bluuebunny/crossref_metadata_2025 huggingface dataset:
Taproot Carbohydrate Concentrations and Stress Tolerance of Contrasting Alfalfa Genotypes
Authors: Boyce Patricia J. , Volenec Jeffrey J.
Published: July 2010

High concentrations of starch in taproots are believed to be essential for tolerance of alfalfa (Medicago sativa L.) to defoliation and for winterhardiness. We used genotypes selected for high (HSt) and low (LSt) taproot starch concentrations to determine if high taproot starch concentrations were necessary to tolerate these stresses. In Exp. 1, roots from transplanted ramets were removed from the field at monthly intervals throughout late fall, winter, and early spring and analyzed for total sugar and starch. In Exp. 2, these genotypes were grown in the field and response to defoliation was examined. In both studies, starch concentrations in roots of the HSt genotype were twofold higher than those of LSt roots at most harvests. In Exp. I, only 5 of 12 LSt ramets regrew in spring of Year 1, while in Year 2 shoot regrowth in spring was lower for the LSt genotype compared with its herbage growth the previous fall. In Exp. 2, root starch concentrations had declined by Day 14 of regrowth to ≈20 and 40 g kg−1 for the LSt and HSt genotypes, respectively, when half of the remaining plants of both lines were defoliated a second time. Taproot starch concentrations of the LSt genotypes were consistently lower than those of the HSt genotype whether defoliated once or twice, but shoot regrowth of LSt plants was always greater than that of HSt plants. Constituents of taproots, in addition to starch, may influence tolerance to defoliation and winterhardiness of alfalfa.
Effects of Air Temperature and Fertilizer Nitrogen on Spike Development in Spring Barley
Authors: Frank Albert B. , Bauer Armand , Black Alfred L.
Published: July 2010

Spring barley (Hordeum vulgare L.) grain yield levels are determined in part by kernel numbers per spike. Planting dates affect grain yields, in part, because of variation in air temperature; hence, there is a need to understand the effects of air temperature during initiation and development of the barley spike. The objectives of this study were to determine the effects of air temperature on the plant development stage, duration of apex differentiation, and number of spikelets per spike. ‘Bowman’ (two‐rowed) and ‘Azure’ (six‐rowed) were grown in controlled environments at constant air temperatures of 18, 22, and 26 °C from seedling emergence to awned‐spikelet stage of spike development of the main stem at fertilizer N levels of 0, 70, and 200 kg N ha−1. Mean Haun stage at apex double ridge was 3.5 for Bowman and 3.8 for Azure; at awned spikelet it was 5.4 for Bowman and 6.0 for Azure. Haun stage of both cultivars at double‐ridge and at awned‐spikelet stage was greater at 26 than at 18 and 22 °C. Days from seedling emergence to double ridge averaged 10.8 d for Azure and 11.7 d for Bowman; to awned spikelet 21 d for Azure and 23 d for Bowman. Duration of spikelet development for Azure was similar (avg. 11 d) at all temperatures, but for Bowman, duration was 7.8, 12.0 and 18.7 d at 18, 22, and 26 °C, respectively. The main stem spike of Bowman deformed and aborted when grown at 26 °C. Kernel numbers of both cultivars were highest at 18 °C. Based on the combined data from the controlled‐environment study and a related field study, kernels per spike decreased by 1.5 for Azure and 0.6 for Bowman for each degree increase in mean daily maximum air temperature during spikelet development. This relationship has utility to predict kernel numbers per spike, and, along with plant population and tiller number, has practical application for predicting grain yield potential 25 to 30 d after seedling emergence.
Forage Evaluation as Influenced by Environmental Replication: A Review
Authors: Cherney Jerome H. , Volenec Jeffrey J.
Published: July 2010

Environment and treatment × environment interactions affect forage research results. This problem becomes even more complicated with forage crops that are biennial or perennial and are harvested several times each growing season. Our objective was to examine the role of environmental replication in forage experiments. A survey of forage researchers was used to determine prevailing opinions on the subject. Many traits are evaluated in forage crops, from biomass yield to basic physiological traits, and environmental impact varies among the traits. Some traits are unaffected by environment or treatment × environment interactions, although evidence must be provided when using this assumption in designing and reporting a study. The hypothesis being tested and the desired range in inferences helps determine the number of environmental regimes. A study must be repeatable (within its range of inferences) such that similar conclusions would reached if the experiment were repeated. We can extend inferences beyond the environments included in the experiment if a historic data base can show the stability of the response across environments. Consider the complex interaction between environment, plant response, and nutritive value of the forage when setting up forage‐quality studies. Multiple harvests in a year can rarely be considered an acceptable form of environmental replication. Although we do not specify number of locations and years for forage experiments, single environments must be properly justified, especially for forage‐quality experiments. If a single environment cannot be justified, then at least two environments are needed. Authors and journal editorial boards should share the responsibility for maintaining scientific quality in forage research.
Inheritance of Leaf Epicuticular Wax Content in Rice
Authors: Haque M. Mahiul , Mackill David J. , Ingram Keith T.
Published: July 2010

Leaf epicuticular wax (EW) is a trait related to drought resistance. Epicuticular wax content is low in rice (Oryza sativa L.) relative to other crops, but great differences among rice cultivars have been observed, as great as 100%. Traditional drought‐resistant upland rices have relatively higher EW content than modern irrigated lowland rices. Our objective was to determine the inheritance of leaf EW content and the prospects for increasing EW levels in improved cultivars. Field, screenhouse, and phytotron experiments were conducted to quantify the EW content in eight rice cultivars. Gas‐liquid chromatography was used to measure EW in parents, F1 progeny of an eight parent diallel crass, and two F2 populations. Area under the three highest GLC peaks, corresponding to C29, C33, and C35 hydrocarbons, accounted for > 90% of EW content. General combining ability effects were highly significant and specific combining ability effects were non significant. Broad‐sense and narrow‐sense heritability were 0.77 and 0.62, respectively. In an F2 population from a cross between highand Iow‐EW parents, EW showed a normal distribution. Few recombinants had EW equal to that of the high wax parent, suggesting polygenic inheritance. While EW is a stable and heritable trait, the F2 data indicate that selection on an individual‐plant basis in early generations would not be very effective. Furthermore, measurement is too difficult to be done on large populations and should be confined to identifying promising parents for hybridization.
Inheritance of Reduced Linolenic Acid Content in Soybean Genotypes A16 and A17
Authors: Fehr Walter R. , Welke Grace A. , Hammond Earl G. , Duvick Daniel N. , Cianzio Sylvia R.
Published: July 2010

Reduction of linolenic acid content in soybean [Glycine max (L.) Merr.] oil is associated with improved odor and flavor characteristics. Germplasm with the lowest content of this fatty acid known in soybean (<25 g kg−1) was identified in 1986 at Iowa State University from the cross of two mutant lines, A5 × A23. The objective of our study was to determine the genetic control of the reduced linolenic acid content in two lines from that cross, AI6 and AfT. The two lines with < 25 g kg−1 linolenic acid were mated reciprocally to ‘Century 84’ (77 g kg−1 linolenic), the mutant line C1640 (37 kg−1 li nolenic) an d the parents, A5 and A23. There was no maternal effect when AI6 and AI7 were crossed to their parents, but a partial maternal effect was observed in crosses with Century 84 and C1640. In the crosses of Al6 and AI7 with Century 84, the segregation of the F2.3 lines satisfactorily fit a 1:14:1 ratio, which would be expected with the segregation of major genes at two independent loci. The data indicated that AI6 and AI7 obtained the fan(A5) allele from A5 and the fan2(A23) allele from A23. The continuous distributions observed in the AI6 and AI7 crosses with Century 84 indicated that minor genes and environmental effects also are important in the expression of linolenic acid content. Consequently, the low linolenic acid content of AI6 and AI7 can be considered a quantitative character for cultivar development programs.
Selection of Superior Female Parents in Sorghum Utilizing A3 Cytoplasm
Authors: Lee Roderick D. , Johnson Blaine E. , Eskridge Kent M. , Pedersen Jeffrey F.
Published: July 2010

Prior to evaluation in hybrid combination, potential female parents of sorghum [Sorghum bicolor (L.) Moench] must be male‐sterilized. A substantial amount of time and effort is expended sterilizing females that are ultimately rejected due to inferior performance when tested in hybrid combination. Being able to identify superior females prior to male‐sterilization would be advantageous and would enable a sorghum breeder to concentrate only on superior females. This research investigated the possibility of utilizing A3 testers, R‐lines that are fertility restorers in Al cytoplasm but bad been male‐sterilized in A3 cytoplasm, for determining the relative value of female sorghum lines when used in hybrid combinations. Standard Al hybrids were compared in the field with their predictor reciprocal A3 hybrids in 1988 and 1989. Analysis of variance revealed no significant differences between cytoplasms. Interactions with cytoplasm, which could potentially limit the utility of this procedure, were not detected. Pairwise t‐tests between specific Al hybrids and their respective reciprocal A3 hybrids revealed few significant differences. These results indicated that the relative performance of hybrid progeny produced by an Al female and an Rl male line can be detected by the relative performance of the reciprocal cross produced by pollinating an A3 sterile version of an Rl line with pollen from the maintainer version of the Al female.
Establishment of ‘Hycrest’ Crested and T‐21076 Thickspike Wheatgrasses in Three Environments
Authors: Montero Carlos M. , Jones Thomas A.
Published: July 2010

Introduced grass species such as standard crested wheatgrass [Agropyron desertorum (Fischer ex Link) Schultes] are most often used to revegetate degraded rangelands in the Inter mountain region of the western USA. Use of native grass species is rising because public land management policies increasingly favor plant materials representative of native flora. Our objective was to compare the population T‐21076, a promising source of germplasm of the native thickspike wbeatgrass [Elymus lanceolatus subsp. lanceolatus (Scribner & Smith) Gould] [Syn‐Elytrigia dasystachya (Hook.) A. Löve & D. Löve], with ‘Hycrest’ crested wheatgrass for forage yield, tiller number, and tiller weight during and after establishment. The relative importance of tiller number and tiller weight for forage yield production was compared using path coefficient analysis. Seedlings were transplanted from a greenhouse to three field environments corresponding to three moisture stress levels where six harvests were evaluated through two growing seasons. Tiller number was more affected by moisture stress than tiller weight. Forage yield production of the caespitose Hycrest was more stable under moisture stress than the rhizomatous T‐21076. T‐21076's forage yield depended mostly on tillering through rhizomatous spread, which was more sensitive to moisture stress than the tillering of Hyerest. Tiller weight of T‐21076 was similar in all environments and was equal or lower than Hycrest's at all harvests. In contrast to T‐21076, Hycrest's forage yield production relied primarily on tiller weight, a more stable trait than tiller number. Increases in Hycrest's tiller weight were able to partially compensate for reductions in its tiller number with increasing moisture stress. The advantages conferred by T.21076's rhizomatous spreading and resultant tillering are probably limited by their sensitivity to moisture stress.
Potato Tuber Production in Response to Reflected Light from Different Colored Mulches
Authors: Matheny Terry A. , Hunt Patrick G. , Kasperbauer Michael J.
Published: July 2010

Colored mulches can affect the spectral balance (quality) and quantity of canopy light, which influences plant developmental patterns. Field studies were conducted to evaluate the influence of light reflected from different colored mulches on potato (Solanum tuberosum L.) tuber production. Potato plants (‘Atlantic’, ‘Kennebec’, ‘Red Pontiac’, and ‘Superior’) were grown in field plots covered with straw mulch that had been painted white, red, pale blue, or in alternating 5‐cm stripes of blue and orange to provide a range of reflected light spectra. An unpainted straw mulch treatment and a no‐mulch control were also used. Far‐red to red (FR/R) ratio and percentage of photosynthetically active radiation (PAR) reflected from the different colored mulches relative to incoming sunlight ranged from 0.82 to 1.29 and from 12 to 46%, respectively. Plants receiving reflected light from the white, pale blue, and striped straw mulches produced > 15% more marketable tubers than the no‐mulch control plants. Red and unpainted straw mulches produced plants that had yields similar to the so‐much control. Similarities in yield and spectral pattern between the unpainted straw mulch and the no‐mulch control indicated that yield increases associated with painted straw mulches were due to alteration in the quality and/or quantity of light reflected from them. It was concluded that potato tuber production can be influenced by colored straw mulches.
Resistance to the Sulfonylurea Herbicides Chlorsulfuron, Amidosulfuron, and DPX‐R9674 in Transgenic Flue‐Cured Tobacco
Authors: Brandle James E. , Labbe H. , Zilkey B. F. , Miki B. L.
Published: July 2010

Only one herbicide is currently available for preemergence broadleaf weed control in flue‐cured tobacco (Nicotiana tabacum L.) grown in Canada. The high cost of registration, coupled with the small crop size, has resulted in few new products becoming available. Herbicide resistance introduced into tobacco by Agrobacterium‐mediated transformation may allow the use of products with existing or impending registrations. We used two new, low‐residual sulfonylurco herbicides: amidosulfuron (3.(4,6‐dimethoxyprymidin.2.yl)‐l‐(N‐methyl‐N‐methylsulfonyl‐aminosulfonylurea) and DPX‐R9674, which is a mixture of thifensulfuron (methyl‐3‐ [[[[(4‐methoxy‐6‐methyl‐ 1,3,5‐triazin‐2‐yl)amino] carbonyl] amino] sulfonyl]‐2‐thiophenecarboxylate) and tribenuron (methyl 2[[[[N‐4‐methoxy‐6‐methyl‐l,3,5‐triazin‐2‐yl)methylamino] carbonyl] amino] sulfonyl] benzoate). These two and chlorsulfuron (2.chloro‐N‐[(4‐methoxy‐6.methyl‐l,3,5‐triazin‐2‐yl) aminocarbonyl] benzenesulfonamide) were applied to two transgenic tobacco genotypes harboring the csrl‐1 gene for chlorsulfuron resistance and compared with an untransformed control. Our purpose was to determine if transgenic seedlings were resistant to DPX‐R9674 and amidosulfuron. The experiment was a factorial in a completely randomized design with 25 replications. The three herbicides were applied to the transgenic and control seedlings at three rates. The transgenic seedlings had significantly higher leaf area, top dry weight, and root dry weight than the untransformed control when sprayed with any of the three herbicides. Seedlings were highly resistant to amidosulfuron and chlorsulfuron. Resistance to DPX‐R9674 in the transgenic seedlings was minimal, which was unexpected, considering that an analysis of AHAS activity revealed high levels of cross‐resistance to chlorsulfuron, DPX.R9674, and amidosulfuron. It is possible that DPX‐R9674 is metabolized into products that are herbicidally active at different AHAS binding sites. One of the transgenic lines was more resistant to herbicide application than the other indicating that selection for maximum gene expression among transgenic lines is a necessary part of transgenic cultivar development. It was concluded that DPX‐R9674 would not be suitable for use with transgenic crops harboring the csrl‐1 gene for chlorsulfuron resistance. The other lowresidual sulfonylurea, amidosulfuron, was more promising.
Sugar Alcohols in Endophyte‐Infected Tall Fescue Under Drought
Authors: Richardson M. D. , Chapman G. W. , Hoveland C. S. , Bacon C. W.
Published: July 2010

Infection of tall fescue (Festuca arundinacea Schreb.) by a fungal endophyte (Acremonium coenophialum Morgan‐Jones & Gains) improves drought tolerance, but the mechanism is unknown. Research was conducted to determine if endophyte‐infected tall fescue subjected to drought stress accumulated sugar alcohols. An infected and uninfected clone of a ‘Kentucky 31’ tall fescue genotype was greenhouse grown in perlite at field capacity or −1.0 MPa for 7 d. Sugar alcohols and other soluble carbohydrates were identified in the leaf blades and sheath. Mannitol and arabitol were identified in sheaths of infected grasses, and arabitol accumulated in infected grasses under drought stress. Infected plants had greater concentrations of fructose and glucose in blades and higher glucose in sheaths than uninfected plants when grown under drought stress. We believe, therefore, that the higher carbohydrate accumulation in infected grasses contributes to osmotic potential and regrowth capacity of endophyte‐infected grasses.
Molecular Genetic Mapping of Soybean: Map Utilization
Authors: Shoemaker Randy C. , Guffy Richard D. , Lorenzen Lisa L. , Specht James E.
Published: July 2010

Studies were conducted to (i) identify molecular probes that have a high probability of detecting polymorphisms among soybean [Glycine max (L.) Merr.] genotypes, (ii) determine the potential for analyzing genome structure using a molecular genetic map, and (iii) demonstrate the feasibility of a molecular pedigree analysis using mapped RFLP markers. Genomic DNA of 51 genotypes representing U.S. midwestern soybean germplasm was digested with the restriction enzymes HindIII, DraI, EcoRI, EcoRV, and TaqI. A random sample of 32 probes detected polymorphisms between paired comparisons of the 51 genotypes with a frequency from 0 to 72%. On average, no enzyme was strikingly better than any other for detecting polymorphisms. Homeologous chromosomal segments were detected, although they were clearly only remnants with recombination distance disparities and many rearrangements. The soybean genome, if indeed an ancient tetraploid, appears to be highly shuffled or diploidized. RFLP data were compared with the pedigrees of the cultivars Harosoy, Corsoy, Williams, and Clark, using from 58 to 105 mapped markers. Markers on Linkage Groups A and E were analyzed in detail to determine the map positions of polymorphisms and to identify chromosomal segments involved in cultivar development. The polymorphism percentage as detected by molecular markers coincided with genetic distance expectations based on pedigrees. These studies have demonstrated that probe‐enzyme combinations can be identified that will be applicable to discerning differences among a broad range of genotypes. Additionally, it has been demonstrated that a detailed RFLP map can be used to increase our understanding of genome evolution and genome structure and, when combined with pedigrees, can be used to determine the ancestral sources of markers in a given cultivar's genome.
Analysis of Culture‐Induced Variation in Soybean
Authors: Amberger Laurie A. , Palmer Reid G. , Shoemaker Randy C.
Published: July 2010

Genetic variation among culture‐regenerated crop plants can be a source of novel and desirable genetic diversity, or it can be a source of detrimental and agronomically unfavorable phenotypic variability. The objectives of this research were to determine the frequency and types of somaclonal variants obtained from culture regenerated soybeans [Glycine max (L.) Merr.]. Four hundred seventy‐five plants were regenerated from nine soybean cultivars via direct somatic embryogenesis from cotyledons of immature zygotic embroyos. Their R1, R2, and R3, progeny were scored for qualitative variation and inheritance of variant phenotypes. In each generation, sufficient numbers of progeny from R0, R1, and R2 plants were grown to ensure a 95% probability of recovering a homozygous recessive phenotype, assuming single‐gene inheritance. Phenotypic variation was observed in the R0, R1, R2, and R3 generations. Variant phenotypes included partial sterility (R0, R1, R2), complete sterility (R0,), abnormal leaf morphology (R0, R1, R2, R3), chlorophyll chimeras (R2, R3), chlorophyll‐deficiencies (R2, R3), changes in growth habit (R2, R3), yellow edges on cotyledons (R3,), no unifoliates (R3), dwarf plants (R2), yellow‐green plants (R3), and isozyme variants (R2). Inheritance studies of chlorophyll‐deficient, curled leaf, and wrinkled leaf plants confirmed that these traits were genetically controlled. Segregation for genetically controlled traits initially was observed in the R2 generation. This study produced variant phenotypes not previously reported that have potential for contributing to the understanding of the soybean genome.
Diallel Analysis of Resistance in White Clover to Southern Root‐Knot Nematode
Authors: Pederson Gary A. , Windham Gary L.
Published: July 2010

Persistence of white clover, Trifolium repens L., is reduced in areas infested with the southern root‐knot nematode, Meloidogyne incognita (Kofoid & White) Chitwood, in the southern USA. Little information is available on the resistance of white clover to M. incognita. This study was conducted to determine the relative importance of general (GCA) and specific (SCA) combining ability, and maternal and maternal reciprocal effects on resistance to M. incognita in selected white clover plants. Three M. incognita‐resistant and three susceptible white clover plants were used as parents in a diallel cross. Progeny from 30 F1 crosses, including reciprocals, and ‘Regal’ white clover (a susceptible cultivar) were evaluated under greenhouse conditions for reaction to inoculation with 1500 M. incognita (Race 4) eggs per plant. Nine weeks after inoculation, the roots were washed and scored on a 0 to 5 scale for egg mass index (EI; 0 = no egg masses, 5 = > 100 egg masses) and for percent of the root system galled (PRSG; 0 = galls, 5 = 91 to 100% galled). Six crosses had EI scores lower than Regal, and nine crosses had PRSG scores lower than Regal. A cross of resistant parents, ND 2 × ND 3, had the lowest EI (2.3) and PRSG (1.1) scores. Both GCA and SCA were significant sources of variation for both EI and PRSG. The GCA effects were more important than SCA effects for both traits. No maternal or nonmaternal reciprocal effects were observed for EI and PRSG. Resistant parents ND 1 and ND 3 produced progeny with the least M. incognita reproduction and galling. No crosses were observed that performed significantly better than expected from the GCA effects of the parents, though two crosses performed worse than expected. Resistance to M. incognita. reproduction and root galling in these and other lines are being used to develop nematode resistant white clover.
Performance of Chlorophyll‐Deficient and Normal Near‐Isolines of Two Soybean Cultivars
Authors: Wilcox James R. , Koller Ronald
Published: July 2010

Leaves of soybean [Glycine max (L.) Merr.] seedlings heterozygous at the y11 locus contain less chlorophyll, but have net CO2 assimilation rates equal to rates of normal green leaves when grown at relatively low irradiance in growth chambers. The y11 allele is lethal in the homozygous condition and plants with this genotype die at the unifoliolate or first trifoliolate stage of development. The purpose of this study was to evaluate effects of the y11 allele on agronomic and physiological characteristics of isolines of two soybean cultivars when grown in the field under normal production conditions. Normal and light green near‐isolines were developed by backcrossing the y11 allele into the cultivars Century and Hobbit. Traits were evaluated in 10‐replicate tests for a 3‐yr period in the field at West Lafayette, IN. Chlorophyll concentration in leaves of the light green isolines averaged 67% of that of normal isolines at the pod‐fill stage of growth. Normal isolines averaged 20% taller at maturity and produced 22% greater yields than light green isolines. Yield reductions of the light green isolines were due primarily to fewer seeds per unit area in 2 yr with typical rainfall patterns. In a very dry year, yield reductions of the light green isolines were due to reductions in both seed number and seed size. Changes in frequency of the y11 allele were observed during four successive generations when the isolines were grown in competition with each other. The light green isolines averaged 70% of the reproductive efficiency of the normal green isolines in these competitive tests.
Mechanisms of Potato Leafhopper Resistance in Soybean Lines Isogenic for Pubescence Type
Authors: Elden Thomas C. , Lambert Lavone
Published: July 2010

Seldom is the potato leafhopper (PLH) [Empoasca fabae (Harris)] a problem on the pubescent soybean [Glycine max (L.) Merr.] cultivars that currently dominate U.S. production. The questions remain, however, whether a higher level of resistance is needed and if alternative mechanisms of resistance are available to combat this potential insect pest. The objectives of this study were to investigate the influence of soybean lines isogenic for pubescence types on PLH feeding damage and oviposition and to determine if the mechanisms of resistance in foliar‐feeding insect resistant breeding lines are effective against the PLH. Soybean lines isogenic for dense, normal, and glabrous pubescence, developed from the genotypes ‘Davis’, ‘Tracy‐M’, and D75‒10169 were subjected to free‐choice and no‐choice laboratory studies to identify specific mechanisms of PLH resistance. The normal and dense pubescent isolines caused a significant reduction in feeding damage, oviposition, and subsequent nymphal populations when compared to glabrous isolines. Dense pubescence resulted in an additional significant reduction in feeding damage and a significant increase in adult mortality. Results indicate that normal pubescence, similar to that found in most soybean cultivars grown in the USA, provides a high level of resistance to the PLH. Besides mechanisms of resistance due to pubescence, this study also identified PLH feeding and oviposition nonpreference types of resistance, not associated with pubescence, in the breeding line D75‒10169, a genotype breed for resistance to foliar feeding insects.
Paraheliotropic Leaf Movements in Common Bean under Different Soil Nutrient Levels
Authors: Fu Qingnong A. , Ehleringer James R.
Published: July 2010

The primary objective of this study was to investigate the possible physiological consequences of paraheliotropic leaf movements in response to soil nutrient levels in well‐watered common bean (Phaseolus vulgaris L. cv. Cahone). In pot‐grown plants, leaflets from low‐fertilizer treatment (LF) plants oriented away from the sun's direct rays, receiving a significantly lower photosynthetic photon flux density (PPFD) than leaflets from high‐fertilizer treatment (HF) plants. Leaf conductance and transpiration rate were significantly lower in LF treatment plants than in HF plants. Interactions among incident PPFD, transpiration rate, and leaf area resulted in equivalent leaf temperatures under different fertilizer levels. Leaf water potential was not significantly different between these treatments Carbon isotope discrimination of HF plants was significantly lower than that of LF plants, indicating that intercellular CO2 concentrations were lower and long‐term water‐use efficiency higher for HF plants. The variations in water‐use efficiency most likely resulted from a lower ratio of photosynthesis to leaf conductance in LF plants than in HF plants. Similar tendencies were observed in field‐grown plants. Photosynthetic light‐saturation point was lower for LF plants than for HF plants. As a result of paraheliotropic leaf movements, incident PPFD on leaflets remained close to the photosynthetic light‐saturation points in both treatments.
Role of Nitrogen Form in Determining Yield of Field‐Grown Maize
Authors: Smiciklas Ken D. , Below Fred E.
Published: July 2010

Although the maize (Zea mays L.) plant can utilize either NH4−N or NO3−N, many hydroponic studies have shown that mixed‐N nutrition (NH4 + NO3) can optimize growth and yield. Results from field studies have been more erratic, however, and may be influenced by genotype. A 2‐yr field study was therefore conducted at Urbana, IL, to evaluate five maize genotypes (B73 × LH51, LH74 × LH51, LH74 × LH82, LHE136 × LH82, and LHE136 × LH123) for plant growth, nutrient content, grain yield, and canopy photosynthesis (Ps) when N was supplied either as calcium nitrate (NO3 plots) or urea plus a nitrification inhibitor (mixed‐N plots). Three of the five genotypes (B73 × LH51, LH74 × LH51, and LHE136 × LH82) increased grain yield (by 6∓8%) when supplied with mixed N, compared with plants supplied with predominantly NO3. However, NO3‐grown plants had equivalent or greater rates of canopy Ps (≈5–10%) than mixed N plants, and the duration of Ps was unaffected by N‐form treatment at photosynthetic photon flux densities of 900 or 1800 μmol photon m−2 s−1. Furthermore, N‐form treatment did not affect the duration of daily canopy Ps. Genotypes responsive to mixed N utilized distinct physiological strategies to achieve increased grain yields. For example, the genotype LHE136 × LH82 increased the partitioning of dry matter to the grain, whereas LH74 × LH51 and B73 × LH51 increased total dry matter production. Mixed‐N nutrition decreased the percentage of aborted kernels for the genotype B73 × LH51 and increased anthesis ovule number per earshoot for LH74 × LH82. Plants of the five genotypes supplied with mixed N also increased whole‐shoot N content at maturity (by 5–14%). Based on these data, we conclude that mixed‐N nutrition can moderately increase grain yield and productivity of certain maize genotypes by altering dry matter accumulation and partitioning, earshoot and ovule development, and N accumulation.
Detection of RFLPs in Perennial Ryegrass, Using Heterologous Probes from Tall Fescue
Authors: Xu W. W. , Sleper David A. , Chao S.
Published: July 2010

Perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea Schreb.) are closely related species and both are widely used for turfgrass and forage. This study was conducted to determine if heterologous genomic clones from tall rescue could be used to detect restriction fragment length polymorphisms (RFLPs) in Lolium. Thirty‐nine randomly chosen clones from the PstI‐genomic library of hexaploid tall rescue were probed to EcoRI and HindIII digested genomic DNA from five perennial ryegrass genotypes, each from a different cultivar. Two‐thirds of the heterologous probes from tall rescue cross‐hybridized to Lolium DNA and detected high levels of polymorphism (69%). There were no significant relationships between polymorphisms and clone size or hybridizing fragment size. It was estimated that an average of 41.2% of the loci examined were homozygous, ranging from 21 to 58% among the five perennial ryegrass genotypes evaluated. Tall fescue clones used in this study exhibited the same cross‐hybridization behavior with Lolium as was observed with the diploid meadow fescue (F. pratensis Huds.) in a previous study, suggesting that the Lolium genome is closely related to that of F. pratensis. The tall rescue DNA clones characterized in this study will be useful in Lolium genetic and breeding studies.
Characterization of Russian Wheat Aphid Resistance in a Hard White Spring Wheat
Authors: Baker Cheryl A. , Webster James A. , Porter David R.
Published: July 2010

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a recently introduced insect pest that is a serious threat to wheat (Triticum aestivum L.) production. While many hexaploid wheat lines have been identified as RWA‐resistant, little is known about the mechanisms of resistance of these lines. This study was conducted to characterize the plant components (i.e., tolerance, antixenosis, and antibiosis) contributing to resistance of PI 140207, a hard white spring wheat, originally collected in Iran, that has a moderate level of resistance to the RWA. In greenhouse beds, PI 140207 exhibited fewer deleterious traits than other RWA‐resistant lines, and thus was selected for further study. A series of tests designed to evaluate levels of tolerance, antixenosis (nonpreference), and antibiosis were conducted in the greenhouse in the spring of 1991. PI 140207 was compared with ‘Pavon’, a RWA‐susceptible hard white spring wheat, in all tests. Tolerance of PI 140207 to RWA feeding, as measured by chlorosis damage rating, was moderate. Antibiosis of Pl 140207, as measured by (i) population growth within an RWA colony, (ii) RWA life history analysis, and (iii) physical condition and weight of 7‐d‐old RWA progeny, was easily detected and differed significantly from Pavon. Antixenosis may also play a small role in the complex interaction of resistance components. PI 140207 is a valuable new source of resistance for germplasm enhancement efforts.
Visual Selection for Forage Yield in Winter Wheat
Authors: Ud‐Din Nasir , Carver Brett F. , Krenzer Eugene G.
Published: July 2010

Winter wheat (Triticum aestivum L.) is used as both a grain and forage crop in the southern Great Plains, but wheat breeding programs traditionally emphasize grain characteristics when evaluating experimental strains. Forage‐yield tests of large segregating populations are expensive and often unfeasible due to limited seed supply in early generations. Therefore, accurate visual prediction of forage yield potential from small plots would appeal to breeders. The objectives of this study were to measure the response to bidirectional visual selection for traits associated with forage yield based on a season‐long index, and to determine the correlated response in grain yield. Twelve lines were divergently selected (six lines in each direction) from each of three F4 populations in the field. Ratings were based on leaf size, tillering capacity, canopy height, and growth habit. A prostrate growth habit was interpreted as undesirable for forage yield potential. The 36 selections and their parents were tested in the F5 (1988‐1989) and F6 (1989‐1990) generations. The high‐selection group exceeded the low‐selection group for fall forage yield (measured prior to winter dormancy) in five of six population‐years. That trend was not observed for winter forage yield measured between dormancy and jointing. Visual selection for traits associated with forage yield did not produce a correlated change in grain yield. This study supports fall forage yield as a useful selection criterion in winter wheat breeding programs.
Sudden Death Syndrome Development in Soybean Cultivars Differing in Resistance to Fusarium solani
Authors: Stephens Paul A. , Nickell Cecil D. , Lim Sung M.
Published: July 2010

Sudden death syndrome (SDS), caused by Fusarium solani (Mart.) Sacc., can cause severe yield reduction in soybean [Glycine max (L.) Merr.]. We evaluated SDS leaf symptom development on six cultivars considered SDS‐susceptible and six considered SDS‐resistant. Micro plot treatments used local noninfested soil inoculated (using an oat‐based inoculum) with a pathogenic F. solani isolate from Arkansas; soil from two different F. solani‐infested sites in Illinois; and, as a control, local noninfested soil. Plants were rated for severity and incidence of SDS leaf symptoms every 5 d drom R1 through R6 developmental stages. Severe chlorosis and necrosis developed on the susceptible cultivars, but not on the resistant cultivars. Variation in symptom severity ranged from 0 to 100%. Cultivar rank based on the area under disease progress curve (AUDPC) was similar to the presumed rank. Correlation between AUDPC and the severity of SDS symptoms at R6 was very high (r = 0.98), indicating that the reaction of soybean to F. solani can be evaluated by rating symptoms at the R6 stage. Analysis of variance for R6 values indicated that cultivar × treatment effects were significnt (P ≤ 0.05). Reactions of soybean cultivars to F. solani populations apparently differ and can cause the ranking of cultivars within a differential set to change. Severity at R6 correlated with reduced pods per plant, but not with plant heiht, maturity, seed weight, or seed quality. Symptoms that developed on F. solani‐inoculated plants were similar to those that developed on plants grown in F. solani‐infested soil. Reaction to F. solani can, therefore, be evaluated using an inoculum of F. solani‐infested oats as an alternative to evaluation at naturally infested locations.
Interpopulation Genetic Variance after Reciprocal Recurrent Selection in BSSS and BSCB1 Maize Populations
Authors: Schnicker Bruce J. , Lamkey Kendall R.
Published: July 2010

Reciprocal recurrent selection is a breeding procedure designed to improve two populations simultaneously by selecting for performance in the interpopulation cross. The objective of this study was to evaluate the effects of II cycles of selection on the mean, genetic variance, and correlations amongtr aits in the interpopulationc ross of the Iowa Stiff Stalk Synthetic (BSSS) and Iowa Corn Borer Synthetic no. 1 (BSCBI) maize (Zea mays L.) populations. Oneh undredr eciprocal full‐sib families from Cycle 0, Cycle 5, and Cycle II of the interpopulation cross between BSSS and BSCBI were evaluated at two locations in 1989 and three locations in 1990. Grain yield increased 0.25 Mg ha‐1 per cycle (6.46%) after II cycles of selection, grain moisture increased 0.85 g kg‐1 per cycle, root lodging decreased 0.23%, and stalk lodging decreased 1.64% (all changes significant at P = 0.01). Estimates of genetic variance for all traits were significantly different from zero, except for root lodging in Cycle II. Genetic variance for grain yield decreased after II cycles of selection, although the differences among cycles were not significant. Root lodging, stalk lodging, anthesis date, and silking date had significant decreases in genetic variance after II cycles of selection. Changeisn heritability generally paralleled changes in genetic variance. Genotypic and phenotypic correlations were seemingly unchangeda cross cycles of selection. The results indicate that reciprocal recurrent selection has been effective in increasing the mean performance of the population cross while maintaining genetic variance.
Inheritance of Phomopsis Seed Decay Resistance in Soybean PI 417479
Authors: Zimmerman Mary S. , Minor Harry C.
Published: July 2010

Phomopsis seed decay (PSD) is part of a major soybean [Glycine max (L.) Merr.] fungal disease complex found in the USA and other areas of the world. The predominant disease organism, Phomopsis longicolla T.W. Hobbs, can cause reductions in seed quality and germination. While some chemical and cultural control measures exist to reduce losses due to this disease, genetic resistance would be desirable. An extensive screening project has identified PI 417479 as resistant to PSD. To most efficiently transfer the disease resistance found in PI 417479 to improved cultivars, knowledge of the inheritance of the trait is needed. Crosses were made between PI 417479 and each of two PSD‐susceptible genotypes, ‘Agripro 350’ and PI 91113. Five generations (F1, F2, F3, B1, and B2, in which B1, represents a backcross between the F1 and the resistant parent and B2 represents backcross between the F1 and the susceptible parent) were generated for each cross. These were tested in 1990 in the field at two locations near Columbi, MO. A sample of seeds from each plant was bioassayed to determine percent PSD incidence. Seeds from plants showing various degrees of infection in 1990 were progeny tested in 1991. Although environment was found to strongly influence disease incidence, results indicate that the PSD resistance found in PI 417479 is controlled by two complementary dominant nuclear genes. We concluded that the resistance genes can be transferred using a backcross procedure.
Parameter Estimation for Predicting Flowering Date of Soybean Cultivars
Authors: Grimm Sadi S. , Jones James W. , Boote Kenneth J. , Hesketh John D.
Published: July 2010

Soybean [Glycine max (L.) Merr.] growth and yield models depend on good predictions of phenological events such as flowering. Parameters for predicting flowering date of 12 cultivars were estimated for various development‐rate models. Date of flowering is predicted by accumulating a daily rate of development, which depends on night length and temperature, until a threshold is reached. Daily development rate is computed by a multiplicative relationship containing two functions: one for describing the variation in development rate with night length under optimal temperature and the other describing variation with temperature under optimal night length. There were 39 to 115 year‐location‐sowing date combinations for each cultivar, covering latitudes from 18°03′ to 45°25′ N lat. The downhill simplex method was used to estimate phenological parameters for each cultivar by minimizing the error sum of squares between observed and simulated flowering dates. Many formulations of the development‐rate model were compared. Linear‐plateau functions for both night length and temperature effects provided the best fit and yielded the most consistent results. The root mean squarerror between observed and simulated dates of flowering ranged from 3.45 to 5.28 d. Correlation coefficients between observed and simulated days from sowing to flowering varied from 0.987 to 0.841, with a decreasing trend from late toward early‐maturity cultivars. There was a clear difference among cultivars with respect to night‐length sensitivity, but a similaresponse to temperature.
Allelic Relationships among Genes for Resistance to Sunflower Rust
Authors: Quresh Zar , Jan Chao‐Chien
Published: July 2010

Sunflower rust, incited by Puccinia helianthi Schwein., is a major disease in sunflower (Helianthus annuus L.) growing areas of the world. Resistance to the four prevalent races is lacking in most of the commercial hybrids. Six accessions (PI 413023, PI 413037, PI 413048, PI 413118, PI 413171, and PI 413175) with a high frequency of rust‐resistant plants were identified. This research examined the allelic relationships among resistance genes present in these wild accessions and the inbred line HAR4. Plants in each PI that were resistant to all four races were crossed, then backcrossed, to the susceptible inbred line HA89; BC1F1 progenies resistant to all four races were identified, and each progeny was heterozygous for the four dominant genes conferring resistance to the four respective races. The F1's of HA89/HAR4 also had four independent dominant genes in heterozygous condition for resistance to the four races. The F1's of HA89/HAR4 were then intercrossed with the BC1F1 rust‐resistant plants derived from the six accessions. Resistant genotypes from the intercrosses were testcrossed with HA89. The resultant progenies indicated that the gene for resistance to each race of rust in five of six wild accessions was different from those of HAR4, whereas genes for resistance in PI 413118 were the same as those in HAR4. The resistant BC1F1's of PI 413023, PI 413118, PI 413171, and PI 413175 were intercrossed. Testcross progeny evaluations revealed that each accession had rust‐resistance genes unique to specific races. The apparent genetic diversity of these rust‐resistant accessions could be exploited to diversify the protection against the four prevailing North American sunflower rust races.
Phytoalexin Assay in Juvenile Sorghum: An Aid to Breeding for Anthracnose Resistance
Authors: Tenkouano Abdou , Miller Fred R. , Hart Gary E. , Frederiksen Richard A. , Nicholson Ralph L.
Published: July 2010

The sorghum [Sorghum bicolor (L.) Moench] plant produces antimicrobial phytoalexins that are essential components of its defense mechanism against attempted infection by Colletotrichum graminicola (Ces.) G.W. Wils., the causal agent of anthracnose. Sorghum phytoalexins are 3‐deoxyanthocyanidin flavonoids shown to be luteolinidin, apigeninidin, and a caffeic acid ester of arabinosyl 5‐O‐apigeninidin. Crosses were made between resistant and susceptible sorghum cultivars to examine the genetic × isolate relationships of the phytoalexin response. Plants were grown in a growth chamber and in the greenhouse and inoculated with two virulent isolates and one avirulent isolate of C. graminicola 7, 21, 35, 49, and 63 d after emergence. Luteolnidin concentration was greater than that of the other phytoalexins in juvenile tissues; however, the ratios of the three compounds changed as the tissues aged and extractable amounts in tissues older than 21 d were lower than in juvenile tissues. All three phytoalexins accumulated to greater concentrations in resistant inbreds and resistant × susceptible F1 progenies than in susceptible inbreds. These relationships were unaffected by the developmental stage of the host. Thus, analysis of phytoalexins in juvenile plants appears to be a potential tool for identification and incorporation of host resistance to C. graminicola in adult plants.
Senescence and Receptivity of Maize Silks
Authors: Bassetti Paolo , Westgate Mark E.
Published: July 2010

Ears of maize (Zea mays L.) fail to produce kernals if pollination is delayed more than a few days after silks emerge. Reproductive failure in aging flowers could be due to loss of silk receptivity to pollen. To test this possibility, we examined the capacity of silks to support pollen germination, tube growth, and the passage of the tube to the ovary as flowers aged. Plants were grown in the greenhouse and silks were pollinated by hand up to 14 d after emergence from the husks. Flowers in the mid‐base region of the ear failed to set kernels when pollinated 7 or more days after their silks emerged. This corresponded to the day the base of the silks began to collapse (senesce). The remaining flowers on the ear failed to set kernels in acropetal succession, coincident with the occurrence of silk senescence. During the first 24 to 36 h of senescence, pollen germination and tube growth proceeded normally. However, once the basal tissue collapsed, tube growth was restricted and fertilization did not occur. These results indicate that kernel set on an ear was closely related to the number of flowers having silks that are not senesced at pollination. Silks of aging flowers lost receptivity initially because the base of the silk collapsed, and pollen tubes were blocked from reaching the ovary. Silk senescence is the primary cause for reproductive failure in maize if pollination does not occur soon after silks emerge from the husk.