Papaya ringspot potyvirus (PRSV) causes major diseases of papaya and cucurb
its in the Indian subcontinent. Based on biological properties, PRSV isolat
es are classified as either papaya infecting (P), or non-papaya infecting (
W) types. To characterise the P and W isolates from India at the molecular
level, c. 1.7 Kb of the 3'-terminal regions comprising a part of the nuclea
r inclusion b (NIb) gene, the complete capsid protein (CP) gene and the unt
ranslated region (UTR) of both the P and W isolates were cloned and sequenc
ed.
Comparative sequence analyses showed that the 3'-UTRs in isolates P and W w
ere 209 nucleotides in length excluding the poly (A) tail, and shared 96% i
dentity. The CP genes of the two isolates were also similar, with 87% nucle
otide identity and 93% amino acid identity. The amino acid differences betw
een the CP genes were mostly confined to the amino terminus. The DAG triple
t associated with aphid transmissibility was present in the CP of isolate W
, but it was replaced by DAD in the P isolate. The partially sequenced NIb
genes were also 90% identical, but isolate W contained an additional amino
acid (threonine) just upstream of the cleavage site (Q/S) between NIb and C
P. This is the first reported comparison of the molecular characterisation
of PRSV-P and W isolates from the Indian subcontinent.