Development of real-time RT-PCR assays for the detection of Cucumber vein yellowing virus (CVYV) and Cucurbit yellow stunting disorder virus (CYSDV) in the whitefly vector Bemisia tabaci

Reverse transcription followed by real-time PCR assays based on TaqMan chemistry have been developed for the detection and quantification of Cucumber vein yellowing virus (CVYV) and Cucurbit yellow stunting disorder virus (CYSDV) in individual adults of the whitefly vector Bemisia tabaci. The method includes an internal control for the detection of a gene from B. tabaci to compensate for variations in extraction efficiency. The assays designed were used to estimate proportions of viruliferous whiteflies collected from commercial greenhouse-grown crops in Spain. In a significant number of whiteflies, both viruses were detected and their amounts were estimated. The assays could be used to assist risk assessment of CVYV and CYSDV which constitute limiting factors in cucurbit crops. They are also suited to investigating the epidemiology and plant-virus-vector relationships in these diseases.

First Report of Southern bean mosaic virus Infecting French Bean in Morocco

Common bean (Phaseolus vulgaris L.) is grown on approximately 1,500 ha in commercial greenhouses and is of major economic importance in the Souss-Massa Region, Agadir, Morocco. Since October 2003, symptoms resembling a viral disease, consisting of pod mosaic and distortion and mild to severe mosaic in leaves, have been observed on bean plants in several greenhouses. Mechanical inoculation with symptomatic leaf extracts produced necrotic local lesions on P. vulgaris 'Pinto' and systemic symptoms similar to those observed in the naturally infected bean plants P. vulgaris 'Donna' (five plants per cultivar). Inoculated and naturally infected samples reacted positively using a double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) to Southern bean mosaic virus (SBMV) (DSMZ, Braunschweig, Germany), a member of the Sobemovirus genus that is transmitted by contact, soil, beetles, and seeds (1). Virions purified from a naturally infected 'Donna' plant contained a 30-kDa polypeptide that reacted positively using sodium dodecyl sulfate polyacrylamide gel electrophoresis and western blot analysis with SBMV antiserum (DSMZ). Reverse transcription-polymerase chain reaction amplification with SMBV primers as described by Verhoeven et al. (2) produced an expected 870-bp band. The amplicon was cloned, sequenced (GenBank Accession No. AJ748276), and compared to those isolates available in GenBank and had a nucleotide sequence identity of 87% and a derived amino acid sequence identity of 95% with an SBMV isolate from Spain (2). During a survey in different areas of the Souss-Massa Region, 20 symptomatic leaf and pod samples were randomly collected from 12 greenhouses (50 ha) where significant commercial losses were suffered because of this virus disease, and all samples were positive using DAS-ELISA for SBMV. To our knowledge, this is the first report of SBMV in Morocco. References: (1) J. H. Tremaine and R. I. Hamilton. Southern bean mosaic virus. No. 274 in: Descriptions of Plant Viruses. CMI/AAB, Kew, Surrey, England, 1983. (2) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 109:935, 2003.