713 research outputs found
Effect of time of harvest on the incidence of Fusarium spp. in kernels of silage corn
The effect of time of harvest (at 75, 50 and 25% of milkline) on the incidence of kernel-borne Fusarium spp. was examined in four silage corn (Zea mays) hybrids (MAIZEX Leafy 4, NK BRAND Enerfeast 1, PIONEER 37M81 and MYCOGEN TMF94) in Ottawa, Ontario, in 2001 and 2002. Eleven Fusarium species were isolated over the 2 yr. Fusarium subglutinans was the dominant species recovered from 28.8% of the kernels. Other frequently isolated species included F. oxysporum (2.6%), F. graminearum (2.5%), F. proliferatum (0.3%) and F. sporotrichioides (0.2%). Trace amounts (< 0.1%) of the remaining six species, F. avenaceum, F. crookwellense, F. culmorum, F. equiseti and F. solani, were recovered from the kernels. When the kernels were harvested at 75, 50 and 25% of milkline, the incidence of F. subglutinans increased from 20.9 to 26.7 and to 38.7%, respectively; that of F. graminearum increased from 1.7 to 2.9 and to 3.1%; and for the total of the five main Fusarium species it increased from 28.7 to 32.2 and to 42.3%. Incidence of the other species was not affected by harvesting date. Of the four silage corn hybrids, NK BRAND Enerfeast1 had a significantly lower incidence of Fusarium species in kernels than the other hybrids, indicating a genotypic variation in resistance to kernel-borne infection by Fusarium species.Lâeffet de trois temps de rĂ©colte, correspondant Ă 75, 50 et 25 % de lâĂ©tat laiteux, sur lâincidence des espĂšces de Fusarium a Ă©tĂ© Ă©tudiĂ© chez les grains de quatre hybrides de maĂŻs (Zea mays) ensilage (MAIZEX Leafy 4, NK BRAND Enerfeast 1, PIONEER 37M81 et MYCOGEN TMF94) en 2001 et 2002 Ă Ottawa, en Ontario. Onze espĂšces de Fusarium ont Ă©tĂ© isolĂ©es pendant ces deux annĂ©es. Le F. subglutinans a Ă©tĂ© lâespĂšce dominante, trouvĂ©e sur 28,8 % des grains. Les autres espĂšces dĂ©tectĂ©es ont Ă©tĂ© les F. oxysporum (2,6 %), F. graminearum (2,5 %), F. proliferatum (0,3 %) et F. sporotrichioides (0,2 %). Des traces (< 0,1 %) des six autres espĂšces, les F. avenaceum, F. crookwellense, F. culmorum, F. equiseti et F. solani, ont aussi Ă©tĂ© dĂ©tectĂ©es sur les grains. Lâincidence du F. subglutinans a augmentĂ© respectivement de 20,9 Ă 26,7 puis Ă 38,7 % en fonction du temps de rĂ©colte (75, 50 et 25 % de lâĂ©tat laiteux), tandis quâelle a augmentĂ© de 1,7 Ă 2,8 puis Ă 3,1 % pour le F. graminearum et de 28,7 Ă 32,2 puis Ă 42,3 % pour les cinq espĂšces principales confondues. Lâincidence des autres espĂšces nâa pas Ă©tĂ© affectĂ©e par les dates de rĂ©colte. Parmi les quatre hybrides Ă lâessai, lâhybride commercial NK BRAND Enerfeast1 a eu la plus basse incidence dâespĂšces de Fusarium dans le grain, ce qui indique quâil existe une variation gĂ©notypique de la rĂ©sistance des grains aux infections causĂ©es par les espĂšces de Fusarium
Pathogenicity of Fusarium species causing head blight in barley
The pathogenicity of eight Fusarium species causing fusarium head blight (FHB) in barley was studied under controlled conditions. Six barley genotypes varying in resistance to FHB were artificially inoculated with six isolates each of F. acuminatum, F. avenaceum, F. crookwellense, F. culmorum, F. equiseti, F. graminearum, F. poae and F. sporotrichioides 10-14 d after heading. Symptoms of FHB were rated as disease severity using a 0-9 scale, 4, 7, 14, 21 and 28 d after inoculation, and as percentage of infected spikelets (IS) after 21 d. All species tested caused head blight symptoms on the barley genotypes, but only F. crookwellense, F. culmorum and F. graminearum resulted in severe disease development (> 65% IS) and were considered highly pathogenic. Fusarium avenaceum had 48% IS, which was significantly lower than those of the three highly pathogenic species and was moderately pathogenic. The remaining species had 65 %) et ont Ă©tĂ© considĂ©rĂ©s comme fortement pathogĂšnes. Avec un PĂI de 48 %, qui Ă©tait significativement infĂ©rieur Ă ceux des trois espĂšces les plus pathogĂšnes, le Fusarium avenaceum a Ă©tĂ© considĂ©rĂ© comme moyennement pathogĂšne. Les autres espĂšces ont eu un PĂI de moins de 15 % et ont Ă©tĂ© considĂ©rĂ©es comme faiblement pathogĂšnes. Des diffĂ©rences significatives (P < 0,05) ont Ă©tĂ© observĂ©es entre les espĂšces pour l'agressivitĂ© parmi les isolats et pour la sensibilitĂ© parmi les gĂ©notypes d'orge, ce qui suggĂšre que le tri pour la rĂ©sistance Ă la FĂ doit faire appel Ă des isolats agressifs ou Ă un mĂ©lange de plusieurs isolats. C'est la premiĂšre fois que le F. crookwellense est signalĂ© comme fortement pathogĂšne et le F. avenaceum comme moyennement pathogĂšne sur l'orge
Non-Fermi liquid angle resolved photoemission lineshapes of Li0.9Mo6O17
A recent letter by Xue et al. (PRL v.83, 1235 ('99)) reports a Fermi-Liquid
(FL) angle resolved photoemission (ARPES) lineshape for quasi one-dimensional
Li0.9Mo6O17, contradicting our report (PRL v.82, 2540 ('99)) of a non-FL
lineshape in this material. Xue et al. attributed the difference to the
improved angle resolution. In this comment, we point out that this reasoning is
flawed. Rather, we find that their data have fundamental differences from other
ARPES results and also band theory.Comment: To be published as a PRL Commen
X-ray Bright Active Galactic Nuclei in Massive Galaxy Clusters II: The Fraction of Galaxies Hosting Active Nuclei
We present a measurement of the fraction of cluster galaxies hosting X-ray
bright Active Galactic Nuclei (AGN) as a function of clustercentric distance
scaled in units of . Our analysis employs high quality Chandra X-ray
and Subaru optical imaging for 42 massive X-ray selected galaxy cluster fields
spanning the redshift range of . In total, our study involves
176 AGN with bright () optical counterparts above a keV flux
limit of . When excluding
central dominant galaxies from the calculation, we measure a cluster-galaxy AGN
fraction in the central regions of the clusters that is times lower
that the field value. This fraction increases with clustercentric distance
before becoming consistent with the field at . Our data
exhibit similar radial trends to those observed for star formation and
optically selected AGN in cluster member galaxies, both of which are also
suppressed near cluster centers to a comparable extent. These results strongly
support the idea that X-ray AGN activity and strong star formation are linked
through their common dependence on available reservoirs of cold gas.Comment: 9 Pages, 4 Figures, accepted for publication in MNRAS, please contact
Steven Ehlert ([email protected]) with any querie
X-ray bright active galactic nuclei in massive galaxy clusters III: New insights into the triggering mechanisms of cluster AGN
We present the results of a new analysis of the X-ray selected Active
Galactic Nuclei (AGN) population in the vicinity of 135 of the most massive
galaxy clusters in the redshift range of 0.2 < z < 0.9 observed with Chandra.
With a sample of more than 11,000 X-ray point sources, we are able to measure,
for the first time, evidence for evolution in the cluster AGN population beyond
the expected evolution of field AGN. Our analysis shows that overall number
density of cluster AGN scales with the cluster mass as .
There is no evidence for the overall number density of cluster member X-ray AGN
depending on the cluster redshift in a manner different than field AGN, nor
there is any evidence that the spatial distribution of cluster AGN (given in
units of the cluster overdensity radius r_500) strongly depends on the cluster
mass or redshift. The scaling relation we measure is
consistent with theoretical predictions of the galaxy merger rate in clusters,
which is expected to scale with the cluster velocity dispersion, , as or . This consistency suggests that AGN in
clusters may be predominantly triggered by galaxy mergers, a result that is
further corroborated by visual inspection of Hubble images for 23
spectroscopically confirmed cluster member AGN in our sample. A merger-driven
scenario for the triggering of X-ray AGN is not strongly favored by studies of
field galaxies, however, suggesting that different mechanisms may be primarily
responsible for the triggering of cluster and field X-ray AGN.Comment: 21 Pages, 8 figures, 5 tables. Submitted to MNRAS. Comments are
welcome, and please request Steven Ehlert for higher resolution figure
Stable Mode Sorting by Two-Dimensional Parity of Photonic Transverse Spatial States
We describe a mode sorter for two-dimensional parity of transverse spatial
states of light based on an out-of-plane Sagnac interferometer. Both
Hermite-Gauss (HG) and Laguerre-Gauss (LG) modes can be guided into one of two
output ports according to the two-dimensional parity of the mode in question.
Our interferometer sorts HG_nm input modes depending upon whether they have
even or odd order n+m; it equivalently sorts LG modes depending upon whether
they have an even or odd value of their orbital angular momentum. It functions
efficiently at the single-photon level, and therefore can be used to sort
single-photon states. Due to the inherent phase stability of this type of
interferometer as compared to those of the Mach-Zehnder type, it provides a
promising tool for the manipulation and filtering of higher order transverse
spatial modes for the purposes of quantum information processing. For example,
several similar Sagnacs cascaded together may allow, for the first time, a
stable measurement of the orbital angular momentum of a true single-photon
state. Furthermore, as an alternative to well-known holographic techniques, one
can use the Sagnac in conjunction with a multi-mode fiber as a spatial mode
filter, which can be used to produce spatial-mode entangled Bell states and
heralded single photons in arbitrary first-order (n+m=1) spatial states,
covering the entire Poincare sphere of first-order transverse modes.Comment: 11 pages, 12 figures, 2 appendice
Deep images of cluster radio halos
New radio data are presented for the clusters A401, A545, A754, A1914, A2219
and A2390, where the presence of diffuse radio emission was suggested from the
images of the NRAO VLA Sky Survey. Sensitive images of these clusters, obtained
with the Very Large Array (VLA)at 20 cm confirm the existence of the diffuse
sources and allow us to derive their fluxes and intrinsic parameters.The
correlation between the halo radio power and cluster X-ray luminosity is
derived for a large sample of halo clusters, and is briefly discussed.Comment: 9 pages, 13 figures, Astron. Astrophys. in pres
X-ray Bright Active Galactic Nuclei in Massive Galaxy Clusters I: Number Counts and Spatial Distribution
We present an analysis of the X-ray bright point source population in 43
massive clusters of galaxies observed with the Chandra X-ray Observatory. We
have constructed a catalog of 4210 rigorously selected X-ray point sources in
these fields, which span a survey area of 4.2 square degrees. This catalog
reveals a clear excess of sources when compared to deep blank-field surveys,
which amounts to roughly 1 additional source per cluster, likely Active
Galactic Nuclei (AGN) associated with the clusters. The excess sources are
concentrated within the virial radii of the clusters, with the largest excess
observed near the cluster centers. The average radial profile of the excess
X-ray sources of the cluster are well described by a power law (N(r) ~ r^\beta)
with an index of \beta ~ -0.5. An initial analysis using literature results on
the mean profile of member galaxies in massive X-ray selected clusters
indicates that the fraction of galaxies hosting X-ray AGN rises with increasing
clustercentric radius, being approximately 5 to 10 times higher near the virial
radius than in the central regions. This trend is qualitatively similar to that
observed for star formation in cluster member galaxies.Comment: 18 Pages, 10 Figures, Submitted to MNRAS. Please contact Steven
Ehlert ([email protected]) for higher resolution figures. Updated to
reflect small changes requested by referee. This version has been accepted
into MNRA
XMM-Newton study of the lensing cluster of galaxies CL0024+17
We present a detailed gravitational mass measurement based on the XMM-Newton
imaging spectroscopy analysis of the lensing cluster of galaxies CL0024+17 at
z=0.395. The emission appears approximately symmetric. However, on the scale of
r~3.3' some indication of elongation is visible in the northwest-southeast
(NW-SE) direction from the hardness ratio map (HRM). Within 3', we measure a
global gas temperature of 3.52\pm0.17 keV, metallicity of 0.22\pm0.07, and
bolometric luminosity of 2.9\pm0.1 \times 10^{44} h^{-2}_{70} erg/s. We derive
a temperature distribution with an isothermal temperature of 3.9 keV to a
radius of 1.5' and a temperature gradient in the outskirts (1.3<r<3'). Under
the assumption of hydrostatic equilibrium, we measure gravitational mass and
gas mass fraction to be M_{200}=2.0\pm0.3 \times 10^{14} h_{70}^{-1} M_{\odot}
and f_{\rm gas}=0.20\pm0.03 h^{-3/2}_{70} at r_{200}=1.05 h^{-1}_{70} Mpc using
the observed temperature profile. The complex structure in the core region is
the key to explaining the discrepancy in gravitational mass determined from
XMM-Newton X-ray observations and HST optical lensing measurements.Comment: 16 pages, 12 figures, to appear in A&
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