Robert A. Graybosch

Waxy wheats: Origin, properties, and prospects

Abstract Starch amylose is synthesized through the activity of the granule-bound starch synthase (GBSS). In wheat (Triticum aestivum L.), there are three structural genes encoding isoforms of GBSS. Naturally occurring mutations (null alleles) resulting in the loss of one or more GBSS isoforms have recently been identified. The presence of one or two GBSS null alleles results in the production of starch with reduced amylose content. Reduced amylose wheats have been termed ‘partial waxy’. Wheats with three GBSS null alleles produce essentially amylose-free, or waxy, starch. Partial waxy wheats are sources of flours with optimal quality characteristics in certain Asian wet noodle products. In addition, partial waxy wheats are essential to the development of waxy wheats with acceptable agronomic performance. Biochemical features of starch from waxy wheats are similar to those of waxy maize. Waxy wheats may find application in the production of modified food starches, as blending wheats for the formulation of superior noodle flours, and as a means to manipulate amylose contents in substrates for extrusion. Flour from waxy wheats may also be used to extend the shelf-life of baked goods, without a concomitant dilution of wheat gluten. Finally, waxy wheat may increase profitability to gluten manufacturers by providing a co-product with added value.

Comparison of phenotypic and molecular marker-based classifications of hard red winter wheat cultivars

Genetic diversity is the basis for successful crop improvement and can be estimated by different methods. The objectives of this study were to estimate the genetic diversity of 30 ancestral to modern hard red winter wheat (Triticum aestivum L.) cultivars adapted to the Northern Great Plains using pedigree information, morphological traits (agronomic measurements from six environments), end-use quality traits (micro-quality assays on 50 g grain or milled flour samples for the six environments), and molecular markers (seed storage proteins separated using SDS-PAGE, 51 SSRs, and 23 SRAP DNA markers), and to determine the relationships of genetic distance estimates obtained from these methods. Relationships among diversity estimates were determined using simple (Pearson) and rank (Spearman) correlation coefficients between distance estimates and by clustering cultivars using genetic-distances for different traits. All methods found a wide range in genetic diversity. The genetic distance estimates based on pedigree had the highest values due to possible over-estimation arising from model assumptions. The genetic diversity estimates based on seed storage protein were lowest because they were the major determinants of end-use quality, which is a highly selected trait. In general, the diversity estimates from each of the methods were positively correlated at a low level with the exceptions of SRAP diversity estimates being independent of morphologic traits (simple correlation), SDS-PAGE, and SSR diversity estimates (rank correlation). However, SSR markers, thought to be among the most efficient markers for estimating genetic diversity, were most highly correlated with seed storage proteins. The procedures used to accurately estimate genetic diversity will depend largely upon the tools available to the researcher and their application to the breeding scheme.

Opportunities and roadblocks in utilizing forages and small grains for liquid fuels

This review focuses on the potential advantages and disadvantages of forages such as switchgrass (Panicum virgatum), and two small grains: sorghum (Sorghumbicolor), and wheat (Triticum aesitvum), as feedstocks for biofuels. It highlights the synergy provided by applying what is known from forage digestibility and wheat and sorghum starch properties studies to the biofuels sector. Opportunities therefore, exist to improve biofuel qualities in these crops via genetics and agronomics. In contrast to cereal crops, switchgrass still retains tremendous exploitable genetic diversity, and can be specifically improved to fit a particular agronomic, management, and conversion platform. Combined with emerging studies on switchgrass genomics, conversion properties and management, the future for genetic modification of this species through conventional and molecular breeding strategies appear to be bright. The presence of brown-midrib mutations in sorghum that alter cell wall composition by reducing lignin and other attributes indicate that sorghum could serve as an important model species for C4-grasses. Utilization of the brown-midrib traits could lead to the development of forage and sweet sorghums as novel biomass crops. Additionally, wheat crop residue, and wheat and sorghum with improved starch content and composition represent alternate biofuel sources. However, the use of wheat starch as a biofuel is unlikely but its value as a model to study starch properties on biofuel yields holds significant promise.

Baking quality of hard winter wheat: Response of cultivars to environment in the Great Plains

Inconsistency of wheat end-use quality has long been a problem for the milling and baking industries, which require high levels of uniformity for modern, high speed, processing. Extensive research was conducted to characterise genetic, environmental, and biochemical factors that contribute to variation in wheat quality. Samples from 17 locations of trials with 30 cultivars grown over two years were evaluated for grain quality, milling yield, mixograph parameters and baking properties. Protein quality and composition of flour samples were determined by SDS sedimentation and size-exclusion chromatography. Test sites were monitored for soil fertility, and meteorological data was collected hourly during grain fill. Additional grain samples and data were collected from six cultivars grown at 11 locations in 1993. Significant variation in end-use quality was observed among samples; variation was attributed to environmental effects, genotype, and their interactions. For many mixograph and baking parameters, variation attributed to environmental effects was of greater magnitude than for genotype. Increasing levels of low molecular weight (LMW) saline soluble proteins were related to a general decline in dough mixing properties and loaf characteristics. However, correlations of protein components with baking parameters were generally low, suggesting limited predictive value. Hours of high temperature stress (>32 °C) during grain fill were associated with loaf volume and SDS sedimentation volume, although in a curvilinear fashion. Increasing temperature stress initially had a positive influence on loaf volume and protein quality; however, when temperature stress exceeded 90 hours, there was a strong negative influence on baking quality. Variation among cultivars for environmental stability was indicated and cultivar responses to temperature stress varied. Relationships with meteorological data suggest opportunities to predict wheat end-use quality through environmental modelling.

Environmental modification of hard red winter wheat flour protein composition

The intrinsic processing quality of wheat (Triticum aestivum L.) cultivars is modified significandy by cultural conditions and climate. In an attempt to understand the biochemical basis of such variation, environmental modification of flour protein content and composition was measured. Thirty hard red winter wheat cultivars and experimental lines were grown at 17 Nebraska environments during 1990 and 1991. Environmental conditions, including grain filling duration, temperature and relative humidity during grain filling, were monitored. Grain yield and test weight also were determined as environmental indicators. Significant linear correlations between flour protein content, as measured by near-infrared spectroscopy, were observed only with the duration of grain filling. Protein quality, as measured by SDS sedimentation volumes and size-exclusion high-performance liquid chromatography, was highly influenced by the frequency of high temperatures during grain filling and by the relative humidity. Observed ranges in genotypic responses (variance) at locations also were altered by environmental factors. Optimal protein quality, as determined by SDS sedimentation volumes, was observed with exposure to less than 90 h of temperature greater than 32 °C during grain filling. Protein quality declined with exposure to a greater number of hours of elevated temperature.

Identification and Characterization of U.S. Wheats Carrying Null Alleles at the wx Loci1

ABSTRACT Granule-bound starch synthase (GBSS) is the primary enzyme responsible for the synthesis of amylose in amyloplasts of cereal endosperm cells. Bread wheats, due to their hexaploid genetic system, carry three genes (wx loci) encoding GBSS. Purification and separation of GBSS from more than 200 North American hexaploid wheats allowed the identification of genotypes that carry null alleles at either the wx-A1 and wx-B1 loci. In addition, the cultivar Ike carried both wx-A1 and wx-B1 null alleles. No wx-D1 nulls were detected. Null alleles were found in 10% of the hard winter wheats tested, but in only 2% of the sampled soft winter wheats. Amylose contents of wheats carrying single null alleles at either the wx-A1 or wx-B1 loci often were lower than those of wild type wheats, but greater reduction in amylose content was observed in Ike. Monoclonal antibodies were used to quantify water-extractable GBSS in both wild-type and null genotypes. Gene dosage compensation was evident, although GBSS content, a...

Wheat Cultivar-Specific Disease Synergism and Alteration of Virus Accumulation During Co-Infection with Wheat streak mosaic virus and Triticum mosaic virus

Triticum mosaic virus (TriMV), the type member of the newly proposed Poacevirus genus, and Wheat streak mosaic virus (WSMV), the type member of Tritimovirus genus of the family Potyviridae, infect wheat naturally in the Great Plains and are transmitted by wheat curl mites. In this study, we examined the ability of these viruses to infect selected cereal hosts, and found several differential hosts between TriMV and WSMV. Additionally, we examined the interaction between WSMV and TriMV in three wheat cultivars at two temperature regimens (19 and 20 to 26 degrees C), and quantified the virus concentration in single and double infections by real-time reverse-transcription polymerase chain reaction. Double infections in wheat cvs. Arapahoe and Tomahawk at both temperature regimens induced disease synergism with severe leaf deformation, bleaching, and stunting, with a 2.2- to 7.4-fold increase in accumulation of both viruses over single infections at 14 days postinoculation (dpi). However, at 28 dpi, in double infections at 20 to 26 degrees C, TriMV concentration was increased by 1.4- to 1.8-fold in Arapahoe and Tomahawk but WSMV concentration was decreased to 0.5-fold. WSMV or TriMV replicated poorly in Mace at 19 degrees C with no synergistic interaction whereas both viruses accumulated at moderate levels at 20 to 26 degrees C and induced mild to moderate disease synergism in doubly infected Mace compared with Arapahoe and Tomahawk. Co-infections in Mace at 20 to 26 degrees C caused increased TriMV accumulation at 14 and 28 dpi by 2.6- and 1.4-fold and WSMV accumulated at 0.5- and 1.6-fold over single infections, respectively. Our data suggest that WSMV and TriMV induced cultivar-specific disease synergism in Arapahoe, Tomahawk, and Mace, and these findings could have several implications for management of wheat viruses in the Great Plains.

Genetic improvement trends in agronomic performances and end-use quality characteristics among hard red winter wheat cultivars in Nebraska

Evaluation of wheat cultivars from different eras allows breeders to determine changes in agronomic and end-use quality characteristics associated with grain yield and end-use quality improvement over time. The objective of this research was to examine the trends in agronomic and end-use quality characteristics of hard red winter wheat cultivars grown in Nebraska. Thirty historically important and popular hard red winter wheat cultivars introduced or released between 1874 and 2000 were evaluated at Lincoln, Mead and North Platte, Nebraska in 2002 and 2003. An alpha lattice design with 15 incomplete blocks of two plots and three replications was used at all locations. Agronomic (days to flowering, plant height, spike length, culm length, grain yield and yield components, and grain volume weight) and end-use quality (flour yield, SDS-sedimentation value, flour protein content, and mixograph time and tolerance) traits were measured in each environment. Highly significant differences were observed among environments, genotypes and their interactions for most agronomic and end-use quality characteristics. Unlike modern cultivars, older cultivars were low yielding, and less responsive to favorable environments for grain yield and yield components. Semidwarf cultivars were more stable for plant height than traditional medium to tall cultivars. All cultivars had high grain volume weight since it is part of the grading system and highly selected for in cultivar release. Modern cultivars were less stable than older cultivars for SDS-sedimentation and mixing tolerance. However, the stability of older cultivars was attributed to their having weak mixing tolerance and reduced SDS-sedimentation values. The reduced protein content of modern cultivars was offset by increased functionality, as measured by mixograph and SDS sedimentation. In conclusion, breeders have tailored agronomic and end-use quality traits essential for hard red winter wheat production and marketing in Nebraska.

Predicting Protein Composition, Biochemical Properties, and Dough-Handling Properties of Hard Red Winter Wheat Flour by Near-Infrared Reflectance

ABSTRACT Breadmaking quality in wheat is one of several considerations that plant breeders face when developing new cultivars. In routine breeding programs, quality is assessed by small-scale dough-handling and bake tests, and to some extent, by biochemical analysis of gluten proteins. An alternative, not yet fully examined, method for wheat flour quality assessment is near-infrared reflectance (NIR) spectrophotometry. The present study was performed on 30 genotypes of hard red winter wheat grown during two crop years at eight to nine locations in the Great Plains area of the United States. Biochemical testing consisted of measuring protein fractions from size-exclusion HPLC (M r > 100k, M r 25–100k, and M r < 25k designated as glutenin, gliadins, and albumin and globulins, respectively), pentosan content, and SDS sedimentation volume. Dough-handling properties were measured on a mixograph and recorded as the time to peak dough development, the peak resistance, the width of the mixing curve, and the width...

Asian Salted Noodle Quality: Impact of Amylose Content Adjustments Using Waxy Wheat Flour

ABSTRACT Fourteen flour blends of two natural wild-type wheat (Triticum aestivum L.) flours, ‘Nuplains’ and ‘Centura’, blended with one waxy flour sample were characterized and processed to Asian salted noodles. The flour amylose content range was <1–29%. Damaged starch contents were 10.4, 7.0, and 6.6% for the waxy wheat, Nuplains, and Centura, respectively. The waxy flour farinograph water absorption was as high as 79.5%, ≈20% higher than the wild-type flours. Because two types of starch granules (wild-type and waxy) existed in the flour blends, two peaks at 82°C (waxy) and 95°C (wild-type) were found in the RVA pasting curves. Reduced amylose content caused high flour swelling volume and power and low falling number. Significant effects of flour amylose content on noodle processing and textural (eating) qualities were found in the study. Noodle qualities, as reflected in covariate analysis, were not significantly affected by the flour blends protein content, SDS-sedimentation volume, mixograph dough d...