Molecular characterization of novel Cucurbit aphid borne yellows virus strains infecting squash and watermelon in India

The pathogen responsible for yellowing and downward rolling of leaves of squash and watermelon plants from Uttar Pradesh state, India, was identified probably as strains of Cucurbit aphid-borne yellows virus (CABYV) through RT-PCR using universal Polerovirus primers followed by sequencing. The full-length genome sequences of an isolate from squash (POL-SQ - 5650 nt) and one from watermelon (POL-WM - 5647 nt) were determined by sequencing the products from RT-PCR with six sets of primers with overlapping products. Sequence comparison and phylogenetic analysis showed that these isolates had closest identity with a recombinant strain obtained between CABYV and Melon aphid-borne yellows virus (MABYV) reported from Taiwan infecting Luffa aegyptiaca (CABYV-R-TW82) rather than other Asian, American, or European isolates. The deduced amino acid sequences of the P0, P1 and P1–P2 proteins showed >10% variation, whereas the P3, P4 and P3–P5 proteins showed <10% variation when compared to the corresponding proteins of other strains of CABYV worldwide. Thus, according to the polerovirus species demarcation threshold, these new sequences should be regarded as representing strains of a novel previously undescribed Polerovirus species. However, based on their sequence similarity and phylogenetic grouping with the recombinant strain from Taiwan we suggest these sequences represent recombinant strains of CABYV. These are the first full-length genome sequences for CABYV strains from India and this study adds watermelon as host for CABYV in India.