Novel allelic variants encoded at the Glu-D3 locus in bread wheat

Low-molecular weight glutenin subunits (LWM-GS) are important components of wheat (Triticum aestivum L.) gluten, with important effects on end-use quality. The LMW-GS are encoded at Glu-3 loci (Glu-A3, Glu-B3 and Glu-D3, on the short arms of chromosomes 1A, 1B and 1D), each of which exhibits extensive allelic variation. Each locus encodes numerous LMW-GS, some of which have similar electrophoretic mobilities, making it difficult to distinguish among Glu-3 loci. Alleles of the Glu-D3 locus of bread wheat are considered the most problematic to assign. To date, six Glu-D3 alleles, designated a, b, c, d, e and f, have been reported. We report five previously undescribed alleles (g, h, i, j and k), and describe a method for characterizing them using a combination of SDS-PAGE and multiplexed PCR-based DNA markers. This method could be used for accurate identification of Glu-D3 alleles, permitting the estimation of the effects of these alleles on end-use quality and the selection of desirable alleles and allelic combinations in wheat breeding.     

The contribution of ear photosynthesis to grain filling in bread wheat (Triticum aestivum L.)

The contribution of ear photosynthesis to grain filling in wheat (Triticum aestivum L.) is not well known. The main objective of this work was to evaluate this contribution through three different experimental approaches: (1) ear photosynthesis was reduced by removing awns or shading the ears (in combination with a defoliation treatment), (2) grain weight per ear was compared in an ‘all shaded’ crop versus plants where only the vegetative parts were shaded (‘ear emerging’), and (3) ear photosynthesis was reduced with DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea), a specific inhibitor of photosystem II.     

Effects of the replacement of Glu-A1 by Glu-D1 locus on agronomic performance and bread-making quality of the hexaploid wheat cv. Courtot

The aim of this study was to evaluate the cumulative and interactive effects on wheat (Triticum aestivum L.) gluten strength and mixing properties of dough associated with the duplication of the Glu-D1 locus. A partially isohomoeoallelic line RR240, in which a segment of the wheat chromosome 1D containing the Glu-D1 locus encoding the Dx2 + Dy12 subunits and translocated to the long arm of the chromosome 1A through homoeologous recombination, was assessed. Agronomic traits and yield components were studied in the translocated line RR240 and compared with the control line cv. Courtot. Both lines were evaluated under field conditions in two experimental years. Technological effects resulting from the duplication of HMW glutenin subunits Dx2 and Dy12 were evaluated using the Alveograph test, the Mixograph test and the baking test. The RR240 line was shown to have a lower agronomic performance for 1000-kernel weight and grain yield. However the duplication of the Glu-D1 allele was associated with a significant effect on dough strength and mixing resistance, and on the Zeleny sedimentation volume. Baking parameters were not significantly modified between both lines although the score values of the CNERNA test were observed to be slightly higher in RR240 than in Courtot.     

Effects of elevated atmospheric CO2 on grain quality of wheat

Wheat (Triticum aestivum L.) is one of the most important agricultural crops worldwide. Due to its high content of starch and unique gluten proteins, wheat grain is used for many food and non-food applications. Although grain quality is an important topic for food and feed as well as industrial processing, the consequences of future increases in atmospheric carbon dioxide (CO₂) concentrations on quality parameters such as nutritional and bread-making rheological properties are still unclear. Wheat productivity increases under CO₂ enrichment. Concomitantly, the chemical composition of vegetative plant parts is often changed and grain quality is altered. In particular, the decrease in grain protein concentration and changes in protein composition may have serious economic and health implications. Additionally, CO₂ enrichment affects amino acid composition and the concentrations of macro- and micro-elements. However, experimental results are often inconsistent. The present review summarises the results from numerous CO₂ enrichment experiments using different exposure techniques in order to quantify the potential impacts of projected atmospheric CO₂ levels on wheat grain yield and on aspects of grain composition relevant to processing and human nutrition.     

Apigenin di-C-glycosides (ACG) content and composition in grains of bread wheat (Triticum aestivum) and related species

Apigenin di-C-glycosides (ACGs) are present in the grain of bread wheat and other related cereals primarily as one or two sets of Wesseley-Moser isomers containing either arabinose and glucose (ACG1) or arabinose and galactose (ACG2) on the A ring of apigenin. These compounds may contribute to the yellow colour of wheat-based products made under alkaline conditions and in addition, have possible roles in a number of plant physiology processes and human health. The aims of this investigation were to survey genetic variation for ACG content and composition in hexaploid bread wheat (Triticum aestivum L.) and to examine ACGs in the putative progenitors of hexaploid wheat and available genetic stocks as a first step towards understanding the mechanisms involved in their biosynthesis and genetic control. Substantial variation in both grain ACG content and the ratio, ACG1/ACG2, were identified within bread wheat cultivars and related species. Genotype controlled the major portion of the variation. ACG content appeared to be a multigenic trait whereas variation in ACG1/ACG2 was associated with a limited number of chromosomes, in particular chromosomes 1B, 7B and 7D. The results suggest that it should be possible to manipulate both ACG content and composition traits through breeding.     

Introgression of a major gene for high grain protein content in some Indian bread wheat cultivars

In bread wheat, high grain protein content (GPC) determines nutritional value, processing properties and quality of the end-product. In view of this, marker-assisted selection (MAS) was performed for introgression of a major gene for high GPC (Gpc-B1) into 10 wheat genotypes. As a result, 124 BC₃F₅/F₆ progenies with Gpc-B1 were developed and evaluated in multi-location field trials. Significant interaction of Gpc-B1 with the recipient parent genotypes and the environment was noticed. However, a total of seven MAS-derived progenies with significantly higher GPC (14.83-17.85%) than their recipient parental genotypes and having no yield penalty were obtained. In these selected progenies, no significant negative correlation of grain yield with GPC (%) or protein yield was observed suggesting that GPC could be improved without yield penalty. This study thus suggested that MAS in combination with phenotypic selection is a useful strategy for development of wheat genotypes with high GPC associated with no loss in yield.     

Diversity of sequences encoded by the Gsp-1 genes in wheat and other grass species

The Gsp-1 genes of wheat encode two components, the “grain softness protein” (whose role in determining texture has not been substantiated) and a 15 residue arabinogalactan peptide (AGP) sequence which is O-glycosylated and is also of unknown function. We have determined genomic Gsp-1 sequences from 29 species within the Triticeae tribe and an additional 12 species from the major subfamilies of the Poaceae (Anomochlooideae, Bambusoideae, Ehrhartoideae, Chloridoideae and Panicoideae). Twelve new AGP sequence types were identified with forms present in Agropyron mongolicum, Secale cereale, Oryza sativa subsp. japonica and Sorghum bicolor containing an extra ten amino acids within the AGP sequence. Phylogenetic analysis showed distinct groupings of AGP/GSP sequence types which had no apparent relationship to the species or even the genus. However, individual forms of AGP forms were associated with specific groups of GSP sequences, providing no evidence that the AGP and GSP-1 parts of the protein have diverged at different rates or in different ways.     

Development of simple and co-dominant PCR markers to genotype puroindoline a and b alleles for grain hardness in bread wheat (Triticum aestivum L.)

Grain hardness is one of the most important quality characteristics of cultivated bread wheat (Triticum aestivum L.). A large deletion in the puroindoline a (Pina) gene or single nucleotide polymorphisms (SNPs) in the puroindoline b (Pinb) gene results in hard grain texture. So far, nine Pina alleles (Pina-D1a–Pina-D1b, Pina-D1k–Pina-D1q) and seventeen Pinb alleles (Pinb-D1a–Pinb-D1g, Pinb-D1p–Pinb-D1ab) have been identified in bread wheat. The major Pina and Pinb alleles identified in hard wheat cultivars are Pina-D1b, Pinb-D1b, Pinb-D1c and Pinb-D1d. In this study, a three-primer PCR system was employed to develop nine co-dominant STS markers for genotyping Pina-D1a and Pina-D1b, whereas temperature-switch (TS) PCR was used to develop six co-dominant SNP markers for genotyping the Pinb-D1a, Pinb-D1b, Pinb-D1c and Pinb-D1d alleles. These STS and TS-PCR markers were used to verify the grain hardness genotype of 100 wheat cultivars. The reliability and genotyping accuracy of TS-PCR markers were confirmed through sequencing of PCR products and a comparison with previously published results. Therefore, STS and TS-PCR markers offer a simple, cost-effective and reliable method for high-throughput genotyping Pina and Pinb alleles to select grain hardness in wheat quality breeding programs and for wheat market classification.     

Isolation and characterization of EMS-induced Dy10 and Ax1 high molecular weight glutenin subunit deficient mutant lines of elite hexaploid wheat (Triticum aestivum L.) cv. Summit

The mixing properties of the dough are critical in the production of bread and other food products derived from wheat. The high molecular weight glutenin subunits (HMW-GS) are major determinants of wheat dough processing qualities. The different alleles of the HMW-GS genes in hexaploid wheat vary in their effect on dough quality. To determine the contribution of the individual HMW-GS alleles, lines deficient in HMW-GS proteins were generated by chemical mutagenesis in the elite bread wheat Triticum aestivum cv. Summit. In this report we describe the identification and characterization of Dy10 and Ax1 deficient lines. Examination of the effect of Dy10 and Ax1 deficiency on dough rheological properties by mixography showed shorter mixing time to reach peak resistance, and weaker and less extensible doughs relative to the wild type control. This is the first time that the role of Dy10 in vivo has been examined apart from the Dx5 + Dy10 allelic pair combination.     

Association of Puroindoline b-B2 variants with grain traits,yield components and flag leaf size in bread wheat (Triticum aestivum L.) varieties of the Yellow and Huai Valleys of China

A total of 169 wheat (Triticum aestivum L.) varieties (landraces and cultivars) were used to asses the relationship between Puroindoline D1 alleles and Puroindoline b-B2 variants and grain hardness, other grain traits, yield components, and flag leaf size. Results indicated that the average SKCS hardness of Pinb-B2v3 varieties was significantly greater than that of Pinb-B2v2 varieties within the soft Puroindoline D1 haplotype sub-group. Conversely, no statistically significant difference was obtained for SKCS hardness between varieties with the Pinb-B2v3 vs. Pinb-B2v2 alleles within the two hard Puroindoline D1 haplotypes (Pinb-D1b and Pinb-D1p sub-groups). Therefore, the Puroindoline b-B2 gene may have a bigger impact on soft wheat varieties than hard. Across all varieties, thousand-kernel weight, grain weight per spike, grain diameter, grain number per spike, flag leaf width and area of Pinb-B2v3 varieties were significantly greater than those possessing Pinb-B2v2. These results indicated that the Pinb-B2v3 allele was associated with preferable grain yield traits compared to the Pinb-B2v2 allele in bread wheat. This study provides evocative information for better understanding the molecular and genetic basis of wheat grain yield.     

Effects of drought and the presence of the 1BL/1RS translocation on grain vitreosity, hardness and protein content in winter wheat

Grain texture is an important component of end-use quality in wheat. The effects of water availability on the components of texture; vitreosity, determined using a Light Transflectance meter (LTm), grain hardness measured using the single-kernel characterisation system (SKCS), and protein content, were studied in field experiments of winter wheat in the UK in 2001/2002 and 2002/2003. Experiments were grown on a drought prone soil and employed a mapping population of 46 doubled haploid (DH) lines and their parents, Beaver (+1BL/1RS, soft wheat) and Soissons (1B, hard wheat). The results showed that drought increased hardness in both seasons, but the effect was never sufficient to move a line from the soft class into the hard class. Puroindoline (PIN)-a:b peak height ratio explained ca. 78% of the variation in hardness, and drought also appeared to increase the amounts of PINs in the grain. Minor quantitative trait loci (QTLs) were found for hardness on chromosomes 2A, 2D, 3A and 6D, also associated with QTLs for PINs. Vitreosity also increased in response to drought in both seasons. Variation in vitreosity explained 7–11% of the overall variation in texture within a hardness class, with hardness increasing on average by 2.2 SKCS units for each 10% increase in the proportion of vitreous grains. The relationship between vitreosity and protein content was poor, despite the fact that protein content also increased in response to drought. Minor QTLs associated with both protein content and vitreosity were found on chromosomes 1B, 4D and 5D. A minor QTL for vitreosity was also found on chromosome 2D. However, there appeared to be no direct relationship between alleles at the Ha locus, the gene which controls the difference between hard and soft wheats, and vitreosity. A positive relationship between the presence of the 1BL/1RS translocation and the proportion of vitreous grains was identified, suggesting that vitreosity was strongly linked to changes in protein quality.     

Effect of tolerance to Septoria tritici blotch on grain yield,yield components and grain quality in Argentinean wheat cultivars

Septoria tritici blotch (STB) caused by Zymoseptoria tritici (Mycosphaerella graminicola) is a major disease of wheat worldwide due to significant losses in grain yield and quality. Disease tolerance is the ability to maintain yield performance in the presence of disease symptoms. Therefore, it could be a useful tool in the management of the disease. Although it is known, that there is disease tolerance to STB in some wheat cultivars, this aspect has not been studied among Argentinean cultivars. The aims of this study were to evaluate genotypic differences in tolerance to STB among Argentinean cultivars, considering the relationship between the area under disease progress curve or the green leaf area or the non-green leaf area duration with the grain yield. In addition the effect of the disease on yield, yield components, test weight, grain protein concentration, wet and dry gluten concentration and the influence of tolerance on these traits was investigated. Field experiments were carried out with ten cultivars in a split-split-plot design during 2010 and 2011. Inoculation treatments were the main plots and cultivars, the subplots. STB significantly reduced grain yield, their components, test weight and increase grain protein and gluten concentration. Cultivar Baguette 10 showed major tolerance to STB, indicated by a consistent low regression slope between the green area duration and yield, while Klein Chaja was non-tolerant due to a high regression slope. However, many cultivars such as Buck Brasil, Buck 75 Aniversario, Klein Escorpion and Klein Flecha had considerably similar regression slopes to Baguette 10, provided good levels of tolerance. Other cultivars presented no significant differences. The correlation coefficient between tolerance and grain yield potential was not significant, suggesting that tolerant high-yielding cultivars can be obtained. No relationship was found between quality group or tolerance with the increase in protein and gluten concentration due to STB either.     

Structure and evolutionary relationships among paralogous genes within the Sec2 locus in rye

The 75K γ-secalins encoded by genes present at the locus Sec2 on chromosome 2R are unique to rye and contribute about half of all rye storage proteins. However, there is a lack of sequence information for paralogous genes in this locus. For this study, 59 γ-secalin paralogous sequences in the Sec2 locus were characterized from a cultivated rye and derived lines after crossing with bread wheat. They had similar structures with conserved sequences in their repetitive regions for the signal peptide, N-terminal, C-terminal and the repeat motif. Their high homology indicated that they originated from an ancestor sequence that existed before the speciation of the genus Secale. Duplication and divergence might have led to the formation of the paralogous genes at Sec2. Besides point mutations, these paralogs showed variations in DNA length due to insertion or deletion events in their repetitive regions. They encoded secalins with deduced molecular weight ranges between 22.2 and 54.5 kDa. These insertion or deletions may be caused by illegitimate recombination and this locus seemed to contribute to increased levels of protein content. However, the incorporation of locus Sec2 may have a negative effect on flour processing quality since it reduced the SDS-sedimentation value.     

Tolerance of longer-term partial stagnant flooding is independent of the SUB1 locus in rice

Longer-term partial stagnant flooding, particularly when it occurs following transient complete submergence causes severe damage to modern rice varieties. Progress was made in developing varieties tolerant of complete submergence through transfer of the Submergence-1 (SUB1) gene into popular varieties. However, SUB1 may not be effective under partial stagnant flooding (SF), as the new varieties may not elongate and continue growth when fully or partially submerged because of the SUB1-mediated suppression of elongation. We tested a set of rice genotypes, including a pair of near-isogenic lines (NILs), Swarna and Swarna-Sub1, under either SF or SF following complete submergence of 12 d. Swarna-Sub1 had higher survival and yield than Swarna following 12 d of submergence, but survival and grain yield of all lines decreased substantially when SF of 15-30 cm followed complete submergence, with the sensitive lines experiencing greater reductions in growth and yield. This suggests the importance of combining SUB1 with tolerance of SF in areas where both stresses are expected during the season. Swarna and Swarna-Sub1 are more sensitive to long-term partial SF than IR49830 and IR42 because of their short stature, and Swarna-Sub1 showed slightly higher reduction in tillering than did Swarna when subjected to deeper SF alone, possibly because of further inhibition of elongation by SUB1 if induced in submerged tissue. The results suggest that tolerance of these genotypes to SF depends less on SUB1 introgression and more so on the genetic background of the recipient genotype, with better performance of the genotypes that are inherently taller, such as IR42 and IR49830. The SUB1 donor landrace FR13A and its derivative breeding line IR49830 had better survival and relatively less reduction in grain yield under SF following complete submergence and under longer-term partial SF, indicating that these genotypes may have genes other than SUB1 for submergence and SF tolerance. For better adaptation to prolonged SF, SUB1 should be introgressed into genotypes that tolerate partial SF through better tillering ability and taller shoots, because SUB1 may not be effective in shorter genotypes, as it promotes survival of submerged plants by hindering shoot elongation to conserve energy reserves. Varieties combining tolerance of prolonged SF with SUB1 will have broader adaptation in flood-prone areas and greater impacts on yield stability.     

Decrease in sorghum grain yield due to the dw3 dwarfing gene is caused by reduction in shoot biomass

Positive correlations between plant height and grain yield have been reported for sorghum. The introduction of stay-green in sorghum, and the associated reduction in lodging, has opened the possibility to exploit this positive association. The aim of this study was to analyse the direct effects of the dwarfing gene dw3 (and therefore plant height) on shoot biomass, grain yield, and yield components in pairs of 3-dwarf genotypes and their isogenic 2-dwarf tall mutants. Isogenic pairs with different genetic backgrounds were grown in three field experiments under nutrient and water non-limiting conditions. Tall mutants were significantly taller and produced more shoot and stem biomass than their shorter counterparts. Generally, tall types yielded more grain than short types, but significant interactions between experiment, genetic background and stature affected the consistency of the results. dw3 only affected grain size and not grain number. Increased grain mass of tall types was associated with significantly greater stem mass per grain at anthesis and greater shoot biomass per grain accumulated between anthesis and maturity. The increased biomass of tall plants was therefore important for increased grain yield under optimum conditions. Potential implications of increased biomass production for drought adaptation are discussed.     

Atmospheric CO2 enrichment changes the wheat grain proteome

Spring wheat (Triticum aestivum L. cv. Triso) was grown in a free-air CO₂ enrichment (FACE) field experiment in order to gain information on CO₂-induced effects on grain composition and quality at maturity. A proteome analysis was performed using two-dimensional gel electrophoresis (2-DE) and protein identification was done with mass spectrometry (MALDI-TOF MS). In elevated CO₂ (526 μl l⁻¹), an increase of 13.5% in grain yield was observed relative to 375 μl l⁻¹ at a low level of significance (P = 0.528). Total grain protein concentration was decreased by 3.5% at a high level of statistical significance. Most importantly, a number of statistically significant changes within the grain proteome were observed, as the levels of 32 proteins were affected by elevated CO₂: 16 proteins were up-regulated and 16 were down-regulated. Our experiment demonstrates that high-CO₂ can markedly affect the proteome of mature wheat grain. The potential role of the proteins, changed in response to CO₂ enrichment, is discussed as some may affect grain quality. For the task of selecting cultivars resistant to CO₂-induced quality loss, we propose to consider the proteins affected by elevated CO₂ identified in this work here.     

Glu A1和 Glu D1位点高分子量谷蛋白亚基共同缺失对弱筋小麦品质的影响

为了研究高分子量谷蛋白亚基(HMWGS)缺失对小麦品质的影响,以 GluA1和 GluD1位点HMWGS共同缺失材料2GS041410作供体亲本,以弱筋小麦品种扬麦13和扬麦18作轮回亲本进行回交,构建不同遗传背景的BC¹F³和BC²F³群体,测定受体、供体亲本的品质,以及回交群体BC¹F³和BC²F³中 GluA1和 GluD1位点HMWGS共同缺失纯合单株及两位点均正常表达纯合单株的品质。结果表明,供体2GS041410具有较低的SDS沉降值、较短的面团形成时间和稳定时间;在BC¹F³和BC²F³中, GluA1和 GluD1位点HMWGS共同缺失对蛋白含量影响不显著,但可显著或极显著降低SDS沉降值和水溶剂保持力(SRC)。 GluA1和 GluD1位点HMWGS双缺失在弱筋小麦品质育种中具有一定的应用价值。     

Effect of the thermostable xylanase B (XynB) from Thermotoga maritima on the quality of frozen partially baked bread

The effect of the recombinantly produced xylanase B (XynB) from Thermotoga maritima MSB8 on the quality of frozen partially baked bread (FPBB) was investigated. Addition of XynB to wheat flour dough resulted in a significant increase in dough extensibility (L), swelling (G), and a decrease in dough resistance to deformation (P), configuration. Bread crumb characteristics were studied by differential scanning calorimeter (DSC) and dynamic-mechanical analysis (DMA). The results show that addition of XynB leads to improvements in the bread quality of FPBB and retards bread staling compared to the control. The greatest improvements were obtained in specific volume (+35.2%) and crumb firmness (−40.0%). The control FPBB was significantly firmer in texture and higher in amylopectin recrystallization than the bread with XynB. During frozen storage of FPBB with and without XynB for 8 weeks, the crumb firmness increased gradually and the specific volume slightly decreased with the frozen storage time. The ΔH values of freezable water (FW) endothermic transitions increased with frozen storage time for all samples. However, addition of XynB lowered the ΔH values indicating a decrease in FW. Therefore, XynB is useful in improving the quality of FPBB. DMA was also used to monitor the shrinking behavior of the samples. Addition of XynB increased the contraction during chilling but significantly diminished the total shrinking and frozen-state shrinking of the bread crumb during the freezing process.     

Agronomic and quality characteristics of triticale (X Triticosecale Wittmack) with HMW glutenin subunits 5+10

Sets of triticale (X Triticosecale Wittmack) lines derived from the cv. Presto with HMW glutenin allele Glu-D1d (subunits 5+10) translocated from bread wheat (Triticum aestivum L.) chromosome 1D to chromosome 1R were evaluated for agronomic and grain quality characteristics in 2002–2005. Two different translocation types were used: (a) single translocation 1R.1D₅₊₁₀-2 where the long arm of 1R carries the wheat segment from 1DL with the Glu-D1d replacing a secalin locus Sec-3, (b) double translocation Valdy where the long arm of 1R has the translocation 1R.1D₅₊₁₀-2 and the short arm has a segment from 1DS carrying wheat loci Gli-D1 and Glu-D3. The presence of Glu-D1d was determined by polyacrylamide gel electrophoresis (PAGE-ISTA) and DNA markers. The tested lines of triticale were compared with the check triticale cv. Presto and with wheat cultivars of different bread making quality (E-C quality classes). Single translocation 1R.1D₅₊₁₀-2 reduced grain yield by 16% and Valdy translocation by 24% as compared with cv. Presto. The Valdy translocation had substantially shortened spike length and reduced specific weight in comparison with check cv. Presto. Wet gluten content (according to the Perten method) was 12% in both translocation types, 8% in check Presto and on average 24% in wheat. Translocations increased the Zeleny sedimentation value (Valdy — 27 ml, 1R.1D₅₊₁₀-2 – 25 ml, cv. Presto — 23 ml). Triticale had a very low Hagberg falling number (FN) of 62–70 s without significant differences, while wheat had on average 301 s. The translocations did not significantly increase loaf volume; however, they improved loaf shape (height/width ratio): Valdy — 0.61, 1R.1D₅₊₁₀-2 – 0.56, cv. Presto 0.44, wheat on average 0.70. The dough was non-sticky in Valdy, slightly sticky in 1R.1D₅₊₁₀-2 and sticky in cv. Presto. Problems with a low FN for improving bread making quality of triticale are discussed. Higher bread making quality can be influenced by appropriate combination with donors of low α-amylase activity.