Detection of a closteroviruslike particle from a corky bark-affected grapevine cultivar

Closteroviruslike particles were mechanically transmitted from in vitro shoot tip cultures of a grapevine affected with corky bark disease to seedlings of Nicotiana benthamiana. Local necrotic lesions appeared 9-12 d and systemic symptoms 14-16 d post-inoculation. This virus had a normal length of 725 nm, striations with a pitch of 3.4 nm and was 10 nm wide. In ISEM tests, the virus was not decorated with antibodies prepared against GVA, NY-1, CA-4, GLRV-1, GLRV-3, ASGV, PVT or CLSV

Detection of capillovirus-like particles in a grapevine affected with rugose wood

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Mechanical sap transmission of a closterovirus from in vitro shoot tip cultures of a leafroll-affected grapevine to Nicotiana benthamiana

Transmission manuelle d'un clostérovirus au Nicotiana benthamiana à partir de cultures in vitro d'une vigne atteinte de l'enroulementDes cultures in vitro d'une vigne de Vitis vinifera Limberger atteinte de l'enroulement ont été broyées dans une solution tampon contenant de la nicotine. Les extraits ont été inoculés sur des feuilles de Nicotiana benthamiana et de 6 autres espèces de plantes herbacées. 3 semaines plus tard, seuls les plants de N. benthamiana ont démontré des symptômes. Ceux-ci consistaient d'un nanissement systémique accompagné d'un éclaircissement des nervures qui se transformait en chlorose interveinale. Les feuilles de ces N. benthamiana contenaient le virus A de la vigne (GVA), démontré par la méthode ISEM

Double-stranded RNA from rupestris stem pitting-affected grapevines

Nucleic acids were extracted from in vitro shoot tip cultures of 31 grapevine cultivars affected with rupestris stem pitting (RSP) disease and from cultures of 11 RSPfree cultivars, 4 of which were disease-free, 2 of which were fleck-affected and 5 of which were grapevine leafroll disease-affected. Analysis of the extracts by polyacrylamide slab gel electrophoresis showed that 21 of the 31 RSP-affected cultivars contained a previously unreported nucleic acid which was absent from the RSP-free controls. Nuclease digestions showed that the nucleic acid was double-stranded RNA (dsRNA). The apparent size of the dsRNA was inconsistent with that expected for either a viroid or a closterovirus. The observation that 10 of the 31 RSP-affected cultivars lacked this dsRNA is consistent with the view that there may be more than one 'RSP-like' disease. The dsRNA detected in this investigation may be associated with one of these diseases

Comparison of RNA extracts from in vitro shoot tip cultures of leafroll-affected and leafroll-free grapevine cultivars

The RNA content of in vitro shoot tip cultures from grapevine leafroll (GLR) disease-affected grapevines was analyzed and compared to that of similar cultures from GLR-free grapevines. A previously unreported low-molecular-weight single-stranded RNA (LMWssRNA) was detected in in vitro shoot tip cultures of 65 % (11 out of 17) of GLR-affected cultivars. This LMWssRNA was absent from disease-free cultivars and may be associated with a virus or a strain of a virus responsible for GLR. Numerous high-molecular-weight (HMW) dsRNA bands were also detected in GLR-affected grapevine cultivars. The intensities and mobilities (apparent molecular weights) of these dsRNA bands varied considerably from one GLR-affected cultivar to the next, but were reproducible for each cultivar. The detection of multiple distinctive RNA banding patterns is consistent with the possibility that more than one agent can cause grapevine leafroll disease

Critical behavior of a fluid in a disordered porous matrix: An Ornstein-Zernike approach

Using a liquid-state approach based on Ornstein-Zernike equations, we study the behavior of a fluid inside a porous disordered matrix near the liquid-gas critical point.The results obtained within various standard approximation schemes such as lowest-order $\gamma$-ordering and the mean-spherical approximation suggest that the critical behavior is closely related to that of the random-field Ising model (RFIM).Comment: 10 pages, revtex, to appear in Physical Review Letter

Avalanches in Breakdown and Fracture Processes

We investigate the breakdown of disordered networks under the action of an increasing external---mechanical or electrical---force. We perform a mean-field analysis and estimate scaling exponents for the approach to the instability. By simulating two-dimensional models of electric breakdown and fracture we observe that the breakdown is preceded by avalanche events. The avalanches can be described by scaling laws, and the estimated values of the exponents are consistent with those found in mean-field theory. The breakdown point is characterized by a discontinuity in the macroscopic properties of the material, such as conductivity or elasticity, indicative of a first order transition. The scaling laws suggest an analogy with the behavior expected in spinodal nucleation.Comment: 15 pages, 12 figures, submitted to Phys. Rev. E, corrected typo in authors name, no changes to the pape

Clusters and Fluctuations at Mean-Field Critical Points and Spinodals

We show that the structure of the fluctuations close to spinodals and mean-field critical points is qualitatively different than the structure close to non-mean-field critical points. This difference has important implications for many areas including the formation of glasses in supercooled liquids. In particular, the divergence of the measured static structure function in near-mean-field systems close to the glass transition is suppressed relative to the mean-field prediction in systems for which a spatial symmetry is broken.Comment: 5 pages, 1 figur

Failure of planar fiber networks

We study the failure of planar random fiber networks with computer simulations. The networks are grown by adding flexible fibers one by one on a growing deposit [K. J. Niskanen and M. J. Alava, Phys. Rev. Lett. 73, 3475 (1994)], a process yielding realistic three dimensional network structures. The network thus obtained is mapped to an electrical analogue of the elastic problem, namely to a random fuse network with separate bond elements for the fiber-to-fiber contacts. The conductivity of the contacts (corresponding to the efficiency of stress transfer between fibers) is adjustable. We construct a simple effective medium theory for the current distribution and conductivity of the networks as a function of intra-fiber current transfer efficiency. This analysis compares favorably with the computed conductivity and with the fracture properties of fiber networks with varying fiber flexibility and network thickness. The failure characteristics are shown to obey scaling behavior, as expected of a disordered brittlematerial, which is explained by the high current end of the current distribution saturating in thick enough networks. For bond breaking, fracture load and strain can be estimated with the effective medium theory. For fiber breaking, we find the counter-intuitive result that failure is more likely to nucleate far from surfaces, as the stress is transmitted more effectively to the fibers in the interior.Peer reviewe

Nucleation in Systems with Elastic Forces

Systems with long-range interactions when quenced into a metastable state near the pseudo-spinodal exhibit nucleation processes that are quite different from the classical nucleation seen near the coexistence curve. In systems with long-range elastic forces the description of the nucleation process can be quite subtle due to the presence of bulk/interface elastic compatibility constraints. We analyze the nucleation process in a simple 2d model with elastic forces and show that the nucleation process generates critical droplets with a different structure than the stable phase. This has implications for nucleation in many crystal-crystal transitions and the structure of the final state