Variability of the coat protein gene of Citrus psorosis virus in Campania, southern Italy.

Variability of the Coat protein (CP) gene of Citrus psorosis virus (CPsV) was assessed serologically, and by sequence analyses of two genomic regions located in the 3' (region C) and 5' (region V) halves of the gene. Analysis of 53 psorosis field sources from Campania, Italy, with 23 monoclonal antibodies revealed nine serogroups and at least ten different epitopes. Sequence analysis of 19 of these sources showed limited nucleotide diversity of the CP gene in the population. Diversity was slightly higher in region V than in region C. Phylogenetic analysis of the V and C regions of the CP showed that the Campania sources of CPsV were clearly separated from the CPsV-4 isolate from Florida. For C region, most of the CPsV sources clustered together, whereas two clusters were observed for region V. The ratio between nonsynonymous and synonymous substitutions for regions C (0.083) and V (0.345) indicated negative selective pressure for amino acid changes, more intense in the C region. No correlation was found between serogroups and specific aminoacid sequences, field location or citrus cultivar.