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Biological, Serological, and Molecular Differences Among Isolates of Potato A Potyvirus

First, second, fifth, sixth, seventh, and ninth authors: Institute of Biotechnology, Viikki Biocenter 1, P.O. Box 56, FIN-00014 University of Helsinki, Finland; third author: Bundesanstalt für Züchtungsforschung an Kulturpflanzen, Institut für Resistenzforschung und Pathogendiagnostik, Postfach 1505, D-06435 Aschersleben, Germany; fourth author: Institute of Biotechnology, Viikki Biocenter 1, P.O. Box 56, FIN-00014 University of Helsinki, Finland, and Institute of Chemical Physics and Biophysics, Akadeemia tee 23, EE0026, Tallinn, Estonia; and eighth author: The Horticultural and Food Research Institute of New Zealand Ltd., Mt. Albert Research Centre, 120 Mt. Albert Road, Private Bag 92 169, Auckland, New Zealand

Sequences of the coat protein (CP) and 3′-end nontranslated region (3′NTR) of 13 isolates and the helper component proteinase (HC) of nine isolates of potato A potyvirus (PVA) were determined and compared with the eight previously determined PVA CP and 3′NTR sequences and one HC sequence. CP amino acid (aa), 3′NTR nucleotide, and HC aa sequence identities were 92.9, 93.4, and 94.8%, respectively. Sequence data, serological tests, and the necrotic local lesions induced in the leaves of the potato hybrid ‘A6’ confirmed that tamarillo mosaic virus is a strain of PVA. The aa substitutions A6T and G7S in the CP N-terminus were correlated with loss of aphid transmissibility. Development of necrotic lesions or nonnecrotic symptoms in the systemically infected leaves or lack of systemic spread in potato cv. King Edward were used to place the PVA isolates into four strain groups, but this grouping was not correlated with any differences in CP, HC, or 3′NTR. Recognition of CP by three monoclonal antibodies was used to place the PVA isolates into three groups different from the four groups above. The epitopes of two mono-clonal antibodies were mapped by site-directed mutagenesis to the same lysine residue at the CP aa 34.