Person: Pixley, K.V.
Loading...
Email Address
Birth Date
Research Projects
Organizational Units
Job Title
Last Name
Pixley
First Name
K.V.
Name
Pixley, K.V.
ORCID ID
0000-0003-4068-7436 8 results
Search Results
Now showing 1 - 8 of 8
- Provitamin A carotenoids in grain reduce aflatoxin contamination of maize while combating vitamin A deficiency(Frontiers, 2019) Suwarno, W.B.; Hannok, P.; Palacios-Rojas, N.; Windham, G.L.; Crossa, J.; Pixley, K.V.Aflatoxin contamination of maize grain and products causes serious health problems for consumers worldwide, and especially in low- and middle-income countries where monitoring and safety standards are inconsistently implemented. Vitamin A deficiency (VAD) also compromises the health of millions of maize consumers in several regions of the world including large parts of sub-Saharan Africa. We investigated whether provitamin A (proVA) enriched maize can simultaneously contribute to alleviate both of these health concerns. We studied aflatoxin accumulation in grain of 120 maize hybrids formed by crossing 3 Aspergillus flavus resistant and three susceptible lines with 20 orange maize lines with low to high carotenoids concentrations. The hybrids were grown in replicated, artificially-inoculated field trials at five environments. Grain of hybrids with larger concentrations of beta-carotene (BC), beta-cryptoxanthin (BCX) and total proVA had significantly less aflatoxin contamination than hybrids with lower carotenoids concentrations. Aflatoxin contamination had negative genetic correlation with BCX (-0.28, p < 0.01), BC (-0.18, p < 0.05), and proVA (-0.23, p < 0.05). The relative ease of breeding for increased proVA carotenoid concentrations as compared to breeding for aflatoxin resistance in maize suggests using the former as a component of strategies to combat aflatoxin contamination problems for maize. Our findings indicate that proVA enriched maize can be particularly beneficial where the health burdens of exposure to aflatoxin and prevalence of VAD converge with high rates of maize consumption.
Publication - Effects of S1 recurrent selection for provitamin A carotenoid content for three open-pollinated maize cultivars(Crop Science Society of America (CSSA), 2014) Dhliwayo, T.; Palacios-Rojas, N.; Crossa, J.; Pixley, K.V.Maize (Zea mays L.) cultivars with increased concentrations of provitamin A (proVA) carotenoids can improve the health of millions of consumers who are vitamin A deficient and rely on maize as a staple food. Three open-pollinated maize cultivars (OP C) were subjected to three cycles of S1 recurrent selection for increased proVA concentration. Agronomic performance of Cycles 0, 1, 2, and 3 for each OP C was evaluated using three replications at 10 locations, and changes in proVA concentration were assessed for hand-pollinated grain produced at two sites. Selection resulted in significant (P < 0.01 for 11, and P < 0.05 for 1 occurrence) linear increases of 25 to 67% per cycle for total proVA, 28 to 60% for b-carotene, 18 to 70% for b-cryptoxanthin, and 11 to 46% for zeaxanthin. These findings are especially significant because, in contrast to recent trends, they demonstrate the feasibility of developing proVAenhanced maize while meeting nutritionists’ recommendations not to sacrifice b-cryptoxanthin and zeaxanthin to increase b-carotene concentration in grain. Grain yield increased in one but decreased (P < 0.01) in two of the OP Cs, and we hypothesize that linkage drag associated with proVA-enhancing genes from exotic donor lines may be responsible for the negative trends. We conclude that breeding proVA-enriched maize without sacrificing b-cryptoxanthin and zeaxanthin concentrations is feasible, but that (i) it remains unknown whether such approaches can achieve the high concentrations of proVA reported elsewhere by using marker-assisted selection for genes that favor b-carotene accumulation, and (ii) that grain yield and agronomic performance should be simultaneously selected if useful cultivars are desired.
Publication - Genome‑wide association analysis reveals new targets for carotenoid biofortification in maize(Springer, 2015) Suwarno, W.B.; Pixley, K.V.; Palacios-Rojas, N.; Kaeppler, S.M.; Babu, R.Genome-wide association analysis in CIMMYT’s association panel revealed new favorable native genomic variations in/nearby important genes such as hydroxylases and CCD1 that have potential for carotenoid biofortification in maize. Abstract Genome-wide association studies (GWAS) have been used extensively to identify allelic variation for genes controlling important agronomic and nutritional traits in plants. Provitamin A (proVA) enhancing alleles of lycopene epsilon cyclase (LCYE) and β-carotene hydroxylase 1 (CRTRB1), previously identified through candidate-gene based GWAS, are currently used in CIMMYT’s maize breeding program. The objective of this study was to identify genes or genomic regions controlling variation for carotenoid concentrations in grain for CIMMYT’s carotenoid association mapping panel of 380 inbred maize lines, using high-density genome-wide platforms with ~476,000 SNP markers. Population structure effects were minimized by adjustments using principal components and kinship matrix with mixed models. Genome-wide linkage disequilibrium (LD) analysis indicated faster LD decay (3.9 kb; r2 = 0.1) than commonly reported for temperate germplasm, and therefore the possibility of achieving higher mapping resolution with our mostly tropical diversity panel. GWAS for various carotenoids identified CRTRB1, LCYE and other key genes or genomic regions that govern rate-critical steps in the upstream pathway, such as DXS1, GGPS1, and GGPS2 that are known to play important roles in the accumulation of precursor isoprenoids as well as downstream genes HYD5, CCD1, and ZEP1, which are involved in hydroxylation and carotenoid degradation. SNPs at or near all of these regions were identified and may be useful target regions for carotenoid biofortification breeding efforts in maize; for example a genomic region on chromosome 2 explained ~16 % of the phenotypic variance for β-carotene independently of CRTRB1, and a variant of CCD1 that resulted in reduced β-cryptoxanthin degradation was found in lines that have previously been observed to have low proVA degradation rates.
Publication - Addressing climate change effects and meeting maize demand for Asia(GMRI, 2011) Zaidi, P.; Babu, R.; Cairns, J.E.; Jeffers, D.P.; Kha, L.Q.; Krishna, G.; Krishna, V.; Mcdonald, A.; Ortiz-Ferrara, G.; Palacios-Rojas, N.; Pixley, K.V.; Prasanna, B.M.; Rashid, Z.; Tadele Tefera; Tiwari, T.P.; Vinayan, M.T.; Vengadessan, V.; Fan, X.M.; Yunbi Xu; Weidong, C.; Zhang, S.; Vivek, B.This includes the extended summaries of the scientific presentations made during the 11th Asian Maize Conference held in Nanning, China, during 7-11 November 2011. The Conference is co-organized by the International Maize and Wheat Improvement Center (CIMMYT), and the Guangxi Maize Research Institute (GMRI), China. The theme of the workshop is "Addressing Climate Change Effects and Meeting Maize Demand for Asia". The 11th AMC brings together over 300 maize scientists, researchers and students from public and private sectors, including participants from several Asian countries, including Bangladesh, Bhutan, China, Colombia, India, Indonesia, Iran, Nepal, Philippines, Thailand, Turkey, Vietnam, besides Italy, Kenya, New Zealand, Mexico, Germany, Myanmar and the USA. The Conference features over 225 presentations, including keynote lectures, invited oral presentations, and poster presentations, besides scientific deliberations and discussions on maize in Asia. The extended summaries includes reviews and research papers on a diverse range of topics, including maize trends, challenges and opportunities in Asia, abiotic and biotic stresses affecting maize production, novel tools for maize improvement, conservation agriculture, nutritional enrichment of maize, participatory plant breeding, community-based seed production, public-private partnerships, maize value chains, policies and socio-economics relevant to Asia.
Publication - Genetic architecture controlling variation in grain carotenoid composition and concentrations in two maize populations(Springer, 2013) Kandianis, C.B.; Stevens. R.; Liu, W.; Palacios-Rojas, N.; Montgomery, K.; Pixley, K.V.; White, W.S.; Rocheford, T.R.The genetic basis for the variation in maize grain carotenoid concentrations was investigated in two F2:3 populations, DEexp × CI7 and A619 × SC55, derived from high total carotenoid and high -carotene inbred lines. A comparison of grain carotenoid concentrations from population DEexp × CI7 grown in different environments revealed significantly higher concentrations and greater trait variation in samples harvested from a subtropical environment relative to those from a temperate environment. Genotype by environment interactions was significant for most carotenoid traits. Using phenotypic data in additive, environment-specific genetic models, quantitative trait loci (QTL) were identified for absolute and derived carotenoid traits in each population, including those specific to the isomerization of-carotene. A multivariate approach for these correlated traits was taken, using carotenoid trait principal components (PCs) that jointly accounted for 97 % or more of trait variation. Component loadings for carotenoid PCs were interpreted in the context of known substrate-product relationships within the carotenoid pathway. Importantly, QTL for univariate and multivariate traits were found to cluster in close proximity to map locations of loci involved in methyl-erythritol, isoprenoid and carotenoid metabolism. Several of these genes, including lycopene epsilon cyclase, carotenoid cleavage dioxygenase1 and beta-carotene hydroxylase, were mapped in the segregating populations. These loci exhibited pleiotropic effects on -branch carotenoids, total carotenoid profile and -branch carotenoids, respectively. Our results confirm that several QTL are involved in the modification of carotenoid profiles, and suggest genetic targets that could be used for the improvement of total carotenoid and -carotene in future breeding populations.
Publication - Formation of heterotic groups and understanding genetic effects in a provitamin a biofortified maize breeding program(Crop Science Society of America (CSSA), 2014) Suwarno, W.B.; Pixley, K.V.; Palacios-Rojas, N.; Kaeppler, S.M.; Babu, R.Developing biofortified maize cultivars is a viable approach to combat the widespread problem of vitamin A deficiency among people for whom maize is a staple food. To enhance CIMMYT's provitamin A maize breeding efforts, this study: 1) evaluated whether separation of experimental maize lines into groups based on maximizing their molecular-marker-based genetic distances (GD) resulted in heterosis for among-group crosses, 2) assessed genetic effects (general and specific combining ability, GCA and SCA) for grain yield and provitamin A concentrations in hybrids among 21 inbred lines representing the three proposed groups, and 3) assessed the association between grain yield and provitamin A concentrations. The lines were crossed following a partial diallel design resulting in 156 hybrids which were evaluated at four environments with two replications of one-row plots. The first plant in each plot was self-pollinated to produce grain for provitamin A analysis. Significant but small yield advantage of among versus within group crosses (0.47 Mg ha-1 21 , P<0.05) suggested that the groups identified by maximizing GD could be a practicalstarting point for further breeding work to develop useful heterotic groups. Furthermore, the GD-proposed heterotic groups were improved by later revising some line assignments to groups using estimates of SCA effects. GCA effects were significant (P<0.01) for all traits, whereas SCA effects were weak (P<0.05) or not significant for provitamin A carotenoid concentrations, indicating that these were controlled primarily by additive gene action. Grain yield was not significantly correlated with provitamin A
Publication - Cell wall composition and biomass digestibility diversity in Mexican maize (Zea mays L) landraces and CIMMYT inbred lines(Consiglio per la Ricerca e la sperimentazione in Agricoltura, Unità di Ricerca per la Maiscoltura, 2013) Muttoni, G.; Palacios-Rojas, N.; Galicia, L.; Rosales Nolasco, Aldo; Pixley, K.V.; Leon, N. deMaize is one of the most important crops worldwide. Historically, breeding efforts in this crop have been primarily focused on the improvement of grain yield and stability and just recently also on the potential utility of maize stover (above ground biomass excluding the grain) as a source of biomass for the production of feed, fiber and cellulosic ethanol. The International Maize and Wheat Improvement Center (CIMMYT) holds one of the largest maize germplasm collections in the world and therefore is an important source of phenotypic and genetic diversity for many traits. Our objectives were to assess the phenotypic diversity for cell wall composition and biomass digestibility in Mexican tropical, subtropical and highland maize landraces and elite maize lines (CMLs) in the CIMMYT germplasm collection, as well as to evaluate the relationship between place of origin of these materials and phenotypic expression of biomass compositional traits. The range of variation for neutral detergent fiber for three groups of landraces was from 47 to 73%. Slightly larger levels of phenotypic variation were observed for this trait in the set of CMLs evaluated (42 to 78%). Some of the inbred lines, such as CML 507, presented superior characteristics in terms of cell wall composition and digestibility. The Tuxpeño tropical-subtropical race, widely used in CIMMYT breeding programs, formed a cluster characterized by high cell wall content and low biomass digestibility. The CIMMYT germplasm collection appears to be a vast source of untapped genetic and phenotypic variation for the improvement of maize biomass composition.
Publication - Validation of the effects of molecular marker polymorphisms in LcyE and CrtRB1 on provitamin A concentrations for 26 tropical maize populations(Springer, 2012) Babu, R.; Palacios-Rojas, N.; Shibin Gao; Jianbing Yan; Pixley, K.V.Vitamin A deficiency (VAD) compromises immune function and is the leading cause of preventable blindness in children in many developing countries. Biofortification, or breeding staple food crops that are rich in micronutrients, provides a sustainable way to fight VAD and other micronutrient malnutrition problems. Polymorphisms, with associated molecular markers, have recently been identified for two loci, LcyE (lycopene epsilon cyclase) and CrtRB1 (¦Â-carotene hydroxylase 1) that govern critical steps in the carotenoid biosynthetic pathway in maize endosperm, thereby enabling the opportunity to integrate marker-assisted selection (MAS) into carotenoid breeding programs. We validated the effects of 3 polymorphisms (LcyE5¡äTE, LcyE3¡äIndel and CrtRB1-3¡äTE) in 26 diverse tropical genetic backgrounds. CrtRB1-3¡äTE had a two-ten fold effect on enhancing beta-carotene (BC) and total provitamin A (proA) content. Reduced-function, favorable polymorphisms within LcyE resulted in 0¨C30 % reduction in the ratio of alpha- to beta-branch carotenoids, and increase in proA content (sometimes statistically significant). CrtRB1-3¡äTE had large, significant effect on enhancing BC and total ProA content, irrespective of genetic constitution for LcyE5¡äTE. Genotypes with homozygous favorable CrtRB1-3¡äTE alleles had much less zeaxanthin and an average of 25 % less total carotenoid than other genotypes, suggesting that feedback inhibition may be reducing the total flux into the carotenoid pathway. Because this feedback inhibition was most pronounced in the homozygous favorable LcyE (reduced-function) genotypes, and because maximum total proA concentrations were achieved in genotypes with homozygous unfavorable or heterozygous LcyE, we recommend not selecting for both reduced-function genes in breeding programs. LcyE exhibited significant segregation distortion (SD) in all the eight, while CrtRB1 in five of eight digenic populations studied, with favorable alleles of both the genes frequently under-represented. MAS using markers reported herein can efficiently increase proA carotenoid concentration in maize.
Publication