Molecular characterisation of papaya ringspot potyvirus isolates from India

Papaya ringspot potyvirus (PRSV) causes major diseases of papaya and cucurbits in the Indian subcontinent. Based on biological properties, PRSV isolates 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 nuclear inclusion b (NIb) gene, the complete capsid protein (CP) gene and the untranslated region (UTR) of both the P and W isolates were cloned and sequenced. Comparative sequence analyses showed that the 3'-UTRs in isolates P and W were 209 nucleotides in length excluding the poly (A) tail, and shared 96% identity. The CP genes of the two isolates were also similar, with 87% nucleotide identity and 93% amino acid identity. The amino acid differences between the CP genes were mostly confined to the amino terminus. The DAG triplet 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 CP. This is the first reported comparison of the molecular characterisation of PRSV-P and W isolates from the Indian subcontinent.