International Maize and Wheat Improvement Center

About: International Maize and Wheat Improvement Center is a nonprofit organization based out in Texcoco, Mexico. It is known for research contribution in the topics: Population & Agriculture. The organization has 1976 authors who have published 4799 publications receiving 218390 citations.

Genetic architecture of grain yield in bread wheat based on genome-wide association studies.

Abstract: Identification of loci for grain yield (GY) and related traits, and dissection of the genetic architecture are important for yield improvement through marker-assisted selection (MAS). Two genome-wide association study (GWAS) methods were used on a diverse panel of 166 elite wheat varieties from the Yellow and Huai River Valleys Wheat Zone (YHRVWD) of China to detect stable loci and analyze relationships among GY and related traits. A total of 326,570 single nucleotide polymorphism (SNP) markers from the wheat 90 K and 660 K SNP arrays were chosen for GWAS of GY and related traits, generating a physical distance of 14,064.8 Mb. One hundred and twenty common loci were detected using SNP-GWAS and Haplotype-GWAS, among which two were potentially functional genes underpinning kernel weight and plant height (PH), eight were at similar locations to the quantitative trait loci (QTL) identified in recombinant inbred line (RIL) populations in a previous study, and 78 were potentially new. Twelve pleiotropic loci were detected on eight chromosomes; among these the interval 714.4–725.8 Mb on chromosome 3A was significantly associated with GY, kernel number per spike (KNS), kernel width (KW), spike dry weight (SDW), PH, uppermost internode length (UIL), and flag leaf length (FLL). GY shared five loci with thousand kernel weight (TKW) and PH, indicating significantly affected by two traits. Compared with the total number of loci for each trait in the diverse panel, the average number of alleles for increasing phenotypic values of GY, TKW, kernel length (KL), KW, and flag leaf width (FLW) were higher, whereas the numbers for PH, UIL and FLL were lower. There were significant additive effects for each trait when favorable alleles were combined. UIL and FLL can be directly used for selecting high-yielding varieties, whereas FLW can be used to select spike number per unit area (SN) and KNS. The loci and significant SNP markers identified in the present study can be used for pyramiding favorable alleles in developing high-yielding varieties. Our study proved that both GWAS methods and high-density genetic markers are reliable means of identifying loci for GY and related traits, and provided new insight to the genetic architecture of GY.

Genetic Diversity in CIMMYT Nontemperate Maize Germplasm: Landraces, Open Pollinated Varieties, and Inbred Lines

Abstract: CIMMYT is the source of improved maize (Zea mays L.) breeding material for a signifi cant portion of the nontemperate maize growing world. Landraces which did not serve as sources for improved maize germplasm may contain untapped allelic variation useful for future breeding progress. Information regarding levels of diversity in different germplasm would help to identify sources for broadening improved breeding pools and in seeking genes and alleles that have not been tapped in modern maize breeding. The objectives of this study were to examine the diversity in maize landraces, modern open pollinated varieties (OPVs), and inbred lines adapted to nontemperate growing areas to fi nd unique sources of allelic diversity that may be used in maize improvement. Twenty-fi ve simple sequence repeat markers were used to characterize 497 individuals from 24 landraces of maize from Mexico, 672 individuals from 23 CIMMYT improved breeding populations, and 261 CIMMYT inbred lines. Number of alleles, gene diversity per locus, unique alleles per locus, and population structure all differ between germplasm groups. The unique alleles found in each germplasm group represent a great reservoir of untapped genetic resources for maize improvement, and implications for hybrid breeding are discussed.

Simulating Effects of Genes for Physiological Traits in a Process-Oriented Crop Model

Abstract: Recent improvements in crop simulation techniques and in understanding of crop genetics suggest the possibility of integrating genetic information on physiological traits into crop simulation models. By using known genotypes, rather than empirically fitted cultivar-specific coefficients, a simulation model should permit more explicit testing of hypotheses concerning the genetic basis of adaptation of cultivars to different environments or production systems. This paper describes and evaluates GeneGro, a version of the dry bean (Phaseolus vulgaris L.) crop simulation model BEANGRO version 1.01 modified to incorporate effects of seven genes affecting phenology, growth habit, and seed size: Ppd, Hr, Fin, Fd, and Ssz-1, and two more genes for seed size inferred from indirect evidence. Thirty cultivars were calibrated for BEANGRO using data from 14 trials conducted in Colombia, Guatemala, Mexico, and Florida. The resulting cultivar-specific coefficients of BEANGRO were replaced with information on specific genotypes of cultivars to create the gene-based model. With cultivar differences specified only by the seven genes, GeneGro explained 31% of observed variation for seed yield, 58% for seed weight, 84% for days to flowering, 85% for days to maturity, 52% for maximum leaf area index, and 36% for canopy dry weight at maturity, but 0% for harvest index. In testing the effectiveness of GeneGro after overall trial and cultivar effects were accounted for through regression analysis, all simulated data except for seed weight showed significant relations with observed data (P ≤ 0.01). Our results indicate that for certain traits surprisingly few genes must be characterized to simulate cultivar differences as accurately as with the BEANGRO model. Furthermore, they suggest a potential for developing models similar to GeneGro for studying the effects of genes on adaptation in other crops.

Dissection of the genetic basis of heterosis in an elite maize hybrid by QTL mapping in an immortalized F2 population

Abstract: The genetic basis of heterosis for grain yield and its components was investigated at the single- and two-locus levels using molecular markers with an immortalized F2 (IF2) population, which was developed by pair crosses among recombinant inbred lines (RILs) derived from the elite maize hybrid Yuyu22. Mid-parent heterosis of each cross in the IF2 population was used to map heterotic quantitative trait loci. A total of 13 heterotic loci (HL) were detected. These included three HL for grain yield, seven for ear length, one for ear row number and two for 100-kernel weight. A total of 143 digenic interactions contributing to mid-parent heterosis were detected at the two-locus level involving all three types of interactions (additive × additive = AA, additive × dominance = AD or DA, dominance × dominance = DD). There were 25 digenic interactions for grain yield, 36 for ear length, 31 for ear row number and 51 for 100-kernel weight. Altogether, dominance effects of HL at the single-locus level as well as AA interactions played an important role in the genetic basis of heterosis for grain yield and its components in Yuyu22.