Coat protein of potyviruses. 4. Comparison of biological properties, serological relationships, and coat protein amino acid sequences of four strains of potato virus Y

Four strains of potato virus Y, PVY-D, PVY-10, PVY-18, and PVY-43, obtained from different Australian sources were compared on the basis of their biological, serological and coat protein structural properties. Each of the strains could be distinguished on the basis of their reactions on selected test plant species. Two of the PVY strains, PVY-D and PVY-10, induced symptoms similar to those produced by the PVYO strain group. The reactions of PVY-18 and PVY-43, although comparable to PVYN in some hosts, did not completely match the description of the PVYN strain group. In contrast to the other three strains, PVY-18 could not be transmitted by Myzus persicae in repeated tests. No difference was observed in the serological properties of the four PVY strains in different assay systems, using polyclonal antisera. The amino acid sequences of the coat proteins of PVY-10, PVY-18, and PVY-43 were obtained and compared with the coat protein sequences of pepper mottle virus (PeMV) [Dougherty WG, Allison RF, Parks TD, Johnston RE, Feild MJ, Armstrong FB (1985) Virology 146: 282-292] and PVY-D [Shukla DD, Inglis AS, McKern NM, Gough KH (1986) Virology 152: 118-125]. The homology between the PVY strains ranged from 96.3 to 99.3% and with the PeMV sequence, 91.4 to 92.9%. Based on this high sequence homology, and the previous observation that coat protein sequences of potyvirus strains are always greater than 90% identical, PeMV could be considered a strain of PVY. However, PVY and PeMV are reported to be only distantly serologically related and on this basis PeMV is currently considered to be an independent member of the Potyvirus group.