Full-length genome sequences of four polerovirus isolates infecting cucurbits in Taiwan determined from total RNA extracted from field samples

Poleroviruses are not mechanically transmittable by sap inoculation, which makes their isolation and multiplication in laboratory hosts for virion extraction and genome sequence analysis difficult. A reverse-transcription polymerase chain reaction (RT-PCR) procedure was modified to amplify the entire genomes of cucurbit-infecting poleroviruses in three sections directly from RNA extracts from infected plant field samples. The procedure was used to determine the first full-length genome nucleotide sequences of four polerovirus isolates from field samples collected in Taiwan. TW1 was identified as Melon aphid-borne yellows virus (MABYV), because it had 90% for P3 and P3-5 and aa identities of 78–88% for all the other proteins. TW19 represents the first full-length sequence for the recently described Suakwa aphid-borne yellows virus (SABYV). The deduced aa sequences for all the proteins of TW19 showed >10% variation compared to all other poleroviruses, though recombination analysis suggested MABYV as the major parent and an unidentified polerovirus as minor parent. R-TW82 was identified as a strain of CABYV, as the deduced CP aa sequence showed >90% identity to that of other CABYV isolates, and recombination analysis suggested that MABYV was the major parent with CABYV the minor parent. Comparative details of the new full-length sequences and their implications on criteria for distinguishing polerovirus species are discussed.