Person: Pixley, K.V.
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Pixley
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K.V.
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Pixley, K.V.
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0000-0003-4068-7436 4 results
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- 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 - 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 - 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.
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