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

Genetic loci controlling carotenoid biosynthesis in diverse tropical maize lines

Open Access JournalThe discovery and use of genetic markers associated with carotenoid levels can help to exploit the genetic potential of maize for provitamin A accumulation more effectively. Provitamin A carotenoids are classes of carotenoids that are precursors of vitamin A, an essential micronutrient in humans. Vitamin A deficiency is a global public health problem affecting millions of people, especially in developing countries. Maize is one of the most important staple crops targeted for provitamin A biofortification to help alleviate vitamin A efficiency in developing countries. A genome-wide association study (GWAS) of maize endosperm carotenoids was conducted using a panel of 130 diverse yellow maize tropical inbred lines genotyped with Genotyping by Sequencing (GBS) SNP markers. Numerous significant association signals co-localizing with the known carotenoid biosynthesis genes crtRB1, lcyE and ZEP1 were identified. The GWAS confirmed previously reported large effects of the two major carotenoid biosynthesis genes lcyE and crtRB1. In addition, significant novel associations were detected for several transcription factors (e.g., RING zinc finger domain and HLH DNA-binding domain super family proteins) that may be involved in regulation of carotenoid biosynthesis in maize. When the GWAS was re-conducted by including the major effects of lcyE and crtRB1 genes as covariates, a SNP in a gene coding for an auxin response factor 20 transcription factor was identified which displayed an association with b-carotene and provitamin A levels. Our study provides a foundation for design and implementation of genomics-assisted selection strategies for provitamin A maize breeding in tropical regions, and advances efforts toward identification of additional genes (and allelic variants) involved in the regulation of carotenoid biosynthesis in plants

Genomic-based-breeding tools for tropical maize improvement

Maize has traditionally been the main staple diet in the Southern Asia and Sub-Saharan Africa and widely grown by millions of resource poor small scale farmers. Approximately, 35.4 million hectares are sown to tropical maize, constituting around 59% of the developing worlds. Tropical maize encounters tremendous challenges besides poor agro-climatic situations with average yields recorded <3 tones/hectare that is far less than the average of developed countries. On the contrary to poor yields, the demand for maize as food, feed, and fuel is continuously increasing in these regions. Heterosis breeding introduced in early 90 s improved maize yields significantly, but genetic gains is still a mirage, particularly for crop growing under marginal environments. Application of molecular markers has accelerated the pace of maize breeding to some extent. The availability of array of sequencing and genotyping technologies offers unrivalled service to improve precision in maize-breeding programs through modern approaches such as genomic selection, genome-wide association studies, bulk segregant analysis-based sequencing approaches, etc. Superior alleles underlying complex traits can easily be identified and introgressed efficiently using these sequence-based approaches. Integration of genomic tools and techniques with advanced genetic resources such as nested association mapping and backcross nested association mapping could certainly address the genetic issues in maize improvement programs in developing countries. Huge diversity in tropical maize and its inherent capacity for doubled haploid technology offers advantage to apply the next generation genomic tools for accelerating production in marginal environments of tropical and subtropical world. Precision in phenotyping is the key for success of any molecular-breeding approach. This article reviews genomic technologies and their application to improve agronomic traits in tropical maize breeding has been reviewed in detail

Measuring the impact of plant breeding on sub-Saharan African staple crops

Published online: 10 Oct 2018Many countries in sub-Saharan Africa (SSA) are facing huge challenges regarding food insecurity, low agricultural output, and agriculturally incurred environmental degradation. A sustainable and increased crop productivity and diversity is essential to achieve food security in a socially, economically, and environmentally sustainable way. Plant breeding is an important factor contributing to the increased crop productivity and diversity, giving farmers access to genetically improved cultivars that yield more, have better resistance to biotic and abiotic stresses, and meet consumer expectations. To motivate and encourage further investments, it is important to measure the actual impact of breeding. This review considers available research on the impact of breeding through yield gain and of food security, focusing on 10 important staple crops in SSA. The overall impression is that breeding produces a very high return on investment. Such investments remain centerpieces for meeting the challenges in this region. The discussion focuses on the most important future breeding priorities for each crop, the actors involved, and the importance of mechanisms for dissemination and farmer adoption, and concludes with some policy recommendations

Major biotic maize production stresses in Ethiopia and their management through host resistance

Biotic stresses are recently evolving very rapidly and posing significant yield losses of maize production in Ethiopia. A number of high yielding maize hybrids, initially developed as tolerant/resistant, have been taken out of production due to their susceptibility to major maize diseases. Furthermore, recent disease and insect pest epidemics have clearly shown the importance of breeding maize for biotic stresses and study the genetics of resistance to the major maize disease pathogens, insect pests and parasitic weeds. This paper gives the general perspective of the major biotic maize production stresses in Ethiopia and the interventions made locally and globally to control these stresses using host resistance. More emphasis was given to grey leaf spot (GLS), turcicum leaf blight (TLB), common leaf rust (CLR), maize streak disease (MSD), maize lethal necrosis (MLN), maize weevil, stalk borers, fall armyworm and Striga. Approaches to conducting genetic analysis and achieving durable host resistance to these stresses, where applicable, are discussed. This information will be used for breeders, private and public maize seed and grain growers who are targeting to operate in Ethiopia and Eastern Africa

Combining ability of extra‐early biofortified maize inbreds under Striga

Striga hermonthica (Del.) Benth parasitism, low soil N, and nutritional deficiencies of normal‐endosperm maize (Zea mays L.) threaten maize yield and exacerbate nutritional problems in sub‐Sahara Africa (SSA). This study was conducted (a) to evaluate genetic variation among extra‐early maturing maize hybrids with provitamin A and quality protein characteristics, (b) to investigate gene action governing the inheritance of Striga resistance, grain yield, low N tolerance, and other measured traits under low‐N, high‐N, and Striga‐infested environments, and (c) to identify hybrids with high yield and stability across environments. One hundred and fifty hybrids developed using North Carolina Design II were evaluated with six checks under low‐N, high‐N, and Striga‐infested environments in Nigeria. Mean squares for hybrids were highly significant (P < .01) for grain yield and other traits across environments. Only general combining ability (GCA) for female and/or male mean squares were significant for measured traits under low N. In addition to significant GCA effects for most traits, specific combining ability was significant (P < .05) for Striga emergence count under Striga infestation, and ear height and ears per plant under high N, indicating that additive and nonadditive genetic effects controlled the inheritance of few traits under Striga and high N, whereas additive genetic effect governed the inheritance of the traits under low N. Hybrids TZEEIORQ 55 × TZEEIORQ 26, TZEEIORQ 49 × TZEEIORQ 75, and TZEEIORQ 52 × TZEEIORQ 43 were high yielding and stable across environments and have potential for improving nutrition and maize yields in SSA