Papaya ringspot potyvirus: isolate variability and the origin of PRSV type P (Australia)

We have sequenced the coat protein gene of nine isolates of papaya ringspot virus (PRSV) including six Australian and three Asian isolates and compared these with four previously reported sequences of PRSV. There was up to 12% sequence variation between isolates at the nucleotide level. However, there was no significant difference between the sequences obtained from Australian isolates irrespective of whether they were PRSV type P (cucurbit or papaya infecting) or PRSV type W (cucurbit infecting) and these isolates were more closely related to one another than to any other isolate. These results imply that PRSV-P, first recorded in Australia in 1991, arose locally from PRSV-W (first recorded in Australia in 1978) rather than being introduced. Further, there was no consistent sequence difference between PRSV-P and PRSV-W isolates that would obviously account for their host range difference.