New Insights into Esca of Grapevine: The Development of Foliar Symptoms and Their Association with Xylem Discoloration.

A new study on the development of foliar symptoms of esca was carried out from 2004 to 2006 in five mature vineyards in Aquitaine, France. Symptoms were monitored for severity and changes over time. Initial foliar symptoms were characterized by the presence of drying zones or discolorations (reddening or yellowing), which are symptoms that have also been attributed to Black Dead Arm (BDA). Then, the less-severely affected leaves persisted throughout the summer and developed into typical "tiger-stripe" symptoms of esca. The most severely symptomatic leaves fell soon after symptoms appeared. Severely diseased vines showed typical apoplectic or acute forms of esca that did not differ from the severe BDA forms. The appearance of leafsymptomatic vines increased uniformly over time, reaching a maximum incidence by the end of July. A second survey in 41 European and Lebanese vineyards showed that longitudinal discolorations were visible under the bark of 95% of the vines showing foliar esca symptoms. These wood symptoms, also previously attributed to BDA, appeared as xylem orange-brown stripes. Thus, foliar symptoms of esca showed transitory phases which overlapped with some BDA descriptions. Most of these symptoms, in the west-palearctic regions that were investigated, were commonly associated with the presence of one or several xylem discolorations.

First Report of Arabis mosaic virus on Grapevine in Spain.

Arabis mosaic virus (ArMV; genus Nepovirus, family Comoviridae) is one of several nepoviruses responsible for infectious degeneration disease of grapevines in Europe (3). The first occurrence in Spain, in the summer of 2007, was found in Val de Salnés, Rias Baixas appellation, Galice on 25-year-old vines of the Albariño variety grafted onto an unidentified rootstock and showing leaf yellowing. The second finding was in the spring of 2008 in Barriobusto, Rioja appellation, Basque Country on 30-year-old vines of Tempranillo variety grafted onto 41B rootstock. In this case, no obvious foliar symptoms were observed but fruit set was very poor. Positive ELISA results were obtained at two different laboratories using antibodies to ArMV obtained from two companies (BIOREBA, Reinach, Switzerland and Sediag, Longvic, France). At a third lab, the presence of ArMV was further confirmed by reverse transcription (RT)-nested PCR using the primers described by Bertolini et al. (1). External primers ArMV 1 and ArMV 2 amplified a fragment of 340 bp from the coat protein region of the virus and internal primers ArMV i1 and ArMV i2 amplified a fragment of 203 bp. The specificity of the amplicons was subsequently confirmed by sequencing and comparison with other ArMV isolates available in the GenBank, EMBL, and DDBJ databases. Alignment performed using Blastn showed 85% nucleotide sequence identity with ArMV isolate NW (Accession No. AY017339). ELISA revealed co-infection with GLRaV-1 in Galice, GLRaV-3 in Rioja, and GFkV at both sites; these other viruses being common in their respective appellations. ArMV could be mechanically transmitted from rooted cuttings onto Chenopodium amaranticolor with an average of a 46% success rate (1:10 tissue/buffer ratio; [2]), but the range was very wide (0 to 100%) and dependent on the individual source vine. No statistical differences were found between nicotine or phosphate buffer for extraction or when using shoot tips or root tips as a source of virus (Fisher's exact test). Infection in C. amaranticolor was symptomless, but detectable by ELISA, and systemic. The Galician grapevine was an isolated plant, replanted on the spot of a dead one. Xiphinema diversicaudatum, the nematode vector of ArMV, was found in the vineyard soil. Only two ArMV-positive vines were found among 1,993 plants analyzed in Galice from 2005 to 2007 (no field data available for the second finding). In Rioja, one positive vine was found in a random sample of 74 vines from two different vineyards. Further testing of the neighboring vines indicated that one of the adjacent plants was also infected. This minimal spread since the vineyard was planted is suggestive of a lack of vectored transmission. In Spain as a whole, the virus seems to be rare and associated with the Atlantic biogeographic region. Both vineyards were planted before certified material became widely available. Currently, statutory testing of grapevine propagation material should prevent further spread. References: (1) E. Bertolini et al. Phytopathology 93:286, 2003. (2) G. P. Martelli, ed. Graft-Transmissible Diseases of Grapevines. Handbook for Detection and Diagnosis, FAO, Rome, 1993. (3) G. P. Martelli and E. Boudon-Padieu. Directory of Infectious Diseases of Grapevines and Viruses and Virus-like Diseases of the Grapevine. Bibliographic Report 1998-2004, CIHEAM, Paris, 2006.

Features on the surface of the tobacco rattle tobravirus particle that are antigenic and sensitive to proteolytic digestion.

The particle proteins of tobraviruses and tobamoviruses share six sequence motifs, two of which are also present in furoviruses and hordeiviruses. Analyses of four different polyclonal antisera to tobacco rattle tobravirus by Pepscan revealed that the C-terminal region of the particle protein was immunodominant. The N-terminal region and a central region (residues 110-121) were more weakly immunogenic. These results suggest that these regions are exposed externally on the assembled virus particle. Papain digestion showed that the C terminus can be removed without apparent structural damage to the particle. The external location of the C-terminal region along the sides of the particle could explain some transmission properties of the rod-shaped viruses.

Antigenic analysis of nematode-transmissible and non-transmissible isolates of tobacco rattle tobravirus using monoclonal antibodies.

Murine monoclonal antibodies (MAbs) were produced against a nematode non-transmissible isolate of tobacco rattle tobravirus (TRV-PLB). Two of the MAbs (SCR 80 and 81) did not react with the serologically closely related isolate TRV-PPK20 (both isolates belong to the PRN serotype), which is readily transmissible by nematodes. When further isolates of the PRN serotype were tested, all the non-transmissible ones reacted with these two MAbs, but so also did some of those that are readily transmissible. SCR 80 and 81 were able to trap TRV-PLB particles onto electron microscope grids and reacted with metatopes located near the C terminus of the particle protein. The epitope recognized by SCR 81 was discontinuous. The MAbs that reacted with both TRV-PLB and TRV-PPK20 recognized either continuous cryptotopes (SCR 78) or discontinuous neotopes (SCR 79 and 82).