bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Volmer-Weber growth mode kinetics for germanium nanoparticles on hafnia
Authors: Coffee Shawn S. , Ekerdt John G.
Published: December 2007

Germanium nanoparticle deposition kinetics were investigated on extended HfO2 surfaces and HfO2 confined within features etched into a 12.5nm SiO2 film. Electron beam lithography was used to pattern square features from 200nmto100μm in width. Hot wire chemical vapor deposition produced Ge nanoparticles on exposed HfO2 surfaces at 0.06–4.2ML∕min fluxes and 700–775K surface temperatures. Using mean-field nucleation descriptions of particle density versus flux and temperature, a noninteger critical cluster nuclei size between 0.27 and 0.4 was found, while the critical cluster formation activation energy of 0.4–0.6eV was estimated assuming a critical cluster size of zero for studies on extended, unpatterned HfO2. Restricting the HfO2 deposition area decreases nanoparticle density compared to the density found on extended surfaces. The density decrease is due to Ge desorption through adatom contact with the silica perimeter, which depletes the system of Ge adatoms that can undergo nucleation. Comparable activation energies for Ge desorption, surface diffusion, and cluster formation obscure the change with temperature an individual process rate has on nanoparticle growth characteristics as the feature size changes.
High glass-forming ability correlated with fragility of Mg–Cu(Ag)–Gd alloys
Authors: Zheng Qiang , Xu Jian , Ma Evan
Published: December 2007

We report bulk metallic glasses with critical diameter (Dc) in the 20–27mm range over a relatively wide composition range in the Mg–Cu–Ag–Gd quaternary system. Such an extraordinary glass-forming ability is correlated with the relatively strong liquid behavior of these alloys in terms of Angell’s [Science 267, 1924 (1995)] fragility concept. The relaxation time of the ternary Mg61Cu28Gd11 and quaternary Mg59.5Cu22.9Ag6.6Gd11 alloys was measured. In terms of the fragility parameter D*, the Mg59.5Cu22.9Ag6.6Gd11 alloy with a critical diameter of 27mm under copper mold casting has a D* of 25, higher than all the bulk metallic glass–forming alloys reported so far. The implications of these findings are discussed.
Coupled phase transformation, chemical decomposition, and deformation in plastic-bonded explosive: Simulations
Authors: Levitas Valery I. , Henson Bryan F. , Smilowitz Laura B. , Zerkle David K. , Asay Blaine W.
Published: December 2007

Numerical simulations of the heating with constant rate of a PBX (plastic-bonded explosive) 9501 formulation consisting of the energetic crystal HMX embedded in a polymeric binder inside of a rigid cylinder is performed. The continuum thermo-mechanochemical model of the behavior of a PBX 9501 developed in the preceding paper [V. I. Levitas, B. F. Henson, L. B. Smilowitz, D. K. Zerkle, and B. W. Asay, J. Appl. Phys. 102, 113502 (2007)] is applied. The model describes the β↔δ phase transformations in crystalline HMX, chemical decomposition of the HMX and binder leading to gas formation, gas leaking from the cylinder, elastic, thermal, and transformational straining, as well as straining due to mass loss. We study the kinetics of the β↔δ phase transformations and pressure buildup, as well as how they are affected by the heating rate, initial porosity and prestrain, HMX and binder decomposition, and gas leaking rule.
Nanosecond electro-optical switching with a repetition rate above 20MHz
Authors: Müller Holger , Chiow Sheng-wey , Herrmann Sven , Chu Steven
Published: December 2007

We describe an electro-optical switch based on a commercial electro-optic modulator (modified for high-speed operation) and a 340V pulser having a rise time of 2.2ns (at 250V). It can produce arbitrary pulse patterns with an average repetition rate beyond 20MHz. It uses a grounded-grid triode driven by transmitting power transistors. We discuss variations that enable analog operation, use the step-recovery effect in bipolar transistors, or offer other combinations of output voltage, size, and cost.
Impedance spectroscopy study of a compositionally graded lead zirconate titanate structure
Authors: Khodorov A. , Rodrigues S. A. S. , Pereira M. , Gomes M. J. M.
Published: December 2007

The dielectric response of a compositionally graded lead zirconate titanate (PZT) structure prepared by pulsed laser deposition was studied as a function of frequency and temperature (from room temperature up to 419 °C) using impedance spectroscopy. The analysis of combined impedance and modulus spectroscopy, as well as complex plane plots, revealed that the bulk grain relaxation was the dominant relaxation process over the frequency and temperature range studied. The calculated bulk grain capacitance of the graded structure shows an anomalous behavior near temperatures related to the phase transition temperatures of the corresponding PZT compositions. The hopping conduction obeying the “universal power law” and an exponent equal to 0.88 was observed to dominate in alternating current conductivity over the entire frequency range from 10 Hz to 2 MHz at room temperature. At higher temperatures the relaxation spectrum was found to be much influenced by the increased direct current (dc) conductivity. The measured low frequency conductivity and the bulk grain dc conductance, calculated from impedance analysis indicate nearly the same Arrhenius-type thermally activated process with activation energies of 1.09 and 1.12 eV, respectively. These values were found to be in excellent agreement with those published in literature for perovskite ferroelectrics and may be attributed to motion of oxygen vacancies or field-enhanced emission of carriers from traps within the bulk.
Device physics and guiding principles for the design of double-gate tunneling field effect transistor with silicon-germanium source heterojunction
Authors: Toh Eng-Huat , Wang Grace Huiqi , Chan Lap , Samudra Ganesh , Yeo Yee-Chia
Published: December 2007

The device physics and guiding principles for the design of the double-gate tunneling field-effect transistor with silicon-germanium (SiGe) heterojunction source are discussed. Two dimensional device simulations were employed to study the influence of the position of the SiGe∕Si heterojunction on band-to-band tunneling and device performance. It is established that band-to-band tunneling occurs at a distance of ∼4nm from the gate edge in the source region. In order for the narrower bandgap of SiGe to play a dominant role, the overlap between the SiGe region and the gate should be such that the whole tunneling path of the electrons is located in SiGe. To harness the maximum benefits of the high band-to-band tunneling rate in SiGe, an overlap of ∼2nm between the SiGe region and the gate would be required.
Life-history traits drive the evolutionary rates of mammalian coding and noncoding genomic elements
Authors: Nikolaev Sergey I. , Montoya-Burgos Juan I. , Popadin Konstantin , Parand Leila , Margulies Elliott H. ,   National Institutes of Health Intramural Sequencing Center Comparative Sequencing Program, Antonarakis Stylianos E.
Published: December 2007

A comprehensive phylogenetic framework is indispensable for investigating the evolution of genomic features in mammals as a whole, and particularly in humans. Using the ENCODE sequence data, we estimated mammalian neutral evolutionary rates and selective pressures acting on conserved coding and noncoding elements. We show that neutral evolutionary rates can be explained by the generation time (GT) hypothesis. Accordingly, primates (especially humans), having longer GTs than other mammals, display slower rates of neutral evolution. The evolution of constrained elements, particularly of nonsynonymous sites, is in agreement with the expectations of the nearly neutral theory of molecular evolution. We show that rates of nonsynonymous substitutions (
d
N) depend on the population size of a species. The results are robust to the exclusion of hypermutable CpG prone sites. The average rate of evolution in conserved noncoding sequences (CNCs) is 1.7 times higher than in nonsynonymous sites. Despite this, CNCs evolve at similar or even lower rates than nonsynonymous sites in the majority of basal branches of the eutherian tree. This observation could be the result of an overall gradual or, alternatively, lineage-specific relaxation of CNCs. The latter hypothesis was supported by the finding that 3 of the 20 longest CNCs displayed significant relaxation of individual branches. This observation may explain why the evolution of CNCs fits the expectations of the nearly neutral theory less well than the evolution of nonsynonymous sites.
Deletion of the BH3-only protein
puma
protects motoneurons from ER stress-induced apoptosis and delays motoneuron loss in ALS mice
Authors: Kieran Dairín , Woods Ina , Villunger Andreas , Strasser Andreas , Prehn Jochen H. M.
Published: December 2007

BH3-only proteins couple diverse stress signals to the evolutionarily conserved mitochondrial apoptosis pathway. Previously, we reported that the activation of the BH3-only protein p53-up-regulated mediator of apoptosis (Puma) was necessary and sufficient for endoplasmic reticulum (ER) stress- and proteasome inhibition-induced apoptosis in neuroblastoma and other cancer cells. Defects in protein quality control have also been suggested to be a key event in ALS, a fatal neurodegenerative condition characterized by motoneuron degeneration. Using the
SOD1
G93A
mouse model as well as human post mortem samples from ALS patients, we show evidence for increased ER stress and defects in protein degradation in motoneurons during disease progression. Before symptom onset, we detected a significant up-regulation of Puma in motoneurons of
SOD1
G93A
mice. Genetic deletion of
puma
significantly improved motoneuron survival and delayed disease onset and motor dysfunction in
SOD1
G93A
mice. However, it had no significant effect on lifespan, suggesting that other ER stress-related cell-death proteins or other factors, such as excitotoxicity, necrosis, or inflammatory injury, may contribute at later disease stages. Indeed, further experiments using cultured motoneurons revealed that genetic deletion of
puma
protected motoneurons against ER stress-induced apoptosis but showed no effect against excitotoxic injury. These findings demonstrate that a single BH3-only protein, the ER stress-associated protein Puma, plays an important role during the early stages of chronic neurodegeneration
in vivo
.
Pulmonary CXCR2 regulates VCAM-1 and antigen-induced recruitment of mast cell progenitors
Authors: Hallgren Jenny , Jones Tatiana G. , Abonia J. Pablo , Xing Wei , Humbles Alison , Austen K. Frank , Gurish Michael F.
Published: December 2007

Chemokine receptors regulate the trafficking of leukocytes by mediating chemotaxis and by their influence on the expression and/or affinity of leukocyte integrins. Using blocking mAb, we showed that antigen-induced recruitment of mast cell progenitors (MCp) to the lung requires interaction of a4 integrins on the MCp with endothelial vascular cell adhesion molecule 1 (VCAM-1). In seeking a chemokine component, we found that CXCR2-deficient but not CCR3- or CCR5-deficient sensitized and antigen-challenged mice have significantly fewer lung MCp 1 day after challenge and fewer tracheal intraepithelial MC 1 week after challenge, implying that recruited MCp provide the source for these mature MC. Unexpectedly, reconstitution of sensitized, sublethally irradiated +/+ and −/− mice with bone marrow cells of either genotype indicated that expression of CXCR2 by the migrating MCp was not required. Instead, receptor function by resident lung cells was required because normal BM did not reconstitute MCp recruitment in irradiated CXCR2−/−mice. The reduced MCp influx into the lung of CXCR2−/−mice was accompanied by reduced induction of VCAM-1 transcripts and reduced endothelial surface expression. Thus, these studies demonstrate a role for a chemokine receptor in regulating endothelial VCAM-1 expression, MCp migration, and the level of intraepithelial MC in the lung of aerosolized, antigen-challenged mice.
RMD-1, a novel microtubule-associated protein, functions in chromosome segregation in Caenorhabditis elegans
Authors: Oishi Kumiko , Okano Hideyuki , Sawa Hitoshi
Published: December 2007

For proper chromosome segregation, the sister kinetochores must attach to microtubules extending from the opposite spindle poles. Any errors in microtubule attachment can induce aneuploidy. In this study, we identify a novel conserved Caenorhabditis elegans microtubule-associated protein, regulator of microtubule dynamics 1 (RMD-1), that localizes to spindle microtubules and spindle poles. Depletion of RMD-1 induces severe defects in chromosome segregation, probably through merotelic attachments between microtubules and chromosomes. Although rmd-1 embryos also have a mild defect in microtubule growth, we find that mutants of the microtubule growth regulator XMAP215/ZYG-9 show much weaker segregation defects. This suggests that the microtubule growth defect in rmd-1 embryos does not cause abnormal chromosome segregation. We also see that RMD-1 interacts with aurora B in vitro. Our results suggest that RMD-1 functions in chromosome segregation in C. elegans embryos, possibly through the aurora B–mediated pathway. Human homologues of RMD-1 could also bind microtubules, which would suggest a function for these proteins in chromosome segregation during mitosis in other organisms as well.
Regulation of lamellipodial persistence, adhesion turnover, and motility in macrophages by focal adhesion kinase
Authors: Owen Katherine A. , Pixley Fiona J. , Thomas Keena S. , Vicente-Manzanares Miguel , Ray Brianne J. , Horwitz Alan F. , Parsons J. Thomas , Beggs Hilary E. , Stanley E. Richard , Bouton Amy H.
Published: December 2007

Macrophages are a key component of the innate immune system. In this study, we investigate how focal adhesion kinase (FAK) and the related kinase Pyk2 integrate adhesion signaling and growth factor receptor signaling to regulate diverse macrophage functions. Primary bone marrow macrophages isolated from mice in which FAK is conditionally deleted from cells of the myeloid lineage exhibited elevated protrusive activity, altered adhesion dynamics, impaired chemotaxis, elevated basal Rac1 activity, and a marked inability to form stable lamellipodia necessary for directional locomotion. The contribution of FAK to macrophage function in vitro was substantiated in vivo by the finding that recruitment of monocytes to sites of inflammation was impaired in the absence of FAK. Decreased Pyk2 expression in primary macrophages also resulted in a diminution of invasive capacity. However, the combined loss of FAK and Pyk2 had no greater effect than the loss of either molecule alone, indicating that both kinases function within the same pathway to promote invasion.
Par3 functions in the biogenesis of the primary cilium in polarized epithelial cells
Authors: Sfakianos Jeff , Togawa Akashi , Maday Sandra , Hull Mike , Pypaert Marc , Cantley Lloyd , Toomre Derek , Mellman Ira
Published: December 2007

Par3 is a PDZ protein important for the formation of junctional complexes in epithelial cells. We have identified an additional role for Par3 in membrane biogenesis. Although Par3 was not required for maintaining polarized apical or basolateral membrane domains, at the apical surface, Par3 was absolutely essential for the growth and elongation of the primary cilium. The activity reflected its ability to interact with kinesin-2, the microtubule motor responsible for anterograde transport of intraflagellar transport particles to the tip of the growing cilium. The Par3 binding partners Par6 and atypical protein kinase C interacted with the ciliary membrane component Crumbs3 and we show that the PDZ binding motif of Crumbs3 was necessary for its targeting to the ciliary membrane. Thus, the Par complex likely serves as an adaptor that couples the vectorial movement of at least a subset of membrane proteins to microtubule-dependent transport during ciliogenesis.
Actin-dependent intranuclear repositioning of an active gene locus in vivo
Authors: Dundr Miroslav , Ospina Jason K. , Sung Myong-Hee , John Sam , Upender Madhvi , Ried Thomas , Hager Gordon L. , Matera A. Gregory
Published: December 2007

Although bulk chromatin is thought to have limited mobility within the interphase eukaryotic nucleus, directed long-distance chromosome movements are not unknown. Cajal bodies (CBs) are nuclear suborganelles that nonrandomly associate with small nuclear RNA (snRNA) and histone gene loci in human cells during interphase. However, the mechanism responsible for this association is uncertain. In this study, we present an experimental system to probe the dynamic interplay of CBs with a U2 snRNA target gene locus during transcriptional activation in living cells. Simultaneous four-dimensional tracking of CBs and U2 genes reveals that target loci are recruited toward relatively stably positioned CBs by long-range chromosomal motion. In the presence of a dominant-negative mutant of β-actin, the repositioning of activated U2 genes is markedly inhibited. This supports a model in which nuclear actin is required for these rapid, long-range chromosomal movements.
How genes find their way inside the cell nucleus
Authors: Carmo-Fonseca Maria
Published: December 2007

Recent progress in live cell imaging suggests a role for nuclear actin in chromatin movement. In this issue, for the first time, a gene locus moving toward a subnuclear compartment was tracked. Motion of the locus is actin dependent, raising the question of whether chromatin movements are random or directed.
Noncanonical Wnt signaling promotes apoptosis in thymocyte development
Authors: Liang Huiling , Coles Andrew H. , Zhu Zhiqing , Zayas Jennifer , Jurecic Roland , Kang Joonsoo , Jones Stephen N.
Published: December 2007

The Wnt–β-catenin signaling pathway has been shown to govern T cell development by regulating the growth and survival of progenitor T cells and immature thymocytes. We explore the role of noncanonical, Wnt–Ca2+ signaling in fetal T cell development by analyzing mice deficient for Wnt5a. Our findings reveal that Wnt5a produced in the thymic stromal epithelium does not alter the development of progenitor thymocytes, but regulates the survival of αβ lineage thymocytes. Loss of Wnt5a down-regulates Bax expression, promotes Bcl-2 expression, and inhibits apoptosis of CD4+CD8+ thymocytes, whereas exogenous Wnt5a increases apoptosis of fetal thymocytes in culture. Furthermore, Wnt5a overexpression increases apoptosis in T cells in vitro and increases protein kinase C (PKC) and calmodulin-dependent kinase II (CamKII) activity while inhibiting β-catenin expression and activity. Conversely, Wnt5a deficiency results in the inhibition of PKC activation, decreased CamKII activity, and elevation of β-catenin amounts in thymocytes. These results indicate that Wnt5a induction of the noncanonical Wnt–Ca2+ pathway alters canonical Wnt signaling and is critical for normal T cell development.
Role of host tissues for sustained humoral effects after endothelial progenitor cell transplantation into the ischemic heart
Authors: Cho Hyun-Jai , Lee Namho , Lee Ji Yoon , Choi Yong Jin , Ii Masaaki , Wecker Andrea , Jeong Jin-Ok , Curry Cynthia , Qin Gangian , Yoon Young-sup
Published: December 2007

Noncellular differentiation effects have emerged as important mechanisms mediating therapeutic effects of stem or progenitor cell transplantation. Here, we investigated the expression patterns and sources of humoral factors and their regional and systemic biological effects after bone marrow (BM)-derived endothelial progenitor cell (EPC) transplantation into ischemic myocardium. Although most of the transplanted EPCs disappeared within a week, up-regulation of multiple humoral factors was sustained for longer than two weeks, which correlated well with the recovery of cardiac function. To determine the source of the humoral factors, we injected human EPCs into immunodeficient mice. Whereas the expression of human EPC (donor)-derived cytokines rapidly decreased to a nondetectable level within a week, up-regulation of mouse (recipient)-derived cytokines, including factors that could mobilize BM cells, was sustained. Histologically, we observed higher capillary density, a higher proliferation of myocardial cells, a lower cardiomyocyte apoptosis, and reduced infarct size. Furthermore, after EPC transplantation, BM-derived stem or progenitor cells were increased in the peripheral circulation and incorporated into the site of neovascularization and myocardial repair. These data indicate that myocardial EPC transplantation induces humoral effects, which are sustained by host tissues and play a crucial role in repairing myocardial injury.
A human postnatal lymphoid progenitor capable of circulating and seeding the thymus
Authors: Six Emmanuelle M. , Bonhomme Delphine , Monteiro Marta , Beldjord Kheira , Jurkowska Monika , Cordier-Garcia Corinne , Garrigue Alexandrine , Dal Cortivo Liliane , Rocha Benedita , Fischer Alain , Cavazzana-Calvo Marina , André-Schmutz Isabelle
Published: December 2007

Identification of a thymus-seeding progenitor originating from human bone marrow (BM) constitutes a key milestone in understanding the mechanisms of T cell development and provides new potential for correcting T cell deficiencies. We report the characterization of a novel lymphoid-restricted subset, which is part of the lineage-negative CD34+CD10+ progenitor population and which is distinct from B cell–committed precursors (in view of the absence of CD24 expression). We demonstrate that these Lin−CD34+CD10+CD24− progenitors have a very low myeloid potential but can generate B, T, and natural killer lymphocytes and coexpress recombination activating gene 1, terminal deoxynucleotide transferase, PAX5, interleukin 7 receptor α, and CD3ε. These progenitors are present in the cord blood and in the BM but can also be found in the blood throughout life. Moreover, they belong to the most immature thymocyte population. Collectively, these findings unravel the existence of a postnatal lymphoid-polarized population that is capable of migrating from the BM to the thymus.
Immune recognition of Pseudomonas aeruginosa mediated by the IPAF/NLRC4 inflammasome
Authors: Sutterwala Fayyaz S. , Mijares Lilia A. , Li Li , Ogura Yasunori , Kazmierczak Barbara I. , Flavell Richard A.
Published: December 2007

Pseudomonas aeruginosa is a Gram-negative bacterium that causes opportunistic infections in immunocompromised individuals. P. aeruginosa employs a type III secretion system to inject effector molecules into the cytoplasm of the host cell. This interaction with the host cell leads to inflammatory responses that eventually result in cell death. We show that infection of macrophages with P. aeruginosa results in activation of caspase-1 in an IPAF-dependent, but flagellin-independent, manner. Macrophages deficient in IPAF or caspase-1 were markedly resistant to P. aeruginosa–induced cell death and release of the proinflammatory cytokine interleukin (IL)-1β. A subset of P. aeruginosa isolates express the effector molecule exoenzyme U (ExoU), which we demonstrate is capable of inhibiting caspase-1–driven proinflammatory cytokine production. This study shows a key role for IPAF and capase-1 in innate immune responses to the pathogen P. aeruginosa, and also demonstrates that virulent ExoU-expressing strains of P. aeruginosa can circumvent this innate immune response.
Dependence of antibody gene diversification on uracil excision
Authors: Di Noia Javier M. , Williams Gareth T. , Chan Denice T.Y. , Buerstedde Jean-Marie , Baldwin Geoff S. , Neuberger Michael S.
Published: December 2007

Activation-induced deaminase (AID) catalyses deamination of deoxycytidine to deoxyuridine within immunoglobulin loci, triggering pathways of antibody diversification that are largely dependent on uracil-DNA glycosylase (uracil-N-glycolase [UNG]). Surprisingly efficient class switch recombination is restored to ung−/− B cells through retroviral delivery of active-site mutants of UNG, stimulating discussion about the need for UNG's uracil-excision activity. In this study, however, we find that even with the overexpression achieved through retroviral delivery, switching is only mediated by UNG mutants that retain detectable excision activity, with this switching being especially dependent on MSH2. In contrast to their potentiation of switching, low-activity UNGs are relatively ineffective in restoring transversion mutations at C:G pairs during hypermutation, or in restoring gene conversion in stably transfected DT40 cells. The results indicate that UNG does, indeed, act through uracil excision, but suggest that, in the presence of MSH2, efficient switch recombination requires base excision at only a small proportion of the AID-generated uracils in the S region. Interestingly, enforced expression of thymine-DNA glycosylase (which can excise U from U:G mispairs) does not (unlike enforced UNG or SMUG1 expression) potentiate efficient switching, which is consistent with a need either for specific recruitment of the uracil-excision enzyme or for it to be active on single-stranded DNA.
Improved Bioassay of Xylella fastidiosa Using Nicotiana tabacum Cultivar SR1
Authors: Francis M. , Civerolo E. L. , Bruening G.
Published: December 2007

Readily transformable Nicotiana tabacum cv. SR1 (Petite Havana) was evaluated as a host for the bioassay of Xylella fastidiosa strains. Plant growing conditions and inoculation methods were optimized to enhance symptom expression 4 to 6 weeks post inoculation. Tobacco plants were inoculated with X. fastidiosa strains associated with almond leaf scorch disease (ALSD) and Pierce's disease (PD) of grapevine in California. All PD strains and the ALSD strain Dixon caused characteristic leaf scorch symptoms, whereas two other ALSD-associated strains (M12 and M23) caused severe leaf chlorosis followed by necrosis, leaf death, and drooping of older leaves. Symptoms began to develop 10 to 14 days post inoculation and proceeded to resemble those of X. fastidiosa-infected grape and almond. The presence of X. fastidiosa in affected plants was confirmed by reisolation of the pathogen, enzyme-linked immunosorbent assay, quantitative polymerase chain reaction (QPCR), and observation of X. fastidiosa cells by transmission and scanning electron microscopy, as well as by confocal laser scanning microscopy, in the xylem cells of inoculated plants. The pathogenicity of selected reisolated strains was confirmed by inoculation of grape plants in the greenhouse. The average levels of X. fastidiosa cells/g of tissue, estimated by QPCR, were higher for PD strains than for ALSD strains and reflected the relative titers of these strains in economic hosts. No symptoms were observed and bacteria were not detected in untreated tobacco or in tobacco inoculated with Xanthomonas campestris pv. campestris or water. Symptoms induced by Xylella fastidiosa in this bioassay were fully expressed within 2 months following inoculation. The described bioassay, under optimized environmental conditions, provides a useful system for studying X. fastidiosa strains (e.g., confirmation of pathogenicity and differentiation of PD and ALSD pathotypes) and for investigating X. fastidiosa–host interactions. N. tabacum cv. SR1 tobacco was a better bioassay host for X. fastidiosa than N. tabacum cvs. Havana, RP1, and TNN described previously.
Graft Transmission and Cultivar Reaction of Citrus to ‘Candidatus Liberibacter americanus’
Authors: Lopes S. A. , Frare G. F.
Published: December 2007

Little is known about ‘Candidatus Liberibacter americanus’, a causal agent of huanglongbing or greening disease in Brazil, or its interaction with citrus trees. Greenhouse experiments were conducted with the objective of determining conditions favorable for transmission from field affected trees to young potted plants, to evaluate the reaction of multiple citrus species to the disease, and to determine the efficiency of pathogen propagation from individual buds. Single buds or bark pieces of various sizes or bark plus wood (budstick) that were removed from symptomatic or asymptomatic branches were used as sources of inoculum. Transmission success was evaluated through polymerase chain reaction analysis of total DNA extracted from leaf samples. Beginning at 4 to 5 months after inoculation, infected plants manifested leaf mottling and symptoms similar to those of iron, manganese, and zinc deficiencies. Blotchy mottled leaves appeared only on sweet oranges and Murcott tangor. Pathogen transmission was higher for these citrus cultivars and species (31.2 to 65.2%) than for limes, mandarins, or Swingle citrumelo (2.0 to 25.0%). Deformed small fruits with brownish columellae also developed on sweet oranges. Only buds and budsticks served as sources of inoculum and the larger the piece of tissue, the higher the transmission efficiency. Experiments initiated during the winter showed lower rates of graft tissue survival but relatively higher percentages of pathogen transmission.
A Method for Inoculation and Evaluation of Rice Sheath Blight Disease
Authors: Park Dong-Soo , Sayler Ronald J. , Hong Yeon-Gyu , Nam Min-Hee , Yang Yinong
Published: December 2007

Sheath blight of rice, caused by Rhizoctonia solani, is one of the most important rice diseases worldwide; however, no rice cultivar has been found to be completely resistant to this fungus. To facilitate detailed analysis of sheath blight resistance at genetic, molecular, biochemical, and functional genomic levels, new methods were developed for effective and uniform infection and accurate evaluation of the disease. The efficiency of R. solani infection was tested on two resistant (Tetep and Jasmine 85) and two susceptible (Chucheongbyeo, Junambyeo) cultivars using three different inoculum types (agar block, liquid cultured mycelia ball, and mycelia suspension). By covering the inoculated sheaths with aluminum foil to maintain humidity, 100% infection rate was achieved in this study. Liquid cultured mycelia balls caused significantly longer lesions (5.4 cm) than other types of inoculum, including agar block (2.4 cm) and mycelia suspension (1.6 cm). An improved method for evaluating sheath blight disease was selected by comparing two methods for evaluating disease severity among three partially resistant cultivars and five susceptible cultivars inoculated with liquid cultured mycelia balls. In addition, a new formula was developed to calculate the disease susceptibility index. Lesion length and the susceptibility index generally were correlated in each leaf, but there were discrepancies between the two evaluation methods due to differences in plant architecture among the cultivars. The susceptibility index calculated using the new formula was the most accurate method for evaluating sheath blight disease across all cultivars. The effect of heading date and panicle number also was evaluated in relation to sheath blight resistance. Cultivars with late heading dates generally were more resistant to sheath blight than those with early heading dates.
Comparative Susceptibilities of Legume Species to Infection by Phakopsora pachyrhizi
Authors: Bonde M. R. , Nester S. E. , Berner D. K. , Frederick R. D. , Moore W. F. , Little S.
Published: December 2007

Knowledge of the host range of Phakopsora pachyrhizi is important to agriculture in the United States because of the distinct possibility that economic losses could occur to crops other than soybean. Furthermore, it is possible that alternative hosts could provide a means of overwintering of the pathogen, providing inoculum to initiate epidemics in future years. To clarify the potential importance of soybean rust on nonsoybean legumes and their role in overwintering of the disease, multiple accessions of clover, cowpea, pea, kudzu, lima bean, snap bean, and single accessions of coffee senna, Florida beggarweed, hemp sesbania, hyacinth bean, partridge pea, and showy crotalaria were inoculated under greenhouse conditions with urediniospores of P. pachyrhizi; infected soybean plants served as a control. The four criteria used to assess susceptibility were lesion density, proportion of lesions with sporulating uredinia, average number of uredinia per lesion, and average uredinia diameter, each determined 2 weeks following inoculation. Based on lesion densities, percentage of lesions with sporulation, and average numbers of uredinia per lesion, soybean, kudzu, and pea were the most susceptible species, followed by snap bean. However, because infected pea plants defoliated rapidly, urediniospore production presumably was limited, lessening the potential for epidemics on pea. Cultivars of snap bean produced numerous brown to reddish-brown lesions, many of which sporulated, but numbers of uredinia per lesion were lower than on soybean, kudzu, or pea. The presence of both tan (susceptible) and reddish-brown (resistant) lesions on kudzu demonstrated physiological differentiation on that host. Some kudzu plants appeared to be potentially excellent hosts for overwintering of the disease. The average number of uredinia per lesion appeared to be a valid measurement with which to compare host susceptibilities, and may have epidemiological significance. High susceptibility of a host was characterized by numerous uredinia with a wide range of sizes within individual lesions. In contrast, low susceptibility to rust was characterized by no or a few small uredinia.
Seasonal Dynamics of Conidial Production Potential ofFusicladium carpophilumon Twig Lesions in Southeastern Peach Orchards
Authors: Scherm H. , Savelle A. T. , Boozer R. T. , Foshee W. G.
Published: December 2007

Conidia produced on overwintered lesions on 1-year-old twigs constitute the only source of primary inoculum for the peach scab fungus, Fusicladium carpophilum; however, there is little quantitative information about the dynamics of sporulation throughout the season. Starting in late winter and continuing until midsummer over a 4-year period, twig segments were sampled every 1 to 2 weeks from peach trees untreated with fungicide from a total of 18 trials (site–cultivar–year combinations) in Georgia, Alabama, and South Carolina. Twig samples were incubated in a moist chamber in the laboratory for 48 h and washed on a wrist-action shaker, and conidial production potential was determined by microscopic counts in aliquots of the wash water. When plotted against calendar date (day of the year), there was considerable variation among cultivars, sites, and years in the temporal pattern of conidial numbers of F. carpophilum. For example, conidia first were detected on samples collected between mid-February and late March, and the highest peak in conidial numbers was observed between late March and mid-May. In contrast, when conidial numbers were expressed as cumulative totals in relation to phenological time (either days after full bloom or days after calyx-split), temporal progress was very similar among trials. Conidial production summarized in this manner generally commenced before bloom and reached 25 and 90% of the seasonal total by calyx-split and 10 weeks after bloom, respectively. A two-parameter sigmoidal function described the relationship between cumulative conidial production and phenological time very well (R2= 0.9727 and 0.9790 for days after full bloom and days after calyx-split, respectively; P < 0.0001, n = 260). Expression of time in degree-days did not improve the relationship between cumulative conidial numbers and phenological time. Thus, knowledge of host tree phenology may be sufficient to derive strategic estimates of disease risk based on the predictable seasonal pattern of conidial production potential; this seasonal, inoculum-based risk estimate may be used to adjust daily infection risk estimates based on models that consider microclimatic conditions affecting pathogen growth and infection.
Biological and Molecular Characterization of an American Sugar Beet-InfectingBeet western yellows virusIsolate
Authors: Beuve Monique , Stevens Mark , Liu Hsing-Yeh , Wintermantel William M. , Hauser Sébastien , Lemaire Olivier
Published: December 2007

Three aphid-transmitted viruses belonging to the Polerovirus genus, Beet mild yellowing virus (BMYV), Beet chlorosis virus (BChV), and Beet western yellows virus (BWYV), have been described as pathogens of sugar beet. We present the complete biological, serological, and molecular characterization of an American isolate of Beet western yellows virus (BWYV-USA), collected from yellow beet leaves. The biological data suggested that BWYV-USA displayed a host range similar to that of BMYV, but distinct from those of BChV and the lettuce and rape isolates of Turnip yellows virus. The complete genomic RNA sequence of BWYV-USA showed a genetic organization and expression typical of other Polerovirus members. Comparisons of deduced amino acid sequences showed that P0 and the putative replicase complex (P1-P2) of BWYV-USA are more closely related to Cucurbit aphid-borne yellows virus (CABYV) than to BMYV, whereas alignments of P3, P4, and P5 showed the highest homology with BMYV. Intraspecific and interspecific phylogenetic analyses have suggested that the BWYV-USA genome may be the result of recombination events between a CABYV-like ancestor contributing open reading frame (ORF) 0, ORF 1, and ORF 2, and a beet Polerovirus progenitor providing the 3′ ORFs, with a similar mechanism of speciation occurring for BMYV in Europe. Results demonstrate that BWYV-USA is a distinct species in the Polerovirus genus, clarifying the nomenclature of this important group of viruses.
Occurrence and Distribution of Pumpkin and Squash Viruses in Illinois
Authors: Jossey S. , Babadoost M.
Published: December 2007

Surveys were conducted during 2004 to 2006 to identify the viruses infecting pumpkin and squash in Illinois. In 2004, 16 jack-o-lantern pumpkin (Cucurbita pepo) samples and one squash (C. pepo) sample were collected from 11 counties. In 2005, 85 jack-o-lantern pumpkin, 12 processing pumpkin (Cucurbita moschata), 37 squash, and six gourd (C. pepo) samples were collected from 54 counties. In 2006, 85 jack-o-lantern pumpkin, 16 processing pumpkin, 51 squash, and 18 gourd samples were collected from 47 counties. Cucumber mosaic virus (CMV), Papaya ringspot virus (PRSV), Squash mosaic virus (SqMV), Tobacco ringspot virus (TRSV), Tomato ringspot virus (ToRSV), Watermelon mosaic virus (WMV), Zucchini yellow mosaic virus (ZYMV), and unknown potyviruses were detected in pumpkin, squash, and gourd fields during the surveys, using enzyme-linked immunosorbent assay (ELISA). Overall, 86, 11, 75, and 79% of jack-o-lantern pumpkin, processing pumpkin, squash, and gourds, respectively, were tested positive for virus infection during the survey. WMV was detected in 47, 46, and 52% of the samples in 2004, 2005, and 2006, respectively, and was the most prevalent virus throughout the state. SqMV was detected in more counties than any other virus because it was identified in 65 and 88% of the counties surveyed in 2005 and 2006, respectively. SqMV was detected in 6, 41, and 48% of the samples in 2004, 2005, and 2006, respectively. During the surveys, CMV was detected in 6, 4, and 3% of the samples; PRSV was detected in 6, 11, and 4% of the samples; and ZYMV was detected in 18, 4, and 4% of the samples tested in 2004, 2005, and 2006, respectively. TRSV was detected in 3% of the samples in 2005, for the first time on pumpkin in Illinois. Pathogenicity of the detected viruses was proved for CMV, PRSV, SqMV, WMV, and ZYMV on summer squash (‘Fortune’ and ‘Grey Zucchini’), jack-o-lantern pumpkin (‘Howden’), and processing pumpkin (‘Dickinson’). All of the viruses were present alone and mixed in the samples tested. Earlier in the growing seasons (July and early August), single-virus infections were detected. Mixed infections were more common from the second week of August until the end of the growing season in October. Dual infection of WMV and SqMV was the most prevalent mixed virus infection detected in Illinois. Most viruses infecting pumpkin and squash showed similar symptoms. The most common symptoms observed in the commercial fields and in the greenhouse studies were light- and dark-green mosaic, veinbanding, veinclearing, puckering, and deformation of leaves of pumpkin, squash, and gourds. Severe symptoms included fernleaf and shoestring on leaves and color breaking and deformation of fruit.
Effects of Fluctuating Soil Temperature and Water Potential on Sclerotia Germination and Apothecial Production of Sclerotinia sclerotiorum
Authors: Mila A. L. , Yang X. B.
Published: December 2007

The effects of fluctuating soil temperature and water potential on sclerotial germination and apothecial production by Sclerotinia sclerotiorum were investigated in growth chamber experiments. In the temperature experiments, temperature fluctuations of 4, 8, 12, and 16°C around a median of 20°C, and a constant of 20°C, were tested. Daily temperature fluctuations of 8°C resulted in highest levels of sclerotial germination and apothecial production. The earliest appearance of apothecia occurred in the 8°C fluctuation treatment, 24 days after the start of the experiment. Sclerotia in the 12°C fluctuation treatment germinated last; its first sclerotium germinated 44 days after experiment initiation. For the soil water potential experiments, constant saturation (approximately –0.001 MPa) and three levels of soil water potential fluctuation from saturation—“low” (–0.03 to –0.04 MPa), “medium” (–0.06 to –0.07 MPa), and “high” (–0.09 to –0.1 MPa)—were tested. Constant saturation yielded the highest number of germinated sclerotia and apothecia. All soil water potential fluctuations were detrimental to sclerotial germination and apothecial production, with sclerotial germination under fluctuating moisture conditions less than a tenth of that occurring under constant saturation. The first sclerotium in the constant saturation treatment germinated in 35 days; however, 76 days were required in the high soil water potential fluctuation treatment.
A Novel Source of Resistance in Wheat to Pyrenophora tritici-repentis Race 1
Authors: Singh Sukhwinder , Bockus William W. , Sharma Indu , Bowden Robert L.
Published: December 2007

Tan spot, caused by the fungus Pyrenophora tritici-repentis, causes serious yield losses in wheat (Triticum aestivum) and many other grasses. Race 1 of the fungus, which produces the necrosis toxin Ptr ToxA and the chlorosis toxin Ptr ToxC, is the most prevalent race in the Great Plains of the United States. Wheat genotypes with useful levels of resistance to race 1 have been deployed, but this resistance reduces damage by only 50 to 75%. Therefore, new sources of resistance to P. tritici-repentis are needed. Recombinant inbred lines developed from a cross between the Indian spring wheat cvs. WH542 (resistant) and HD29 (moderately susceptible) were evaluated for reaction to race 1 of the fungus. Composite interval mapping revealed quantitative trait loci (QTL) on the short arm of chromosome 3A explaining 23% of the phenotypic variation, and the long arm of chromosome 5B explaining 27% of the variation. Both resistance alleles were contributed by the WH542 parent. The QTL on 5BL is probably tsn1, which was described previously. The 3AS QTL (QTs.ksu-3AS) on 3AS is a novel QTL for resistance to P. tritici-repentis race 1. The QTL region is located in the most distal bin of chromosome 3AS in a 2.2-centimorgan marker interval. Flanking markers Xbarc45 and Xbarc86 are suitable for marker-assisted selection for tan spot resistance.
Improved Microassays Used to Test Natural Product-Based and Conventional Fungicides on Plant Pathogenic Fungi
Authors: Abril Maritza , Curry Kenneth J. , Smith Barbara J. , Wedge David E.
Published: December 2007

Seven important plant pathogenic fungi (Botrytis cinerea, Colletotrichum acutatum, C. fragariae, C. gloeosporioides, Fusarium oxysporum, Phomopsis obscurans, and P. viticola) valuable in screening fungicides were tested. Our procedure included washing conidia to reduce germination times, incorporating Roswell Park Memorial Institute 1640 as a medium of known composition, and using coverslips in the 24-well cell culture clusters to document the effect of fungicides on fungal morphology. The natural product-based fungicide, sampangine, a sampangine analog, 4-bromosampangine, plus seven conventional fungicides (benomyl, captan, cyprodinil, fenbuconazole, fenhexamid, iprodione, and kresoxim-methyl) were tested in vitro for their ability to inhibit germination and growth of the seven fungal species. Sampangine inhibited germination in all fungi except C. acutatum. Comparison of results of germination and morphology microbioassays with results of microtiter assays suggests that some fungicides stop fungal germination, whereas others only slow down fungal growth. We hypothesize that sampangine, except against C. acutatum, has the same physical mode of action, germination inhibition, as the conventional fungicides captan, iprodione, and kresoxim-methyl. 4-Bromosampangine caused morphological anomalies including excessive branching of germ tubes of C. fragariae and splaying and branching of germ tubes of B. cinerea.
Insect Vectors (Hemiptera: Cixiidae) and Pathogens Associated with the Disease Syndrome “Basses Richesses” of Sugar Beet in France
Authors: Bressan Alberto , Sémétey Olivier , Nusillard Benoit , Clair Denis , Boudon-Padieu Elisabeth
Published: December 2007

The syndrome “basses richesses” (SBR) is a disease of sugar beet in eastern France associated with two phloem-restricted, nonculturable plant pathogens: a stolbur phytoplasma and a γ-3 proteobacterium, here called SBR bacterium. Three planthopper (Hemiptera: Cixiidae) species were found to live near and within sugar beet fields in eastern France: Cixius wagneri, Hyalesthes obsoletus, and Pentastiridius leporinus. The role of these planthoppers in spreading the two pathogens to sugar beet was studied. Based on its abundance and high frequency of infection with the SBR bacterium, P. leporinus was considered to be the economic vector of SBR disease. C. wagneri, the primary vector of ‘Candidatus Phlomobacter fragariae’ to strawberry in western France, also was found to be infected by the SBR bacterium and to transmit the pathogen to sugar beet. Neither C. wagneri nor P. leporinus were infected by stolbur phytoplasma. Populations of H. obsoletus living on bindweed (Convolvulus arvensis) and nettle (Urtica dioica) collected near sugar beet fields did not carry the SBR bacterium, but were highly infected with two restriction fragment length polymorphism-differentiable stolbur phytoplasma isolates. In transmission assays, only the bindweed phytoplasma isolate was transmissible to and pathogenic on sugar beet. When compared with controls, the bindweed stolbur phytoplasma and SBR bacterium similarly reduced the biomass of sugar beet plants, but the phytoplasma caused greater reductions in taproot biomass and sugar content than the SBR bacterium.