Discrimination of four soybean dwarf virus strains by dot-blot hybridization with specific probes.

Soybean dwarf virus (SbDV) is divided into four strains (YS, YP, DS, and DP) on the basis of host symptoms in infected soybean plants and on aphid vector specificity. To detect and discriminate each strain of SbDV by dot-blot hybridization, probes Y, D, S, and P were prepared. Probes Y and D, covering most of the 3'-noncoding region of the viral genome containing the sequence of small subgenomic RNA, could discriminate strains in accord with the host symptoms. Probes S and P were derived from the 5'-half of open reading frame 5 encoding the N-terminal half of the readthrough domain which is closely related to the aphid vector specificity of each strain. Thus, the four SbDV strains could be discriminated by the combination of these probes. This method, based on a procedure specific to the SbDV sequence, is a good alternative for routine examination of infected plants in soybean breeding programs for evaluation of resistance to SbDV and for assessment of the distribution of each strain in epidemiological studies.

The N-Terminal Region of the Readthrough Domain Is Closely Related to Aphid Vector Specificity of Soybean dwarf virus.

ABSTRACT It has been speculated that the N-terminal half of the readthrough domain (RTD) encoded by open reading frame 5 of Soybean dwarf virus (SbDV) is related to the vector specificity. To further investigate this hypothesis, transmissibility via aphids was tested on 17 SbDV isolates and comparisons of the deduced amino acid sequences of the coat protein (CP) and other proteins encoded by the RTD were made between these isolates. Isolates were distinguished into four strains: YS, causing yellowing in soybean and transmittable by Aulacorthum solani; DS, causing dwarfing and transmittable by A. solani; YP, causing yellowing and transmittable by Acyrthosiphon pisum; and DP, causing dwarfing and transmittable by A. pisum. Phylogenetic analysis showed that the trees for the CP and the C-terminal half of the RTD sequences contained clusters of isolates of the same symptom type, whereas the tree for the N-terminal half of the RTD contained clusters of isolates of the same aphid vector type. These results agreed with our previous data of the complete nucleotide sequences of four SbDV isolates, and strongly indicated a close relationship between the N-terminal half of the RTD amino acid sequences and aphid transmission specificity of SbDV.