Genomic heterogeneity in Pea seed-borne mosaic virus isolates from Pakistan, the centre of diversity of the host species, Pisum sativum

Abstract

A range of isolates of Pea seed-borne mosaic virus (PSbMV) was compared in the segments of the genome representing the partial NIb/CP/UTR and the partial P1-Pro/HC-Pro coding regions. Nucleotide and amino acid sequences, and a phylogenetic analysis of the CP region, divided isolates with available sequence information into two groups, one representing pathotype 4, the other pathotype 1. The pathotype 1 group showed greater diversity than the pathotype 4 group. A comparison of 14 isolates, S6 (a pathotype 4 isolate), US (a pathotype 1 isolate) and 12 isolates from Pakistan, by ribonuclease protection assay (RPA) using cRNA transcripts of the cloned partial NIb/CP/UTR regions of the S6, US and Pakistani isolate PK9 placed them into three distinct phylogenetic groups. RPA with a partial P1-Pro/HC-Pro cRNA probe identified a greater level of variation which was too high to be used for generating an overall phylogeny. Thus, RPA identified greater molecular diversity in PSbMV than described hitherto.We conclude that, in addition to the pathotypes 1 and 4 typified by US and S6 respectively, isolates of PSbMV from Pakistan include previously unrecognised molecular variants, and this accords with our previous recognition of new pathotypes from Pakistan.