5,535 research outputs found
Development of a rapid and highly sensitive direct-PCR assay to detect a single conidium of Botrytis cinerea Pers.:Fr in vitro and quiescent forms in planta
“Direct-PCR” amplifications of Botrytis cinerea-specific genomic sequences, without any DNA purification step or time consuming sample preparation, were developed. A single copy sequence of 0.7 Kb in the Botrytis cinerea genome was amplified in reactions containing no more than 1 x 105 to 1 single conidium. As a demonstrative application, this assay was applied to detect B. cinerea in different parts of immature grape berries (at ‘pea size’), when previously inoculated with conidia at flowering. Using this method we showed the presence of quiescent Botrytis in the receptacle area only. Cloning and sequencing of the fragment confirmed the single sequence gene of B. cinerea. These results demonstrate that the method is easy to apply and of sufficiently high sensitivity to detect the presence of B. cinerea in immature grape berries. Its use for studies on the development of grey mould and improved control of the disease in vineyards is discussed
Effects of resveratrol, viniferins and pterostilbene on Plasmopara viticola zoospore mobility and disease development
The effects of stilbenes (resveratrol, δ- and ε-viniferins, and pterostilbene) on the mobility of zoospores of Plasmopara viticola and on subsequent disease development were studied in vitro. δ-viniferin and pterostilbene are the most toxic stilbenes concerning zoospore mobility (ED50 : 14.6 and 28.3 μM) and disease development (ED50 : 14.7 and 12.7 μM). The analysis of stilbenes in leaf cells of resistant (Solaris) and susceptible (Chasselas) grape cultivars artificially inoculated with P. viticola has shown that very high amounts of stilbenic phytoalexins accumulate at the site of infection of the resistant cultivar compared to the susceptible one
Magnetic resonance spectroscopy of perpendicularly magnetized permalloy multilayer disks
Using a Magnetic Resonance Force Microscope, we compare the ferromagnetic
resonance spectra of individual micron-size disks with identical diameter, 1
m, but different layer structures. For a disk composed of a single 43.3 nm
thick permalloy (Py) layer, the lowest energy mode in the perpendicular
configuration is the uniform precession. The higher energy modes are standing
spin-waves confined along the diameter of the disk. For a Cu(30)/Py(100)/Cu(30)
nm multilayer structure, it has been interpreted that the lowest energy mode
becomes a precession localized at the Cu/Py interfaces. When the multilayer is
changed to Py(100)/Cu(10)/Py(10) nm, this localized mode of the thick layer is
coupled to the precession of the thin layer
Nanoscale Suppression of Magnetization at Atomically Assembled Manganite Interfaces
Using polarized X-rays, we compare the electronic and magnetic properties of
a La(2/3)Sr(1/3)MnO(3)(LSMO)/SrTiO(3)(STO) and a modified
LSMO/LaMnO(3)(LMO)/STO interface. Using the technique of X-ray resonant
magnetic scattering (XRMS), we can probe the interfaces of complicated layered
structures and quantitatively model depth-dependent magnetic profiles as a
function of distance from the interface. Comparisons of the average electronic
and magnetic properties at the interface are made independently using X-ray
absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). The
XAS and the XMCD demonstrate that the electronic and magnetic structure of the
LMO layer at the modified interface is qualitatively equivalent to the
underlying LSMO film. From the temperature dependence of the XMCD, it is found
that the near surface magnetization for both interfaces falls off faster than
the bulk. For all temperatures in the range of 50K - 300K, the magnetic
profiles for both systems always show a ferromagnetic component at the
interface with a significantly suppressed magnetization that evolves to the
bulk value over a length scale of ~1.6 - 2.4 nm. The LSMO/LMO/STO interface
shows a larger ferromagnetic (FM) moment than the LSMO/STO interface, however
the difference is only substantial at low temperature.Comment: 4 pages, 4 figure
Histological and biochemical criteria for objective and early selection of grapevine cultivars resistant to Plasmopara viticola
Grapevine breeding is the most effective way to create cultivars resistant to downy mildew (Plasmopara viticola), and to reduce the number of fungicide applications. Four criteria, including histological and biochemical analyses, based on the level of different mechanisms of resistance to grapevine downy mildew, were tested on 42 different cultivars. Plantlets were artificially inoculated with downy mildew and the sporangia density was measured spectrophotometrically 6 d after infection. Callose synthesis in stomata and δ- and ε-viniferin levels at the site of infection were recorded 48 h after inoculation. These observations have allowed the 42 cultivars to be divided into 5 groups: very resistant (VR), resistant (R), less susceptible (LS), susceptible (S) and highly susceptible (HS). All 4 criteria have to be applied to assign the resistance level closer to field conditions. This method allows to rapidly evaluate the level of resistance of seedlings to downy mildew thereby leading to a reduction in duration of the breeding program by several years.
Electronic control of the spin-wave damping in a magnetic insulator
It is demonstrated that the decay time of spin-wave modes existing in a
magnetic insulator can be reduced or enhanced by injecting an in-plane dc
current, , in an adjacent normal metal with strong spin-orbit
interaction. The demonstration rests upon the measurement of the ferromagnetic
resonance linewidth as a function of in a 5~m diameter
YIG(20nm){\textbar}Pt(7nm) disk using a magnetic resonance force microscope
(MRFM). Complete compensation of the damping of the fundamental mode is
obtained for a current density of , in
agreement with theoretical predictions. At this critical threshold the MRFM
detects a small change of static magnetization, a behavior consistent with the
onset of an auto-oscillation regime.Comment: 6 pages 4 figure
Suppressed Magnetization at the Surfaces and Interfaces of Ferromagnetic Metallic Manganites
What happens to ferromagnetism at the surfaces and interfaces of manganites?
With the competition between charge, spin, and orbital degrees of freedom, it
is not surprising that the surface behavior may be profoundly different than
that of the bulk. Using a powerful combination of two surface probes, tunneling
and polarized x-ray interactions, this paper reviews our work on the nature of
the electronic and magnetic states at manganite surfaces and interfaces. The
general observation is that ferromagnetism is not the lowest energy state at
the surface or interface, which results in a suppression or even loss of
ferromagnetic order at the surface. Two cases will be discussed ranging from
the surface of the quasi-2D bilayer manganite
(LaSrMnO) to the 3D Perovskite
(LaSrMnO)/SrTiO interface. For the bilayer manganite,
that is, ferromagnetic and conducting in the bulk, these probes present clear
evidence for an intrinsic insulating non-ferromagnetic surface layer atop
adjacent subsurface layers that display the full bulk magnetization. This
abrupt intrinsic magnetic interface is attributed to the weak inter-bilayer
coupling native to these quasi-two-dimensional materials. This is in marked
contrast to the non-layered manganite system
(LaSrMnO/SrTiO), whose magnetization near the interface
is less than half the bulk value at low temperatures and decreases with
increasing temperature at a faster rate than the bulk.Comment: 15 pages, 13 figure
Anomalous temperature behavior of resistivity in lightly doped manganites around a metal-insulator phase transition
An unusual temperature and concentration behavior of resistivity in
has been observed at slight doping
(). Namely, introduction of copper results in a splitting of
the resistivity maximum around a metal-insulator transition temperature
into two differently evolving peaks. Unlike the original -free
maximum which steadily increases with doping, the second (satellite) peak
remains virtually unchanged for , increases for and finally
disappears at with . The observed phenomenon
is thought to arise from competition between substitution induced strengthening
of potential barriers (which hamper the charge hopping between neighboring
sites) and weakening of carrier's kinetic energy. The data are well fitted
assuming a nonthermal tunneling conductivity theory with randomly distributed
hopping sites.Comment: 10 REVTEX pages, 2 PostScript figures (epsf.sty); to be published in
JETP Letter
Anomalous spin susceptibility and magnetic polaron formation in the double exchange systems
The magnetic susceptibility and spin-spin correlation of the double-exchange
model for doped manganites are investigated through the Monte Carlo
calculations on the three-dimensional lattice model. Deviations of the
susceptibility from the Curie-Weiss behavior above the ferromagnetic ordering
temperature seem to indicate a formation of local ferromagnetic clusters
in the vicinity of , which is consistent with recent electron paramagnetic
resonance experiments for LaCaMnO. A further analysis of
the spin-spin correlations show the ferromagnetic cluster size to be
three-to-four lattice spacings, suggesting that the charge carriers may form
magnetic polarons.Comment: 5 pages, 5 figures, Late
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