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Molecular Identification, Reverse Transcription-Polymerase Chain Reaction Detection, Host Reactions, and Specific Cytopathology of Artichoke yellow ringspot virus Infecting Onion Crops

First, second, and fifth authors: Plant Pathology laboratory, Faculty of Agriculture, Aristotle University of Thessaloniki, P.O. Box 269, 54124 Thessaloniki, Greece; second author: National Agricultural Research Foundation, Plant Protection Institute, P.O. Box 324, 57001 Thermi, Thessaloniki, Greece; third author: Biologische Bundesanstalt für Land- und Forstwirtschaft (BBA), Inst. für Biochemie und Pflanzenvirologie, Braunschweig, Germany; and fourth author: German Collection of Microorganisms and Cell Cultures, Division of Plant Virology, Braunschweig, Germany

An isometric virus ca. 25 nm in diameter with angular contour was isolated from onion plants showing yellow leaf striping and necrotic tips. The virus was mechanically transmitted onto 28 species of indicator plants belonging to five families, viz. Amaranthaceae, Chenopodiaceae, Cucurbitaceae, Leguminosae, and Solanaceae where it causes ring spots, malformations, and/or tip necrosis. Cytopathological studies in infected Nicotiana benthamiana tissues revealed cytoplasmic inclusions resembling those caused by Artichoke yellow ringspot virus (AYRSV), a member of the family Comoviridae. Host range and symptomatology of the onion virus were also similar to AYRSV. A high seed transmission rate (20%) was found in onion. Reverse transcription-polymerase chain reaction using degenerate primers specific for the family Comoviridae allowed amplification of RNA-dependent RNA polymerase sequences, which upon sequence analysis and comparison with AYRSV isolates from Cynara scolymus (AYRSV-AtG) and Vicia faba (AYRSV-F) were highly similar, thus providing evidence that the nepovirus AYRSV is infecting onion in the field.