Airborne transmission of tomato mosaic Tobamovirus and its occurrence in red spruce in the northeastern United States

To test the hypothesis that tomato mosaic Tobamovirus (ToMV) is transmitted by an airborne mechanism, virus-free red spruce (Picea rubens Sarg.) seedlings were planted in four raised, plywood boxes lined with plastic and filled with a Promix-sand (3:1, v/v) mixture. In July 1993, two boxes were placed at 1015 m (site 1) and two at 960 m (site 2) elevation on Whiteface Mountain, N.Y. ToMV was detected by enzyme-linked immunosorbent assay (ELISA) in seedling roots at both sites in August 1994. Mean virus concentration within seedling roots was significantly greater in the seedlings placed at site 1 than site 2. Significant differences in the incidence of infected seedlings were not detected between the two sites. To test the hypothesis that ToMV incidence and concentration in red spruce across the northeast United States varied by sampling date and plot location, roots were collected in June and September 1993 from dominant and codominant trees on nine plots in New York, Vermont, New Hampshire, and Maine and assayed for ToMV by ELISA. A significant difference in incidence of infection was observed among plots, and between sampling dates. Twenty-five and 11% of the total variance in virus concentration within red spruce roots were explained by the nested, random factors plot location and tree, respectively.