An integrated molecular and conventional breeding scheme for enhancing genetic gain in maize in Africa

Open Access Journal; Published online: 06 Nov 2019Maize production in West and Central Africa (WCA) is constrained by a wide range of interacting stresses that keep productivity below potential yields. Among the many problems afflicting maize production in WCA, drought, foliar diseases, and parasitic weeds are the most critical. Several decades of efforts devoted to the genetic improvement of maize have resulted in remarkable genetic gain, leading to increased yields of maize on farmers’ fields. The revolution unfolding in the areas of genomics, bioinformatics, and phenomics is generating innovative tools, resources, and technologies for transforming crop breeding programs. It is envisaged that such tools will be integrated within maize breeding programs, thereby advancing these programs and addressing current and future challenges. Accordingly, the maize improvement program within International Institute of Tropical Agriculture (IITA) is undergoing a process of modernization through the introduction of innovative tools and new schemes that are expected to enhance genetic gains and impact on smallholder farmers in the region. Genomic tools enable genetic dissections of complex traits and promote an understanding of the physiological basis of key agronomic and nutritional quality traits. Marker-aided selection and genome-wide selection schemes are being implemented to accelerate genetic gain relating to yield, resilience, and nutritional quality. Therefore, strategies that effectively combine genotypic information with data from field phenotyping and laboratory-based analysis are currently being optimized. Molecular breeding, guided by methodically defined product profiles tailored to different agroecological zones and conditions of climate change, supported by state-of-the-art decision-making tools, is pivotal for the advancement of modern, genomics-aided maize improvement programs. Accelerated genetic gain, in turn, catalyzes a faster variety replacement rate. It is critical to forge and strengthen partnerships for enhancing the impacts of breeding products on farmers’ livelihood. IITA has well-established channels for delivering its research products/technologies to partner organizations for further testing, multiplication, and dissemination across various countries within the subregion. Capacity building of national agricultural research system (NARS) will facilitate the smooth transfer of technologies and best practices from IITA and its partners

Agronomic performance of elite drought tolerant maize (Zea mays L.) hybrids under natural disease inoculation in the rainforest of Nigeria.

The tropical rainforest agroecology is highly vulnerable to a myriad of plant disease infections and the likelihood that farmers would adopt a new maize cultivar largely depends on its resistance to the common diseases. In the present study, a set of newly developed single cross drought tolerant maize hybrids were evaluated under natural disease inoculation and their performance for grain yield, breeder’s traits, and response to infections by four cosmopolitan foliar diseases were assessed. A trial comprising 96 experimental hybrids and 4 hybrid checks were planted over two rainy seasons at Ikenne using a 10 x 10 triple-­‐lattice design. Hybrids differed significantly (p < 0.0001) for grain yield and other measured traits. Significant hybrid x year interaction was also observed for all traits except plant aspect. Ranking of mean grain yields of hybrids between the two years revealed moderate but highly significant correlation (r = 0.50, p < 0.0001). All measured traits except curvularia were negatively and significantly correlated (r = -­‐0.16 to -­‐0.58, p < 0.0001) with grain yield. Mean grain yields ranged between 2,282 and 6,132 kg ha-­‐1 with a trial mean of 4,509 kg ha-­­‐1. The top five yielders exceeded the best drought tolerant check (M1026-­‐7; 5,485 kg ha-­­‐1) by a least 2 standard errors whereas the top 20 hybrids produced significantly higher yields than the best commercial check (Oba 98; 4,150 kg ha-­­‐1) and had mostly favorable scores for the breeder’s traits and response to foliar disease infections. Promising high yielding and drought tolerant hybrids that have appreciable resistance to common foliar diseases can be selected among the tested genotypes

Quantitative trait loci mapping for resistance to maize streak virus in F2: 3 population of tropical maize

Open Access Article; Published online: 01 Feb 2020Maize streak virus (MSV) continues to be a major biotic constraint for maize production throughout Africa. Concerning the quantitative nature of inheritance of resistance to MSV disease (MSVD), we sought to identify new loci for MSV resistance in maize using F2:3 population. The mapping population was artificially inoculated with viruliferous leafhoppers under screenhouse and evaluated for MSVD resistance. Using 948 DArT markers, we identified 18 quantitative trait loci (QTLs) associated with different components of MSVD resistance accounting for 3.1–21.4% of the phenotypic variance, suggesting that a total of eleven genomic regions covering chromosomes 1, 2, 3, 4, 5 and 7 are probably required for MSVD resistance. Two new genomic regions on chromosome 4 revealed the occurrence of co-localized QTLs for different parameters associated with MSVD resistance. Moreover, the consistent appearance of QTL on chromosome 7 for MSVD resistance is illustrating the need for fine-mapping of this locus. In conclusion, these QTLs could provide additional source for breeders to develop MSV resistance

Maize genetic improvement for enhanced productivity gains in West and Central Africa

During the past 45 years, the genetic improvement programs of IITA and its partners have made spectacular progress in developing high-yielding crop varieties that offered best-bet solutions to major production constraints, such as, cassava mosaic, maize streak, Striga, soybean rust, insect pests, and even drought. These have led to dramatic increases in the production of cassava, maize, soybean, cowpea, and yam in sub-Saharan Africa that have directly contributed to increases in food availability and indirectly to improvements in national economies. This section presents the status, progress, and achievements, and also outlines future work on crop improvement by genetic enhancement in IITA's six crops

Retention of Pro-vitamin A Carotenoids in Ogi Powder as Affected by Packaging Materials and Storage Conditions

The effect of different packages and storage conditions on the retention of pro-vitamin A carotenoids (pVAC) in ogi powder produced from yellow-seeded maize was investigated to study its storage stability on micronutrient retention. The ogi powder produced was packaged in a high-density polyethylene bag (HDPE), a polypropylene woven sack (PP), and a polyvinyl chloride container (PVC), and stored in different conditions for 12 weeks with sampling done at three-week intervals for pVACanalysis. At the end of the storage period, ogi powder packaged in HDPE stored outside the storage box had the highest percentage retention (31.32%) of trans-β-carotene and that packaged in PVC container stored in the lighted compartment had the least (21.57%). Therefore, HDPE could be a good package for the retention of trans-β-carotene (which is the most bioactive) in ogi powder when stored at a temperature of 27°C and relative humidity of 73%

Optimizing sample size for molecular characterization of open-pollinated maize (Zea mays L.) varieties using simple sequence repeat markers

Molecular-based characterization of open-pollinated varieties (OPVs) in maize is useful to define their unique profiles. A total of 58 SSR markers selected from a panel of 70 were used for genotyping three samples of 30, 50 and 100 plant bulks for each of 32 OPVs. The SSR markers detected a total of 253 alleles in the 32 maize OPVs across the three bulk samples. The number of alleles per marker varied from 2 to 7, with an overall mean of 4.36. The genetic distance among the OPVs varied from 0.17 to 0.93 with an average of 0.70 ± 0.007 for bulk samples of 30 plants, 0.20 to 0.91 with an overall mean of 0.70 ± 0.007 for bulk samples of 50 plants and from 0.30 to 0.95 with an average of 0.75 ± 0.006 for bulk samples of 100 plants. Cluster analysis separated the 32 maize OPVs into two major groups, which were further separated into two sub-groups for each type of bulk sample. The groupings of the OPVs into two major groups and their corresponding sub-groups was consistent with known breeding history (common parentage) and common target traits during development of the OPVs irrespective of the sample size used. However, in the bulk samples of 50 and 100 plants, some sub-groups were composed of OPVs with mixed maturity classes and diverse genetic backgrounds. Of the three independent bulk samples, the smallest sample size of 30 plants was found to be optimal for characterizing heterogeneous and heterozygous maize populations and OPVs owing to its cost-effectiveness and relative ease of sample processing

Stacking tolerance to drought and resistance to a parasitic weed in tropical hybrid maize for enhancing resilience to stress combinations

Open Access JournalMaize is a food security crop cultivated in the African savannas that are vulnerable to the occurrence of drought stress and Striga hermonthica infestation. The co-occurrence of these stresses can severely damage crop growth and productivity of maize. Until recently, maize breeding in International Institute of Tropical Agriculture (IITA) has focused on the development of either drought tolerant or S. hermonthica resistant germplasm using independent screening protocols. The present study was therefore conducted to examine the extent to which maize hybrids simultaneously expressing resistance to S. hermonthica and tolerance to drought (DTSTR) could be developed through sequential selection of parental lines using the two screening protocols. Regional trials involving 77 DTSTR and 22 commercial benchmark hybrids (STR and non-DTSTR) were then conducted under Striga-infested and non-infested conditions, managed drought stress and fully irrigated conditions as well as in multiple rainfed environments for 5 years. The observed yield reductions of 61% under managed drought stress and 23% under Striga-infestation created desirable stress levels leading to the detection of significant differences in grain yield among hybrids at individual stress and non-stress conditions. On average, the DTSTR hybrids out-yielded the STR and non-DTSTR commercial hybrids by 13–19% under managed drought stress and fully irrigated conditions and by −4 to 70% under Striga-infested and non-infested conditions. Among the DTSTR hybrids included in the regional trials, 33 were high yielders with better adaptability across environments under all stressful and non-stressful testing conditions. Twenty-four of the 33 DTSTR hybrids also yielded well across diverse rainfed environments. The genetic correlations of grain yield under managed drought stress with yield under Striga-infestation and multiple rainfed environments were 0.51 and 0.57, respectively. Also, a genetic correlation between yields under Striga-infestation with that recorded in multiple rainfed environments was 0.58. These results suggest that the sequential selection scheme offers an opportunity to accumulate desirable stress-related traits in parents contributing to superior agronomic performance in hybrids across stressful and diverse rainfed field environments that are commonly encountered in the tropical savannas of Africa

Markertrait association analysis of functional gene markers for provitamin A levels across diverse tropical yellow maize inbred lines

Background: Biofortification of staple crops is a cost effective and sustainable approach that can help combatvitamin A and other micronutrient deficiencies in developing countries. PCR -based DNA markers distinguishingalleles of three key genes of maize endosperm carotenoid biosynthesis (PSY1, lcyE and crtRB1) have been developedto facilitate maize provitamin A biofortification via marker assisted selection. Previous studies of these functionalDNA markers revealed inconsistent effects. The germplasm previously employed for discovering andvalidating these functional markers was mainly of temperate origin containing low frequencies of the favourableallele of the most significant polymorphism, crtRB1-5_TE. Here, we investigate the vitamin A biofortification potentialof these DNA markers in a germplasm panel of diverse tropical yellow maize inbred lines, with mixed geneticbackgrounds of temperate and tropical germplasm to identify the most effective diagnostic markers forvitamin A biofortification.Results: The functional DNA markers crtRB1-5_TE and crtRB1-3_TE were consistently and strongly associated withprovitamin A content across the tropical maize inbred lines tested. The alleles detected by these two functionalmarkers were in high linkage disequilibrium (R2 = 0.75) and occurred in relatively high frequency (18%). Genotypescombining the favourable alleles at the two loci (N = 20) displayed a 3.22 fold average increase in _-carotenecontent compared to those genotypes lacking the favourable alleles (N = 106). The PSY1 markers were monomorphicacross all of the inbred lines. The functional DNA markers for lcyE were associated with lutein, and with the ratio ofcarotenoids in the alpha and beta branches, but not with provitamin A levels. However, the combined effects of thetwo genes were stronger than their individual effects on all carotenoids.Conclusions: Tropical maize inbred lines harbouring the favourable alleles of the crtRB1-5_TE and 3_TE functionalmarkers produce higher levels of provitamin A. Such maize lines can be used as donor parents to speed up thedevelopment of provitamin A biofortified tropical maize varieties adapted to growing conditions and consumerpreferences, providing a route towards mitigation of vitamin A malnutrition in Sub-Saharan Africa

Performance of tropical maize hybrids under conditions of low and optimum levels of nitrogen fertilizer application grain yield, biomass production and nitrogen accumulation

Nitrogen (N) is the most limiting mineral nutrient in the soils of the major maize producing areas of West and Central Africa. Low soil N and sub-optimal application of N fertilizers lead to N deficiency and poor grain yield (GY) in maize. Maize varieties with improved grain yield under low soil N and increased performance under optimal N availability could be beneficial to low input agriculture. This study evaluated the performance of a selection of experimental and commercial hybrids under suboptimal and optimal N fertilizer applications. Significant differences were observed among the hybrids, as well as significant interactions between hybrid and N level for GY and other measured attributes, with the severity of variation increasing as the level of N decreases. Mean GY reductions across the years was 76.5% at no-N and 35.4% at low-N. Depending on N treatment, GY varied from 0.48 to 4.42 Mg ha-1, grain N content from 0.17 to 1.26 g plant-1, total N content at harvest from 0.33 to 2.00 g plant-1, above ground biomass at silking from 30.6 to 91.2 g plant-1 and at maturity from 39.9 to 191.1 g plant-1. Number of kernels was the GY component most severely reduced by N stress and had significant (p = 0.001) positive correlation with GY at all N levels. Six hybrids (4001/4008, KU1409/4008, KU1409/9613, 4008/1808, 4058/Fun 47-4, and 1824/9432) which showed consistent above average grain yields under no-N, low-N, high-N and across N levels were found and their use could further be investigated

Performance based grouping of adapted and exotic drought tolerant maize (Zea mays L) inbred lines under stressed and nonstressed conditions

Knowledge of the heterotic responses of elite adapted and exotic maize inbred lines can facilitate their utilization for population improvement and hybrid development. In the present study, a line x tester mating design was used to determine the combining ability of 20 elite drought-tolerant maize inbred lines developed at CIMMYT and IITA and to classify them into heterotic groups under diverse growing conditions. The 20 lines were crossed each with two inbred line testers representing the tropical and temperate heterotic pattern established in West and Cental Africa (WCA), to generate 40 testcrosses. A trial comprising the 40 testcrosses along with the cross between the two testers and three hybrid checks were evaluated at two environments in the dry season and at six environments in the rainy season. GCA effects were more important than SCA effects in controlling grain yield in both seasons. Two exotic lines in the dry season and four exotic lines in the rainy season had significantly positive GCA effects. Only EXL22 was identified as a superior line in the two seasons. Only two adapted lines had significantly positive GCA effects in either or both seasons while three adapted lines consistently had significantly negative GCA effects in both seasons. Hybrid between EXL22 and tester 9071 showed broad adaptation to all test environments. The two testers separated some of the lines into two main heterotic groups. the lines in each heterotic group and the good combiners will be utilized for developing populations for extracting new improved inbred lines