Molecular variability of apple chlorotic leaf spot virus in different hosts and geographical regions

ABSTRACT: A fragment of 500 nt corresponding to 85% of the coat protein (CP) gene of 35 isolates of apple chlorotic leaf spot virus (ACLSV) from different hosts and geographical areas were sequenced and the results were compared with those already available. Sequence alignments at the amino acid level showed that most of the variability was present in the N-terminal part of the CP cistron (overlapping with the movement protein) whereas the C-terminus was significantly less divergent. Four isolates (APR-EA5, PE 150, PE 154 and PE 297) differed in showing high variability throughout the CP gene. Phylogenetic analysis at the nucleotide and amino acid level clustered the isolates in two groups: A, containing the great majority of the isolates, and B, containing the above four diverging isolates. A few subclusters could be identified in group A: pome fruit isolates clustered together in two different groups, one being close to the two almond isolates and one subcluster containing all the Spanish isolates. One subgroup was composed of three similar sequences each obtained from different hosts (peach, apricot, plum) originating from three different countries (Italy, Lebanon and Jordan, respectively). In Western blot analysis, three different migration rates were found for the CPs of ten representative isolates. No correlation was observed between the electrophoretic mobility of CPs and the phylogenetic groups, indicating that other factors besides the primary structure must account for the different electrophoretic mobilities observed.