Molecular Variability Among Isolates of Prunus Necrotic Ringspot Virus from Different Prunus spp.

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Abstract
Viral sequences amplified by polymerase chain reaction from 25 isolates of Prunus necrotic ringspot virus (PNRSV), varying in the symptomatology they cause in six different Prunus spp., were analyzed for restriction fragment polymorphisms. Most of the isolates could be discriminated by using a combination of three different restriction enzymes. The nucleotide sequences of the RNA 4 of 15 of these isolates were determined. Sequence comparisons and phylogenetic analyses of the RNA 4 and coat proteins (CPs) revealed that all of the isolates clustered into three different groups, represented by three previously sequenced PNRSV isolates: PV32, PE5, and PV96. The PE5-type group was characterized by a 5' untranslated region that was clearly different from that of the other two groups. The PV32-type group was characterized by an extra hexanucleotide consisting of a duplication of the six immediately preceding nucleotides. Although most of the variability was observed in the first third of the CP, the amino acid residues in this region, which were previously thought to be functionally important in the replication cycle of the virus, were strictly conserved. No clear correlation with the type of symptom or host specificity could be observed. The validity of this grouping was confirmed when other isolates recently characterized by other authors were included in these analyses.