Tomato Spotted Wilt Virus Isolates in Japan are Grouped into Two Strains

Abstract

Five isolates of tomato spotted wilt virus (TSWV), designated N, M, P, W and K, collected from different prefectures in Japan, were characterized and compared on their properties of nucleocapsid (N) protein and S RNA. Nucleocapsid of each isolate was purified by ultracentrifugation followed by metrizamide isopycnic density-gradient. Molecular weights of N proteins were 30 K in case of N, M and P isolates, while those of W and K isolates were 32 K. Moreover, difference of chromatograms between 30 K and 32 K N proteins digested by lysyl endpeptidase was observed. By Western blot analysis, specific antibody to N protein of N isolate reacted to N protein of N, M and P isolates, whereas specific antibody to that of W isolate could detect only those of W and K isolates without non-specific reactions. When S RNA was compared by glyoxalated agarose gel electrophoresis, molecular weights of S RNAs of N, M and P isolates were 1.02×10⁶, while those of W and K isolates were 1.21×10⁶. In Northern blot hybridization analysis using S RNA from either N or W isolate as probe, S RNA from N isolate tightly hybridized with S RNAs of N, M and P isolates, and S RNA from W isolate hybridized only with those of W and K isolates. Based on the results obtained, TSWV isolates which occurred in Japan were grouped into two strains. The one was designated as ordinary strain (TSWV-O; N, M and P isolates) and the other was watermelon strain (TSWV-W; W and K isolates).