BIOLOGICAL, SEROLOGICAL, AND MOLECULAR DIFFERENCES AMONG ISOLATES OF POTATO A POTYVIRUS

Sequences of the coat protein (CP) and 3'-end nontranslated region (3' NTR) of 13 isolates and the helper component proteinase (HC) of nine i solates 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 ide ntities were 92.9, 93.4, and 94.8%, respectively. Sequence data, serol ogical tests, and the necrotic local lesions induced in the leaves of the potato hybrid 'A6'-confirmed that tamarillo mosaic virus is a stra in of PVA. The aa substitutions A6T and G7S in the CP N-terminus were correlated with loss of aphid transmissibility. Development of necroti c lesions or nonnecrotic symptoms in the systemically infected leaves or lack of systemic spread in potato cv. King Edward were used to plac e 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 int o three ,groups different from the four groups above. The epitopes of two monoclonal antibodies were mapped by site-directed mutagenesis to the same lysine residue at the CP aa 34.