Wisteria Vein Mosaic Virus Detected for the First Time in Iran from an Unknown Host by Analysis of Aphid Vectors

Abstract

The development of reverse transcription-polymerase chain reaction using degenerate primers against conserved regions of most potyviral genomes enabled sampling of the potyvirome. However, these assays usually involve sampling potential host plants, but identifying infected plants when they are asymptomatic is challenging, and many plants, especially wild ones, contain inhibitors to DNA amplification. We used an alternative approach which utilized aphid vectors and indicator plants to identify potyviruses capable of infecting common bean (Phaseolus vulgaris). Aphids were collected from a range of asymptomatic leguminous weeds and trees in Iran, and transferred to bean seedlings under controlled conditions. Bean plants were tested serologically for potyvirus infections four-weeks post-inoculation. The serological assay and symptomatology together indicated the presence of one potyvirus, and symptomology alone implied the presence of an unidentified virus. The partial genome of the potyvirus, encompassing the complete coat protein gene, was amplified using generic potyvirus primers. Sequence analysis of the amplicon confirmed the presence of an isolate of Wisteria vein mosaic virus (WVMV), a virus species not previously identified from Western Asia. Phylogenetic analyses of available WVMV sequences categorized them into five groups: East Asian-1 to 3, North American and World. The Iranian isolate clustered with those in the World group. Multiple sequence alignment indicated the presence of some genogroup-specific amino acid substitutions among the isolates studied. Chinese isolates were sister groups of other isolates and showed higher nucleotide distances as compared with the others, suggesting a possible Eastern-Asian origin of WVMV, the main region where Wisteria might have originated.

Keywords: Wisteria vein mosaic virus; aphid-transmission approaches; potyvirome; potyviruses; vectorome.

Fig. 1

(A) Apterous aphid species Aphis craccivora (left), and A. fabae (right), collected from a locust tree (Robinia sp.). (B) Virus-like symptoms induced on common bean (Phaseolus vulgaris) leaves inoculated by the aphids: isolate Th-W2259, left, and isolate Th-W2260, right.

Fig. 2

A maximum likelihood (ML) tree constructed from coat protein gene sequences of Wisteria vein mosaic virus isolates. Numbers at each node indicate the percentage of supporting bootstrap samples in ML and neighbor-joining methods, respectively. The homologous sequence of an isolate of soybean mosaic virus (accession no. FJ640971) was used as the outgroup. The sequence of the isolate Th-W2259 (in green) was obtained in this study.

Fig. 3

Amino acid sequence alignment of complete or partial coat protein sequences of representative isolates of Wisteria vein mosaic virus belonging to five phylogenetic groups: East Asian-1 to 3, North American and World. The sequence of the isolate Th-W2259 was obtained in this study. Amino acid substitutions are shown in black rectangles. Substitutions unique to the World and East Asian-3 groups are shown in dotted rectangles. The sequence of Beijing isolate was used as the reference sequence.