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.     

Chemical control of weeds in wheat (Triticum aestivum L.) in Iran

Experiments were conducted in 2006–2007 at six research stations of the Iranian Plant Protection Research Institute to study the efficacy of different herbicides to control weeds in wheat. Treatments included mesosulfuron-methyl plus iodosulfuron-methyl-sodium plus mefenpyr-diethyl (WG) at 45 + 45 + 135 g a.i./ha, respectively, sulfosulfuron at 21, 31.5, 42 and 51 g a.i./ha, chlorsulfuron at 15 g a.i./ha, bromoxynil plus MCPA at 600 g a.i./ha with clodinafop propargyl at 64 g a.i./ha, sulfosulfuron plus metsulfuron-methyl at 36 g a.i./ha, mesosulfuron-methyl plus iodosulfuron-methyl-sodium plus mefenpyr-diethyl (OD) at 15 + 3 + 45 g a.i./ha, respectively, and a full season weed-free control. Herbicides were applied at wheat tillering. Results showed that sulfosulfuron plus metsulfuron-methyl, and bromoxynil plus MCPA with clodinafop propargyl resulted in satisfactory weed control and wheat grain yield at most locations. Weed control efficacy of both formulations of mesosulfuron-methyl plus iodosulfuron-methyl-sodium was variable across locations. Efficacy of the OD formulation appears to depend upon location, so that application of this herbicide at Shiraz and Gorgan resulted in better weed control compared to use of the WG. Satisfactory performance of the OD formulation at Gorgan and Shiraz could be attributed in part to the even pattern of rainfall distribution during the growing season and wheat cultivar used, respectively. With respect to grain yield, however, the OD formulation was better than WG formulation at most of the locations.     

Weed management in no-till winter wheat (Triticum aestivum L.)

In general, effective weed control in no-tillage systems is based on the use of herbicides. However, the development of appropriate weed management strategies can help to reduce the amount of herbicides applied.     

Waxy endosperm accompanies increased fat and saccharide contents in bread wheat (Triticum aestivum L.) grain

The contents of fat, starch, pentosan, fructan, β-glucan and several mono- and oligosaccharides in grain were evaluated to find out the possible effects of the Wx-D1 gene of bread wheat using two sets of near-isogenic waxy and non-waxy lines and two low-amylose mutant lines with a common genetic background of Kanto 107. These materials have two non-functional Wx-A1b and Wx-B1b alleles in common. Waxy near-isogenic lines with a non-functional Wx-D1d allele showed consistently increased contents of fat, total fructan, β-glucan, glucose, fructose, sucrose, 1-kestose, 6-kestose, neokestose, nystose and bifurcose compared with non-waxy lines with a functional Wx-D1a allele throughout three growing/harvest seasons. Starch and total pentosan contents were inconsistently influenced by the allelic status of the Wx-D1 locus, while water-soluble pentosan and raffinose contents were not affected. The compositional changes of a low-amylose mutant line with an almost non-functional Wx-D1f allele were closely similar to those of waxy near-isogenic lines, while significantly different changes were barely observed in another low-amylose mutant line with a partly functional Wx-D1g allele in two seasons. These results showed that the Wx-D1 gene has pleiotropic effects on the fat and saccharide contents of bread wheat grain.     

Wheat (Triticum aestivum L.) puroindoline functionality in bread making and its impact on bread quality

Wheat puroindolines (PINs) spontaneously adsorb at air/water interfaces and show excellent foaming properties. They can positively impact bread quality, in which the formation of stable foam is important for product quality. The impact of endogenous PINs on bread quality was studied by preparing gluten–starch blends from isolated gluten and starch fractions with different PIN levels, which allowed largely retaining the interaction between PINs and flour components. Our results indicate that blends with high PIN levels yielded more homogeneous crumb structures with fine gas cells than bread made with blends containing medium or low PIN levels. However, the mechanism by which PINs exert this crumb improving effect is not clear. Varying PIN levels impacted neither dough extensibility nor did it result in different PIN levels in dough liquor. Lipid removal yielded bread with a less homogeneous crumb gas cell distribution, indicating that lipids also are required to obtain good crumb structure.     

Field-based evaluation of vernalization requirement,photoperiod response and earliness per se in bread wheat (Triticum aestivum L.)

Vernalization requirement, photoperiod response and earliness per se (EPS) of bread wheat cultivars are often determined using controlled environments. However, use of non-field conditions may reduce the applicability of results for predicting field performance as well as increase the cost of evaluations. This research was undertaken, therefore, to determine whether field experiments could replace controlled environment studies and provide accurate characterization of these three traits among winter wheat cultivars. Twenty-six cultivars were evaluated under field conditions using two natural photoperiod regimes (from different transplanting dates) and vernalization pre-treatments. Relative responses to vernalization (RRV_GDD) and photoperiod (RRP_GDD) were quantified using the reciprocal of thermal time to end of ear emergence, whereas earliness per se was estimated by calculating thermal time from seedling emergence until end of ear emergence for fully vernalized and lately planted material. An additional index based on final leaf numbers was also calculated to characterize response to vernalization (RRV_FLN). To test whether the obtained indices have predictive power, results were compared with cultivar parameters estimated for the CSM-Cropsim-CERES-Wheat model Version 4.0.2.0. For vernalization requirement, RRV_GDD was compared with the vernalization parameter P1V, for photoperiod (RRP_GDD), with P1D, and for earliness per se, EPS was compared with the sum of the component phase durations. Allowing for variation in EPS in the calibration improved the relation between observed versus simulated data substantially: correlations of RRP_GDD with P1D increased from r² = .34 (p < .01), to .82 (p < .001), and of RRV_GDD with P1V, from r² = .88 (p < .001), to .94 (p < .001). In comparisons of observed versus simulated anthesis dates for independent field experiments, the estimated model coefficients resulted in an r² of .98 (p < .001) and root mean square error of 1d. Overall, the results indicated that combining planting dates with vernalization pre-treatments can permit reliable, quantitative characterization of vernalization requirement, photoperiod response and EPS of wheat cultivars. Furthermore, emphasize the need for further study to clarify aspects that determine EPS, including whether measured EPS varies with temperature or other factors.     

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.     

Impact of nitrogen amount and timing on the potential of acrylamide formation in winter wheat (Triticum aestivum L.)

Acrylamide (AA), a potential human carcinogen, is formed in strongly heated carbohydrate-rich food as a part of the Maillard reaction. The amino acid asparagine (Asn) and reducing sugars are considered to be the main precursors for AA formation. In a 2-year field trial the impact of nitrogen (N) amount and timing on the content of AA precursors and the potential of AA formation in different winter wheat cultivars (cv.) were studied in association with respective grain yields and parameters of baking quality. Depending on year, cultivar and nitrogen treatment Asn contents ranged between 4 and 18 mg 100 g⁻¹ flour dry-matter (DM). Nitrogen treatments affecting crude protein contents in flours above 13% caused a considerable increase in free Asn. Nitrogen amounts of 220 kg N ha⁻¹ increased the contents of free Asn by between 130% and 270% depending on year and cultivar compared to the untreated controls. A close linear correlation between the content of free Asn and the potential of AA formation (2004: R² = 0.89, 2005: R² = 0.83) could be observed, whereas no correlation could be found between reducing sugars and the potential of AA formation, pointing to the importance of free Asn as the limiting and thus determining factor for the AA formation potential in wheat flours. To reach high crude protein contents and good sedimentation values demanded for breadstuffs, nitrogen amounts of at least 180 kg N ha⁻¹ were necessary. Nitrogen fertilization measures resulting in high crude protein contents above 13% enhanced the potential of AA formation by increasing the content of free Asn in flours. As long as demands from traders and producers for flour with high crude protein contents are not revised, lowering Asn contents and thus the potential for AA formation by application of N amounts below 180 kg N ha⁻¹ and abandoning the late application of N do not appear to be successful ways to reduce the risk of AA formation in breadstuffs.     

Growth stage impacts tolerance of winter wheat (Triticum aestivum L.) to broadcast flaming

Organic wheat producers are interested in testing propane flaming as part of an integrated weed management program for organic wheat production. Therefore, the objective of this study was to collect baseline information on winter wheat tolerance to broadcast flaming as influenced by its growth stage at the time of flaming and dose of propane. Field experiments were conducted at the Haskell Agricultural Laboratory of the University of Nebraska, Concord, Nebraska in 2007–2008 and 2008–2009 utilizing six doses of propane applied at four growth stages including: four leaves-4L, three tillers-3 T, shoot elongation-SE and boot stage-BS. The propane doses were 0, 12, 31, 50, 68 and 87 kg ha⁻¹ and were applied using a custom built flamer driven at a constant speed of around 6 km h⁻¹. Crop response to propane doses was described by log-logistic models based on visual estimates of crop injury, various yield components (spikes m⁻², kernels spike⁻¹ and 1000-kernel weight) and grain yield. Overall response to flaming was influenced by the growth stage of wheat and propane dose. In general, wheat at 3 T was the most tolerant and at BS was the most susceptible stage to broadcast flaming. Flaming negatively affected all yield components of wheat. Reduction of grain yield increased with increase in propane dose at each growth stage. The maximum yield losses of about 21%, 32%, 63% and 74% were obtained with the highest propane dose of 87 kg ha⁻¹ applied at 3 T, SE, 4L and BS growth stages, respectively. Due to unacceptable yield loss, the use of broadcast flaming in winter wheat at the tested growth stages is not recommended.     

Characterisation of the first wheat (Triticum aestivum L.) nucleotide pyrophosphatase/phosphodiesterase resembling mammalian counterparts

A formerly unknown nucleotide pyrophosphatase/phosphodiesterase (NPP) of wheat (Triticum aestivum L.) (TaNPP) was recombinantly produced in Pichia pastoris (TaNPPr) following assembly of the sequence out of wheat ESTs using sequences of known NPPs. Simultaneously, a phosphodiesterase was purified to homogeneity from wheat germs, characterised and identified as TaNPP. TaNPP contains the highly conserved catalytic substrate and metal binding residues and displays properties [high pH optimum, glycosylation, high thermostability and inhibition by EDTA and adenosine 5′-monophosphate (AMP)] similar to those of mammalian enzymes characterised earlier. The sequence of TaNPP includes that of a putative transmembrane domain, a characteristic of most NPPs. Both recombinant and native TaNPP partially occur as oligomeric proteins on SDS PAGE. Upon addition of DTT, both migrate as monomeric proteins. Part of the native wheat protein even occurs in its truncated form, thus lacking the transmembrane region. Out of a range of tested natural substrates, TaNPP had the highest affinity towards adenine containing nucleotides. While Michaelis-Menten kinetics were valid in the low substrate concentration range, at higher concentrations, they were no longer applicable. TaNPP shows no similarity to the recently characterised rice and barley enzymes and, is hence, one of the first characterised plant NPPs resembling mammalian NPPs.     

Relative amounts of tissues in mature wheat (Triticum aestivum L.) grain and their carbohydrate and phenolic acid composition

Hand dissection of mature grains from two common wheats (Triticum aestivum L., cv. Caphorn and cv. Crousty) were performed to quantitatively assess their tissue composition and to obtain homogeneous samples of embryonic axis, scutellum, starchy endosperm, aleurone layer, hyaline layer, outer pericarp and a composite layer made up of testa+hyaline layer+inner pericarp. Polymeric neutral sugar and phenolic acid contents of the samples were determined and used to identify specific composition patterns in each tissue irrespective of the cultivar. The scutellum and embryonic axis showed the lowest amount of carbohydrates with similar relative amounts of arabinose and xylose (Ara+Xyl), but the scutellum differed from the embryonic axis in its high phenolic acid, in particular ferulate dehydrodimer, content. The peripheral layers of the grains were mainly composed of cell wall polysaccharides, chiefly arabinoxylans but with differing structures. The hyaline layer was mostly composed of arabinoxylan with extremely low Ara/Xyl ratio (0.1), with high amounts of ferulic acid monomers and hence very weakly crosslinked. The aleurone layer differed from the outer pericarp by its much lower Ara/Xyl ratio and lower amounts of ferulic acid dimers and trimers. High proportions of ether-linked phenolic acids (released by alkali at 170 °C) were detected specifically in the seed coat and tissues in the crease region. The possible application of biochemical markers found in the various tissues to monitor wheat grain fractionation processes is discussed.     

Tolerance of winter wheat (Triticum aestivum L.) to pre-emergence and post-emergence application of saflufenacil

Saflufenacil is a new herbicide being developed for pre-plant burndown for non-selective removal of broadleaf weeds and pre-emergence (PRE) broadleaf weed control in field crops, including maize, soybean, sorghum and wheat. As part of studying the potential use pattern of this herbicide, four field studies were conducted in 2006 and 2007 at Concord, northeast Nebraska, to determine winter wheat tolerance to PRE and post-emergence (POST) applications of saflufenacil. The fall POST applications were conducted at the 2–3 leaf stage (5 cm height) whereas the spring POST and tank-mixes studies were sprayed at the 4th node stage (40 cm height) of crop. Dose-response curves based on log-logistic model were used to determine the ED (effective dose) values of saflufenacil for visual ratings of crop injury and relative yield. There was no crop injury or yield reduction with PRE applied saflufenacil dose of up to 400 g a.i. ha⁻¹. However, there was significant crop injury in the POST applications in the fall (up to 95%) and in the spring (up to 67%). There was also yield reduction of as much as 66% in the fall and 58% in the spring POST applications. Addition of adjuvants also increased crop injury levels. For example, at 14 days after treatment in the fall applications, about 5% visual crop injury (ED₅) was evident with 82, 67 and 10 g a.i. ha⁻¹ of saflufenacil compared with 51, 30 and 11 g a.i. ha⁻¹ in the spring, with no adjuvant, or non-ionic surfactant (NIS), or crop oil concentrate (COC), respectively. Saflufenacil at half the proposed used dose of 25 g a.i. ha⁻¹ was safe to mix with the currently used POST herbicides of wheat with no visible crop injury and yield reduction. PRE applications of saflufenacil would be safe for use in winter wheat; however, the POST application of saflufenacil alone or with the adjuvant NIS or COC produces unacceptable injury and yield loss. These results are similar to the proposed PRE use pattern of saflufenacil. In addition, the proposed label does not suggest the POST use of saflufenacil in winter wheat, or any other cereal crops, which is similar to what we have concluded from this study.     

Response of spring planted barley (Hordeum vulgare L.), oats (Avena sativa L.) and wheat (Triticum aestivum L.) to mesotrione

There is little information on the response of spring planted barley (Hordeum vulgare L.), oats (Avena sativa L.) and wheat (Triticum aestivum L.) to mesotrione under Ontario environmental conditions. Four field studies were conducted in Ontario, Canada over a two-year period (2008 and 2009) to evaluate the sensitivity of spring planted cereals (barley, oats, and wheat) to pre-emergence (PRE) and post-emergence (POST) applications of mesotrione at 50, 100, and 150 g ai ha⁻¹. Mesotrione applied PRE caused minimal visible injury at 3, 7, 14 and 28 days after emergence (DAE) and had no adverse effect on plant height or yield of barley, oats and wheat. Mesotrione applied POST caused as much 11% injury and reduced plant height as much as 6% in spring planted cereals. Injury was higher in wheat compared to barley or oats. Mesotrione applied POST had no adverse effect on the yield of barley or oats but decreased the yield of wheat as much as 14%. Based on this study, mesotrione applied PRE at 50, 100 or 150 g ai ha⁻¹ can be safely used in spring planted barley, oats, and wheat. Mesotrione applied POST at the proposed dose of 50, 100 or 150 g ai ha⁻¹ can also be safely used in spring planted barley and oats. However, mesotrione applied POST results in unacceptable injury in spring planted wheat.     

Analysis of starch swelling power in Australian breeding lines of hexaploid wheat (Triticum aestivum L.)

Starch is the major component of wheat (Triticum aestivum L.) grain and is composed of two large glucan molecules, amylose and amylopectin. The ratio between the two polymers types influences the water absorbing properties of starch upon heating, and thus affects the end-use of grain and purified starch. In this study, we evaluated the starch swelling power (SSP) values in seven wheat populations developed from crosses involving low-SSP lines. Analysis of starch produced by the F₂ generation plants showed that the largest SSP variation (11.4–16.2) and lowest SSP mean (13.9) was obtained for a population derived from doubled haploid lines SM1028 (SSP = 14.5) and VK306 (SSP = 13.6). The population of 360 lines was advanced by single seed descent to the following generations for further studies. Starch analysis of grain produced by F₄ generation lines in two field locations during 2006 and in a greenhouse environment during 2005 showed that SSP values were relatively stably inherited. The average broad-sense heritability was 73% and significant (P < 0.001) genotype × genotype and genotype × environment interactions were seen. Starches with the highest and lowest SSP values were inversely related to amylose concentration determined by high pressure liquid chromatography (HPLC)–size exclusion chromatography (SEC) of debranched starch. Developed lines with the lowest SSP values surpassed 40% in apparent amylose concentration. The study illustrates that screening for SSP in early generations can be used to develop wheat lines with desired starch swelling characteristics.     

Influence of high temperature and terminal moisture stress on dormancy in wheat (Triticum aestivum L.)

Preharvest sprouting is common in cereals that lack grain dormancy if maturing grain is exposed to rain. Over three successive seasons wheat genotypes with a range of dormancy levels, were exposed to moisture stress and periods of high temperature stress (>30 °C) in controlled field trials. Dormancy assessments were based on a germination index of hand threshed grain throughout grain filling. There were three main results. First, moisture stress combined with consistently high temperature during grain filling was associated with induced dormancy in Cunderdin, (germination index of 0.41) in a normally non-dormant genotype (germination index normally >0.80), but no additional dormancy in DM 2001, a dormant genotype (germination index normally <0.10). In contrast sudden heat shocks (>30 °C max. for >12 days) at 30–50 days post-anthesis reduced dormancy, germination index increase of 0.42 on average across five genotypes. Secondly, whilst dormancy was affected by moisture and heat stress, genotypes maintained their relative rankings across environments and genotype had the most effect on dormancy (70–92% of the variation in germination index) with DM 2001 and DH 22 more dormant than DH 56, DH 45 and Cunderdin. Finally, the effect of environment was different for different genotypes; those with partial dormancy (germination index usually 0.20–0.50, DH 56 and DH 45) were most influenced by the environmental conditions with germination indexes ranging from 0.06 to 0.85 depending on environment. Consequently avoidance of high temperatures, moisture stress, and maturity × stress interactions, are important prerequisites in screening for genotypes with genetic differences in dormancy.     

Storage-induced changes in einkorn (Triticum monococcum L.) and breadwheat (Triticum aestivum L. ssp. aestivum) flours

To assess the effect of ageing on alpha-amylase activity, falling number, pasting properties and SDS sedimentation volume, whole meal and white flours of einkorn (cv Monlis) and bread wheat (cv Serio) were stored in darkness at different temperatures and analysed several times up to 374 days. Pregerminated bread wheat flours (cv Blasco) were also evaluated.     

Seasonal conditions influence dormancy and preharvest sprouting tolerance of wheat (Triticum aestivum L.) in the field

Preharvest sprouting occurs following rainfall after maturity and reduces grain quality and value. Dormancy at maturity is a trait frequently used by wheat breeders to improve tolerance to sprouting. To determine the environmental influence on the predicative relationship between dormancy at maturity and improved preharvest sprouting tolerance, dormancy (germination index) at maturity and grain quality (falling number) at maturity and then, after rainfall, was measured over three seasons. Based on the results it was possible to draw three main conclusions. Firstly, genotypes with strong dormancy (germination index <0.20) which have the embryo and seed coat component of dormancy maintained a falling number >300 s at all sites and seasons for the 2-month period after maturity despite receiving up to 122 mm of rain. Adequate preharvest sprouting tolerance also occurred in dormant genotypes, with just the embryo component; in all but the most severe conditions. Secondly, though the effect of environment and interaction of genotype and environment was significant, the G by E interaction did not account for a large proportion of the variation (<6%) in sprouting tolerance (measured by falling number after rainfall) or change the relative rankings of preharvest sprouting tolerance. Finally, other defects associated with rainfall during grain filling such as black point and fungal staining may slightly reduce dormancy estimates and preharvest sprouting tolerance. For this reason grain defects need to be improved in parallel with preharvest sprouting tolerance. In conclusion, strong dormancy provides a reliable source of preharvest sprouting tolerance in the field.     

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.     

Influence of long-term nitrogen fertilization on micronutrient density in grain of winter wheat (Triticum aestivum L.)

A long-term (1999–2007) field experiment was conducted to investigate the effects of three nitrogen (N) fertilization rates (0, 130, and 300 kg N/ha) on micronutrient density in wheat grain and its milling fractions. At maturity, grains were harvested and fractionated into flour, shorts, and bran for micronutrient and N analysis. N fertilization increased iron (Fe), zinc (Zn), and copper (Cu) density in wheat grain compared to the control. Increase of N application rate from 130 to 300 kg N/ha, however, did not further increase the three micronutrient densities in grain. Micronutrient concentrations were usually highest in the bran and lowest in the flour. High N application increased Zn and Cu densities in all three milling fractions and increased Fe concentration in shorts and bran but not in flour. N application did not affect the manganese (Mn) concentration in grain. N fertilization changed the proportions of Fe and Cu in flour and bran but did not affect the distribution of Zn. Because N fertilization increased micronutrient accumulation in wheat grain, proper management of N fertilization has the potential to enhance the nutritional quality of this important food.