Diagnostics and Molecular Biology Section, Science & Advice for Scottish Agriculture, Edinburgh, UK Characterization of Viruses Infecting Potato Plants from a Single Location in Shetland, an Isolated Scottish Archipelago Rasmus asmus J. J. Mortensen ortensen 1,2 1,2 , Xinyi inyi Shen hen 1,3 1,3 , Alex lex Reid eid 1 and and Vincent incent Mulholland ulholland 1 AuthorsÕ addresses: 1 Diagnostics and Molecular Biology Section, SASA (Science & Advice for Scottish Agriculture), Roddinglaw Road, Edinburgh EH12 9FJ, UK; 2 Present address: Department of Physics and Nanotechnology, Aalborg University, Skjernvej 4A, 9220 Aalborg Øst, Denmark; 3 Present address: Department of Soil Environmental Sciences, Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China (correspondence to V. Mulholland. E-mail: vince.mulholland@sasa.gsi.gov.uk) Received November 13, 2009; accepted January 5, 2010 Keywords: Potato virus A, Potato virus S, Potato virus V, Potato virus X, Scotland, Shetland Abstract Sequence data were obtained from 29 isolates of Potato virus A (PVA), Potato virus S (PVS), Potato virus V (PVV) and Potato virus X (PVX) infecting nine tubers from Shetland, one of the most remote inhab- ited islands in the United Kingdom. These isolates were sequenced in the coat protein region, as were 29 Scottish mainland isolates of the same four potato virus species, and these 58 isolates were compared to previously published sequence data. This has allowed the characterization of viruses from a relatively iso- lated location, where there is little production of ware potatoes and no seed potato production. Phylogenetic homogeneity of the Shetland isolates of PVS and PVV was apparent. PVX was more heterogeneous, and Shetland isolates cluster with the Scottish isolates in a group which includes Asian and European isolates. For PVA, the majority of the Shetland and Scottish mainland isolates formed a predominantly Scottish grouping, with the remaining Shetland and Scottish mainland isolates clustering with a previously charac- terized Scottish isolate. There were three main groups of PVA, of which the Scottish grouping was the only one which did not have a fully characterized represen- tative. To extend the characterization of PVA, the nucleotide sequence of the full polyprotein region encoding all the gene products of an isolate from Shetland was determined. Introduction Potato viruses represent a significant threat to potato crops worldwide and have been the subject of much study, particularly of their impact on commercial potato production (Salazar 1996) and germplasm movement (Jeffries 1998). Potato virus A (PVA) is an aphid-transmitted virus of the genus Potyvirus, family Potyviridae. It has a natural host range limited to potato, causing mild symptoms but with some culti- vars remaining asymptomatic. It is found worldwide and can cause yield reduction of up to 40% (Wale et al. 2008). When PVA occurs in combination with Potato virus X (PVX; genus Potexvirus, family Flexivir- idae) and ⁄ or Potato virus Y (PVY; genus Potyvirus, family Potyviridae), the disease symptoms may be severe. Potato virus S (PVS; genus Carlavirus, family Flexiviridae) is commonly transmitted mechanically but can also be aphid transmitted. It is the most fre- quently found potato virus occurring worldwide, but induces mild symptoms, with yield losses of <20% (Wetter 1971). Potato virus V (PVV; genus Potyvirus) is aphid transmitted and has a natural host range con- fined to potato (Calvert et al. 1980). PVV is predomi- nantly symptomless in most potato cultivars. European isolates of PVV, thought to have reached the United Kingdom in the early 1970s (Calvert et al. 1980), have little genetic variability and have no known strains (Oruetxebarria and Valkonen 2001). PVX has a worldwide distribution and is readily trans- mitted mechanically (Jeffries 1998). Symptoms are usu- ally mild mosaic and mottle, with a yield reduction of 15–20%, but mixed infections with PVA may result in extreme losses. PVX can be classified into strains on the basis of resistance breaking or virulence ⁄ hypersen- sitivity (Cockerham 1955, 1970). In single infections, PVA, PVS, PVV and PVX usually induce mild symp- toms, as outlined previously, but simultaneous This article, ÔCharacterization of Viruses Infecting Potato Plants from a Single Location in Shetland, an Isolated Scottish ArchipelagoÕ was written by R. J. Mortensen, X. Shen, A. Reid and V. Mulholland of Science & Advice for Scottish Agriculture. It is published with the permission of the Controller of HMSO and the Queen’s Printer for Scotland. J Phytopathol 158:633–640 (2010) doi: 10.1111/j.1439-0434.2010.01672.x Ó 2010 Crown copyright