Immunolocalization of tomato mosaic tobamovirus in roots of red spruce seedlings

The objective of this study was to determine the location of tomato mosaic tobamovirus (ToMV) in red spruce (Picea rubens) seedling roots. Roots were collected from uninfected and infected spruce seedlings at biweekly intervals, fixed in formaldehyde-glacial acetic acid-50% ethanol (1: 1: 18), embedded in paraffin, sectioned, and tested by indirect immunofluorescence (IF). ToMV was detected by IF in infected, but not in uninfected red spruce roots. All seedlings that tested positive by IF had previously tested positive by enzyme-linked immunosorbent assay. Fluorescence was observed most frequently 2 weeks after inoculation in cortical and epidermal cells, as well as in the lateral root primordia. The ToMV was not observed in vascular tissue, the root cap, or meristematic cells. Virus distribution was uneven, and occurred in localized, concatenated pockets, parallel to the axis of the apical meristem. In older seedlings, fluorescence was associated with irregular-shaped vesicles in cortical cells.