The genomic diversity of field isolates of rice [Oryza sativa] black-streaked dwarf Fijivirus

Rice black-streaked dwarf Fijivirus (RBSDV) infects rice, maize, wheat, oat and barley. The virus in transmitted by planthopper, Laodelphax striatellus. In Japan, RBSDV was first reported in Nagano in 1952. In Hokkaido, RBSDV had not been reported until 1992, when diseased rice plants, whose symptoms were similar to those infected with RBSDV, were observed in Asahikawa city. The field isolate of the disease transmitted to rice, barley, wheat and maize by a planthopper, L. striatellus, was found to be serologically related to RBSDV. A partially purified preparation from a rice plant infected with the field isolate revealed spherical virus particles of about 60 nm in diameter with spikes which was the same as those of RBSDV. However, when electrophoretic profile of its dsRNAs was compared with a RBSDV isolate maintained at Hokkaido University (RBSDV-H) by 10% Laemmli's polyarcylamide gel electrophoresis (Laemmli's PAGE), its RNAs showed a similar but distinct profile from that of RBSDV-H. Therefore, we examined relationship between genomes of RBSDV-H and the field isolate using genomic hybridization. All the genomic segments of the field isolate reacted with RBSDV-H total genomic RNAs labeled at their 5' termini. Furthermore, three field isolates intensely reacted with RBSDV specific probe in dot blot hybridization. Based on these results, the field isolate was identified as RBSDV and this was the first record of the occurrence of RBSDV in Hokkaido.