SEASONAL PATTERN OF TOMATO MOSAIC TOBAMOVIRUS INFECTION AND CONCENTRATION IN RED SPRUCE SEEDLINGS

Tomato mosaic tobamovirus (ToMV) infects red spruce (Picea rubens) and causes significant changes in its growth and physiology. The mechanis m of infection and the pattern of virus concentration in seedling root s and needles were investigated. One-year-old red spruce seedlings wer e obtained from the nursery in April and June 1995 and August 1996 and tested for ToMV using enzyme-linked immunosorbent assay (ELISA). Viru s-free seedlings were divided into three treatments: control, root ino culated, and needle inoculated, Two control, five root-inoculated, and five needle-inoculated seedlings were sampled destructively at biweek ly intervals for 3 months and then tested for ToMV by ELISA. ToMV was transmitted to seedlings by root hut not by needle inoculation. The vi rus wits detected in 67 to 100% of roots but in less than 7% of needle s of root-inoculated seedlings. The percent infection of root-inoculat ed seedlings caused significantly between the April and June and betwe en the April and August inoculation periods. Virus concentration in in fected seedling roots increased initially, peaked within 4 weeks posti noculation, and steadily declined thereafter. Significant differences in ToMV concentrations in roots also were detected among inoculation p eriods and sampling dates, Early spring may represent the optimal time for infection of seedlings, as well as for assaying roots for ToMV.