19,944 research outputs found
Detección de marcadores microsatélites asociados con la resistencia al añublo bacterial de la yuca (Manihot esculenta Crantz) en Colombia
Una de las principales estrategias para el manejo del Añublo Bacterial de la Yuca (CBB), causado por Xanthomonas axonopodis pv. manihotis es el uso de resistencia varietal, que implica desarrollar variedades de yuca con resistencia genética duradera. Para tal fin, es necesario conocer los genes que dominan la resistencia a la enfermedad, detectando inicialmente marcadores moleculares asociados con la respuesta fenotipica de la planta, siendo este el principal objetivo del presente estudio. Inicialmente, se evaluó la reacción a CBB de 4 familias de yuca BCI (retrocruce 1), se seleccionó la más segregante bajo presión natural de inóculo en Villavicencio (Meta, Colombia) y se confirmó la respuesta a CBB en condiciones de invernadero en CIAT (Palmira, Valle). La familia GM 315 presentó la mejor segregación, siendo la más adecuada para buscar asociación entre su reacción fenotípica y la presencia de un marcador molecular. Para esto, se evaluaron 486 cebadores microsatélites mediante análisis de grupos segregantes (BSA), encontrándose que 17 de ellos mostraron polimorfismo entre los grupos contrastantes y solo uno de ellos, el cebador SSRY 65, mostró diferencias significativas entre individuos resistentes y susceptibles. Al evaluar este cebador en toda la familia segregante se encontró asociación entre su presencia y los individuos evaluados fenotípicamente como resistentes en campo e invernadero, con una probabilidad mínima de P=0,OOl5 y P=0,OO7 respectivamente, en una prueba de Chicuadrado de independencia. Adicionalmente, a partir de los resultados obtenidos en el análisis estadístico, se calcularon los valores predictivos, especificidad y sensibilidad del marcador SSRY 65. Con base en los valores predictivos positivos generados, es posible sugerir la utilización de este marcador en pruebas diagnósticas para detectar la presencia de una banda específica en individuos resistentes de familias genéticamente relacionadas con la familia GM 315. = A major strategy for managing Cassava Bacterial blight (CBB), caused by Xanthomonas axonopodis pv. manihotis, is to use varietal resistance, that is, to develop cassava varieties with lasting genetic resistance. A search for the genes that dominate resistance to the disease was initially conducted by seeking the molecular markers associated with the plant s phenotypic response to CBB. The response in four BC1 (backcross 1) cassava families was accordingly evaluated under natural disease pressure at Villavicencio (Meta, Colombia). The most segregating family was then selected, and its response to CBB was verified under greenhouse conditions at CIAT (Palmira, Valle). Family GM 315 presented the best segregation, so, it was the most suitable for seeking association between its phenotypic reaction and the presence of a molecular marker. Of 486 microsatellite primers evaluated by bulked segregant analysis (BSA), 17 showed polymorphism among contrasting groups. Only one primer, SSRY 65, showed significant differences between resistant and susceptible individuals. On evaluating this primer for the entire segregating family, an association was found between its presence and individuals evaluated phenotypically as resistant in the field and greenhouse (minimum P = 0.0015 and P = 0.007, respectively, in a chi-square test of independence). With the results of the statistical analysis, the predictive values, specificity, and sensibility of marker SSRY 65 were calculated. The positive predictive values generated indicate that this marker can be used in diagnostic tests to detect the presence of a specific band in resistant individuals of families genetically related to the GM 315 family
Making Ends Meet: String Unification and Low-Energy Data
A long-standing problem in string phenomenology has been the fact that the
string unification scale disagrees with the GUT scale obtained by extrapolating
low-energy data within the framework of the minimal supersymmetric standard
model (MSSM). In this paper we examine several effects that may modify the
minimal string predictions and thereby bring string-scale unification into
agreement with low-energy data. These include heavy string threshold
corrections, non-standard hypercharge normalizations, light SUSY thresholds,
intermediate gauge structure, and thresholds arising from extra matter beyond
the MSSM. We explicitly evaluate these contributions within a variety of
realistic free-fermionic string models, including the flipped SU(5), SO(6) x
SO(4), and various SU(3) x SU(2) x U(1) models, and find that most of these
sources do not substantially alter the minimal string predictions. Indeed, we
find that the only way to reconcile string unification with low-energy data is
through certain types of extra matter. Remarkably, however, many of the
realistic string models contain precisely this required matter in their
low-energy spectra.Comment: 10 pages, standard LaTeX, 1 figure (Encapsulated PostScript), version
published in Phys. Rev. Lett. 75 (1995) 264
Near-Infrared Polarimetric Adaptive Optics Observations of NGC 1068: A torus created by a hydromagnetic outflow wind
We present J' and K' imaging linear polarimetric adaptive optics observations
of NGC 1068 using MMT-Pol on the 6.5-m MMT. These observations allow us to
study the torus from a magnetohydrodynamical (MHD) framework. In a 0.5" (30 pc)
aperture at K', we find that polarisation arising from the passage of radiation
from the inner edge of the torus through magnetically aligned dust grains in
the clumps is the dominant polarisation mechanism, with an intrinsic
polarisation of 7.0%2.2%. This result yields a torus magnetic field
strength in the range of 482 mG through paramagnetic alignment, and
139 mG through the Chandrasekhar-Fermi method. The measured
position angle (P.A.) of polarisation at K is found to be similar to the
P.A. of the obscuring dusty component at few parsec scales using infrared
interferometric techniques. We show that the constant component of the magnetic
field is responsible for the alignment of the dust grains, and aligned with the
torus axis onto the plane of the sky. Adopting this magnetic field
configuration and the physical conditions of the clumps in the MHD outflow wind
model, we estimate a mass outflow rate 0.17 M yr at 0.4
pc from the central engine for those clumps showing near-infrared dichroism.
The models used were able to create the torus in a timescale of 10
yr with a rotational velocity of 1228 km s at 0.4 pc. We conclude
that the evolution, morphology and kinematics of the torus in NGC 1068 can be
explained within a MHD framework.Comment: 14 pages, 4 figures, Accepted by MNRA
Accretion-Induced Lithium Line Enhancements in Classical T Tauri Stars: RW Aur
It is widely accepted that much of the stochastic variability of T Tauri
stars is due to accretion by a circumstellar disk. The emission line spectrum
as well as the excess continuum emission are common probes of this process. In
this communication, we present additional probes of the circumstellar
environment in the form of resonance lines of low ionization potential
elements. Using a set of 14 high resolution echelle observations of the
classical T Tauri star (CTTS), RW Aur, taken between 1986 and 1996, we
carefully measure the continuum veiling at each epoch by comparing more than
500 absorption lines with those of an appropriate template. This allows us to
accurately subtract out the continuum emission and to recover the underlying
photospheric spectrum. In doing so, we find that selected photospheric lines
are enhanced by the accretion process, namely the resonance lines of LiI and
KI. A resonance line of TiI and a low excitation potential line of CaI also
show weak enhancements. Simple slab models and computed line bisectors lead us
to propose that these line enhancements are markers of cool gas at the
beginning of the accretion flow which provides an additional source of line
opacity. These results suggest that published values of surface lithium
abundances of classical T Tauri stars are likely to be overestimated. This
would account for the various reports of surface lithium abundances in excess
of meteoritic values among the extreme CTTS. Computing LTE lithium abundances
of RW Aur in a low and then high accretion state yields abundances which vary
by one order of magnitude. The low accretion state lithium abundance is
consistent with theoretical predictions for a star of this age and mass while
the high accretion state spectrum yields a super-meteoritic lithium abundance.Comment: 28 pages, 8 figures, accepted by Ap
Brown Dwarfs in the Pleiades Cluster Confirmed by the Lithium Test
We present 10 m Keck spectra of the two Pleiades brown dwarfs Teide 1 and
Calar 3 showing a clear detection of the 670.8 nm Li resonance line. In Teide
1, we have also obtained evidence for the presence of the subordinate line at
812.6 nm. A high Li abundance (log N(Li) >= 2.5), consistent with little if any
depletion, is inferred from the observed lines. Since Pleiades brown dwarfs are
unable to burn Li the significant preservation of this fragile element confirms
the substellar nature of our two objects. Regardless of their age, their low
luminosities and Li content place Teide 1 and Calar 3 comfortably in the
genuine brown dwarf realm. Given the probable age of the Pleiades cluster,
their masses are estimated at 55 +- 15 Jupiter masses.Comment: 14 pages gzipped and uuencoded. Figures are included. Also available
at http://www.iac.es/. Accepted for publication in ApJ Letter
Distance to flood meadows as a predictor of use of Nothofagus pumilio forest by livestock and resulting impact, in Patagonia, Argentina
Seedling browsing by livestock has been indicated as major threat for forest sustainability use. Nothofagus pumilio forests are part of the livestock raising system in Patagonia, but because of the sparse understory cover, livestock graze mainly on flood meadows within the forest matrix. The complexity of the environment under study (forests and flood meadows) means that an adaptive predictor is needed to evaluate the intensity of resource use by livestock in order to assess its effect on the forest. Distance to flood meadows was evaluated as a predictor of the use intensity of the forest by livestock and its effect on the understory. The study was conducted at three sites in Chubut Province, Patagonia-Argentina. We established transects in the forest 320 m long, starting at the edge flood meadow-forest. In these transects, the livestock presence indicators (soil compaction, density of feces and trails) and composition of the understory were evaluated. Generalized Linear Model for repeated measures for longitudinal data were used. The indicators showed that distance is efficient for estimating forest use intensity by livestock. The understory varied with distance, the cover of exotic herbaceous was higher near the flood meadow. Far from the flood meadow, the cover was entirely composited of native species. The results support the use of distance to flood meadows as a tool for decision making in livestock and forest management in N. pumilio forests, and for further research on livestock effect on the forest.Fil: Quinteros, Claudia Pamela. Centro de Investigación y Extensión Forestal Andino Patagónico; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lopez Bernal, Pablo Martin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Centro de Investigación y Extensión Forestal Andino Patagónico; ArgentinaFil: Gobbi, Miriam E.. Universidad Nacional del Comahue. Centro Regional Universitario Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bava, Jose Omar. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Centro de Investigación y Extensión Forestal Andino Patagónico; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068
We present sub-arcsecond 7.513 m imaging- and spectro-polarimetric
observations of NGC 1068 using CanariCam on the 10.4-m Gran Telescopio
CANARIAS. At all wavelengths, we find:
(1) A 90 60 pc extended polarized feature in the northern ionization
cone, with a uniform 44 polarization angle. Its polarization
arises from dust and gas emission in the ionization cone, heated by the active
nucleus and jet, and further extinguished by aligned dust grains in the host
galaxy. The polarization spectrum of the jet-molecular cloud interaction at
24 pc from the core is highly polarized, and does not show a silicate
feature, suggesting that the dust grains are different from those in the
interstellar medium.
(2) A southern polarized feature at 9.6 pc from the core. Its
polarization arises from a dust emission component extinguished by a large
concentration of dust in the galaxy disc. We cannot distinguish between dust
emission from magnetically aligned dust grains directly heated by the jet close
to the core, and aligned dust grains in the dusty obscuring material
surrounding the central engine. Silicate-like grains reproduce the polarized
dust emission in this feature, suggesting different dust compositions in both
ionization cones.
(3) An upper limit of polarization degree of 0.3 per cent in the core. Based
on our polarization model, the expected polarization of the obscuring dusty
material is 0.1 per cent in the 813 m wavelength range. This
low polarization may be arising from the passage of radiation through aligned
dust grains in the shielded edges of the clumps.Comment: 17 pages, 10 figures, accepted for publication at MNRA
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