Maize Improvement Programs Research Articles

Assessing the Potential of Extra-Early Maturing Multiple Stress-tolerant Maize Hybrids Under Different Rates of Nitrogen

Decline in soil fertility is a major constraint to maize production. This study aimed to assess the agronomic performance of improved maize varieties under different nitrogen rates to identify low nitrogen tolerant varieties. Five multiple stress-tolerant maize hybrids, developed by maize improvement program of the International Institute of Tropical Agriculture (IITA), and an open-pollinated variety used as check were evaluated under three levels nitrogen at two locations during 2019 growing season. The experiment was laid out in a split-plot experiment with three replications at each location. Nitrogen rates and varieties were the main and secondary factors, respectively. Data collected on grain yield and its related traits and were subjected to analysis of variance at 5% level of significance. The average grain yield of the six varieties under different nitrogen levels ranged from 2.2 t/ha at 0 kgN/ha in Angaradébou to 5.3 t/ha at 76 kgN/ha in Komkoma. Hybrid TZEEQI 342 × TZEEQI 7 showed high grain yield (4.0 t/ha) across the two agro-ecologies while varieties TZEE-W Pop STR QPM Co × TZEEQI 7 (3.7 t/ha) and TZdEEI 91 × TZEEI 21 (3.6 t/ha) had comparable grain yield. These hybrids were also less susceptible to nitrogen stress. They are the promising genotypes for Angaradébou localities while farmers around Komkoma should continue to cultivate TZEE-W Pop DT STR QPM.

Cytogenetics of maize in Mexico as a field of transnational exchange: The case of Takeo Ángel Kato Yamakake

Societal Impact StatementMaize is one of the most consumed grains worldwide. Its production and international trade are expected to continue increasing because of its use as animal fodder and direct human food. Although maize's history spans millennia, in the last century it underwent significant changes due to genetic engineering, particularly during the Green Revolution. Due to maize's importance for current food security and energy production, it is fundamental to understand this engineering process to assess the implications of current styles of maize production for local and global landscapes, scientific institutions, and transnational networks of agricultural science.Summary This article aims to explain how Mexican agricultural expertise contributed to the development of cytogenetics as a specialized field in the study of the diversity of maize within the framework of the Green Revolution. To this end, the article follows the work of Mexican agronomist Takeo Ángel Kato Yamakake within the activities of the Inter‐American Maize Improvement Program (IMIP), formally established in 1960. By reconstructing the debate on the genetic implications of chromosomal structure and function, this study contributes to the historiography devoted to the role played by local experts in the classification, experimentation, and conservation of maize. The article is based on sources from Mexico and the United States, an interview with Kato, and the consultation of the database “Rockefeller Fellows. Individual Mobility Awards at Rockefeller‐endowed Organizations, 1914‐1970.” Kato's trajectory provides an overview of agronomy in Mexico and shows the relevance of transnational exchange in the establishment of plant cytogenetics. Kato's academic activity features collaborations with key figures such as Edwin Wellhausen, Albert Longley, Barbara McClintock, W. Gallinat, Czeslawa Prywer, and Almiro Blumenschein. A Green Revolution era quest to unravel the origin of maize as a way of perfecting its genetic manipulation fueled the interest in establishing cytogenetics in Mexico. However, the irruption of the molecular approach made the study of the position of chromosomal knobs less of a priority. Despite this, classical cytogenetics, under Kato's leadership, remains a field that contributed to the knowledge of the vegetal genome, even when the IMIP disappeared and the logic of the Green Revolution lost its centrality.

Heterotic grouping of provitamin A-enriched maize inbred lines for increased provitamin A content in hybrids

BackgroundThe establishment of heterotic groups of inbred lines is crucial for hybrid maize breeding programs. Currently, there is no information on the heterotic patterns of the Provitamin A (PVA) inbred lines developed in the maize improvement program of the International Institute of Tropical Agriculture (IITA) to form productive PVA enriched hybrids for areas affected by vitamin A deficiency. This study assessed the feasibility of classifying PVA-enriched inbred lines into heterotic groups based on PVA content without compromising grain yield in hybrids. Sixty PVA inbred lines were crossed to two testers representing two existing heterotic groups. The resulting 120 testcrosses hybrids were evaluated for two years at four locations in Nigeria.ResultsThe two testers effectively classified the inbred lines into two heterotic groups. The PVA-based general combining ability and specific combining ability (HSGCA) method assigned 31 and 27 PVA enriched maize inbred lines into HGB and HGA, respectively, leaving two inbred lines not assigned to any group. The yield-based HSGCA method classified 32 inbred lines into HGB and 28 inbred lines into HGA. Both PVA and yield-based heterotic grouping methods assigned more than 40% of the inbred lines into the same heterotic groups. Even though both PVA and yield-based heterotic grouping of the inbred lines differed from the clusters defined by the DArTag SNP markers, more than 40% of the inbred lines assigned to HGA were present in Cluster-1 and 60% of the inbred lines assigned to HGB were present in Cluster-3. Interestingly, the inbred lines assigned to the same heterotic groups based on PVA content and grain yield were distributed across the three Ward’s clusters. The PVA-based HSGCA was identified as the most effective heterotic grouping method for breeding programs working on PVA biofortification.ConclusionsSelecting PVA enriched maize inbred lines with diverse genetic backgrounds from the three marker-based clusters may facilitate the development of productive hybrids with high PVA content and for generating source populations to develop more vigorous maize inbred lines with much higher concentrations of PVA.

Genetic structure analysis and identifying key founder inbred lines in diverse elite sub-tropical maize inbred lines

Understanding the genetic relationships between the key founder inbred lines and derived inbred lines could provide insight into the breeding history and the structure of genetic diversity of the available elite inbred lines with desirable target traits. The maize improvement program at the International Institute of Tropical Agriculture (IITA) analyzed the pedigree information of 623 sub-tropical maize inbred lines generated at the IITA maize breeding program to identify the key founder inbred lines. We also used 5032 SNP markers to assess the genetic similarities of the founder inbred lines with their progenies subsequently developed for specific target traits. The results of pedigree analysis and SNP markers-based similarity scores identified 20 key founder inbred lines with significant contributions to the development of drought tolerant, early maturing, productive, Striga resistant, provitamin A enriched, and quality protein maize inbred lines. In our breeding program, line TZMi501 belonging to a flint heterotic group (HGA), and TZMi407-S and TZMi214, representing the dent heterotic group (HGB), were identified as the most useful founder inbred lines. The 623 inbred lines were consistently separated into four clusters based on Ward’s hierarchical clustering, structure, and principal component analyses, with the 20 founder inbred lines spread into all clusters. The founder inbred lines were more genetically related to the productive inbred lines but showed genetic divergence from the provitamin A enriched inbred lines. These results provide a better understanding of the breeding history of the sub-tropical maize inbred lines to facilitate parental selection aligned to existing heterotic groups for use in breeding programs targeting the improvement of essential traits in maize.

Will future maize improvement programs leverage the canopy light-interception, photosynthetic, and biomass capacities of traditional accessions?

Maize germplasm has greater latent potential to address the global food and feed crisis because of its high radiation, water and nutrient efficiencies. Photosynthetic and canopy architectural traits in maize are important in determining yield. The present study aimed to screen a subset of local maize accessions in Sri Lanka to evaluate their photosynthetic, biomass and yield related traits and to identify resource efficient germplasm. Experiments were carried out in the Ampara district of Sri Lanka. Eight maize accessions viz; SEU2, SEU6, SEU9, SEU10, SEU14, SEU15, SEU17 and SEU17 and two elite F1 cultivars (cv. Pacific-999 and cv. Bhadra) were analyzed under field conditions. Our results showed that maize genotypes produced a lower leaf area index (LAI) at the third and tenth week after field planting (WAP). However, the LAI was significantly increased in six WAP by Pacific-999, SEU2, SEU9, and SEU15. A similar trend was observed for percentage of light interception at three WAP (47%), six WAP (>64%), and decreased at 10 WAP. In addition, LAI maximum values were between 3.0 and 3.5, allowing 80% of the incident light to be intercepted by maize canopies. The estimated light extinction coefficient (k) remained lower (<0.5), suggesting that maize leaves are eractophilic canopies. Although fractional interception (f) varies, SEU2 and SEU9 had the highest values (0.57), and quantum yields of PSII (>0.73) in dark-adapted leaves. In addition, Pacific-999, SEU2, SEU9, and SEU17 had significantly higher rates of photosynthesis with minimal stomatal conductance and transpiration rates. As a result, they outperformed the control plants in terms of biomass, cob weight and grain yield. This suggests that native maize germplasm could be introduced as novel, less resource-intensive cultivars to sustain global food security.

Maize Breeding for Low Nitrogen Inputs in Agriculture: Mechanisms Underlying the Tolerance to the Abiotic Stress

Nitrogen (N) is essential for sustaining life on Earth and plays a vital role in plant growth and thus agricultural production. The excessive use of N fertilizers not only harms the economy, but also the environment. In the context of the environmental impacts caused by agriculture, global maize improvement programs aim to develop cultivars with high N-use efficiency (NUE) to reduce the use of N fertilizers. Since N is highly mobile in plants, NUE is related to numerous little-known morphophysiological and molecular mechanisms. In this review paper we present an overview of the morpho-physiological adaptations of shoot and root, molecular mechanisms involved in plant response to low nitrogen environment, and the genetic effects involved in the control of key traits for NUE. Some studies show that the efficiency of cultivars growing under low N is related to deep root architecture, more lateral roots (LR), and sparser branching of LR, resulting in lower metabolic costs. The NUE cultivars also exhibit more efficient photosynthesis, which affects plant growth under suboptimal nitrogen conditions. In this sense, obtaining superior genotypes for NUE can be achieved with the exploitation of heterosis, as non-additive effects are more important in the expression of traits associated with NUE.

Genotype and Phenotype Coefficient of Variance in Maize (Zea mays L.)

The present investigation was carried out with 30 maize inbred lines at Seed Research Technology Centre, Rajendranagar, PJTSAU. Analysis of variance revealed significant differences among the inbreds for all the traits studied. The phenotypic coefficient of variance (PCV) was slightly higher than the genotypic coefficient of variance (GCV) indicating the role of experimental variance in the total variance. High PCV and GCV were observed for SVI-2 whereas cob yield per plant and grain yield per plant showed high PCV and moderate GCV. It indicated the presence of a high degree of variability. Ear height, 100- grain weight, seed vigour index – I and speed of germination had moderate PCV and GCV. High heritability coupled with high genetic advance was observed in ear height, 100-seed weight, cob yield per plant, seed vigour index-1, seed vigour index-2, speed of germination and grain yield per plant indicating the preponderant role additive gene action in inheritance and simple selection would be effective for yield improvement. Based on GCV, PCV, heritability and genetic advance over mean seven traits (ear height, ear length, cob yield per plant, grain yield per plant, SVI-1, SVI-2 and speed of germination) are given importance during the selection of inbred lines. The current study reveals the existence of proper genetic variability among the characters which can be applied to a maize improvement programme.

Relationships between Grain Weight and Other Yield Component Traits of Maize Varieties Exposed to Heat-Stress and Combined Heat- and Water-Stress Conditions

It is necessary to identify the appropriate traits that influence yield in a given environment as part of a breeding programme. The objective of this study was to identify the morphological traits that contribute to maize grain weight (GWt) under abiotic stress conditions. Three drought-tolerant maize varieties were grown under no-stress (NHWS), heat-stress (HS), and combined heat- and water-stress (CHWS) conditions. Data from 19 morphological traits were analysed. The correlation results revealed that eight traits consistently produced a significant positive relationship with GWt under the three growth conditions. The path coefficient analysis revealed that in the NHWS, HS, and CHWS conditions, five traits consistently had a positive direct effect on the GWt. Given the magnitude of the positive direct effects, increasing dry biomass yield, harvest index, and grain number in the NHWS; grain number, harvest index, and ear width in the HS; and harvest index, days till silk appearance, leaf chlorophyll content, and grain number in the CHWS will increase GWt. Under various abiotic stress conditions, maize phenotypic expression varied. Therefore, the identified traits that contributed positively to GWt under various stress conditions should be considered when developing a maize improvement programme in a stress-prone environment.

Morpho-Physiological and Molecular Characterization of Maize (Zea Mays L.) Genotypes for Drought Tolerance

Maize is abstemiously sensitive to drought. Drought distresses almost all characteristics of maize growth in variable degrees at all phases of life cycle. Drought pressure, predominantly at flowering period, has been recognized as the most destructing aspect restraining maize production and productivity. So, improving drought tolerance has become the top priority in maize improvement programs. In the current study, 80 genotypes of maize including 66 hybrid, 12 parents and 2 check (drought tolerant HKI1105 and drought susceptible HKI1128 respectively) were included. These genotypes grown under irrigated and partial irrigated conditions and laid out in a randomized block design with two replications. Under irrigated condition, grain yield ranged between 36.29g to 129.6g with a mean value of 73.06g. Whereas under partial irrigated condition, grain yield arrayed between 23.6g to 155.58g with an average worth of 66.11g. Under partial irrigated conditions correlation studies of grain yield displayed significant and positive correlation with relative water contents (RWC) and membrane stability index (MSI) while negative correlation was detected with turgid weight (TW) and saturation water deficit (SWD). Furthermore, molecular characterization also performed employing 20 droughts linked polymorphic microsatellite markers. A total of 110 alleles with a mean of 5.5 alleles per marker were amplified. Cluster analysis revealed that genotypes HKI1105 fallen in a group with 47 other genotypes, so possibility exist that all the genotypes may be drought tolerant. Drought tolerant genotypes and polymorphic microsatellite markers may be further validated and potentially employed in molecular marker-aided breeding to develop drought tolerant cultivar in maize.

Developing and deploying an efficient genotyping workflow for accelerating maize improvement in developing countries.

Background: Molecular breeding is an essential tool for accelerating genetic gain in crop improvement towards meeting the need to feed an ever-growing world population. Establishing low-cost, flexible genotyping platforms in small, public and regional laboratories can stimulate the application of molecular breeding in developing countries. These laboratories can serve plant breeding projects requiring low- to medium-density markers for marker-assisted selection (MAS) and quality control (QC) activities. Methods: We performed two QC and MAS experiments consisting of 637 maize lines, using an optimised genotyping workflow involving an in-house competitive allele-specific PCR (KASP) genotyping system with an optimised sample collection, preparation, and DNA extraction and quantitation process. A smaller volume of leaf-disc size plant samples was collected directly in 96-well plates for DNA extraction, using a slightly modified CTAB-based DArT DNA extraction protocol. DNA quality and quantity analyses were performed using a microplate reader, and the KASP genotyping and data analysis was performed in our laboratory. Results: Applying the optimized genotyping workflow expedited the QC and MAS experiments from over five weeks (when outsourcing) to two weeks and eliminated the shipping cost. Using a set of 28 KASP single nucleotide polymorphisms (SNPs) validated for maize, the QC experiment revealed the genetic identity of four maize varieties taken from five seed sources. Another set of 10 KASP SNPs was sufficient in verifying the parentage of 390 F 1 lines. The KASP-based MAS was successfully applied to a maize pro-vitamin A (PVA) breeding program and for introgressing the aflatoxin resistance gene into elite tropical maize lines. Conclusion: This improved workflow has helped accelerate maize improvement activities of IITA's Maize Improvement Program and facilitated DNA fingerprinting for tracking improved crop varieties. National Agricultural Research Systems (NARS) in developing countries can adopt this workflow to fast-track molecular marker-based genotyping for crop improvement.

Developing and deploying an efficient genotyping workflow for accelerating maize improvement in developing countries

Background: Molecular breeding is an essential tool for accelerating genetic gain in crop improvement, towards meeting the need to feed an ever-growing world population. Establishing low-cost, flexible genotyping platforms in small, public and regional laboratories can stimulate the application of molecular breeding in developing countries. These laboratories can serve plant breeding projects requiring low- to medium-density markers for marker-assisted selection (MAS) and quality control (QC) activities. Methods: We performed two QC and MAS experiments consisting of 637 maize lines, using an optimised genotyping workflow involving an in-house competitive allele-specific PCR (KASP) genotyping system with an optimised sample collection, preparation, and DNA extraction and quantitation process. A smaller volume of leaf-disc size plant samples was collected directly in 96-well plates for DNA extraction, using a slightly modified CTAB-based DArT DNA extraction protocol. DNA quality and quantity analyses were performed using a microplate reader, and the KASP genotyping and data analysis was performed in our laboratory. Results: Applying the optimized genotyping workflow expedited the QC and MAS experiments from over five weeks (when outsourcing) to two weeks and eliminated the shipping cost. Using a set of 28 KASP single nucleotide polymorphisms (SNPs) validated for maize, the QC experiment revealed the genetic identity of four maize varieties taken from five seed sources. Another set of 10 KASP SNPs was sufficient in verifying the parentage of 390 F1 lines. The KASP-based MAS was successfully applied to a maize pro-vitamin A (PVA) breeding program and for introgressing the aflatoxin resistance gene into elite tropical maize lines. Conclusion: This improved workflow has helped accelerate maize improvement activities of IITA's Maize Improvement Program and facilitated DNA fingerprinting for tracking improved crop varieties. National Agricultural Research Systems (NARS) in developing countries can adopt this workflow to fast-track molecular marker-based genotyping for crop improvement.

Genetic Variation and Genotype by Environment Interaction for Agronomic Traits in Maize (Zea mays L.) Hybrids.

In order to develop high-yielding genotypes of adapted maize, multilocation trials of maize were performed including forty-five maize hybrids exploiting genetic variability, trait associations, and diversity. The experiments were laid out in an RCB design and data were recorded on eight yield and yield-contributing traits, viz., days to anthesis (AD), days to silking (SD), anthesis–silking interval (ASI), plant height (PH), ear height (EH), kernels per ear (KPE), thousand-kernel weight (TKW), and grain yield (GY). An analysis of variance (ANOVA) showed significant variation present among the different traits under study. The phenotypic coefficient of variance (PCV) showed a higher value than the genotypic coefficient of variance (GCV), indicating the environmental influence on the expression of the traits. High heritability coupled with high genetic advance was found for these traits, indicative of additive gene action. The trait associations showed that genotypic correlation was higher than phenotypic correlation. Based on genetic diversity, the total genotypes were divided into four clusters, and the maximum number of 16 genotypes was found in cluster IV. Among the eight yield and yield-contributing traits, PH, ASI, EH, and TKW were the important traits for variability creation and were mostly responsible for yield. Genotypes G5, G8, G27, G29, and G42 were in the top ranks based on grain yield over locations, while a few others showed region-centric performances; all these genotypes can be recommended upon validation for commercial release. The present findings show the existence of proper genetic variability and divergence among traits, and the identified traits can be used in a maize improvement program.

Photosynthetic pigments in maize (Zea mays) vis-Ã -vis biological performance and host selection by Sesamia inferens

In the present study, host selection behaviour and biological performance of Sesamia inferens on different maize (Zea mays L.) genotypes was investigated in 2018–19, and constitutive and insect damage-induced levels of various photosynthetic pigments were determined. There were significant differences in larval period, larval survival, larval weight, pupal period, pupal weight, adult emergence, and fecundity of S. inferens on the test maize genotypes. The S. inferens that fed on maize genotypes, viz. CPM 2, CPM 4, CPM 8, CPM 15 and CML 345 showed significant increase in developmental period, decrease in larval weight, and reduced larval survival, adult emergence and fecundity as compared to other test genotypes. The S. inferens larval recovery and preference were significantly lower, while the larvae took longer time to establish in the whorls of CPM 2, CPM 15 and CML 345 as compared to other test maize genotypes. The chlorophyll A, chlorophyll B and total chlorophyll content varied significantly in the seedlings of different maize genotypes, under healthy and S. inferens damaged conditions (except, chlorophyll B), while the genotype × treatment interactions were non-significant. The differences for total carotenoids were non-significant. The S. inferens infestation reduced these photosynthetic pigments in the seedlings of all test maize genotypes, except Basi Local, with lowest reduction in CPM 2. The study suggests that the maize genotypes, viz. CPM 2, CPM 4, CPM 8, CPM 15 and CML 345 have greater detrimental effects on the development, survival and fecundity of S. inferens, and can be used in maize improvement program.

Developing and deploying an efficient genotyping workflow for accelerating maize improvement in developing countries

Background: Molecular breeding is an essential tool for accelerating genetic gain in crop improvement, towards meeting the need to feed an ever-growing world population. Establishing low-cost, flexible genotyping platforms in small, public and regional laboratories can stimulate the application of molecular breeding in developing countries. These laboratories can serve plant breeding projects requiring low- to medium-density markers for marker-assisted selection (MAS) and quality control (QC) activities. Methods: We performed two QC and MAS experiments consisting of 637 maize lines, using an optimised genotyping workflow involving an in-house competitive allele-specific PCR (KASP) genotyping system with an optimised sample collection, preparation, and DNA extraction and quantitation process. A smaller volume of leaf-disc size plant samples was collected directly in 96-well plates for DNA extraction, using a slightly modified CTAB-based DArT DNA extraction protocol. DNA quality and quantity analyses were performed using a microplate reader, and the KASP genotyping and data analysis was performed in our laboratory. Results: Applying the optimized genotyping workflow expedited the QC and MAS experiments from over five weeks (when outsourcing) to two weeks and eliminated the shipping cost. Using a set of 28 KASP single nucleotide polymorphisms (SNPs) validated for maize, the QC experiment revealed the genetic identity of four maize varieties taken from five seed sources. Another set of 10 KASP SNPs was sufficient in verifying the parentage of 390 F1 lines. The KASP-based MAS was successfully applied to a maize pro-vitamin A (PVA) breeding program and for introgressing the aflatoxin resistance gene into elite tropical maize lines. Conclusion: This improved workflow has helped accelerate maize improvement activities of IITA's Maize Improvement Program and facilitated DNA fingerprinting for tracking improved crop varieties. National Agricultural Research Systems (NARS) in developing countries can adopt this workflow to fast-track molecular marker-based genotyping for crop improvement.

Molecular characterization and multi-environmental evaluation of field corn (Zea mays) inbreds for kernel traits

Kernel size and kernel weight are important yield attributing traits in maize (Zea mays L.). Though yield hascomplex inheritance, understanding and improvement of yield per se becomes relatively easy, when maize breedingis targeted for genetic enhancement of yield component traits. In the present investigation, a set of 45 tropical fieldcorn inbred lines were evaluated under three environments and at different location for kernel length, kernel thicknessand kernel weight traits. In a given location, environmental influence on the expression of these traits were negligibleas it was evident by exhibition of high heritability (broad sense) for the traits under study, however pooled effect ofenvironments showed some interactions. Based on the AMMI stability value, the inbred lines AI 04 followed by AI 37,AI 18, AI 25 and AI 35 were selected as highly stable genotypes for its yield per se. Inbred lines were characterizedusing gene-based markers linked to kernel traits. It was observed that molecular markers rightly classified the inbredlines into different groups based on their trait means. Furthermore, the makers, umc1890 and umc1120 were putativelylinked to kernel weight and kernel thickness respectively. These markers may be utilized for identification of suitabledonor and genetic improvement of kernel traits driven maize improvement program.

GENETIC DIVERGENCE AMONG MAIZE (ZEA MAYS L.) INBRED LINES USING MORPHOMETRIC MARKERS

Genetic divergence study is imperative in breeding programmes in order to select distant parents. Forty maize inbred lines were assessed using morphometric markers to identify the potential inbred lines for yield and its component traits. The inbred lines were raised in α-RBD design replicated twice during kharif 2019. The morphological diversity analysis was done as per the standard statistical procedures using Mahalanobis D2-statistic. Analysis of variance revealed significant mean sum of squares due to genotypes for all the traits suggesting ample amount of genetic variability present among them. Moderate PCV, GCV and high heritability coupled with moderate genetic advance was observed for grain yield per plant, plant and cob placement height. Grain yield per plant exhibited significant positive correlation with all the traits except days to 50 per cent pollen shed and silking. Path analysis revealed high direct effects of days to 50 per cent pollen shed, harvest index, grains per row and 100 grain-weight on grain yield per plant therefore these morphometric traits would be the best selection indices to select high yielding genotypes. D2-statistics grouped 40 maize genotypes into three clusters. Cluster III has the highest cluster mean values for all the traits.Seven genotypes viz., 4186-4-05-1-1, LM-14, BAJIM-08-27, BIOM 10, LQPM24×1114-5, 9180-2, LDH 5(Vivek-21-1) were superior over the best check on the basis of mean performance and disease resistance and were diverse therefore, could be used in maize improvement program.

Genetic variability, heritability, trait associations and path coefficient analysis of maize (Zea mays L.) inbreed lines

Maize (Zea mays L.) is the first most vital cereal share for the productivity, but the second in its production area coverage next to tef, in Ethiopia. However, its development and productivity are influenced by biotic and abiotic factors. The absence of tolerant maize verities and or inbreed lines also another significant problem. Therefore, the present study was targeted to assess the magnitude of genetic variability, heritability and genetic advance of traits, to verify the genotypic and phenotypic associations between essential characteristics and determine the relationship of features with grain yield and direct and indirect effects using path coefficient analysis. The experiment was conducted at Pawe Agricultural Research Center using 23 inbred lines with RCB design with 3 replications. Results revealed that significant (P&lt;0.01) variations were observed between inbred lines in yield and yield-related traits. Moderate to the high genotypic coefficient of variation, heritability and genetic advance as the percentage of mean values were recorded for plant height, ear height and grain yield. Plant height, ear height and number of ears were observed significant to highly significant positive phenotypic and genotypic associations with grain yield. In contrast, days to 50% anthesis and silk emergence, plant and ear aspects were showed negatively significant associations with grain yield at both genotypic and phenotypic levels. The highest grain yield was recorded from A7033 (8.3 t ha-1), CML197 (6 t ha-1) and CML202 (5.5 t ha-1) and these lines could be best female parents’ foe crop maize improvement programs.

Genetic diversity and population structure of early and extra-early maturing maize germplasm adapted to sub-Saharan Africa

BackgroundAssessment and effective utilization of genetic diversity in breeding programs is crucial for sustainable genetic improvement and rapid adaptation to changing breeding objectives. During the past two decades, the commercialization of the early and extra-early maturing cultivars has contributed to rapid expansion of maize into different agro-ecologies of sub-Saharan Africa (SSA) where maize has become an important component of the agricultural economy and played a vital role in food and nutritional security. The present study aimed at understanding the population structure and genetic variability among 439 early and extra-early maize inbred lines developed from three narrow-based and twenty-seven broad-based populations by the International Iinstitute of Tropical Agriculture Maize Improvement Program (IITA-MIP). These inbreds were genotyped using 9642 DArTseq-based single nucleotide polymorphism (SNP) markers distributed uniformly throughout the maize genome.ResultsAbout 40.8% SNP markers were found highly informative and exhibited polymorphic information content (PIC) greater than 0.25. The minor allele frequency and PIC ranged from 0.015 to 0.500 and 0.029 to 0.375, respectively. The STRUCTURE, neighbour-joining phylogenetic tree and principal coordinate analysis (PCoA) grouped the inbred lines into four major classes generally consistent with the selection history, ancestry and kernel colour of the inbreds but indicated a complex pattern of the genetic structure. The pattern of grouping of the lines based on the STRUCTURE analysis was in concordance with the results of the PCoA and suggested greater number of sub-populations (K = 10). Generally, the classification of the inbred lines into heterotic groups based on SNP markers was reasonably reliable and in agreement with defined heterotic groups of previously identified testers based on combining ability studies.ConclusionsComplete understanding of potential heterotic groups would be difficult to portray by depending solely on molecular markers. Therefore, planned crosses involving representative testers from opposing heterotic groups would be required to refine the existing heterotic groups. It is anticipated that the present set of inbreds could contribute new beneficial alleles for population improvement, development of hybrids and lines with potential to strengthen future breeding programs. Results of this study would help breeders in formulating breeding strategies for genetic enhancement and sustainable maize production in SSA.

Environmental impact and genetic expressions of new drought tolerant maize genotypes in derived savannah agro-ecology

Reduced water resources in sub-Saharan Africa will not only pose threat to the livelihood of poor resource farmers, but also food security in the region. Drought tolerant (DT) maize varieties hold promise to reducing poor resourced farmers’ vulnerability and improve food security in sub-Saharan Africa. Ten maize genotypes obtained from the International Institute of Tropical Agriculture (IITA), were evaluated in 2015 and 2016 using a randomized complete block design experiment with three replications to estimate their genetic variability and predict their genetic advances in the derived savannah agro-ecology. Growth, phenological and yield data were collected from 10 middle row plants. Genetic advance, genotypic, phenotypic and environmental coefficients of variations and their variances were estimated. Principal component and hierarchical cluster analyses were also performed. The dendrogram showed that at 80% dissimilarity point, the genotypes were grouped into clusters A, B and C in both years. The first two principal components explained 91.8% and 93.3% of the total variation in 2015 and 2016, respectively. Number of grains cob-1, plant height and number of days to physiological maturity were consistent in explaining the variations observed in the maize population. Heritability estimates in broad sense ranged from 1.35% for number of leaves to 87.43% for grain yield per hectare. The genetic parameters studied showed significant variations among the growth, phenological and yield data collected that warrants selection and maize improvement program using the DT maize inbred lines in derived savannah agro-ecology.

Mapping genomic regions for red flour beetle (Tribolium castaneum (Herbst)) resistance in teosinte (Zea mays L. subsp. parviglumis H. H. Iltis &amp; Doebley) derived maize backcross inbred line population

The development of maize germplasm with resistance to red flour beetle requires identification of donors of resistant traits and understanding of the genetic mechanisms underlying resistance. As resistance sources are scarce in elite maize lines, teosinte (Zea mays ssp. parviglumis; 2n = 20) following insect bioassay was found to be resistant and therefore used as parent in a cross with flour beetle susceptible but superior maize inbred line DI-103 for development of backcross inbred line (BIL) mapping population with a view to identify genomic regions conferring resistance. Data on four resistance parameters namely, weight loss (WL), number of insect progeny emerged, kernel damage (KD) and flour produced (FP) were collected on 141 BILs. Highly significant differences were found amongst BILs for all the parameters indicating substantial variability in the population for the traits probably contributed by teosinte. Based on cumulative susceptibility index (CSI), 83 BILs were scored as resistant and can be utilized as donor for flour beetle resistance in maize improvement programs. Principal component analysis was conducted and first three principal components contributing 92.36% of the total phenotypic variation were identified. Highly significant positive correlations were found between all trait combinations except for correlation between WL and KD which was positive but non-significant. A total of 18 marker linked genomic regions were found to be significantly associated with red flour beetle resistance. Two major quantitative trait loci (QTLs) were detected on chromosome 1 and 3 for KD and they explained 11.17% and 14.88% of the total phenotypic variation, respectively. Highest number of colocalized QTLs i.e., 3 were detected for KD and FP. These linked markers after further validation can be used in future for indirect selection for resistance to red flour beetle in maize.