150 research outputs found
Prevalence of QoI resistance and mtDNA diversity in the Irish Zymoseptoria tritici population
peer-reviewedThe emergence and spread of Quinone outside Inhibitor (QoI) fungicide resistance in the Irish Zymoseptoria tritici population in the early 2000s had immediate impacts on the efficacy of the entire group of fungicides for the control of septoria tritici blotch. As a result, a dramatic reduction in the quantities applied to winter wheat occurred in the following seasons. Even in the absence of these fungicides, the frequency of the resistance allele, G143A in the pathogens mtDNA has remained exceptionally high (>97%), and as such, it can be anticipated that continued poor efficacy of current QoI fungicides will be observed. Amongst the isolates with G143A, differences in sensitivity to the QoI pyraclostrobin were observed in vitro. The addition of the alternative oxidase (AOX) inhibitor salicylhydroxamic acid increased sensitivity in these isolates, suggesting some continued impairment of respiration by the QoI fungicides, albeit weak. Interestingly, amongst those tested, the strains from a site with a high frequency of inserts in the MFS1 transporter gene known to enhance QoI efflux did not exhibit this increase in sensitivity. A total of 19 mtDNA haplotypes were detected amongst the 2017 strain collection. Phylogenetic analysis confirmed the suggestion of a common ancestry of all the haplotypes, even though three of the haplotypes contained at least one sensitive strain
Evolution of decreased sensitivity to azole fungicides in western European populations of Plenodomus lingam (cause of Phoma leaf spot / stem canker on oilseed rape)
Plenodomus lingam (Leptosphaeria maculans) and P. biglobosus (L. biglobosa) are related fungal pathogens causing Phoma leaf spot and stem canker, an internationally damaging disease of oilseed rape (Brassica napus) and other brassicas. In Europe, fungicides used for disease management are mainly sterol 14α-demethylase (CYP51) inhibitors (DMIs/azoles); quinone outside inhibitors (QoIs), and succinate dehydrogenase inhibitors (SDHIs) are also used. Decreased DMI sensitivity has emerged in Australian and eastern European P. lingam populations. Decreased sensitivity is mediated by promoter inserts in CYP51 resulting in target site overexpression. In the present study, based on in vitro sensitivity testing, we report decreased DMI (prothioconazole-desthio and mefentrifluconazole) sensitivity in modern western European isolates of P. lingam (collected 2022-23) compared to baseline historical (1992-2005) isolates. Around 85% of the modern western European P. lingam isolates collected, for which the CYP51 promoter region was sequenced, carried a promoter insert but target site alterations were not detected. Six different CYP51 promoter inserts were identified, with a 237 bp fragment of the Sahana transposable element most frequently detected. Inserts were typically associated with a 3 to 10 fold decrease in sensitivity to the DMIs tested. In contrast to P. lingam, PCR screening revealed that CYP51 promoter inserts were absent in modern western European P. biglobosus isolates (collected 2021-23). The combined data indicate P. lingam isolates lacking an insert were similarly (or slightly more) sensitive to the DMIs tested for P. biglobosus, whereas those carrying an insert were slightly less sensitive than P. biglobosus. No clear evidence for substantive sensitivity shifts to the QoI (pyraclostrobin) or SDHI (boscalid) fungicides tested was obtained for either Plenodomus species
Observations of the BL Lac Object 3C 66A with STACEE
We present the analysis and results of recent high-energy gamma-ray
observations of the BL Lac object 3C 66A conducted with the Solar Tower
Atmospheric Cherenkov Effect Experiment (STACEE). During the 2003-2004
observing season, STACEE extensively observed 3C 66A as part of a
multiwavelength campaign on the source. A total of 33.7 hours of data was taken
on the source, plus an equivalent-duration background observation. After
cleaning the data set a total of 16.3 hours of live time remained, and a net
on-source excess of 1134 events was seen against a background of 231742 events.
At a significance of 2.2 standard deviations this excess is insufficient to
claim a detection of 3C 66A, but is used to establish flux upper limits for the
source.Comment: Accepted for publication in the Astrophysical Journa
New constraints on Planck-scale Lorentz Violation in QED from the Crab Nebula
We set constraints on O(E/M) Lorentz Violation in QED in an effective field
theory framework. A major consequence of such assumptions is the modification
of the dispersion relations for electrons/positrons and photons, which in turn
can affect the electromagnetic output of astrophysical objects. We compare the
information provided by multiwavelength observations with a full and
self-consistent computation of the broad-band spectrum of the Crab Nebula. We
cast constraints of order 10^{-5} at 95% confidence level on the lepton Lorentz
Violation parameters.Comment: 23 pages, 9 figures. v2: added comments and references, matches
version accepted by JCA
Multiwavelength Observations of Markarian 421 in March 2001: an Unprecedented View on the X-ray/TeV Correlated Variability
(Abridged) We present a detailed analysis of week-long simultaneous
observations of the blazar Mrk421 at 2-60 keV X-rays (RXTE) and TeV gamma-rays
(Whipple and HEGRA) in 2001. The unprecedented quality of this dataset enables
us to establish firmly the existence of the correlation between the TeV and
X-ray luminosities, and to start unveiling some of its more detailed
characteristics, in particular its energy dependence, and time variability. The
source shows strong, highly correlated variations in X-ray and gamma-ray. No
evidence of X-ray/gamma-ray interband lag is found on the full week dataset (<3
ks). However, a detailed analysis of the March 19 flare reveals that data are
not consistent with the peak of the outburst in the 2-4 keV X-ray and TeV band
being simultaneous. We estimate a 2.1+/-0.7 ks TeV lag. The amplitudes of the
X-ray and gamma-ray variations are also highly correlated, and the TeV
luminosity increases more than linearly w.r.t. the X-ray one. The strong
correlation supports the standard model in which a unique electrons population
produces the X-rays by synchrotron radiation and the gamma-ray component by
inverse Compton scattering. However, for the individual best observed flares
the gamma-ray flux scales approximately quadratically w.r.t. the X-ray flux,
posing a serious challenge to emission models for TeV blazars. Rather special
conditions and/or fine tuning of the temporal evolution of the physical
parameters of the emission region are required in order to reproduce the
quadratic correlation.Comment: Correction to authorship. Minor editorial changes to text, figures,
references. 22 pages (emulateapj), 12 figures (47 postscript files) Published
in ApJ, 2008 April 20 (ADS: 2008ApJ...677..906F
Search for Primordial Black Holes with SGARFACE
The Short GAmma Ray Front Air Cherenkov Experiment (SGARFACE) uses the
Whipple 10 m telescope to search for bursts of rays. SGARFACE is
sensitive to bursts with duration from a few ns to 20 s and with
-ray energy above 100 MeV. SGARFACE began operating in March 2003 and
has collected 2.2 million events during an exposure time of 2267 hours. A
search for bursts of rays from explosions of primordial black holes
(PBH) was carried out. A Hagedorn-type PBH explosion is predicted to be visible
within 60 pc of Earth. Background events were caused by cosmic rays and by
atmospheric phenomena and their rejection was accomplished to a large extent
using the time-resolved images. No unambiguous detection of bursts of
rays could be made as the remaining background events mimic the expected shape
and time development of bursts. Upper limits on the PBH explosion rate were
derived from the SGARFACE data and are compared to previous and future
experiments. We note that a future array of large wide-field air-Cherenkov
telescopes equipped with a SGARFACE-like trigger would be able to operate
background-free with a 20 to 30 times higher sensitivity for PBH explosions.Comment: 18 pages, 30 figures, accepted by Astroparticle Physics, corrected
author list and Section 2.
A Search for Dark Matter Annihilation with the Whipple 10m Telescope
We present observations of the dwarf galaxies Draco and Ursa Minor, the local
group galaxies M32 and M33, and the globular cluster M15 conducted with the
Whipple 10m gamma-ray telescope to search for the gamma-ray signature of
self-annihilating weakly interacting massive particles (WIMPs) which may
constitute astrophysical dark matter (DM). We review the motivations for
selecting these sources based on their unique astrophysical environments and
report the results of the data analysis which produced upper limits on excess
rate of gamma rays for each source. We consider models for the DM distribution
in each source based on the available observational constraints and discuss
possible scenarios for the enhancement of the gamma-ray luminosity. Limits on
the thermally averaged product of the total self-annihilation cross section and
velocity of the WIMP, , are derived using conservative estimates for
the magnitude of the astrophysical contribution to the gamma-ray flux. Although
these limits do not constrain predictions from the currently favored
theoretical models of supersymmetry (SUSY), future observations with VERITAS
will probe a larger region of the WIMP parameter phase space, and
WIMP particle mass (m_\chi).Comment: 33 pages, 12 figures, accepted for publication in the Astrophysical
Journa
Multiwavelength Observations of the Blazar Mrk 421 in December 2002 and January 2003
We report on a multiwavelength campaign on the TeV gamma-ray blazar Markarian
(Mrk) 421 performed during December 2002 and January 2003. These target of
opportunity observations were initiated by the detection of X-ray and TeV
gamma-ray flares with the All Sky Monitor (ASM) on board the Rossi X-ray Timing
Explorer (RXTE) and the 10 m Whipple gamma-ray telescope.The campaign included
observational coverage in the radio (University of Michigan Radio Astronomy
Observatory), optical (Boltwood, La Palma KVA 0.6m, WIYN 0.9m), X-ray (RXTE
pointed telescopes), and TeV gamma-ray (Whipple and HEGRA) bands.
At TeV energies, the observations revealed several flares at intermediate
flux levels, peaking between 1 and 1.5 times the flux from the Crab Nebula.
While the time averaged spectrum can be fitted with a single power law of
photon index Gamma =2.8, we find some evidence for spectral variability.
Confirming earlier results, the campaign reveals a rather loose correlation
between the X-ray and TeV gamma-ray fluxes. In one case, a very strong X-ray
flare is not accompanied by a comparable TeV gamma-ray flare. Although the
source flux was variable in the optical and radio bands, the sparse sampling of
the optical and radio light curves does not allow us to study the correlation
properties in detail.
We present a simple analysis of the data with a synchrotron-self Compton
model, emphasizing that models with very high Doppler factors and low magnetic
fields can describe the data.Comment: Accepted for publication in the Astrophysical Journa
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