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Introgression of the crtRB1 gene into quality protein maize inbred lines using molecular markers.

ABSTRACT: Quality protein maize (QPM; Zea mays L.) has effectively enhanced levels of the amino acids, lysine, and tryptophan, over normal maize and provided balanced dietary protein for the health and development of monogastric animals and humans. However, as in normal maize, QPM varieties are low in provitamin A (ProVA), a precursor of vitamin A, which can lead to vitamin A deficiency in humans when maize is a significant part of their diet. In this study, maize inbred Hp321-1 carrying the favorable alleles crtRB1-5'TE-2 and crtRB1-3'TE-1 that can enhance levels of ProVA, was used as donor for improving ProVA in QPM inbred lines CML161 and CML171. Functional markers for identifying the favorable alleles crtRB1-5'TE-2 and crtRB1-3'TE-1 were used in foreground selection, and simple sequence repeat markers were used in background selection for the BC1F1, BC2F1, and BC2F2 generations. The background recovery rates were 77.4 and 84.5 % for CML161 and CML171 populations, respectively, in the BC1F1 generation, and 89.9 and 92.1 % in the BC2F2 generation. With foreground and background selection, the mean ProVA concentration has been improved from 1.60 µg g(-1) in the parent of CML161 to 5.25 µg g(-1) in its BC2F3 offspring, from 1.80 µg g(-1) in the parent of CML171 to 8.14 µg g(-1) in its BC2F3 offspring while maintaining similar QPM characteristics of the recurrent parents. The success from this study offers maize breeders a procedure for increasing ProVA in QPM lines, which will greatly mitigate vitamin A deficiency and protein-energy malnutrition in developing countries.

SUBMITTER: Liu L

PROVIDER: S-EPMC4503869 | biostudies-other | 2015

REPOSITORIES: biostudies-other

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Introgression of the <i>crtRB1</i> gene into quality protein maize inbred lines using molecular markers.

Liu Li L Jeffers Daniel D Zhang Yudong Y Ding Meiling M Chen Wei W Kang Manjit S MS Fan Xingming X

Molecular breeding : new strategies in plant improvement 20150716 8

Quality protein maize (QPM; <i>Zea mays</i> L.) has effectively enhanced levels of the amino acids, lysine, and tryptophan, over normal maize and provided balanced dietary protein for the health and development of monogastric animals and humans. However, as in normal maize, QPM varieties are low in provitamin A (ProVA), a precursor of vitamin A, which can lead to vitamin A deficiency in humans when maize is a significant part of their diet. In this study, maize inbred Hp321-1 carrying the favora ...[more]

PMID: 26190934

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Project description:BackgroundKnowledge of germplasm diversity and relationships among elite breeding materials is fundamentally important in crop improvement. We genotyped 450 maize inbred lines developed and/or widely used by CIMMYT breeding programs in both Kenya and Zimbabwe using 1065 SNP markers to (i) investigate population structure and patterns of relationship of the germplasm for better exploitation in breeding programs; (ii) assess the usefulness of SNPs for identifying heterotic groups commonly used by CIMMYT breeding programs; and (iii) identify a subset of highly informative SNP markers for routine and low cost genotyping of CIMMYT germplasm in the region using uniplex assays.ResultsGenetic distance for about 94% of the pairs of lines fell between 0.300 and 0.400. Eighty four percent of the pairs of lines also showed relative kinship values ≤ 0.500. Model-based population structure analysis, principal component analysis, neighbor-joining cluster analysis and discriminant analysis revealed the presence of 3 major groups and generally agree with pedigree information. The SNP markers did not show clear separation of heterotic groups A and B that were established based on combining ability tests through diallel and line x tester analyses. Our results demonstrated large differences among the SNP markers in terms of reproducibility, ease of scoring, polymorphism, minor allele frequency and polymorphic information content. About 40% of the SNPs in the multiplexed chip-based GoldenGate assays were found to be uninformative in this study and we recommend 644 of the 1065 for low to medium density genotyping in tropical maize germplasm using uniplex assays.ConclusionsThere were high genetic distance and low kinship coefficients among most pairs of lines, clearly indicating the uniqueness of the majority of the inbred lines in these maize breeding programs. The results from this study will be useful to breeders in selecting best parental combinations for new breeding crosses, mapping population development and marker assisted breeding.

Project description:Molecular characterization is important for efficient utilization of germplasm and development of improved varieties. In the present study, we investigated the genetic purity, relatedness and population structure of 265 maize inbred lines from the Ethiopian Institute of Agricultural Research (EIAR), the International Maize and Wheat Improvement Centre (CIMMYT) and the International Institute of Tropical Agriculture (IITA) using 220,878 single nucleotide polymorphic (SNP) markers obtained using genotyping by sequencing (GBS).Only 22% of the inbred lines were considered pure with <5% heterogeneity, while the remaining 78% of the inbred lines had a heterogeneity ranging from 5.1 to 31.5%. Pairwise genetic distances among the 265 inbred lines varied from 0.011 to 0.345, with 89% of the pairs falling between 0.301 and 0.345. Only <1% of the pairs had a genetic distance lower than 0.200, which included 14 pairs of sister lines that were nearly identical. Relative kinship analysis showed that the kinship coefficients for 59% of the pairs of lines was close to zero, which agrees with the genetic distance estimates. Principal coordinate analysis, discriminant analysis of principal components (DAPC) and the model-based population structure analysis consistently suggested the presence of three groups, which generally agreed with pedigree information (genetic background). Although not distinct enough, the SNP markers showed some level of separation between the two CIMMYT heterotic groups A and B established based on pedigree and combining ability information.The high level of heterogeneity detected in most of the inbred lines suggested the requirement for purification or further inbreeding except those deliberately maintained at early inbreeding level. The genetic distance and relative kinship analysis clearly indicated the uniqueness of most of the inbred lines in the maize germplasm available for breeders in the mid-altitude maize breeding program of Ethiopia. Results from the present study facilitate the maize breeding work in Ethiopia and germplasm exchange among breeding programs in Africa. We suggest the incorporation of high density molecular marker information in future heterotic group assignments.

Project description:BackgroundInformation on population structure and genetic diversity of germplasm in a breeding programme is useful because it enhances judicious utilisation of genetic resources to achieve breeding objectives. Seventy early maturing provitamin A (PVA) quality protein maize (QPM) inbreds developed by the IITA- maize improvement programme were genotyped using 8171 DArTseq markers. Furthermore, 96 hybrids derived from 24 selected inbreds plus four checks were evaluated under low-N and optimal environments in Nigeria during 2016 and 2017. Genotypic and phenotypic data of inbreds and hybrids respectively, were analysed to (i) assess the level of genetic dissimilarities and population structure of the inbreds, and (ii) investigate the grain yield performance of derived hybrids under low-N, optimal and across environments.ResultsGenetic diversity among the seventy inbreds was high varying from 0.042 to 0.500 with an average of 0.357. Sixty-six inbred lines with probabilities ?0.70 were assigned to a single group. The population structure analysis, the UPGMA phylogeny, and the principal Coordinate Analysis (PCoA) of the DArTseq markers revealed a clear separation of five groups and each followed pedigree records. Clustered inbreds displayed common characteristics including high PVA levels, and drought and low-N tolerance. The top performing hybrid, TZEIORQ 40?×?TZEIORQ 26 out-yielded the best hybrid control, TZEIOR 127?×?TZEIOR 57 by 8, 3, and 9% under low-N, optimal, and across environments, respectively. High repeatability estimates were detected for grain yield under each and across environments. Similarly, high breeding efficiency of 71, 70 and 72% were computed under low-N, optimal, and across environments, respectively.ConclusionsThe UPGMA clustering, the structure analysis, and the PCoA consistently revealed five groups which largely followed pedigree information indicating the existence of genetically distinct groups in the inbred lines. High repeatability and breeding efficiency values estimated for grain yield of hybrids under low-N, optimal and across environments demonstrated that high productive hybrids could be developed using inbreds from the opposing clusters identified by the DArTseq markers. The 15 top performing hybrids identified, particularly TZEIORQ 40?×?TZEIORQ 26 and TZEIORQ 29?×?TZEIORQ 43 should be further evaluated for release and commercialization in SSA.

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Introgression of the crtRB1 gene into quality protein maize inbred lines using molecular markers.

Publications

Introgression of the <i>crtRB1</i> gene into quality protein maize inbred lines using molecular markers.

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