Hard Red Winter Wheat Cultivars Research Articles

Genetic Trends in Winter Wheat Grain Quality with Dual‐Purpose and Grain‐Only Management Systems

Hard winter wheat (Triticum aestivum L.) grain harvested from a dual-purpose (forage plus grain) crop is often perceived by users to have inferior end-use quality compared with that of a grain-only crop. In this paper, we determine if that perception has a scientific basis and if long-term genetic changes in grain quality are equally expressed under two management systems commonly practiced in the southern Great Plains. Uniform trials were established under grain-only and dual purpose management systems, each featuring whole-plot treatments of a foliar fungicide and split-plot treatments of 12 hard red winter (HRW) wheat cultivars spanning nearly 80 yr of genetic improvement. The study was conducted for 4 yr at the Wheat Pasture Research Center near Marshall, OK. Dual-purpose experiments were grazed from November through late February or early March of each year. Variables measured were kernel hardness, grain protein, flour yield, mixing time and tolerance, large-kernel fraction, kernel weight, and kernel diameter. The effect of fungicide treatment was not significant. Cultivar × system interactions were generally absent, and the correlation between management systems varied from r = 0.74 to 0.99 (P < 0.01), indicating a high level of consistency in quality between systems. Kernel weight in the dual-purpose system did not reach the same level as in the grain-only system for some cultivars, though kernel diameter was not negatively affected. Grain protein and dough strength, measured by mixing time and tolerance, were unaffected by management system. Significant genetic progress was observed in both systems for only the physical quality attributes (kernel weight and diameter, and percent large kernels). With exception of kernel weight, we detected no detrimental effect of the dual-purpose management system on cultivar performance, or on cultivar differences associated with breeding, for several characteristics commonly used to estimate bread wheat quality.

Response of Winter Wheat to Simulated Stand Reduction

Environmental stresses can reduce winter wheat (Triticum aestivum L.) stands to less than optimum densities, forcing producers to assess yield potential from early season plant densities. Our objectives were to assess changes in yield and associated traits resulting from varying spring plant densities, and to determine if these responses varied by cultivar. Three hard red winter wheat cultivars were grown at seven population densities in seven Montana environments. Plant density levels ranging from 10 to 100% of target stand were achieved for each cultivar by planting 215 seeds m−2 in the fall and replacing winter wheat seed with spring wheat seed in proportion to the desired spring survival for each treatment. Cultivars did not differ in mean spring plant density or grain yield but differed for yield components, test weight, and protein concentration. The response to increasing plant density was generally not cultivar specific, as plant density interactions with cultivar were significant only for kernels spike−1. Grain yield increased, as did spikes m−2 and kernels m−2, while kernel weight and kernels spike−1 decreased with increasing spring plant density. Response to increasing spring plant density varied with environment for all traits, but environment effects and linear and quadratic plant density terms accounted for 95% of the variation in interaction means for all traits except tillers plant−1. Maximum grain yield occurred at 140 plants m−2, and 21.5 plants m−2 produced winter wheat grain yield equal to spring wheat grain yield for the same environments.

Yield Components of Wheat Grown under High Temperature Stress during Reproductive Growth

ABSTRACTHigh temperature is a major determinant of wheat (Triticum aestivum L.) development and growth, decreasing yields by 3 to 5% per 1°C increase above 15°C in plants under controlled conditions. Even greater yield differences have been reported between favorable and unfavorable temperature conditions in the field. The objective of this study was to identify the yield components of the hard red winter wheat cultivar Karl 92 that are affected by controlled high temperature during maturation of intact plants under simulated field populations. Plants at a final density of 144 m2 were grown in the greenhouse until anthesis and transferred to growth chambers for temperature treatment. Day/night temperatures of 20/20, 25/20, 30/20, and 35/20°C were imposed from 10 and 15 d after anthesis until ripeness in two experiments, and temperatures of 25/20, 30/20, and 35/20°C were applied from 20 d after anthesis until ripeness in a third experiment. Grain yield was reduced by 78%, kernel number was reduced by 63%, and kernel weight was reduced by 29% at 35/20°C compared with 20/20°C from 10 d after anthesis until ripeness. The yield loss from high temperature applied during this period was much greater than for previous controlled‐environment studies. Kernel numbers in treatments applied during early reproductive growth in our study were as sensitive to high temperature as wheat plants in previous field studies. High temperature applied 15 d after anthesis until ripening reduced grain yield 18%. Since kernel number was set by this time, the loss was exclusively due to decreased kernel weight. High temperature imposed from 20 d after anthesis decreased kernel weight by 18%.

Wheat Cultivar Tolerance to Atrazine

Winter wheat (Triticum aestivum L.) in the Texas High Plains often follows a crop or fallow period where atrazine was used for weed control. A study was conducted in 1991–1992 and repeated in 1993–1994 to determine if differences exist among commonly grown winter wheat cultivars in their tolerance to atrazine. Eighteen hard red winter wheat cultivars common to the region were planted on 13 Nov. 1991, and 26 Oct. 1993, in plots treated with 0, 0.25, 0.5, 0.75, and 1.0 lb a.i. /acre atrazine. Variation in atrazine tolerance was observed among cultivars and years, but cultivar differences in atrazine tolerance were identified. Cultivars that exhibited tolerance to atrazine were ‘Triumph’, ‘Scout’, ‘Siouxland 89’, ‘TAM 107’, and ‘Quantum 588A’. Most susceptible cultivars were ‘TAM 109’, ‘TAM 200’, ‘TAM 201’, and ‘TAM 202’. These data suggest cultivars are available to minimize yield loss for planting in fields where atrazine residues in soil are suspected. Alternatively, where atrazine is applied to wheat stubble after harvest, cultivars that are susceptible to atrazine could be planted to aid in control of volunteer wheat. Research Question Atrazine is commonly used to control weeds in sorghum, corn, and during fallow periods in the Texas High Plains. When wheat is planted in soil previously treated with atrazine, the potential for crop injury exists, especially in soils that have a high pH and low organic matter content. Little research has been done to determine if hard red winter wheat cultivars differ in their tolerance to atrazine under field conditions. The objectives of this study were to determine if commonly grown hard red winter wheat cultivars differ in their tolerance to atrazine and to develop a database for guidance to producers faced with atrazine residues in fields to be planted to wheat, or who desire to plant cultivars susceptible to atrazine. Literature Summary Studies have shown that wheat cultivars differ in tolerance to metribuzin and cyanazine under field conditions. Because of chemical similarities of atrazine to these herbicides, it seems likely that differences in cultivar tolerance to atrazine may exist. A greenhouse study in Arkansas revealed differences in wheat cultivar seedling response to atrazine. Study Description Field studies were conducted during 2-yr cycles near Bushland, TX during 1991–1992 and 1993–1994. Soil was a Pullman clay loam and is typical of the soils found in the southern Great Plains. Soil organic matter at the site was 1.2% and pH was 7.5. The experimental area had been neither cropped nor treated with herbicides during the previous 2 yr. In order to simulate residual carryover, atrazine was applied in strips (blocks) prior to wheat planting at 0, 0.25, 0.5, 0.75, and 1.0 lb a.i/acre. Eighteen hard red winter wheat cultivars (Table 1) common to the region were planted across the atrazine blocks in three replications in a split-plot arrangement. Differences in wheat cultivar tolerance to atrazine were determined by collecting data for percent stand and grain yield reduction. Applied Questions Do differences exist between winter wheat cultivars in their tolerance to atrazine? In both years tested there were clearly differences in wheat cultivar tolerance to atrazine. Which cultivars consistently showed the most tolerance and susceptibility to atrazine? Cultivars that exhibited tolerance to atrazine in both years were Triumph, Scout, Siouxland 89, followed by TAM 107 and Quantum 588A (Table 1). Most susceptible cultivars in both years were TAM 109, TAM 200, TAM 201, and TAM 202. Recommendation How can producers utilize wheat cultivar tolerance differences to atrazine? Producers who desire to plant wheat in fields that may contain atrazine residue can minimize atrazine injury by planting tolerant cultivars while avoiding those that are most susceptible. If a cropping system involves the use of atrazine after wheat harvest, it may be desirable to plant one of the susceptible TAM cultivars in order to improve control of volunteer wheat. Table 1. Quantitative summary of wheat cultivar tolerance to atrazine from studies conducted during the 1991–1992 and 1993–1994 growing seasons at Bushland, TX. Tolerant Intermediate Susceptible Siouxland 89 Karl TAM 202 Triumph Mesa TAM 200 Scout Thunderbird TAM 201 Quantum 588A 2158 TAM 109 TAM 107 Abilene Hawk Bronco 2157 Chisholm

Influence of Tillage System on Soft Red Winter Wheat Cultivar Selection

Soft red winter wheat (Triticum aestivum L.) producers in the southeastern USA are adopting no-till production practices. Official wheat cultivar testing programs, however, are conducted in conventional-till. The objective of this research was to determine whether soft red winter wheat cultivars perform differently across tillage systems, indicating the need for no-till cultivar testing programs. Twelve winter wheat cultivars commonly produced in the southeastern USA were tested in a split-plot design with tillage system as the main effect. The test was located in the North Carolina Piedmont and Coastal Plain in 1996 and 1997. In the Piedmont the soil type was Hiwassee clay loam (fine, kaolinitic, thermic Typic Rhodudults), and in the Coastal Plain the soil was Goldsboro sandy loam (fineloamy, siliceous, subactive, Aquic Paleudults). Plant density after emergence, head density at harvest, kernel weight, grain yield, and test-weight were determined and compared across cultivars and tillage systems. For each of these variables, environment and cultivar effects were significant (P ≤ 0.05). Tillage system had a significant effect only on plant density with average no-till stands being 8.3 % lower than those in the conventional-till system. Relative cultivar performance, or rank, did not change across tillage systems for any of these variables. Consequently, soft red winter wheat cultivars that perform well in conventional-till will probably be the best adapted for no-till production. Separate cultivar trials are not required for the two tillage systems.

Genetic Analyses of Agronomic Traits Controlled by Wheat Chromosome 3A

Previous studies with chromosome substitution lines between hard red winter wheat (Triticum aestivum L.) cultivars Cheyenne (CNN) and Wichita (WI) identified genes on chromosome 3A of WI which affect grain yield, yield components, grain volume weight, plant height, and anthesis date. This study was conducted to determine if the trait variation caused by chromosome 3A could be explained by major or minor gene segregation and if these genes are pleiotropic, linked, or independent on the chromosome. A population of recombinant inbred chromosome lines for chromosome 3A (RICLs‐3A), developed between CNN and a chromosome substitution line CNN(WI3A), was evaluated in multi‐location field trials in 3 yr. Our results indicate significant differences (P ≤ 0.05) between parental lines and among RICLs for grain yield, 1000‐kernel weight, plant height, and anthesis date, but not for kernel number per spike, spike number per square meter, and grain volume weight. A 1:1 genetic ratio for anthesis date suggested the presence of a single segregating locus controlling the trait. None of the other agronomic traits could be separated into unequivocal groups and hence, major genes were not detected. This indicates that the traits were controlled either by several genes or few genes with enough environmental influence, or both, to obscure their effects. Significant correlations and possible crossover products between anthesis date, plant height, and 1000‐kernel weight suggest that these traits were controlled either by linked gene(s) or by pleiotropic genes with additional genes affecting one of the traits.

Relationships Between Small‐Scale Wheat Quality Assays and Commercial Test Bakes

ABSTRACTTypical commercial bakeries in the United States are highly mechanized, mass‐production facilities. U.S. hard wheat breeding programs use small‐scale physical dough testing and pup loaf bake procedures to identify and select improved quality genotypes. The accuracy of such approaches in the prediction of commercial‐scale quality performance is poorly understood. Samples from six hard red winter wheat cultivars grown in 11 locations over three harvest years were used to correlate grain hardness, small‐scale test bakes, mixograph variables, and various measures of flour protein composition with quality assessments from commercial test laboratories. Samples were milled on both pilot‐ and small‐scale mills. Protein content and 100‐g pup loaf volume were more often significantly correlated with commercial test bake variables than all other small‐scale variables. Stepwise multiple regression models explained, on average, ≈40% of the variation in commercial test bake procedures. Mixograph properties, pup loaf volumes and absorption, and flour protein content were the most frequent variables identified in model development. Pup loaf bake results on pilot‐ and small‐scale milled flours were highly correlated. Differences in milling technology do not appear to be a significant source of error in relating small‐scale test bakes to commercial quality.

Quality Response of Twelve Hard Red Winter Wheat Cultivars to Foliar Disease Across Four Locations in Central Kansas

ABSTRACTTwelve hard red winter wheat cultivars were grown at four locations in central Kansas to evaluate the role of foliar fungal diseases on wheat end‐use quality in 1995. Disease was allowed to develop naturally on control plots and was controlled partially on plots treated with a systemic fungicide. After harvest, wheat samples were evaluated for the impact of the disease complex (leaf rust, tan spot, speckled leaf blotch) on physical grain quality, grain protein, milling properties, flour absorption, and peak mixing time. Data were analyzed using a mixed model to account for random (location and block) and fixed (cultivar and fungicide) effects. Location significantly influenced quality characteristics except kernel size and peak mixing time. The magnitudes of variation among random effects on all quality characteristics were larger for location than for the interactions between location × cultivar and location × fungicide. The fixed effects portion of the analysis revealed that the cultivar × fungicide treatment interaction significantly affected test weight, kernel protein, and flour absorption. Fungicide treatment resulted in significant increases in yield and kernel weight. Cultivar significantly affected all quality characteristics except kernel size and peak mixing time. Disease resistance exerted a significant influence on yield and test weight. The economic benefit associated with improved wheat quality from fungicide treatment was variety specific. Three cultivars (TAM 107, Karl 92, and Ike), which account for 50% of the 1997 planted wheat acres in Kansas, demonstrated positive improvements in test weight and protein in response to fungicide treatment.

Separation of Wheat Proteins by Two‐Dimensional Reversed‐Phase High‐Performance Liquid Chromatography Plus Free Zone Capillary Electrophoresis

ABSTRACTGliadins and glutenins from four hard red winter wheat cultivars were separated by a novel two‐dimensional (2D) technique. Protein extracts were separated by reversed‐phase high performance liquid chromatography as the first dimension with each 30‐sec interval collected separately. Those fractions were then separated by free‐zone capillary electrophoresis (FZCE) for the second dimension. Data was combined into 2D surface contour plots similar to traditional gel electrophoresis 2D maps. For HPLC, C8 and C18 columns were used in the first dimension to separate gliadins and glutenins, respectively. Uncoated fused silica capillaries (27 cm × 25 μm, i.d.) were used for the 2D FZCE separations. Differences in the 2D maps of both gliadin and glutenin fractions were found between pairs of both closely related and sister lines that varied in quality.

Comparison of Virulence and Isozyme Phenotypes of Pgt-QCCJ and Great Plains Races of Puccinia graminis f. sp. tritici

ABSTRACT Stem rust race Pgt-QCCJ was first found in the Great Plains of the United States in 1989, collected primarily from barley. This race became a major part of the Puccinia graminis f. sp. tritici population, even though it is virulent to only a few hard red winter wheat cultivars in the central Great Plains and to barley in the northern Great Plains. It threatens barley production in the northern Great Plains of the United States and Canada due to virulence to Rpg-1. Six differences in virulence and two in isozyme banding patterns from the most similar stem rust races make it unlikely that QCCJ arose as a mutant. Thus, QCCJ likely arose through sexual or parasexual recombination. Sexual recombination in the Great Plains is unlikely, as it has not been detected in many years. Avirulence to 'McNair 70l' is only known from the Pacific Northwest of the United States and adjacent Canada. The rust population in this area is of sexual origin, and the pattern of virulence/avirulence and isozyme banding for QCCJ occurs there. Pgt-QCCJ likely originated in the Pacific Northwest during or before 1989 and was wind-transported into the Great Plains.

Grain Yield and Breadmaking Quality of Wheat Lines with the Leaf Rust Resistance Gene Lr41

Some of the many disease‐resistance genes transferred into common wheat (Triticum aestivum L.) by interspecific hybridization have been underutilized in agriculture because of associated negative effects on productivity and end‐use quality. The Lr41 gene conferring resistance to leaf rust (caused by Puccinia recondita Rob. ex Desm.) was transferred from the wild diploid goatgrass [Triticum tauschii (Coss.) Schmal], the chromosomes of which recombine readily with those of common wheat (Fritz et al., 1995a). Thus its chromosomesr ecombine readily with those of wheat. This study had three objectives: (i) determine the direct and linked effects of Lr41 on 15 productivity and quality traits in hard red winter wheat under disease‐free conditions; (ii) to determine the effects of resistance conferred by Lr41 under a severe leaf rust epidemic and under a light infection; and (iii) to determine the amount of damage inflicted by diseases other than leaf rust in those environments. Six BC2F2‐derived common wheat lines with Lr41, along with their recurrent parents (hard red winter wheat cultivars TAM 107, TAM 200, and Century), were evaluated in three field experiments with and without fungicide treatment in 1992 and 1994. Lr41 increased grain yield and milling quality under heavy leaf rust infection with no negative effects on those traits in disease‐free plots. However, Lr41 was associated with reduced bake‐mixing time and water absorption in the absence of disease. Effects of other diseases depended heavily upon the genetic backgrounds (i.e., recurrent parents) of backcross lines. There should be no serious impediments to the use of Lr41 in breeding programs.

An Economic Evaluation of Wheat Cultivars Based on Grain and Forage Production

Wheat (Triticum aestivum L.) is extensively used for both forage for cattle (Bos taunts L.) and grain from the same planting in the southern Great Plains. Little information on the impact of cultivar selection on the economic return in such a wheat production system is available. Forage and grain yield data from 12 hard red winter wheat cultivars grown in nine environments were evaluated to assess the economic impact of cultivar selection. Trials in each environment were a randomized complete block design with four to six replications. Forage data were collected until the early joint stage of growth, and grain yield was obtained from the same plots. Forage data were converted into pounds of beef and then return from beef using three conversion procedures, since tested conversion ratios were not available. Returns from beef and grain were summed and cultivars were ranked in each environment. Rank statistics were used to evaluate cultivar stability across environments. Environmental mean forage and grain yields varied widely, 367 to 2450 for forage and 13.8 to 52.2 bu/acre for grain, resulting in average net returns across environments ranging from $2.29 to $164.78/acre. Higher grain yielding cultivars were not among the highest forage yielding cultivars, emphasizing the need to use the combined economic return in decisionmaking. Net return by cultivar across environments ranged from $51.18 to $78.47/acre. Cultivar rankings were consistent across environments, across methods of calculating conversion of forage into beef, and across price scenarios for both beef and grain. Producers interested in using wheat for both forage and grain can effectively choose cultivars based upon net return per acre, but choosing based on forage or grain yield alone seldom resulted in greatest economic return.

Wheat Permittivity Measurements in Free Space

Requirements for a free space microwave transmission measurernent system for determining the permittivity of grain are analyzed. Experimental verification of these requirements is providedfor two cultivars ofhard red winter wheat of various densities, moisture contents and temperatures in the frequency range from 10 to 18 GHz. Uncertainties in the dielectric constant determination are less than ±1%, and those for the loss factor are less than ,±.3%.

Environmental modification of hard red winter wheat flour protein composition

The intrinsic processing quality of wheat ( Triticum aestivum L.) cultivars is modified significantly 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.

Reciprocal substitutions analysis of embryo induction and plant regeneration from anther culture in wheat (Triticum aestivum L.)

Reciprocal substitutions for all chromosomes between the hard red winter wheat cultivars Wichita and Cheyenne were used to investigate the effects of individual chromosomes, as well as their interactions with the genetic background, on androgenesis. Duplicate lines for each chromosome were included to check background homogeneity. Six experiments, two for each genome, were performed. In each experiment, 14 substitution lines, their 14 duplicate lines, and the two parental genotypes ('Cheyenne' and 'Wichita') were studied. The experimental design was a randomized block with three replications. 'Wichita' and 'Cheyenne' differed significantly in embryo yield and green plant regeneration (except green plant regeneration for the B-genome tests) and were equal for albino and total plant regeneration. Embryogenesis was influenced by some chromosomes of the A, B, and D genomes; green plant production was influenced by all chromosomes of the A and D genomes except 5D; albino and total plant regeneration were affected by some chromosomes of the B and D genomes. Reciprocal effects were obtained with chromosomes 1A, 7A, 1B, 5B, 1D, and 2D for embryogenesis, chromosomes 2D and 7D for green plant regeneration, and chromosome 2D for total plant regeneration. Reciprocal substitution lines revealed reciprocal effects of homologous chromosomes, as well as interactions between substituted chromosomes and their specific genetic background.

Occurrence and Symptom Expression of American Wheat Striate Mosaic Virus in Wheat in Kansas

Extracts of winter wheat with viruslike symptoms from Comanche County, Kans., did not react with antisera to viruses previously found infecting wheat in the state, nor was the virus mechanically transmissible to wheat, maize, or sorghum. Leaves of infected wheat developed thin, chlorotic striations that were more severe on the abaxial than adaxial surface. The virus reacted with American wheat striate mosaic virus (AWSMV) antiserum and was vectored by the painted leafhopper (Endria inimica), confirming the virus as AWSMV. A protein of 59 kDa, consistently detected in extracts of infected leaves, reacted with antiserum to AWSMV in Western blots. This is the first report of AWSMV in the Southern Great Plains region. Experiments showed that, on some cultivars, AWSMV caused brown necrotic streaking of culms and glumes, a symptom not described previously for wheat infected by this virus. Hard red winter wheat cultivars Ike, Karl, and TAM 107 had positive enzyme-linked immunosorbent assay values, but exhibited few or no symptoms.

Photosynthesis and Water‐Use Efficiency of Awned and Awnletted Near‐Isogenic Lines of Hard Winter Wheat

Awned hard red winter wheat (HRWW, Triticutn aestivum L.) cultivars have prevailed in the Great Plains since the introduction of ‘Turkey’ wheat in the 1870s, but the role of awns in wheat productivity is unclear. Awns may serve a photosynthetic function during periods of drought stress, and may actually compensate for flag leaf photosynthesis reduced by drought stress. Our objectives were to determine the effect of genetic awn suppression on photosynthesis and instantaneons or season‐long measurements of water‐use efficiency (WUE), and to monitor associated changes in kernel characteristics. Plants of awned and awnletted near‐isogenic lines of three contemporary HRWW cnitivars (TAM 107, Century, and Mustang) were grown controlled‐environment chambers under well‐watered and waterdeficit conditions. Photosynthetic rates of spikes and flag leaves were measured separately at two stages of kernel development. Whole‐plant and grain WUE were measured based on actual water use. Under well‐watered conditions, net photosynthetic rates of awnletted spikes were significantly lower than awned spikes for all cnitivars at 1~1 d after anthesis (DAA) and for two cultivars at 24 DAA. Under water‐deficit conditions, rates were significantly lower for awnletted spikes of Mustang and TAM 107 at 14 DAA, while no differences were found at 24 DAA. No differences were found between isolines for flag leaf photosynthesis at either stage. Generally, differences in kernel characteristics were nonsignificant between awned and awnletted lines. Although some instantaneous photosynthetic measurements suggested higher WUE of awned spikes, this difference did not result in higher WIrE based on whole‐plant biomass or grain weight for awned isolines.

Quantifying Acquired Thermal Tolerance in Winter Wheat

High temperature stress limits productivity of winter wheat (Triticum aestivum L.) in many environments. Identification of thermal tolerant germplasm is needed to improve plant productivity under heat stress. In this study we used 2,3,5‐triphenyltetrazolium chloride OWC) reduction, an indicator of mitochondrial activity, to characterize cultivar differences for acquired thermal tolerance in winter wheat. Seven‐day‐old seedlings of six hard red winter wheat cultivars grown at 25°C were aeelimated at 37°C for 24 h followed by a 50°C incubation for 2 h. Leaf sections sampled after each temperature treatment were infiltrated with TTC and the resultant formazan was ethanol‐extracted for optical density measuremenatt 530 nm. Under these test conditions, the TTC assay detected differential tolerance (expressed as percent cell viability of the 50°C treated tissue compared to the 37°C treated tissue) which ranged from a low of 6% for ‘Siouxland’, to a high of 72% for ‘TAM 108’. The results of this study show that TTC reduction can be used to measure differences in acquired thermal tolerance in winter wheat.

Straw Quality of 10 Wheat Cultivars under Conventional and No‐Till Systems

AbstractStraw of small‐grain cereal is an important source of feed for maintenance of ruminant livestock. Information on the nutritional quality of wheat (Triticum aestivum L.) straw under conservation tillage system is limited. Grain and straw (leaves and stem) samples were obtained from a previous tillage by cultivar field study conducted on a Bethany silt loam (fine, mixed, thermic Pachic Paleustoll) from 1984 to 1987 near El Reno, OK, to determine the straw quality of 10 hard red winter wheat cultivars grown under conventional (moldboard plow) and no‐till systems. Straw was analyzed for neutral‐detergent fiber (NDF), aciddetergent fiber (ADF), lignin (LIG), crude protein (CP), and in vitro dry matter digestibility (IVDMD). Fiber (ADF and NDF) and LIG concentrations of straw from the early‐maturity cultivars were higher (P ≤ 0.05) than medium and late maturity cultivars. Crude protein (5 to 12 g kg−1) and IVDMD(25 to 39 g kg−1) concentrations were lower in early‐maturing than in medium‐ and late‐maturing cultivars among years. Neutral‐detergent fiber and ADF concentrations of all cultivars were not affected by tillage system; however, LIG of early‐maturing cultivars (Chisholm and Vona) grown under a no‐till system was 9 to 24 g kg−1 lower in 1985 and 1986 than in conventionally tilled plots. In vitro dry matter digestibility of all cultivars was not consistently affected by tillage system: no significant difference in 1984, while straw IVDMD from no‐till plots of all cultivars averaged 9 g kg−1 lower in 1985 and 13 g kg−1 lower in 1986, compared with conventionally tilled plots. Straw quality of the 10 wheat cultivars varied among maturity groups, but the effect of tillage system on straw quality was minimal.

Effect of Awn Suppression on Grain Yield and Agronomic Traits in Hard Red Winter Wheat

Producers in the southern Great Plains who utilize wheat for grain, hay, or late‐season grazing would benefit from awnless hard red winter (HRW) wheat cultivars if yield potential is maintained relative to awned cultivars. The influence of awn suppression in contemporary cultivars in the southern Great Plains is unknown. Our objective was to determine the genetic effect of awn suppression on grain yield and agronomic traits measured in several HRW backgrounds and Oklahoma production environments. Experimental materials were derived by two methods from the same source populations: ‘TAM 107’*2/‘McNair 1003’, ‘Mustang’*2/McNair 1003, and ‘Century’*2/ McNair 1003. Bulk populations of lines were derived randomly from either homozygous awned or awnletted (spikes with one to three tip awns) F2 plants in each cross. The six bulk populations were evaluated in 11 environments. In a separate experiment, 78 pairs of awned and awnletted F3‐derived sib lines (26 pairs per cross) were evaluated in four environments. No differences in grain yield were detected between awned and awnletted bulk populations from Mustang or Century, but a significant decrease in yield was found for the awnletted TAM 107 population. Significant decreases in test weight were associated with the awnletted character in all backgrounds. The Century‐awnletted population had longer spikes, greater spike harvest index, and more kernels per spike than the Century‐awned bulk. In 69% of the sib‐pair comparisons, the awnletted sib did not differ significantly from the awned sib in grain yield. Where significant differences occurred, the awned sib was always higher yielding. It may be possible to develop awnletted lines with acceptable yield performance in the Great Plains, but close attention must be given to test weight to maintain current expectations of awned cultivars.