Barley yellow streak mosaic virus (BaYSMV) was first described and reported in Montana and Alberta, Canada, more than 17 years ago (1). Since then, it has been detected in two other locations: Pocatello Valley, ID (3), and across the border in Utah. BaYSMV has now been found in the Alaskan interior. In July 1999, dry-land barley (Hordeum vulgare L.) growing in University of Alaska-Fairbanks experimental plots exhibited symptoms similar to those described for BaYSMV, including parallel chlorotic streaks and leaf banding. Mechanical inoculation of Nicotiana benthamiana with diseased barley sap produced systemic mosaic symptoms. As previously reported for BaYSMV sap-transmission tests (2), parallel inoculations to barley plants yielded no symptoms. Electron microscopy of leaf dips and minipurifications of infected N. benthamiana revealed long filamentous particles that matched the size and shape reported for BaYSMV (1). Ultrathin sections of diseased barley and N. benthamiana leaves displayed characteristic virus particles. BaYSMV was confirmed by immuno-sorbent electron microscopy assays (4) and western blot analysis with polyclonal antiserum. Long filamentous BaYSMV particles appeared only on grids coated with BaYSMV antiserum and exposed to diseased N. benthamiana sap. Total protein extracts from diseased barley tissue and inoculated N. benthamiana, as well as with protein extracted from partially purified preparations, were applied to a 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis minigel and stained with Coomassie blue. Diseased samples, but not healthy controls, contained a protein of ≈33 kDa that was within the size range of a previously described protein from partially purified BaYSMV particles (2). Western blot analysis with an Immuno-Blot alkaline phosphatase assay system (Bio-Rad Laboratories, Hercules, CA) confirmed that the protein reacted with polyclonal BaYSMV. This is the first serological documentation of a BaYSMV-specific protein and that the ≈33-kDa protein is the main antigen recognized by the BaYSMV polyclonal antiserum. Based on virus particle shape and size, symptomology, mechanical transmission host range, and serology, we conclude that BaYSMV is associated with the barley disease observed. Barley yellow streak mosaic virus disease outbreaks are associated with recurring drought and are accompanied by infestations of the brown wheat mite vector, Petrobia latens Müller (1), so it is not surprising that this report coincides with abnormally dry conditions occurring throughout the 1990s in the interior of Alaska.
References: (1) N. L. Robertson and T. W. Carroll. Science 240:1188, 1988. (2) N. L. Robertson and T. W. Carroll. Plant Dis. 75:839, 1991. (3) J. S. Skaf et al. Plant Dis. 76:861, 1992. (4) J. S. Skaf and T. W. Carroll. Plant Dis. 79:1003, 1995.
