Citrus mealybug (Hemiptera: Pseudococcidae) movement and population dynamics in an arbor-trained vineyard.

The citrus mealybug, Planococcus citri (Risso) (Hemiptera: Pseudococcidae), is the main grapevine pest in vineyards in some countries, such as Spain and Brazil. In Galician vineyards (northwestern Spain), mealybug population levels are low because the accumulated degree-days are lower than in other grapevine-growing areas. The main problem caused by mealybugs is the transmission of viruses, even at low infestation levels. The active period of citrus mealybug in the study vineyard lasted from July until December, with an important movement peak at the end of July and August and a lower peak in November. The mealybug mainly moved upward along arbor-trained plants, and there were no important downward movements at the end of the season as has been described for other grapevine mealybugs. The mealybugs were normally restricted to the woody organs and were only present on leaves, branches, and green canes (always close to woody parts) in plants with high infestations. The movement of mealybugs between plants does not seem to take place by contact between green organs. Passive aerial transport and movement of pruning remains may play an important role in mealybug movement and thus in spread of the virus. The number of mealybugs carrying Grapevine leafroll-associated virus 3 (GLRaV-3) was found to represent approximately 75% of mealybugs caught in a GLRaV-3 infected vineyard.

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.

Field Transmission of Grapevine Leafroll Associated Virus 3 (GLRaV-3) by the Mealybug Planococcus citri.

The spatial distributions of grape plants with symptoms of grapevine leafroll in nine vineyards in the Galician wine-growing region Rías Baixas (northwestern Spain) were analyzed. In five, significant aggregations of diseased plants and/or disease gradients toward one of the borders of the plots constituted indirect evidence of vector transmission by a nonflying vector. From 1991 to 1995, vines from two vineyards were tested for grapevine leafroll associated virus 3 (GLRaV-3) by enzyme-linked immunosorbent assay. In one of these vineyards, which had been virus-free when planted, GLRaV-3 was detected 3 years after planting. In the second, the incidence of GLRaV-3 increased from 33 to 83% between 1991 and 1995. The mealybug Planococcus citri was associated with the infected plants in this vineyard. GLRaV-3 was present in P. citri, and under controlled conditions this mealybug transmitted GLRaV-3 to five of five previously healthy grape plants.

First Report of Grapevine Virus A in Spain.

Grapevine trichovirus A (GVA), a flexuous, filamentous, phloem-limited virus with an approximately 7.3-kbp RNA genome, is widespread in grapevines showing symptoms of leafroll and/or rugose wood. The virus can be mechanically inoculated to Nicotiana benthamiana and N. clevelandii. A field survey of diseased Vitis vinifera white and red cultivars was carried out in Pontevedra (northwest Spain) during the autumn of 1993. We detected the presence of GVA in vines showing leafroll symptoms by an immunocapture-reverse transcription-polymerase chain reaction (PCR) method (2) with GVA-specific primers (1). Bands of the expected size of 430 bp were obtained with extracts from petioles and stem bark as reaction substrates. To verify these results, Northern (RNA) blots with double-stranded (ds) RNAs isolated from grapevines were prepared. Hybridization was positive in two out of 10 samples analyzed. The probe was a 32P-labeled 430-bp PCR product amplified from extracts of N. benthamiana plants infected with GVA strain Is151 (gift of A. Mina-fra). The specificity of this probe was confirmed in dot blot hybridization, as a positive signal was obtained with extracts from GVA-inoculated N. benthamiana, but not with extracts of phosphate buffer-inoculated N. benthamiana, turnip mosaic potyvirus-inoculated Arabidopsis thaliana, or potato potyvirus Y-inoculated N. xanthi plants. The probe did not hybridize to dsRNAs extracted from enzyme-linked immunosorbent assay-positive GLRaV-III-infected grapevines. GVA has been identified in other Mediterranean countries, but to our knowledge this is the first report of the detection of GVA in Spain. References: (1) A. Minafra and A. Hadidi. J. Virol. Methods 47:175, 1994. (2) G. Nolasco et al. J. Virol. Methods 45:201, 1993.