bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of Four Spring Wheat Cultivars to Drought Stress
Authors: Moustafa M. A. , Boersma L. , Kronstad W. E.
Published: July 2010

Identification and understanding of the mechanism of drought tolerance in wheat (Triticum aestivum L.) cultivars has long been a major goal of plant breeders. Our objective was to determine if leaf water potential, osmotic potential, yield, and yield components could be used to differentiate apparent drought tolerance among the cultivars. Four spring wheat cultivars (Giza 165, Gemmiza 1, Klassic, and SPHE3) from different geographic regions were grown in a greenhouse at 20/ 15°C with 12 h of daylight augmented with artificial lighting and subjected to water stress imposed by withholding irrigation at different stages of growth. The three treatments were: no stress (WI); 10 d stress at tillering W2); and 10 d stress at heading W3). Water stress caused large differences for yield and yield components. For the W3 treatment, Giza 165, Gemmiza 1, and SPHE3 had yield decreases of 44%, 43%, and 18%, respectively, while Klassic had a yield increase of 4%. The average slopes of the turgor vs leaf water potential plots were 0.56 for Giza 165 and Gemmiza I vs 0.43 for Klassic and SPHE3 at heading. The difference between the two groups was statistically significant as determined by the 95% Tukey test. Stress applied at either tillering or heading gave similar results but effects were more pronounced when stress was applied at heading. It was not possible to determine if osmotic adjustment contributed to the differences between cultivars in response to water stress.
Post‐Harvest Alteration of In Vitro Translatable mRNA Population in Alfalfa (Medicago sativa L.)
Authors: Ferullo Jean‐Marc , Vézina Louis‐P. , Castonguay Yves , Allard Guy , Nadeau Paul , Willemot Claude , Laberge Serge
Published: July 2010

During harvest and post‐harvest handling, alfalfa (Medicago sativa L.) forage undergoes metabolic changes that result in a rapid, significant loss of nutritional quality, especially in protein content. In the present work, the hypothesis was raised that these changes might be initiated by the onset of specific metabolic changes under the control of de novo gene expression. Changes in the population of translatable poly(A) + RNA from alfalfa leaves after harvest were monitored by in vitro translation followed by a two‐dimensional polyacrylamide gel electrophoresis (2D‐PAGE) analysis of translation products. In a first experiment, which involved plants grown in a growth chamber, the disappearance of 34 of about 120 translation products present before harvest and the appearance of 37 new ones were observed. Comparison of harvest stress with heat shock, cold, and water deficit, revealed that 14 of the 37 translation products increased specifically after harvest, whereas most of the decreasing polypeptides were common to all treatments. In a second experiment, alfalfa was grown and harvested in open field conditions. Among the 40 polypeptides found to increase after harvest, 23 were common with those induced in the first experiment. These results suggest that harvest leads to both specific and non‐specific stress responses within plant cells, that result not only in the disappearance of many mRNA species, but also in the de novo expression of several mRNAs. Further characterization of genes whose expression is specifically induced during post‐harvest could provide tools for the study of post‐harvest metabolism and its modification by genetic engineering.
Diversity among Populations of Switchgrass Based on RAPD Markers
Authors: Gunter L. E. , Tuskan G. A. , Wullschleger S. D.
Published: July 2010

Information on the amount of genetic diversity in switchgrass (Panicum virgatum L.) is necessary to enhance the effectiveness of breeding programs and germplasm conservation efforts. This study characterized and assessed genetic diversity by means of RAPD markers among 14 populations representing upland and lowland switchgrass ecotypes. Forty‐five of 128 primers produced polymorphic markers among sets of genomic DNA pooled from individual genotypes of each population. Five primers were selected to amplify a total of 91 polymorphic loci among genotypes. The RAPD markers were scored for presence or absence of bands to generate distance matrices for cluster analysis. Overall similarity was 65% among populations compared to 81% within populations. Blackwell and Caddo were the most similar populations (78%) based on RAPD markers, whereas Alamo and Forestburg were the most divergent (53%). Cluster analysis clearly segregated populations into two main groups (putatively based on ecotype) and united individual genotypes within a population into discrete groups within the larger clusters. Although the relationship between ploidy level and ecotype remained unclear, RAPD profiles can be used to identify switchgrass populations and may be useful in predicting relationships between experimental germplasm sources and released populations.
Evaluation of Apomictic Reproduction in a Set of 39 Chromosome Maize‐Tripsacum Backcross Hybrids
Authors: Kindiger B. , Sokolov V. , Khatypova I. V.
Published: July 2010

An apomictic form of hybrid maize (Zea mays L.) would provide an immortalized line which would be stabilized against genetic change. The development of agronomically superior, apomictic maize hybrids could provide a superior level of food security in developing nations as well as altering commercial and public maize breeding programs‐systems in developed nations. Backcross selections obtained from an apomictic, 38‐chromosome (20 maize + 18 Tripsacum L.) maize‐Tripsacum hybrid have resulted in the development of apomictic, 39‐chromosome individuals with 30 maize + nine Tripsacum chromosomes. The identification of these materials advances two major objectives: (i) the elimination of nine Tripsacum chromosomes which do not possess the gene(s) controlling apomictic reproduction; and (ii) the continued refinement of an apomictic maize line. This study was conducted to determine whether the 39 chromosome materials reproduce by apomixis. Evaluations were performed by means of cytological, isozyme, and molecular DNA methods to assay the cytological and genetic uniformity within and between the families. The lack of variation within families and among their offspring indicates that both families reproduce by apomixis. In addition, the successful transfer of apomictic genes from Tripsacum, into a maize‐Tripsacum backcross hybrid with 2n = 3x = 30 maize and 1n = 1x = 9 Tripsacum chromosomes, is demonstrated. The generation of these materials indicates that continued breeding and selection within such materials could result in the eventual development of a hybrid maize with an apomictic reproductive system.
Soybean Fibrous Root Heritability and Genotypic Correlations with Agronomic and Seed Quality Traits
Authors: Pantalone Vincent R. , Burton Joseph W. , Carter Thomas E.
Published: July 2010

A major obstacle in selecting for increased soybean [Glycine max (L.) Merr.l seed protein concentration lies in the negative genetic correlation between seed yield and protein. The plant introduction PI 416937 has extensive fibrous root surface area that contributes to increased nitrogen fixation. PI 416937 also exhibits drought tolerance. It may be an important breeding line in the Southeast region of the USA, which is vulnerable to drought stress during soybean development. The development of breeding lines with superior root systems may be an effective way of stabilizing soybean production in drought‐prone regions. The objectives of this study were to estimate the heritability of phenotypic root score and genotypic correlations between root score and seed yield, seed protein concentration, seed oil concentration, and seed weight. A peanut inverter was used to excavate F2 plants of a population from the cross ‘Lee 74’ × PI 416937. The root systems were scored visually, based on the percentage of fibrous root area. F2:3 and F2:4 rows were grown at two locations, Clayton and Kinston, NC, in 1992 and 1993. Ten plants per plot were evaluated for root score at the R7 stage of development. Heritability estimates for root score were 0.39 on an entry‐mean basis from testing in 2 yr and two locations, and 0.24 from a realized heritability estimate. The genotypic correlation between root score and seed protein concentration was positive (rG = 0.42). This is encouraging and suggests that PI 416937 is a valuable germplasm resource for developing high protein, high yielding breeding lines.
Growth and Yield Responses of Field‐Grown Sweetpotato to Elevated Carbon Dioxide
Authors: Biswas P. K. , Hileman D. R. , Ghosh P. P. , Bhattacharya N. C. , McCrimmon J. N.
Published: July 2010

Root crops are important in developing countries, where food supplies are frequently marginal. Increases in atmospheric CO2 usually lead to increases in plant growth and yield, but little is known about the response of root crops to CO2 enrichment under field conditions. This experiment was conducted to investigate the effects of CO2 enrichment on growth and yield of field‐grown sweetpotato [Ipomoea batatas (L.) Lam.]. Plants were grown in open‐top chambers in the field at four CO2 levels ranging from 354 (ambient) to 665 μmol mol−1 two growing seasons. Shoot growth was not affected significantly by elevated CO2. Yield of storage roots increased 46 and 75% at the highest CO2 level in the 2 yr. The yield enhancement occurred through increases in the number of storage roots in the first year and through increases in both the number and size of the storage roots in the second year. Storage‐root/shoot ratios increased 44% and leaf nitrogen concentrations decreased by 24% at the highest CO2 level. A comparison of plants grown in the open field to plants grown in open‐top chambers at ambient CO2 concentrations indicated that open‐top chambers reduced shoot growth in the first year and storage‐root yield in both years. These results are consistent with the majority of CO2‐enrichment studies done on pot‐grown sweetpotato.
Photosynthetic Characteristics in Wheat Exposed to Elevated O3 and CO2
Authors: Rudorff B. F. T. , Mulchi C. L. , Lee E. , Rowland R. , Pausch R.
Published: July 2010

Tropospheric trace gases such as CO2 and O3 have progressively increased over the past century and are predicted to increase to levels at which they may have a significant impact on agricultural production. The effects of CO2 enrichment and O3 air pollution on leaf photosynthesis (Pn) and stomatal conductance (g5) were investigated. Two soft winter wheat (Triticum aestivum L.) cultivars, Massey in 1991 and Saluda in 1992, were studied in field experiments at Beltsville, MD, by means of open‐top chambers to mimic atmospheric environments predicted for the first half of the 21st century. Plants were exposed to two levels of O3 (charcoal filtered air and ambient air + an average of 40 nmol O3 mol−1 from Monday–Friday of every week). Ozone treatments were superimposed on two CO2 treatments (350 μmol CO2 mol− and 500 μmol CO2 mol−1). Averaged over O3 treatments, Pn was stimulated during the early and late growing season under enriched CO2. Averaged over CO2 treatments, high O3 exposure had a negative impact on Pn early in the season of 1992 and a major impact late in the season of 1991 and 1992 due to premature senescence. Decreases in gs occurred under the enriched CO2 environment and to a lesser extent with high O3. Interactive effects on Pn and gs were mostly absent. It is likely that if CO2 and O3 concentrations continue to increase, the beneficial effect of CO2 enrichment on Pn may be partially negated by O3‐induced stress. Conversely, damaging effects of O3 on Pn may be compensated by elevated atmospheric CO2.
Seed and Seedling Characteristics Contributing to Variation in Early Vigor among Temperate Cereals
Authors: López‐Castañeda C. , Richards R. A. , Farquhar G. D. , Williamson R. E.
Published: July 2010

Seedling characteristics between germination and the two leaf stage are principally responsible for variation in early leaf area development, or vigor, among temperate cereals. There is compelling evidence that this greater vigor confers substantial benefits in crops grown in dryland Mediterranean‐type environments. Experiments were conducted to determine the important factors that are likely to be responsible for variation in early vigor among barley (Hordeum vulgare L.), bread wheat (Triticum aestivum L.), durum wheat (T. turgidum var durum), triticale (Triticosecale Wittm.), and oat (Avena sativa L.) cultivars. Variation among and within species in the following factors was examined: (i) time to emergence, (ii) efficiency of utilization of seed reserves, (iii) shoot biomass formed from seed reserves and attributed to a larger plumule relative to the radicle, (iv) embryo size, (v) size of leaf epidermal cells, and (vi) leaf expansion rate during the lower temperatures in winter. Seeds of a similar mass were used in all experiments to eliminate the effects of seed size. The superior vigor of barley and triticale compared with the two wheat species and oat previously found in field experiments were confirmed. The size of the embryo was the single most important factor to account for differences in vigor among the species. It accounted for ≈ 90% of the variation in vigor between the species. Earlier emergence in barley accounted for the remaining variation in vigor. The breadth of the first seedling leaf is suggested as an indirect estimate of early vigor that integrates embryo size and specific leaf area and could be used in a breeding program to increase the vigor of cereals.
Soluble Carbohydrates in White Lupin Seeds Matured at 13 and 28°C
Authors: Górecki Ryszard J. , Brenac Patrick , Clapham William M. , Willcott Julie B. , Obendorf Ralph L.
Published: July 2010

Maturation of white lupin seed (Lupinus albus L. cv. Ultra) at 28°C results in later flowering and reduced seed yield in plants grown from these seed compared with plants grown from seed matured at 13°. The objectives of this study were to determine the changes in seed mass and soluble carbohydrates of white lupin seed as affected by seed maturation temperature. Fourteen soluble carbohydrates were identified and quantified by high resolution gas chromatography of the trimethylsilylimidazole‐derivatization products. Reducing sugars were not detected, and sucrose was 10 to 15% of total soluble carbohydrates in the axis and 12 to 20% in the cotyledons. Seventy to 80% of the total soluble carbohydrates were raffinose, stachyose, and verbascose. In addition to the raffinose series oligosaccharides, four series of galactosyl cyclitols were present including the galactinol series, galactopinitol A series, galactopinitol B series, and fagopyritol B1 series. Seed matured at 28°C accumulated only 53 to 70% as much dry matter as seeds matured at 13<C. Only minor changes in the raffinose series oligosaccharides were observed. Pinitol and the galactose‐containing pinitols were more than doubled by seed maturation at 28°C, but collectively, these compounds are <10% of the total soluble carbohydrates. We conclude that the effect of seed maturation temperature on the composition and concentration of soluble carbohydrates is minimal.
Potassium Fertilization Related to Cold Resistance in Bermudagrass
Authors: Miller Grady L. , Dickens Ray
Published: July 2010

Applications of high rates of potassium are often made in an attempt to increase winter hardiness of bermudagrass [Cynodon dactylon (L.) Pers.] turfs. Research was conducted to evaluate two bermudagrass cultivars field‐grown on a high sand based soil mix and a native soil for the influence of applied K on cold resistance. A field study with six K rates ranging from 0 to 390 kg ha−1 growing month−1 were applied to ‘Tifdwarf’ and ‘Tifway’ bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy] established on a sand‐peat (9:1 by volume) and a Uchee loamy sand (loamy, siliceous, thermic Arenic Hapludult) during 1992–1994. Potassium chloride or K2SO4 were compared as sources of K and were applied with twice monthly N applications. Elemental soil and plant leaf tissue concentrations were measured periodically during the course of the study. By means of an electrolyte leakage (EL) method, predicted lethal temperatures were identified for rhizome samples removed from the field monthly from October through March of 1992–1993 and 1993–1994. Lethal temperatures estimated by EL were compared with those obtained by means of a recovery growth method. Extractable K in the growth media (12‐204 kg K ha−1) and leaf tissue K concentrations (8.9–17.3 g K kg−1 i DM) increased with increasing K rates. Application of high rates of K had no effect on predicted lethal temperatures or plant regrowtho Lethal temperatures for Tifdwarf ranged from °5.8 to −7.0°C, whereas those of Tifway varied from −6.8 to −8.4°C. High K rates appear to not increase bermudagrass rhizome cold resistance; therefore, there may be no benefit to using rates beyond those that provide sufficient K levels for normal growth.
Restriction Digestion of Arbitary Amplification Fragments of Annual Bluegrass
Authors: Sweeney P. M. , Danneberger T. K.
Published: July 2010

The production of co‐dominant markers by digesting arbitrarily primed amplification fragments with restriction endonucleases would be useful in genetics and plant breeding studies. The feasibility of generating restriction amplification fragment length polymorphism (RAFLP) for use as genetic markers for annual bluegrass (Poa annua L.) was evaluated. Five restriction enzymes that (HindIII, Kpnl, Pstl, Apal, and Smal) successfully digested DNA in the amplification buffer tested were used to digest arbitrarily amplified DNA from P. annua. These restriction enzymes used in conjunction with 53 primers identified 82 restriction loci. Evaluation of 44 loci revealed three RAFLP markers. These and other RAFLP markers should be useful as codominant genetic markers for P. annua and other species where few genetic markers exist, little genomic information is available, or tissue is limited.
Herbicide Resistant Transgenic Sugarcane Plants Containing the bar Gene
Authors: Gallo‐Meagher M. , Irvine J. E.
Published: July 2010

We have obtained herbicide resistant transgenic sugarcane plants (Saccharum spp. hybrids) of the commercial cultivar NCo 310. A particle inflow gun was used to bombard embryogenic calli obtained from immature inflorescences with microprojectiles coated with a plasmid containing the coding region of the bar gene fused to the maize ubiquitin‐l(Ubi‐1) promoter, first exon, and first intron. Shoots were regenerated from calli selected for resistance to bialaphos (1 mg/L), and rooted on herbicide‐containing medium (3 mg/L). Plants regenerated on selective media were screened for the presence of the bar gene by polymerase chain reaction. Northern blot analysis showed that transgenics were producing chimeric transcripts of the proper size. Most of the transformants examined displayed resistance to the commercial herbicide Ignite applied either to leaf segments or to the entire plant at dosages lethal to noutransformed controls. Southern blot analysis confirmed stable integration of three to 10 copies of the transgene into the sugarcane genome. A well‐characterized transformant was submitted to three rounds of vegetative propagation, as well as through meristem culture. All resulting propagated clones displayed herbicide resistance comparable to the original transformant. The above results demonstrate that the bar gene can be an effective selectable marker in sugarcane transformation studies.
AFLP Analysis of Gene Pools of a Wild Bean Core Collection
Authors: Tohme Joe , Gonzalez D. Orlando , Beebe Steve , Duque Myriam C.
Published: July 2010

Studies of diversity permit conclusions about the genetic structure of species. Systematically developed core collections are a particularly good tool for such purposes. The objective of this study was to evaluate the genetic structure between and within gene pools of a core collection of wild Phaseolus vulgaris L. using the technique of amplified restriction polymorphism (AFLP) analysis. DNA fingerprint patterns of 114 genotypes were analyzed by the NTSYS program. Major groups or gene pools were recognized in Mesoamerica, Colombia, the northern Andes of Ecuador and northern Peru, and the southern Andes, although the separation among gene pools was not wide. A unique segment of germplasm from northern Peru showed greater genetic distance than the other gene pools. Although most Mexican wild beans formed a rather homogenous group, a small number of accessions clustered with the Andean gene pool, and accessions from Guatemala tended to cluster apart from Mexican accessions. In the southern Andean gene pool, more discrete groups were formed which were associated with certain regions such as Argentina, possibly reflecting greater geographic and genetic isolation. Colombian accessions appeared to be highly introgressed with germplasm from other areas. AFLP analysis produced a large amount of data in a short period, thus permitting greater insights into the genetic structure of wild beans than had been possible with other methods of analysis.
Considerations in Design and Analysis of Experiments to Measure Stomatal Conductance of Wheat
Authors: Clarke J. M. , Clarke F. R.
Published: July 2010

Stomatal conductance of wheat (Triticum spp.) is frequently measured in studies of adaptation. The objectives of this study were to determine the effects of diurnal environmental variation on observed differences in stomatal conductance among durum wheat (T. turgidum L. var. durum) genotypes and to assess techniques to improve precision in irrigated field trials. Stomatal conductance measurements were made with a steady‐state porometer, usually on clear, calm days because conductance declined by as much as 25% as clouds briefly obscured the sun. Variation in leaf temperature and photosynthetically active photon flux density were not consistently effective covariates for adjustment of observed conductance values. Adjustment for environmental variability in stomatal conductance with a spatial analysis technique improved precision relative to randomized complete‐block analysis in five of six cases and improved correlation among sampling dates. Increased replication rather than increased sub‐sampling within replications would facilitate growing trials with more treatments without loss of precision or additional cost.
Phytosiderophore Release Related to Susceptibility of Wheat to Iron Deficiency
Authors: Hansen N. C. , Jolley V. D. , Berg W. A. , Hodges M. E. , Krenzer E. G.
Published: July 2010

Some wheat (Triticum aestivum L. emend. Thell.) genotypes when grazed by livestock and subsequently used for grain production develop Fe deficiency chlorosis and decline in grain yield. Wheat is known to release phytosiderophores (compounds involved in Fe mobilization and uptake) in response to Fe deficiency stress. These studies conducted in environmental growth chambers correlated the release of phytosiderophore from the roots of eight wheat genotypes with field chlorosis scores from Oklahoma grazing trials. Plants were grown hydroponically in low Fe nutrient solutions and phytosiderophore release was measured with an Fe‐binding assay. Since grazing exacerbates Fe deficiency chlorosis development, the eight genotypes were tested both with and without clipping. Phytosiderophore release with time was summed to improve correlation compared with individual daily measurements. The field chlorosis scores and the sum of the first six phytosiderophore release measurements (Days 6 to 11 after imposition of low Fe treatment) from unclipped wheat were not correlated (r = −0.17, P = 0.70), but the sum of the last five days (13 to 17) was highly correlated with field chlorosis scores (r = −0.82, P = 0.01). Clipping did not greatly improve the relationship (r = −0.83, P = 0.008). Correlation coefficients were more consistent for individual days when plants were clipped. Three‐day sums of phytosiderophore release provided good correlations when data were collected in the latter stages of Fe deficiency development (Day 11). Identification of chlorosis resistant lines by monitoring phytosiderophore release will by‐pass years of field trials and should be implemented by plant breeders where wheat is managed concurrently for forage and grain production on calcareous soils.
Twenty Cycles of Biparental Mass Selection for Prolificacy in the Open‐Pollinated Maize Population Golden Glow
Authors: Maita R. , Coors J. G.
Published: July 2010

Selection for increased ears per plant may be an effective method for increasing grain yield in maize (Zea mays L.). Since 1970, biparental mass selection for prolificacy has been carried out in the open‐pollinated maize population Golden Glow. The objectives of this study were to (i) evaluate the direct and correlated responses to 20 cycles of mass selection for prolificacy in Golden Glow, and (ii) relate changes prolificacy to the population's performance at different plant population densities. Yield trials were conducted in 1993 at Madison and Arlington, WI, and in 1994 at Madison, Arlington, and Hancock, WI. In each location and year, the trials were grown at four plant population densities: 28 889 plants ha−1; 44 444 plants ha−1; 57 778 plants ha−1; and 73 333 plants ha−1. Ears per plant increased by 3.3% per cycle, from an average of 0.98 ears plant−1 for C0 to 1.63 ears plant−1 for C20. Grain yield per plant and grain yield per hectare both increased by 1% per cycle, from 126.5 g plant−1 and 5.91 Mg ha−1 for C0 to 151.9 g plant−1 and 7.16 Mg ha−1 for C20. Days to midpollen, days to midsilk, silk delay, and grain moisture decreased across cycles of selection. Root lodging decreased while stalk lodging did not change. Number of ears per plant was significantly and positively correlated with both grain yield per plant (r = 0.71) and grain yield per hectare (r = 0.76). The later, more prolific cycles yielded more than the initial population at high plant population density. The principal benefit of prolificacy for Golden Glow is that it may contribute to the population's ability to produce grain under competitive stress.
Hybrid Soybean Seed Production: Comparison of Three Methods
Authors: Lewers K. S. , St. Martin S. K. , Hedges B. R. , Widrlechner M. P. , Palmer R. G.
Published: July 2010

Improved methods to produce hybrid soybean [Glycine max (L.) Merr.] seed could augment several types of research. Two previously described methods, the traditional method and the dilution method, require insect‐facilitated cross‐pollination of ms ms nuclear male‐sterile plants. The traditional method requires a substantial time investment during flowering to remove fertile siblings, and the dilution method requires a substantial amount of land and pollen‐parent seed. Because time, land, and seed are limited, a more efficient method would be valuable. The cosegregation method was developed, utilizing close genetic linkage between the W1 locus and the Ms6 locus. The W1 ___, seedling has a purple hypocotyl; the w1 w1 seedling has a green hypocotyl. The ms6 ms6 plant is male sterile and female fertile. Approximately 97% of the purple‐hypocotyl seedlings, W1 ___, in a line segregating for the w1 and ms6 alleles in coupling phase will he fertile, Ms6 ___, and can be removed as a pollen source at the first‐trifoliolate stage. Our objective was to evaluate and compare the three methods of hybrid soybean seed production for seed yield, efficiency, and hybrid seed purity and quality. We used a randomized complete‐block design (three replications per location, three locations, two years). The cosegregation method gave higher seed yield, better efficiency, and equal or better seed quality (percentage germination, 100‐seed weight) than the other methods. Male‐sterile plants yielded an average of 28.6 seeds plant−1 with the cosegregation method, 18.2 seeds plant−1 with the traditional method, and 9.5 seeds plant−1 with the dilution method. The cosegregation method will be useful in several research areas, including genetic control of complex traits, prediction of parental value, recurrent selection, and commercialization of hybrid soybean.
The Second Phase of Cold Hardening: Freezing Tolerance and Fructan Isomer Changes in Winter Cereal Crowns
Authors: Livingston David P.
Published: July 2010

Cold‐hardening plants at above freezing temperatures significantly contributes to their overall winter hardiness. However, little research has been conducted on hardening at temperatures below freezing, before freezing injury results. To determine the effect of hardening at below freezing temperatures, barley (Hordeum vulgare L.) and oat (Avena sativa L.) were grown and hardened under controlled conditions and freeze tested after being held at − 3°C from 1 to 7 d. A significant hardening effect was observed after exposure to below freezing temperatures. The biggest change, a reduction of 7°C in the temperature at which 50% of the population survives, occurred after 7 d at −3°C in the winter hardy oat cultivar, Wintok. The additional hardening appeared related to changes in carbohydrate concentration. While wheat (Triticum aestivum L.) and rye (Secale cereale L.) were not freeze tested, their changes in carbohydrates were even greater than oat and barley. In oat, the concentrations of all 15 fructan isomers of degree of polymerization 3 to 5 were lower after the below freezing treatment while the concentration of fructose and sucrose were higher. Some carbohydrate concentrations were highly correlated with freezing survival under these conditions, but the exact mechanisms behind this relationship are not understood. Controlled freeze tests which consistently quantitate the effect of individual mechanisms will allow plant breeders and geneticists to more effectively screen germplasm for winter hardiness genes.
Root Hydraulic Conductance in Pima Cotton: Comparison of Reverse Flow, Transpiration, and Root Pressurization
Authors: Yang Shudong , Grantz David A.
Published: July 2010

Methods to measure root hydraulic conductance (KR, MPa; 1/resistance) under field conditions or with large plants have proven difficult to develop. We evaluated three contrasting methods of determining root conductance, a laboratory method based on hydrostatic pressure‐induced root exudation, a potential field method based on hydrostatic pressure‐induced reverse flow, and a generally applicable method involving natural gradients in water potential generated by transpiration. Pima cotton (Gossypium barbadense L.; cv S‐6) was grown in solution (hydroponically) or in potting soil in a glasshouse. Experiments were conducted 3 to 8 wk after emergence, when leaf area ranged from 0.05 to 0.25 m2 plant−1. Reverse flow and root exudation increased linearly with applied pressure between 0.2 and 0.5 MPa. Transpiration increased linearly with decreasing (transpiration‐ induced) root xylem water potential between −0.5 and −2.5 MPa. In both solution‐ and soil‐grown plants, transpiration and reverse tlow yielded comparable KR. In solution‐grown plants, root exudation yielded KR about 20% lower than the other methods. In soil‐grown plants, root exudation did not yield reproducible data. All three methods indicated that KR per plant increased with increasing plant size. In contrast, KR per unit leaf area, a functional measure of hydraulic efficiency, was similar for plants of all sizes. The excellent agreement between the reverse flow and transpirational methods suggests that both may have physiological validity. The root exudation method may underestimate KR in solution‐grown plants, and to a greater extent in soil‐grown plants.
Influence of Moving Height, Nitrogen Source, and Iprodione on Brown Patch Severity in Perennial Ryegrass
Authors: Fidanza Michael A. , Dernoeden Peter H.
Published: July 2010

Brown patch (Rhizoctonia solani Kühn) is a destructive disease of turfgrasses, but more is known regarding its management with fungicides than by cultural practices. This field study was conducted to determine the influence of mowing height and nitrogen (N) source on brown patch severity. ‘Caravelle’ perennial ryegrass (Lolium perenne L.) was subjected to two mowing heights (1.7 versus 4.5 cm) and fertilized with one of eight N sources at rates of 196 kg N ha−1 yr−1 from 1991 to 1993. Plots were split with one‐half receiving iprodione [3‐(3,5‐dichlorophenyl)‐N‐(1‐methylethyl)‐2,4‐dioxo‐1‐imidazolidine‐carboxamide)] (3.1 kg ai ha−1 applied on a 21‐d interval) and the other half receiving none. The complete combination of treatments were assessed at Silver Spring, MD, and in a second trial the N sources alone were assessed on a perennial ryegrass fairway in Pikesville, MD. In non‐fungicide‐treated plots, turf maintained at 1.7 cm was blighted more by brown patch in 1991, but in 1992 and 1993 blighting was more severe in plots mowed to a height of 4.5 cm. Blighting was reduced by iprodione at both mowing heights, and summer turfgrass quality was improved in all plots receiving N plus iprodione. Ammonium sulfate in 1991 and Sustane and Ringer Lawn Restore‐treated turf in 1992 were associated with less blighting among non‐fungicide‐treated plots at Silver Spring. Non‐fungicide‐treated Sustane and Ringer Lawn Restore plots had blight levels equivalent to most fungicide‐treated plots in 1992, but the quality of non‐fungicide‐treated plots was inferior. No N source had any significant effect on brown patch at Pikesville in any year. No single N source combined with iprodione was consistently associated with improved disease suppression or turf quality. There was no apparent relationship between brown patch severity and soil pH or crown tissue carbohydrates. Plant parasitic nematode population densities were not influenced by any N source.
RFLP Mapping and Marker‐Assisted Selection of Soybean Cyst Nematode Resistance in PI 209332
Authors: Concibido V. C. , Denny R. L. , Lange D. A. , Orf J. H. , Young N. D.
Published: July 2010

Soybean cyst nematode (Heterodera glycines Ichinohe; SCN) is one of the most serious disease problems of soybean [Glycine max (L.) Merrill], but the genetic basis of SCN resistance is complex and poorly understood. This study was conducted to identify genomic regions that confer partial resistance to SCN in soybean PI 209332 through the use of DNA genetic markers. By testing three different races of SCN, we also assessed race‐specificities of putative resistance loci. Mapping was performed in two related populations, one an F2:3 population and the other an F5:6 recombinant inbred line population, both derived from a single cross between ‘Evans’ and PI 209322. To identify resistance loci, SCN disease responses for all lines in the mapping populations were contrasted with DNA marker genotypes at 98 restriction fragment length polymorphism (RFLP) marker loci spread throughout the soybean genome. A major partial‐resistance locus on linkage group ‘G’ (P < 0.0001) near RFLP marker C006V was effective against all three SCN race isolates tested. This locus explained 35% of total phenotypic variation in the SCN disease response to a Race 1 SCN population, 50% of the response to a Race 3 SCN population, and 54% of the response to a Race 6 SCN population. Additional putative SCN resistance loci (P < 0.002) were identified on soybean linkage groups ‘D’, ‘J’, ‘L’, and ‘K’. Detecting some of these minor loci was complicated by strong masking phenotypic effects of the major resistance locus near C006V. Some of the putative resistance loci behaved in a race‐specific manner. Based on RFLP genotype at the F2 generation, marker‐assisted selection for the resistance locus on linkage group ‘G’ was evaluated and found to be 90% accurate in selecting F5:6 lines resistant to SCN, comparable in accuracy to phenotypic selection for SCN resistance.
Characterization of the Variability in Lysine Content for Normal and opaque2 Maize Endosperm
Authors: Moro Glóverson L. , Habben Jeffrey E. , Hamaker Bruce R. , Larkins Brian A.
Published: July 2010

Endospermly sine content is genetically variable in maize (Zea mays L.) germplasm, but its level is below the minimum dietary standard set by the FAO. Increasing the content of this essential amino acid in endosperm proteins depends on understanding the mechanisms regulating the synthesis and accumulation of lysine‐rich proteins. In this study, we analyzed the variability for lysine and protein contents in maize endosperm. Amounts of total protein, zeins, and non‐zeins measured by microKjeldahl, and lysine content, estimated by amino‐acid analysis, were determined for 93 maize inbreds. Additionally, an ELISA was used to estimate the relative content of the protein synthesis factor EF‐1α in 20 selected genotypes. Considerable differences in lysine content were observed among normal and opaque2 genotypes, with the effect of the mutation being highly dependent on the genetic background. We detected a high correlation between the lysine content and the concentration of total non‐zein proteins and EF‐1α. An assay for EF‐1α concentration may provide a simple and inexpensive method from breeding programs to select for improved protein quality.
Comparison of DNA Marker Technologies in Characterizing Plant Genome Diversity: Variability in Chinese Sorghums
Authors: Yang Wenpeng , de Oliveira Antonio C. , Godwin Ian , Schertz Keith , Bennetzen Jeffrey L.
Published: July 2010

Chinese sorghums [Sorghum bicolor (L.) Moench] are reputed to have a narrow genetic base, resulting from infrequent introduction of exotic germplasm into China. We have used several different molecular approaches to evaluate diversity and relatedness in a selection of 34 Chinese sorghums. The results indicated that different DNA marker technologies for germplasm assessment yield comparable results, but that a relatively new technique termed inter‐simple sequence repeat amplification (ISSR) was relatively rapid, reproducible, and inexpensive. Extensive diversity was observed within the Chinese sorghums, and all lines could be easily differentiated. Different lines collected from the same locality were found to exhibit particularly high levels of relatedness. Contrary to expectations, improved varieties were found to contain more diversity and to be more different from each other than were the Chinese landraces studied, suggesting recent introduction of non‐Chinese germplasm into these improved materials.
Environmental Influences on the Frequency and Viability of Meiotic and Apomeiotic Cells of a Diploid Mutant of Alfalfa
Authors: Barcaccia Gianni , Tavoletti Stefano , Falcinelli Mario , Veronesi Fabio
Published: July 2010

Apomixis involves the parthenogenetic development of apomeiotic eggs. It has the potential of cloning plants through seed, and thus furnishes a unique opportunity in alfalfa breeding for developing superior cultivars with permanently fixed heterosis. Megasporogenesis of a meiotic mutant of alfalfa Medicago sativa subsp, falcata (L.) Arcang. (2n = 2x = 16), named PG‐F9, that produced 2n second division restitution (SDR) and apomeiotic eggs at high frequencies, was cytologically analyzed by both stain‐clearing and sectioning techniques. The restitutional 2n egg formation was mainly due to the omission of the second meiotic division. The absence of cytokinesis was also documented after a normal second meiotic division. The concurrent examination of integument growth, cell appearance, and nucleoins size associated with either the absence of degenerating meiotic products or aposporic initials in the ovules allowed the production of apomeiotic 2n megaspores to be ascribed to a diplosporic pathway. The mutant PG‐F9 was grown in the field and in a growth chamber and the frequencies of normal, restitutional, and diplosporic cells were recorded under both environments. Restitutional 2n megaspore formation (dyads and triads with 2n chalazal megaspores) and the suppression or modification of meiosis leading to apomeiotic 2n megaspore production were influenced by environmental conditions. The frequency of normal tetrads was three times higher in the field (23.08%) than in the growth chamber (7.91%). The same trend was found for functional reduced chalazal megaspores. The frequency of restitutional cells was largely preserved in the two environments (51.92% in the field versus 50.31% in the growth chamber). The omission of normal meiosis resulting in diplosporic cells increased from 16.35% in the field to 26.27% in the growth chamber. The fertility of seed set and seeds per pod values of PG‐F9 in controlled matings carried out in the field and in the growth chamber using different diploid and tetraploid pollen sources furnished information on 2n egg viability and partially supported the cytological results. The discrepancy observed indicated that some 2n megaspores were unable to develop into a functional embryo sac.
RFLP Detection of 2n Pollen Formation by First and Second Division Restitution in Perennial Ryegrass
Authors: Chen C. , Sleper D. A. , Chao S. , Johal G. S. , West C. P.
Published: July 2010

Unreduced gametes can be used to transfer desirable traits from parent to polyploid offspring. Codominant restriction fragment length polymorphism (RFLP) markers were applied to determine the mechanism of 2n pollen formation in diploid (2n = 2x = 14) Lolium perenne L. Sixty heterologous probes were randomly chosen from a Festuca arundinacea Schreb. PstI‐genomic DNA library. A total of 30 and 33 heterozygous allelic loci were detected in two genotypes of parental L. perenne, respectively, based on segregation of RFLP loci in 13 triploid (3x) and two tetraploid (4x) hybrids, produced in 1993, between diploid L. perenne and tetraploid F. mairei St. Yves. Approximately 30 and 83% of the heterozygosity was transmitted by 2n pollen from L. perenne into two tetraploid hybrids, respectively. Both meiotic first division restitution (FDR) and second division restitution (SDR) occurred in 2n pollen formation in L. perenne. Omission of the second meiotic division (OS) and fusion of adjacent polar nuclei (FA) were found during microsporogenesis. These two mechanisms were supposedly responsible for forming 2n gametes by SDR and FDR, respectively. Formation of 2n pollen in diploid L. perenne could facilitate efficient transfer of germplasm from diploid to higher ploidy levels in Lolium and Festuca.
The Origin of Bermudagrass (Cynodon) Off‐Types Inferred by DNA Amplification Fingerprinting
Authors: Caetano‐Anollés Gustavo , Callahan Lloyd M. , Gresshoff Peter M.
Published: July 2010

DNA amplification fingerprinting (DAF) with arbitrary oligonucleotide primers can specify genetic relationships between closely related plant accessions. In this study, DAF was used to characterize bermudagrass (Cynodon) species and cultivars of interspecific crosses, evaluate genetic diversity and origin of bermudagrass off‐types, and certify authenticity of cultivar stocks. Arbitrary octamer primers produced complex and reproducible amplification profiles with high levels of polymorphic DNA. An initial analysis of 13 bermudagrass cultivars was used as a reference to establish genetic relationships between cultivar Tifway and off‐types that produce patches exhibiting contrasting morphology and performance. Phenetic analysis using cluster (UPGMA) and ordination (PCO) techniques showed that Tifway was genetically stable and that off‐types were genetically distant to Tifway and represent a heterogeneous group of bermudagrass probably of interspecific hybrid origin. While Tifway standards from different sources could not be differentiated from each other, the off‐types were diverse at the genetic level, their origin being clearly from sod contamination and not from somatic mutation. DAF was used to fingerprint samples in “phyto‐forensic” applications, identifying bermudagrass plant material based on unique reference profiles generated with selected primers. Exclusions were observed in 63% of 93 bermudagrass samples believed related to cultivars Tifway, Tifgreen, and Tifdwarf. Conversely, calculation of fingerprint matching coefficients facilitated inferences on the probability of a match in inclusion cases as applied to cultivar verification, seed certification, and cultivar protection. This study presented the foundation for the identification of mistakes in plantings, mislabeled plant materials, and contamination or substitutions of sod fields.
Salt Sensitivity and the Activities of the H+‐ATPases in Cotton Seedlings
Authors: Lin Howard , Salus Sandra S. , Schumaker Karen S.
Published: July 2010

Salinity is a major problem confronting agriculture in arid environments. Sensitivity to high levels of salt in plants is associated with an inability to effectively remove Na+ ions from the cell cytoplasm. The ability to compartmentalize Na+ may result, in part, from stimulation of the H+‐ATPases on the plasma membrane (PM‐ATPase) and vacuolar membrane (V‐ATPase). These H+‐pumping ATPases may provide the driving force for Na+ transport via Na+‐H+ exchangers. In a salt‐sensitive line of cotton (Gossypium hirsutum L.), greater relative reductions in root length and root fresh weight than in hvpocotyl length of seedlings grown in 75 rmM/ NaCI indicated that the root was most affected by salt stress. To determine if the H+‐ATPases are involved in the response to salt, we compared activities of the PMand V‐ATPases from roots in salt‐sensitive cotton seedlings grown with or without 75 rmM/ NaCI. Higher PM‐ATPase activity (42%) was observed in seedlings grown in 75 rmM/ NaCI. This stimulation was specific for Na+, was not observed when Na+ was added to membrane fractions, and was not due to an increase in PM‐ATPase protein levels. V‐ATPase protein accumulation was unaffected by growth in the presence of Na+, and activity was unaffected by Na+ in the growth medium or by Na+ added to membrane fractions. These studies suggest that although the PM‐ATPase responds to increased Na+, activity of the transport proteins on the plasma membrane alone may be insufficient to regulate intracellular Na+ levels. In addition, the inability of the V‐ATPase to respond to increased levels of Na+ indicates that salt sensitivity in cotton seedlings may result, in part, from a lack of effective driving force for compartmentalization of Na+.
Ear‐Fill Effects on Yield and Quality of Silage Corn
Authors: Coors J. G. , Albrecht K. A. , Bures E. J.
Published: July 2010

The relationship between yield and forage quality of corn (Zea mays L.) is influenced by maturity and strength of reproductive sink. Our objective was to isolate the effect of ear fill alone on stover and whole‐plant quality. Three hybrids (Pioneer Brand 3394, 3417, and 3504) were evaluated in Wisconsin during 1992 and 1993. Developing ear shoots were covered, partially covered, or left uncovered before pollen shed to create three levels of ear fill: 0, 50, and 100%. Wholeplant and stover samples were collected from plants harvested at approximately 300 g kg−1 dry matter concentration and evaluated for dry matter yield, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and in vitro true digestibility (VTD). As ear fill increased from 0 to 100%, wholeplant CP decreased by 10 g kg−1, NDF decreased by 86 g kg−1, ADF decreased by 42 g kg−1, ADL decreased by 1 g kg−1, and IVTD increased by 37 g kg−1. For stover, CP decreased by 18 g kg−1, NDF increased by 136 g kg−1, ADF increased by 94 g kg−1, ADL increased by 6 g kg−1, and IVTD decreased by 55 g kg−1. Digestibility of stover NDF increased by 15 g kg−1. An effective ear was clearly necessary to realize maximumto tal dry matter yield and quality.