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First Report in Argentina of Apple stem pitting virus Causing Pear Vein Yellows Disease in Pear

Apple stem pitting virus (ASPV) is an important latent virus of apple trees transmitted by grafting. In pear trees, ASPV is associated with pear vein yellows and pear necrotic spot diseases. Symptoms consist of chlorotic leaf banding and red mottling and flecking along the veins and necrotic spotting in some cultivars may also occur (4). During the spring of 2007, chlorotic leaf banding was observed in Bartlett pear (Pyrus communis L.) trees from one orchard in Bahía Blanca (Buenos Aires Province) and in Anjou, Packham, Abate Fetel, and Bartlett pears in another orchard in General Roca (Río Negro Province). The percentage of symptomatic plants was 10% in both cases. Pooled samples consisting of eight leaves per tree, 25 samples from Bahía Blanca and 25 samples from General Roca, were tested by double-antibody sandwich (DAS)-ELISA with a polyclonal antiserum from BIOREBA AG (Reinach, Switzerland). Five samples from Bahía Blanca and ten from General Roca were positive by DAS-ELISA. Only four positive samples by DAS-ELISA were also positive by immunocapture-reverse transcription (RT)-PCR using virions trapped in a microcentrifuge tube (3). A fragment of 370 bp was amplified with specific primers from each of these four samples. Amplicons were cloned and the nucleotide sequences were determined for one clone of each sample (GenBank Accession Nos. GQ356781, GQ356782, GQ356783, and GQ356784). All sequences had the highest identities with coat protein genes of ASPV. One of them was 94% identical with the coat protein gene of isolate PA66 isolate from Germany (GenBank Accession No. D21829.1) (1). Losses in pear by ASPV have not been demonstrated yet in Argentina. However, when the virus is present with other virus or virus-like diseases, a synergistic effect may occur and growth reduction may exceed 50% (2). Because of the mild symptoms in pear plants, nurserymen or growers must take care when they select material for propagation, in part because laws requiring virus-free propagation material do not exist in Argentina. To our knowledge, this is the first report of ASPV in pears in Argentina.

References: (1) W. Jelkmann. J. Gen. Virol. 75:1535, 1994. (2) A. L. Jones and H. S. Aldwinckle. Compendium of Apple and Pear Diseases. The American Phytopathological Society, St. Paul, MN, 1990. (3) W. Menzel et al. J. Virol. Methods 99:81, 2002. (4) M. Németh. Virus, Mycoplasma and Rickettsia Disease of Fruit Trees. Martinus Nijhoff Publishers, Dordrecht, the Netherlands, 1986.