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Characteristics and Distribution of Potato Latent Carlavirus (Red LaSoda Virus) in North America

A carlavirus (code name RLSV and subsequently named potato latent carlavirus, PotLV) with serological and biological characteristics different from those of potato M carlavirus (PVM) and potato S carlavirus (PVS) was detected in the potato (Solanum tuberosum) cultivar Red LaSoda by the Scottish Agricultural Science Agency in 1992. During a routine electron microscope testing of accessions in the Vancouver Collection of Virus-Free Potatoes growing in the California winter test in 1993, a filamentous rod-shaped virus similar to PVS and PVM was found in a Red LaSoda clone from Nebraska. The virus was isolated and purified. The monoclonal antibody, MAb 4E12, which is highly specific to the PotLV virus, was developed. From 1994 to 1998, the accessions in the Vancouver Collection of Virus-Free Potatoes were assayed by triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA) using the 4E12 MAb. Seven accessions tested from 1994 to 1996 were infected with PotLV. None of the 270 and 267 accessions in this collection tested positive for this virus in 1997 and 1998, respectively. In 1997 and 1998, the 137 accessions in the U.S. National Varietal Collection maintained at Presque Isle, Maine, were also assayed using the 4E12 MAb. The cultivars High Plains, Platte, and Red LaSoda were the only accessions that tested positive for PotLV. Nicotiana benthamiana, N. megalosiphon, and N. occidentalis are new systemic hosts for PotLV. TAS-ELISA with the 4E12 MAb is now part of the standardized test for PotLV in Canada.