1,618 research outputs found
Pyramiding of Ryd2 and Ryd3 conferring tolerance to a German isolate of Barley yellow dwarf virus-PAV (BYDV-PAV-ASL-1) leads to quantitative resistance against this isolate
Barley yellow dwarf virus (BYDV) is an economically important pathogen of barley, which may become even more important due to global warming. In barley, several loci conferring tolerance to BYDV-PAV-ASL-1 are known, e.g. Ryd2, Ryd3 and a quantitative trait locus (QTL) on chromosome 2H. The aim of the present study was to get information whether the level of tolerance against this isolate of BYDV in barley can be improved by combining these loci. Therefore, a winter and a spring barley population of doubled haploid (DH) lines were genotyped by molecular markers for the presence of the susceptibility or the resistance encoding allele at respective loci (Ryd2, Ryd3, QTL on chromosome 2H) and were tested for their level of BYDV-tolerance after inoculation with viruliferous (BYDV-PAV-ASL-1) aphids in field trials. In DH-lines carrying the combination Ryd2 and Ryd3, a significant reduction of the virus titre was detected as compared to lines carrying only one of these genes. Furthermore, spring barley DH-lines with this allele combination also showed a significantly higher relative grain yield as compared to lines carrying only Ryd2 or Ryd3. The QTL on chromosome 2H had only a small effect on the level of tolerance in those lines carrying only Ryd2, or Ryd3 or a combination of both, but the effect in comparison to lines carrying no tolerance allele was significant. Overall, these results show that the combination of Ryd2 and Ryd3 leads to quantitative resistance against BYDV-PAV instead of tolerance
Resonances in a spring-pendulum: algorithms for equivariant singularity theory
A spring-pendulum in resonance is a time-independent Hamiltonian model system for formal reduction to one degree of freedom, where some symmetry (reversibility) is maintained. The reduction is handled by equivariant singularity theory with a distinguished parameter, yielding an integrable approximation of the Poincaré map. This makes a concise description of certain bifurcations possible. The computation of reparametrizations from normal form to the actual system is performed by Gröbner basis techniques.
Pacer cell response to periodic Zeitgebers
Almost all organisms show some kind of time periodicity in their behavior.
Especially in mammals the neurons of the suprachiasmatic nucleus form a
biological clock regulating the activity-inactivity cycle of the animal. This
clock is stimulated by the natural 24-hour light-dark cycle. In our model of
this system we consider each neuron as a so called phase oscillator, coupled to
other neurons for which the light-dark cycle is a Zeitgeber. To simplify the
model we first take an externally stimulated single phase oscillator. The first
part of the phase interval is called the active state and the remaining part is
the inactive state. Without external stimulus the oscillator oscillates with
its intrinsic period. An external stimulus, be it from activity of neighboring
cells or the periodic daylight cycle, acts twofold, it may delay the change
form active to inactive and it may advance the return to the active state. The
amount of delay and advance depends on the strength of the stimulus. We use a
circle map as a mathematical model for this system. This map depends on several
parameters, among which the intrinsic period and phase delay and advance. In
parameter space we find Arnol'd tongues where the system is in resonance with
the Zeitgeber. Thus already in this simplified system we find entrainment and
synchronization. Also some other phenomena from biological experiments and
observations can be related to the dynamical behavior of the circle map
Circular dichroism of cholesteric polymers and the orbital angular momentum of light
We explore experimentally if the light's orbital angular momentum (OAM)
interacts with chiral nematic polymer films. Specifically, we measure the
circular dichroism of such a material using light beams with different OAM. We
investigate the case of strongly focussed, non-paraxial light beams, where the
spatial and polarization degrees of freedom are coupled. Within the
experimental accuracy, we cannot find any influence of the OAM on the circular
dichroism of the cholesteric polymer.Comment: 3 pages, 4 figure
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