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

IMPACTS OF INTERNATIONAL MAIZE BREEDING RESEARCH IN DEVELOPING COUNTRIES, 1966-98

This report, which updates and extends the findings of an earlier CIMMYT study published in 1994, documents the impacts of international maize breeding research in the developing world. Covering the period 1966-98, the report reviews public and private investment in maize breeding research, describes the products of public and private maize breeding programs, estimates farm level adoption of modern varieties (MVs), and estimates the gross value of additional grain production attributable to international breeding efforts. Although private companies have greatly increased their investment in maize breeding research in recent years, public maize breeding programs still play an important role, especially in breeding for subsistence-oriented farmers. Seed sales data show that the maize seed industry in many developing countries has effectively been privatized and that hybrid seed sales now dominate sales of all other seed types. The area planted to MVs continues to expand at an impressive rate. Maize MVs are currently grown on at least 58.8 million ha in developing countries, including at least 21.2 million ha planted to MVs that contain CIMMYT germplasm. The gross value of additional grain production attributable to the adoption of maize MVs in developing countries is estimated to range from US$3.7 million to US$ 11.1 billion per year. Analysis of varietal pedigrees shows that breeders in both the public and private sectors have made extensive use of CIMMYT germplasm. Over 54% of publicly bred MVs released in the developing world since 1966 have contained CIMMYT germplasm. The pedigrees of many privately bred cultivars are confidential, but CIMMYT germplasm was present in 58% of MVs developed by private breeding programs being sold in the late 1990s for which pedigree information is available. The gross benefits attributable to CIMMYT's maize breeding program are estimated to range from US$167 million to US$ 1.5 billion per year.Productivity Analysis,

Comparative transcriptomics uncovers alternative splicing changes and signatures of selection from maize improvement

Background: Alternative splicing (AS) is an important regulatory mechanism that greatly contributes to eukaryotic transcriptome diversity. A substantial amount of evidence has demonstrated that AS complexity is relevant to eukaryotic evolution, development, adaptation, and complexity. In this study, six teosinte and ten maize transcriptomes were sequenced to analyze AS changes and signatures of selection in maize domestication and improvement. Results In maize and teosinte, 13,593 highly conserved genes, including 12,030 multiexonic genes, were detected. By identifying AS isoforms from mutliexonic genes, we found that AS types were not significantly different between maize and teosinte. In addition, the two main AS types (intron retention and alternative acceptor) contributed to more than 60% of the AS events in the two species, but the average unique AS events per each alternatively spliced gene in maize (4.12) was higher than that in teosinte (2.26). Moreover, 94 genes generating 98 retained introns with transposable element (TE) sequences were detected in maize, which is far more than 9 retained introns with TEs detected in teosinte. This indicates that TE insertion might be an important mechanism for intron retention in maize. Additionally, the AS levels of 3864 genes were significantly different between maize and teosinte. Of these, 151 AS level-altered genes that are involved in transcriptional regulation and in stress responses are located in regions that have been targets of selection during maize improvement. These genes were inferred to be putatively improved genes. Conclusions We suggest that both maize and teosinte share similar AS mechanisms, but more genes have increased AS complexity during domestication from teosinte to maize. Importantly, a subset of AS level-increased genes that encode transcription factors and stress-responsive proteins may have been selected during maize improvement

Genetic Characterization of a Core Set of a Tropical Maize Race Tuxpeño for Further Use in Maize Improvement

The tropical maize race Tuxpeño is a well-known race of Mexican dent germplasm which has greatly contributed to the development of tropical and subtropical maize gene pools. In order to investigate how it could be exploited in future maize improvement, a panel of maize germplasm accessions was assembled and characterized using genome-wide Single Nucleotide Polymorphism (SNP) markers. This panel included 321 core accessions of Tuxpeño race from the International Maize and Wheat Improvement Center (CIMMYT) germplasm bank collection, 94 CIMMYT maize lines (CMLs) and 54 U.S. Germplasm Enhancement of Maize (GEM) lines. The panel also included other diverse sources of reference germplasm: 14 U.S. maize landrace accessions, 4 temperate inbred lines from the U.S. and China, and 11 CIMMYT populations (a total of 498 entries with 795 plants). Clustering analyses (CA) based on Modified Rogers Distance (MRD) clearly partitioned all 498 entries into their corresponding groups. No sub clusters were observed within the Tuxpeño core set. Various breeding strategies for using the Tuxpeño core set, based on grouping of the studied germplasm and genetic distance among them, were discussed. In order to facilitate sampling diversity within the Tuxpeño core, a minicore subset of 64 Tuxpeño accessions (20% of its usual size) representing the diversity of the core set was developed, using an approach combining phenotypic and molecular data. Untapped diversity represents further use of the Tuxpeño landrace for maize improvement through the core and/or minicore subset available to the maize community

Genetic Variations of Leaf Trait in Maize (Zea mays L.) under Drought Stress in Different Growth Stages

Maize is the third most important food crop worldwide, and it is more sensitive to drought. Two field experiments were conducted under drought in different growth stages at two locations, the Demonstration Farm, Faculty of Agriculture, University of Khartoum, at Shambat, and the Gezira Research Station Farm, at Medani, in season (2003/2004). To estimate the pattern of inheritance, determine the relative magnitude of genetic variation effects for a number of leaves/plant and leaf area index in fifteen maize genotypes. A split-plot design, layout within randomized complete block design with three replications was used for the experiment. Significant differences among genotypes were detected in all traits, except, leaf area index (30 and 60 days) and number of leaves/plant (45 days). High genotypic coefficient of variation, genetic advance and heritability were exhibited by a number of leaves/plant for 60 days. Grain yield was significantly and positively associated at the phenotypic level with the leaf area index and a number of leaves/plant at 60 days. Thus the characters leaf area index and number of leaves/plant to be the important traits which would be an effectual in selection for maize improvement under drought stress at different growth stages. Based on their positive association with grain  yield, the traits  leaf area index and number of leaves/plant would be the exploited for improving grain yield and facilitate further efforts in the maize improvement program in the country. Keywords: correlation; heritability; morphological traits; vegetative and reproductive phases; water stres