Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, Summerland, BC, Canada
Ontario Ministry of Agriculture, Food and Rural Affairs, Harrow, ON, Canada
Laboratory Services Division, University of Guelph, Guelph, ON, Canada
Centre for Plant Health, Canadian Food Inspection Agency, Sidney, BC, Canada
Central Science Laboratory, York, UK
During the winter of 2000, tomatoes (Lycopersicon esculentum) with a bright yellow leaf mosaic were observed in a commercial greenhouse in southern Ontario, Canada. Examination of leaf extracts, using leaf dips and immunosorbent absorption electron microscopy (ISEM), showed flexuous rods consistent with the potexvirus group. Polyclonal antibodies raised against the original Peruvian Pepino mosaic virus (PepMV) isolate (1) and commercial antibodies obtained from Deutsche Sammlung von Mikro-organismen und Zellkulturen (DSMZ), GmbH, Braunsweig, Germany, and Plant Research International (PRI), Wageningen, the Netherlands, were used in ISEM. Leaves tested positive in double-antibody sandwich-enzyme-linked immunosorbent assay (ELISA) with antibodies from DSMZ and PRI. A triple-antibody sandwich-ELISA obtained from Adgen Ltd. (Nellies Gate, UK) gave similar results. Potato virus X did not react with PepMV antiserum in ELISA. Positive PepMV ELISA controls were a U.K. and a Dutch isolate supplied by R. Mumford and R. A. A. van Vlugt, respectively, and DSMZ. Using primers generated from a sequence of the RNA polymerase region of a U.K. PepMV isolate (R. Mumford, unpublished data), a reverse transcription-polymerase chain reaction test showed the expected 312-bp amplicon for the Canadian, Dutch, and U.K. isolates. The primer sequences used were forward 5′ CTA TTA CAA CTC CGG AAG CCA 3′ and reverse 5′ TGG TCT GGC CAG GCT TTG AC 3′. The three isolates were maintained in tomato cv. Bush Beefsteak. When mechanically inoculated on L. esculentum cv. Rapsodie, the Canadian isolate caused a bright yellow mosaic in 1 to 2 weeks, while the two European isolates caused a faint yellow mosaic and mild puckering of the leaves. When mechanically inoculated on 17 indicator plants, the Canadian isolate had a host range similar to the U.K. isolate. The most striking difference in symptoms occurred in L. pimpinellifolium, in which the Canadian isolate caused a yellow mosaic, the Dutch isolate caused no symptoms, and the U.K. isolate caused a marked puckering of the leaves, suggesting virus strain differences among the isolates. Tomato fruits originating from the United States were collected during border inspections by the Canadian Food Inspection Agency and tested for PepMV by ELISA with antisera from DSMZ. PepMV was not detected in 7 samples from California, but was detected in 6 of 12 samples from Colorado, 6 of 7 samples from Arizona, and 1 of 5 samples from Texas. PepMV was originally isolated from pepino (Solanum muricatum) in Peru in 1980 (1) and subsequently from tomato in the Netherlands in 1999 (2). To our knowledge, this is the first report of PepMV in North America.
References: (1) R. Jones et al. Ann. Appl. Biol. 94:61, 1980. (2) R. A. A. van Vlugt et al. Plant Dis. 84:103, 2000.