosses consisted of good x good and good x poor general combiners, which indicates that GCA was a good predictor of grain yield. Therefore, priority should be given for yield selection in progenies and hybridization of specific crosses with desirable SCA when breeding acid-soil-tolerant maize.

ABSTRACTVitamin A deficiency is rampant in Africa. High provitamin A maize (Zea mays L.) inbreds have been developed by the International Maize and Wheat Improvement Center (CIMMYT) in Mexico, but the inbred lines do not have the abiotic stress tolerance levels needed for production in sub‐Saharan Africa. In this study, 30 hybrids obtained from crosses of 22 provitamin A and five yellow elite inbred lines from the Drought Tolerant Maize for Africa (DTMA) project were evaluated with four local check hybrids (two white and two yellow) and a Zambian orange hybrid. Evaluation was done under drought, a combination of drought and heat, low N, low P, random drought stress, and optimum conditions for two seasons. Yield was reduced by 43.27, 79.55, 68.42, and 44.27% under random drought stress, managed drought stress, a combination of drought and heat stress, and low N stress, respectively. Sixteen hybrids performed better than four checks under managed drought stress. One hybrid ranked in the top 10 hybrids in all the test environments. The β‐carotene concentration of hybrids was in the expected range (4.29–12.55 μg g−1) for the first‐generation medium to high provitamin A maize genotypes, but on average, drought and low N stress reduced β‐carotene by >60%. However, some hybrids retained a high percentage of β‐carotene under stress conditions. Sufficient variability for yield and β‐carotene content was demonstrated in the hybrids to allow for effective selection.

Evaluation of regional on-farm variety trials in Eastern and Southern Africa 2011

Yield can be increased under stress conditions by manipulating the traits that limit yield under these conditions. Tassel size is one such trait. A few branched-1 mutation (Fbr1) was introduced into the maize breeding programme of CIMMYT as a strategy to improve drought tolerance. The aim of this study was to evaluate yield performance of Fbr1 maize lines and hybrids under optimum and stress environments, and to determine associations between tassel size and grain yield under stress and optimum environments. Genotype effects were highly significant for all traits and genotype by environment (GxE) interaction effects were significant for all traits except for kernel row number and anthesis silking interval. Generally Fbr1 x Fbr1 hybrids had lower grain and pollen yields, and were less adapted to abiotic stress conditions. Positive relationships between grain yield components and pollen yield components were found except for association of prolificacy with tassel branch number and total tassel length under drought stress and optimum conditions. We were expecting that the Fbr1 genotypes could potentially increase grain yield under drought stress. It seems that grain yield improvement and stress tolerance is determined by multiple factors, which, when put together can additively contribute to increased yield performance. Although reduction in tassel size could be one of these many factors that contribute to improved grain yield under stress conditions, the factor cannot bring significant improvement on its own. Our results show that the Fbr1 trait reduce pollen production in genotypes with few tassel branches resulting in reduced kernel set and the problem worsens under drought and low N stress. We recommend selection for shorter and lighter tassels to improve grain yield without compromising on tassel size to ensure sufficient pollen availability, especially under stress environments.

Single nucleotide polymorphism (SNP) markers are regarded as efficient, compared to other marker types in genetic characterization of maize (Zea mays L.) germplasm because of their vast coverage of the maize genome. The objectives of this study were to (a) genetically fingerprint 'few-branched-1' (Fbr1) and normal tasselled CIMMYT elite lines using SNP markers, to assess their relatedness and level of homozygosity and (b) to determine SNP-based genetic distance among these maize lines and to find association of genetic distances with specific combining ability (SCA), mid-parent heterosis (MPH), high-parent heterosis (HPH) and mean grain yield of the hybrids. Twenty-six CIMMYT maize lines (12 with the Fbr1 gene, and 14 normal-tasselled) were genotyped using 1074 SNP marker loci. Fifteen of these lines were used in two separate diallel mating designs: a 9x9 and 6x6 crossing set-up, to make hybrids for yield evaluation. Average residual heterozygosity of SNP loci ranged from 0.2-36.1%, with an average of 8.2%, well above the expected ranges for residual heterozygosity found in maize inbred lines. The polymorphic information content (PIC) for the 1074 SNP loci ranged from 0.015-0.50, with an average of 0.25. Mean genetic distance for all pair wise comparisons of lines was lower (0.30) suggesting a high level of relatedness among lines. A number of elite CIMMYT lines were successfully converted to Fbr1, and were homozygous for the 1074 SNP loci, thus could be used in breeding programmes involving these new tassel mutants. The unweighted paired group method using arithmetic averages (UPGMA) cluster analysis revealed two discrete clusters for the inbred lines, reflecting heterotic groups used by CIMMYT. In the principal component (PC) analysis, PC1 and PC2 explained 10.87 and 9.08% respectively, of the molecular variance in tassel size for the 1074 SNPs. The results confirmed molecular markers as a powerful complement for use in genetic characterization, in assigning lines into defined heterotic groups and in examining the relationships among inbred lines at deoxyribonucleic acid (DNA) level. Marker-based genetic distances were positively correlated with hybrid performance, SCA and heterosis indicating that they could accurately predict hybrid performance in this set of germplasm. Grain yield for the hybrids ranged from 0.49-2.48 kg/plot, with an average of 1.80 kg/plot. Hybrids from closely related parental lines (according to SNP-based genetic distances) had the lowest mean grain yield, lowest SCA effects for grain yield, and had the lowest heterosis values. Thus, SNP-based genetic distance information would be useful for effective selection by avoiding genetically similar lines when selecting parents for breeding programmes that require genetically diverse lines as parents.

Open‐pollinated varieties (OPVs) still represent a significant proportion of the maize (Zea mays L.) seed system in many countries of sub‐Saharan Africa. The International Maize and Wheat Improvement Centre (CIMMYT) has been breeding improved maize varieties for the stress‐prone environments experienced by most smallholder farmers in eastern and southern Africa for over 30 yr. Hybrid breeding is now the major focus of the CIMMYT breeding pipeline. However, OPVs are generated within the hybrid pipeline. This is the first study to document genetic gain for maize grain yield under both optimal and stress (random and managed drought, low nitrogen [N], and maize streak virus [MSV]) conditions within the CIMMYT eastern and southern African OPV breeding pipeline. Genetic gain was estimated using the slope of the regression on the year of OPV release in regional trials over a 12‐yr period (1999–2011). Open‐pollinated varieties were separated into two maturity groups, early (<70 d to anthesis) and intermediate‐late (>70 d to anthesis). Genetic gain in the early maturity group under optimal conditions, random drought, low N, and MSV was 109.9, 29.2, 84.8, and 192.9 kg ha−1 yr−1. In the intermediate‐late maturity group, genetic gain under optimal conditions, random drought, low N, and MSV was 79.1, 42.3, 53.0 and 108.7 kg ha−1 yr−1. No significant yield gains were made under managed drought stress for both maturity groups. Our results show continued improvement in OPVs for both yield potential and stress tolerance.

Maize is not inherently tolerant to soil acidity but due to the ever increasing demand for the crop in the developing world, production of maize on acid soils continues to expand. Breeding for maize acid soil tolerance is the best strategy to improve yield under these conditions. Therefore, the current study was done to determine the general combining ability (GCA) of eight acid-soil tolerant and susceptible inbred lines and the specific combining ability (SCA) of cross combinations of these lines for grain yield under acid and non-acid soils. The eight lines were crossed using a diallel mating design to produce 28 single cross hybrids for evaluation under acid and non-acid soils at four sites for two seasons. Line C2 was the best general combiner under both soil environments while A2/C1 and A1/C2 had the highest desirable SCA effects under optimal conditions. Loss in grain yield and sensitivity to low pH stress was higher among genotypes in light textured soils than heavy soils. Non-additive gene action was more important than additive gene action in conditioning grain yield under both environments. Results revealed that it was feasible to improve grain yield under low pH and optimum soils from the set of genotypes used in the current study.

Genetic gain within the CIMMYT Eastern and Southern Africa (ESA) hybrid maize (Zea mays L.) breeding program from 2000 to 2010 was recently estimated at 0.85 to 2.2% yr−1 under various environmental conditions. Over 100 varieties were disseminated from CIMMYT to farmers in ESA, hence the need to check genetic diversity and frequency of use of parents to avoid potential narrowing down of the genetic base. Fifty‐five parents from CIMMYT ESA used in the hybrids were fingerprinted using genotyping‐by‐sequencing. Data analysis in TASSEL and MEGA6 generated pairwise genetic distances between parents of 0.004 to 0.4005. Unweighted pair group method with arithmetic mean (UPGMA) analysis produced two clusters (I and II) with two subclusters each (A and B) and two sub‐subclusters (IAi and IAii). Principal coordinate analysis produced three clusters where IAi and IIA from the UPGMA analysis formed independent clusters while IAii, IB, and IIB clustered together. Lines were separated by pedigree and origin. Ninety‐five percent frequency of pairwise genetic distances ranged between 0.2001 and 0.4000. However, only four of the 55 parents (CML444, CML395, CML312, and CML442) were each used in 15 to 30 of the 52 hybrids evaluated in the genetic gain study. The remaining 51 were used in one to four hybrids. Frequent use of the four parents gave 29 to 58% of the hybrids a narrow genetic base, posing risk in case of pest or disease outbreaks. Parents evaluated do not represent the genetic base of CIMMYT ESA but parents of the best‐performing hybrids selected from 2000 to 2010. Breeders should ensure a wide genetic base for released varieties to avoid breakdown in case of pest or disease outbreaks.

Hybrid crops are underutilized in many developing countries. Subsistence farmers in sub-Saharan Africa (SSA) rely predominantly on outdated hybrids and open-pollinated varieties, which has limited the region's ability to achieve food security and agricultural sustainability goals. Key challenges in SSA include lack of access to improved hybrid seed, insufficient infrastructure to support a formal seed system, and limited smallholder farmer access to input and output markets. Implementing improved seed systems and creating greater market access will require engagement from the public and private sector and the governments within Africa. This paper reviews the importance of hybrids in agriculture, the challenges associated with creating new hybrids, and the technological advancements that will enable more efficient production of quality hybrids in Africa.

La semilla de maiz hibrido proporciona a los agricultores variedades que poseen caracteristicas geneticas mejoradas, como el alto potencial de rendimiento y combinaciones de caracteres unicas para combatir las enfermedades y condiciones de cultivo adversas. Sin embargo, la calidad de la semilla hibrida depende fundamentalmente de los metodos de produccion en campo que se utilicen ––los cuales deben cumplir con normas que garanticen la calidad–– y de la implementacion de un manejo agronomico apropiado. Si bien la produccion de semilla de variedades de maiz de polinizacion libre es relativamente sencilla, la produccion de semilla hibrida requiere que se apliquen practicas de campo adicionales que son esenciales para lograr una buena produccion.

The potential impacts of investing in drought tolerant maize (DTM) in 13 countries of eastern, southern and western Africa were analyzed through an innovative economic surplus analysis framework, to identify where greatest economic returns and poverty reduction may be achieved. Assuming a potential full replacement of improved varieties with DTM varieties, by 2016 there would be economic gains of US$ 907 million over all countries under conservative yield gains, or US$ 1,535 million under optimistic yield gains. Largest gains in terms of consumer and producers surplus are in Nigeria, Zimbabwe and Malawi. However, in terms of production gains and poverty reduction, the countries gaining most are Nigeria, Kenya and Malawi (in terms of production); and Zimbabwe, Malawi and Kenya (number of people out of poverty). A total of 4 million people — both producers and consumers— would have their poverty greatly reduced in all countries. To achieve these impacts, deployment strategies are discussed and various options are suggested, which depend on local context and state of the national seed sectors.

Quality protein maize (QPM) technology is relatively new in Zimbabwe and farmer awareness of QPM was low. Participation of smallholder farmers in the development of QPM breeding objectives and dissemination strategies was solicited through participatory rural appraisal (PRA) techniques. Seventy two farmers participated; the farmers were involved in the Mother Baby Trial (MBT) projects in four selected villages from three districts of Zimbabwe. Data collection techniques included work-sharing, village or resource mapping, Venn diagramming, semi structured interviewing, matrix scoring and ranking and pairwise ranking. The results suggested that protein malnutrition was prevalent in the districts. Maize was the most important crop and farmers grew three types of maize, namely landrace ("Hickory King"), open pollinated varieties (OPV) and hybrid varieties all representing normal endosperm maize. Hybrids were dominant and produced mainly for sale, while "Hickory King", although not supported by the formal seed system, continued to be produced for home consumption because of its superior taste, white kernel color, large kernel size, high kernel density, kernel hardness, and perceived weevil-resistance. Lateness and foliar disease susceptibility were the disadvantages of Hickory King. The ideal maize variety should be early-maturing, with a high yield potential, drought tolerant, foliar disease resistant and stem borer tolerant. For any QPM variety to be acceptable, farmers expected it to combine the agronomic attributes of hybrids and the grain quality characteristics of "Hickory King", an "heirloom" variety. To effectively promote the adoption of QPM, the Agricultural Research and Extension (AREX) arm of government was the farmers' choice compared to other modes of information dissemination which were radio, television, newspaper, church NGO and councillor.

This study aimed at estimating the implicit prices farmers are willing to pay (WTP) for maize traits with deliberate focus on drought tolerance. Using choice experiment, we generated 12600 observations from a random sample of 1400 households in communal areas within 14 districts of Zimbabwe. Taste parameters and heterogeneities (scale and residual taste) were estimated using the generalized multinomial logit model (G-MNL) and its different versions. Drought tolerance, grain yield, large grain size, covered cob tip, big cob and semi flint texture were the most preferred traits by rural Zimbabweans. The WTP values were estimated using the WTP space approach. Sample farmers are, for example, willing to pay a premium for drought tolerance that is 1.75 times the amount they are willing to pay for an increase of 1 ton in grain yield per acre, 8.3 times the value they attach for a change from small to big cob size, and 14.7 times the willingness to pay for semi-flint texture over dent texture of maize. The uncertainty that DT might not be appealing to poor farmers as much as some other technologies can only be cleared only if the promotion of DT materials is done in the right manner and to the right farm community. Innovative ways of promoting DT maize vis-a-vis creating awareness in contextual understanding of drought and drought risk shall be employed to enhance adoption of new DT maize varieties by risk prone farming communities. Given the high level of rural literacy and the high rate of adoption of improved maize in Zimbabwe, trait based promotion and marketing of varieties would be the right strategy.

ABSTRACT The seed industry in southern Africa (Angola, Malawi, Mozambique, Zambia and Zimbabwe) has three important features: first, dominance of the government as buyer and distributor of seed; second, a high market share and power of few seed companies; and third, a sustained but incomplete effort to harmonize the seed policy in the region. The challenges the seed industry is facing are lack of basic seed, poor production infrastructure, lack of skill in seed production, challenges to access and multiply seeds of varieties released from public institutions, lack of purchasing power among smallholder farmers, high transaction cost of seed marketing, market-distorting interventions by governments, lack and misuse of market information, free riding, lack of working capital financing, and breaching of contract by seed growers. Important policy implications have been drawn from this study, which include strengthening national research systems, strategic capacity building along the maize seed value chain, improving the access to financial services, developing and implementation of agreed protocols of SADC for seed policy harmonization.

Given the accumulating evidence of climate change in sub-Saharan Africa, there is an urgent need to develop more climate resilient maize systems. Adaptation strategies to climate change in maize systems in sub-Saharan Africa are likely to include improved germplasm with tolerance to drought and heat stress and improved management practices. Adapting maize systems to future climates requires the ability to accurately predict future climate scenarios in order to determine agricultural responses to climate change and set priorities for adaptation strategies. Here we review the projected climate change scenarios for Africa’s maize growing regions using the outputs of 19 global climate models. By 2050, air temperatures are expected to increase throughout maize mega- environments within sub-Saharan Africa by an average of 2.1°C. Rainfall changes during the maize growing season varied with location. Given the time lag between the development of improved cultivars until the seed is in the hands of farmers and adoption of new management practices, there is an urgent need to prioritise research strategies on climate change resilient germplasm development to offset the predicted yield declines.

Nutritional advantages of quality protein maize (QPM) (Zea mays L.) over normal endosperm maize (NM) were previously demonstrated by several researchers. However, QPM grain quality loss occurs when a QPM crop receives pollen from NM. This is because the opaque-2 gene allele that confers the QPM trait is recessive. The objective was to estimate outcrossing levels and patterns in QPM growing adjacent to NM. White grain QPM crops were grown on nine blocks of 0.21 ha each surrounded by at least a 10-m band of yellow NM at two sites in Zimbabwe. At maturity 160 samples of five QPM ears each were randomly selected to determine outcrossing. Outcrossing was estimated as percentage of yellow kernels on each ear. Ordinary kriging was used to estimate outcrossing levels in areas that were not sampled. Both prediction and error surfaces were produced for each block using the best ordinary kriging model out of the available 11 in ArcMAP 9.2 computer package. Results indicated that five models (exponential, stable, pentaspherical, rational quadratic, and J-Bessel) predicted outcrossing patterns of the nine experiments. Outcrossing levels were high (63 to 83%) in the peripheral areas of the QPM crops, but less than 20% outcrossing was observed on at least 60% of each of the crop areas with no significant compromise of QPM quality based on a QPM quality index of 0.8. In conclusion, QPM and NM can coexist, and ordinary kriging could be used in visualizing spatial distribution of outcrossing in a QPM crop.