Severity of infection of Moroccan barley yellow dwarf virus PAV isolates correlates with variability in their coat protein sequences

Biological properties and deduced amino acid sequences of the overlapping coat and 17kDa proteins were compared for 12 barley yellow dwarf virus PAV-type isolates collected at different locations in Morocco. The biological variability of the 12 isolates was investigated by inoculation to a set of as many as eight barley cultivars and an oat cultivar. Significant biological variability was observed among the Moroccan PAV-type isolates, with the isolates falling into two clusters. Cluster 1 contained isolates MA9501, MA9502, MA9504, MA9512 and MA9513, and cluster 2 the MA9415, MA9505, MA9508, MA9511, MA9514, MA9516 and MA9517. Isolates of cluster 2 produced more severe symptoms and stunting than did those of cluster 1 when inoculated to appropriate index plants. In parallel, the nucleic acid sequences were obtained for the region containing the cistron coding for the coat protein (CP) and 17 kDa protein for all 12 isolates by reverse transcription followed by the polymerase chain reaction. Sequence homology grouping yielded the same two clusters of the isolates as found by measuring biological variability. Comparisons of the CP sequences between the two clusters revealed 87.4% to 90.5% nucleotide identity and 82.6% to 87.6% amino acid identity. Comparison with other sequenced isolates demonstrated that the CP's of cluster 1 were closely related to the Australian (Vic-PAV), the North American (NY-PAV, P-PAV), and Japanese (JPN-PAV) PAV-type isolates. The CP's of cluster 2, on the other hand, were closely related to the North American PAV-129 isolate. Finally, an RFLP test on CP gene-derived PCR products has been developed which distinguishes between the two clusters of the PAV-type isolates.