Author Archive

The usefulness of iron bioavailability as a target trait for breeding maize (Zea mays L.) with enhanced nutritional value

Posted by Carelia Juarez on , in Journal Articles

Published in Field Crops Research 123(2): 153-160, 2011

The usefulness of iron bioavailability as a target trait for breeding maize (Zea mays L.) with enhanced nutritional value

Kevin V. Pixley, Natalia Palacios-Rojas and Raymond P. Glahn

Iron (Fe) deficiency is the most widespread nutritional problem, affecting as many as half of the world’s population. Only a small fraction (2–15%) of Fe from plant sources is typically bioavailable, that is, available for absorption and nutritionally useful for humans. This study evaluated Fe concentration and bioavailability for three diverse sets of 12, 14 and 16 maize hybrids grown in two- or three-location trials to assess the feasibility of selecting for Fe bioavailability in breeding programs. Bioavailability of Fe, assessed using the in vitro digestion/Caco-2 cell model, varied significantly among hybrids in two of the three trials. Location effects were larger than location by genotype interaction effects, additive but not non-additive gene action was significant, and heritability estimates were mostly between 0.55 and 0.65 for Fe bioavailability estimators. Bioavailability of Fe was not associated with Fe concentration in grain or with grain yield. Negative correlation of Fe bioavailability with zinc concentration in grain for one of the three hybrid trials, and positive correlation with provitamin A concentrations in one trial were indicative of inhibitor and enhancer effects on Fe bioavailability, respectively. Although use of the Caco-2 cell model is promising, particularly because it integrates the whole meal, or food matrix effect on Fe bioavailability, the complex nature of the assay and moderate heritability of bioavailability estimators make it most suitable as an intermediate selection tool, following high throughput selection for molecular markers of Fe bioavailability, currently in development by other researchers, and preceding validation and efficacy trials with animal and human models.

 

 

Simulation Modeling in Crop Breeding

Posted by Carelia Juarez on , in Journal Articles

Published in Journal of the Indian Society of Agricultural Statistics 65(2): 225-235, 2011

Simulation Modeling in Crop Breeding

Jiankang Wang

Along with the fast developments in molecular biology and biotechnology, a large amount of biological data is available from genetic studies of important breeding traits in plants, which in turn provides an opportunity for undertaking genotypic selection in the breeding process. However, gene information has not been effectively used in crop improvement due to the lack of appropriate tools. The simulation approach can utilize the vast and diverse genetic information, predict the cross performance and compare different selection methods. Hence, the best performing crosses and effective breeding strategies can be identified. QuLine and QuHybrid are computer tools capable of defining a range from simple to complex genetic models and simulating breeding processes for developing final advanced lines and hybirds. Based on the results from simulation experiments, breeders can optimize their breeding methodology and greatly improve the breeding efficiency. In this paper, we first introduce the underlying principles of simulation modeling in crop enhancement, and then summarize several applications of QuLine in comparing different selection strategies, precision parental selection using known gene information, and the design approach in breeding. Breeding simulation allows the definition of complicated genetic models consisting of multiple alleles, pleiotropy, epistasis and gene-by-environment interaction, and provides a useful tool to efficiently use the wide spectrum of genetic data and information available to the breeders.

Population- and genome-specific patterns of linkage disequilibrium and SNP variation in spring and winter wheat (Triticum aestivum L.)

Posted by Carelia Juarez on , in Journal Articles

Published in BMC Genomics  11: 727, 2010

Population- and genome-specific patterns of linkage disequilibrium and SNP variation in spring and winter wheat (Triticum aestivum L.)

 Shiaoman Chao, Jorge Dubcovsky, Jan Dvorak, Ming-Cheng Luo, Stephen P. Baenziger, Rustam Matnyazov, Dale R. Clark, Luther E. Talbert, James A. Anderson, Susanne Dreisigacker, Karl Glover, Jianli Chen, Kim Campbell, Phil L. Bruckner, Jackie C. Rudd, Scott Haley, Brett F. Carver, Sid Perry, Mark E. Sorrells and Eduard D. Akhunov

Background: Single nucleotide polymorphisms (SNPs) are ideally suited for the construction of high-resolution genetic maps, studying population evolutionary history and performing genome-wide association mapping experiments. Here, we used a genome-wide set of 1536 SNPs to study linkage disequilibrium (LD) and population structure in a panel of 478 spring and winter wheat cultivars (Triticum aestivum) from 17 populations across the United States and Mexico.

Results: Most of the wheat oligo pool assay (OPA) SNPs that were polymorphic within the complete set of 478 cultivars were also polymorphic in all subpopulations. Higher levels of genetic differentiation were observed among wheat lines within populations than among populations. A total of nine genetically distinct clusters were identified, suggesting that some of the pre-defined populations shared significant proportion of genetic ancestry. Estimates of population structure (FST) at individual loci showed a high level of heterogeneity across the genome. In addition, seven genomic regions with elevated FST were detected between the spring and winter wheat populations. Some of these regions overlapped with previously mapped flowering time QTL. Across all populations, the highest extent of significant LD was observed in the wheat D-genome, followed by lower LD in the A- and B-genomes. The differences in the extent of LD among populations and genomes were mostly driven by differences in long-range LD ( > 10 cM).

Conclusions: Genome- and population-specific patterns of genetic differentiation and LD were discovered in the populations of wheat cultivars from different geographic regions. Our study demonstrated that the estimates of population structure between spring and winter wheat lines can identify genomic regions harboring candidate genes involved in the regulation of growth habit. Variation in LD suggests that breeding and selection had a different impact on each wheat genome both within and among populations. The higher extent of LD in the wheat D-genome versus the A- and B-genomes likely reflects the episodes of recent introgression and population bottleneck accompanying the origin of hexaploid wheat. The assessment of LD and population structure in this assembled panel of diverse lines provides critical information for the development of genetic resources for genome-wide association mapping of agronomically important traits in wheat.

Implication of rate and time of nitrogen application on wheat (Triticum aestivum. l .) yield and quality in Kenya

Posted by Carelia Juarez on , in Journal Articles

Published in Journal of Animal & Plant Sciences 9(2): 1141-1146, 2011

Implication of rate and time of nitrogen application on wheat (Triticum aestivum. l .) yield and quality in Kenya

 P.A. Ooro, J.N. Malinga, D.G. Tanner and T.S. Payne

 In Kenya, Nitrogen is the first limiting macro-element on many farms where bread wheat (Triticum aestivum) has been grown continuously for more than a decade. On-farm trials were conducted in Kenya by superimposing the treatments on farmers’ fields in Nakuru (5 sites), Uasin Gishu (3 sites), and Timau (2 sites) districts during the main growing seasons of 1997-99. This was to study the effect of rate and time of application of fertilizer nitrogen (N) on bread wheat ( Triticum aestivum) grain yield, yield components, and grain quality. Wheat grain samples from the ten (N) nitrogen rates and timing treatments combined across replications were analysed at the Small Grain Institute, Bethlehem, Republic of South Africa for milling and baking quality in accordance with standard analytical procedures (Pyler, 1973; Kent, 1983; Hoseney, 1986). Results revealed that flour protein content (FPC) and grain nitrogen (GN) increased significantly in response to N rate. Nitrogen application increased timing of sedimentation (SDSS) rate and loaf volume, but decreased the kernel weight, falling number (FLN) and flour yield (FLY) percentage. N application had P<0.05 effects only on mixing development time (MDT), FLN and (SDSS). Split application of N resulted in superior quality attributes than when the entire N was applied at once. The sensitivity of rate and time of N application was found to be greater in the wheat quality attributes than the grain yield and yield components. These results can therefore be used insituations where good wheat prices are determined on the basis of grain quality.

Grain and Tortilla Quality in Landraces and Improved Maize Grown in the Highlands of Mexico

Posted by Carelia Juarez on , in Journal Articles

Published in  Plant Foods for Human Nutrition 66(2): 203-208, 2011

Grain and Tortilla Quality in Landraces and Improved Maize Grown in the Highlands of Mexico

Gricelda Vázquez-Carrillo, Silverio García-Lara, Yolanda Salinas-Moreno, David J. Bergvinson and Natalia Palacios-Rojas

The maize produced in the highlands of Mexico (>2,400 masl) is generally not accepted by the flour and masa and tortilla industry. The objective of this work was to evaluate the grain quality and tortilla properties of maize landraces commonly grown in the highlands of Mexico and compare them with improved germplasm (hybrids). Germplasm analysis included 11 landraces, 32 white hybrids, and six yellow hybrids. Grain quality was analyzed for a range of physical and chemical factors, as well as for alkaline cooking quality. Landrace grains tended to be heterogeneous in terms of size, hardness and color. All landraces had soft-intermediate grains with an average flotation index (FI) of 61%. In contrast, hybrid grains were homogenous in size and color, and harder than landrace grains, with a FI of 38%. Protein, free sugars, oil and phenolic content in landraces were higher than in the hybrids. Significant correlations were found between phenolic content and tortilla color (r = −0.60; p < 0.001). Three landraces were identified as appropriate for the masa and tortilla industry, while all the hybrids evaluated fulfilled the requirements of this industry.

Global incidence of wheat rusts and powdery mildew during 1969–2010 and durability of resistance of winter wheat variety Bezostaya 1

Posted by Carelia Juarez on , in Journal Articles

Published in European Journal of Plant Pathology 1-18, 2011

Global incidence of wheat rusts and powdery mildew during 1969–2010 and durability of resistance of winter wheat variety Bezostaya 1

Alexey Morgounov, Hale Ann Tufan, Ram Sharma, Beyhan Akin, Ahmet Bagci, Hans-Joachim Braun, Yuksel Kaya, Mesut Keser, Thomas S. Payne, Kai Sonder and Robert McIntosh

Disease incidence and severity was studied for winter wheat variety Bezostaya 1 and susceptible checks based on data from international nurseries from 1969 to 2010 and from 51 countries across major winter wheat production regions totalling 1,047 reports. The frequency of leaf rust and stripe rust occurrence was stable over time with marked increases in severity in 2001–2010 especially in Europe and Central and West Asia. Substantial global reductions in stem rust occurrence were recorded and attributed primarily to use of resistance genes although the recent emergence of race Ug99 makes wheat more vulnerable. The occurrence of powdery mildew remained globally stable over time. It was the most important foliar disease in Western and Southern Europe, where the frequency was very high for all time periods coupled with slight increases in severity during 2001–2010. The durable resistance of variety Bezostaya 1 to all four diseases was demonstrated in the study using comparisons of disease severities of Bezostaya 1 and the most susceptible entries. The Lr34/Yr18/Pm38 pleiotrophic set possessed by Bezostaya 1 is currently an important target for selection because it is now amenable to molecular selection. Increased use of genes like Lr34 combined with strategies to minimize cultivation of extremely susceptible varieties will contribute to long term maintenance of low and non-damaging disease levels. The durable disease resistance of Bezostaya 1, combined with its adaptability and good end-use quality, was a significant reason for its huge impact in agriculture over the last 50 years.

 

Does ear C sink strength contribute to overcoming photosynthetic acclimation of wheat plants exposed to elevated CO2?

Posted by Carelia Juarez on , in Journal Articles

Published  in Journal of  Experimental  Botany  62(11): 3957-3969, 2011

Does ear C sink strength contribute to overcoming photosynthetic acclimation of wheat plants exposed to elevated CO2?

Iker Aranjuelo, Llorenç Cabrera-Bosquet, Rosa Morcuende, Jean Christophe Avice, Salvador Nogués, José Luis Araus, Rafael Martínez-Carrasco and Pilar Pérez

Wheat plants (Triticum durum Desf., cv. Regallo) were grown in the field to study the effects of contrasting [CO2]conditions (700 versus 370 μmol mol−1) on growth, photosynthetic performance, and C management during the post-anthesis period. The aim was to test whether a restricted capacity of sink organs to utilize photosynthates drives a loss of photosynthetic capacity in elevated CO2. The ambient 13C/12C isotopic composition (δ13C) of air CO2 was changed from –10.2‰ in ambient [CO2] to –23.6‰ under elevated [CO2] between the 7th and the 14th days after anthesis in order to study C assimilation and partitioning between leaves and ears. Elevated [CO2] had no significant effect on biomass production and grain filling, and caused an accumulation of C compounds in leaves. This was accompanied by up-regulation of phosphoglycerate mutase and ATP synthase protein content, together with down-regulation of adenosine diphosphate glucose pyrophosphatase protein. Growth in elevated [CO2] negatively affected Rubisco and Rubisco activase protein content and induced photosynthetic down-regulation. CO2 enrichment caused a specific decrease in Rubisco content, together with decreases in the amino acid and total N content of leaves. The C labelling revealed that in flag leaves, part of the C fixed during grain filling was stored as starch and structural C compounds whereas the rest of the labelled C (mainly in the form of soluble sugars) was completely respired 48 h after the end of labelling. Although labelled C was not detected in the δ13C of ear total organic matter and respired CO2, soluble sugar δ13C revealed that a small amount of labelled C reached the ear. The 12CO2 labelling suggests that during the beginning of post-anthesis the ear did not contribute towards overcoming flag leaf carbohydrate accumulation, and this had a consequent effect on protein expression and photosynthetic acclimation.