A report on the detection and management of a finding of PSTVd (Potato Spindle Tuber Viroid) in potato breeding material in Northern Ireland, UK.

Potato Spindle Tuber Viroid (PSTVd) is an infectious unencapsidated, small, circular, single-stranded RNA, that causes serious losses in infected potato plants. The pathogen has been detected in several European countries, including in England in the UK. In August 2016, the National Plant Protection Organisation of the Netherlands reported a finding of PSTVd in breeding material that originated in Northern Ireland, UK. A scheme of testing was carried out in Northern Ireland to identify the source of the infected breeding material. Trace-forward and trace-back tests identified 21 infected samples, of which 16 were from true seed samples, out of a total of 591 tested up to November 2016. The number of positive findings in true seed was further reduced to 4 after the samples were surface sterilized. Tests indicated that the infection probably entered the breeding station in Northern Ireland in the mid 1980s, with limited spread in the collection via contaminated breeding equipment. The instance of spread in the field could not be ruled out. Eradication efforts included removal and destruction of infected field stocks and neighbouring stocks, destruction of stored museum material by deep burial, and destruction of other field material by ploughing and exposing tubers to frost. The risk of potato genitor material for spreading PSTVd is discussed. The situation of PSTVd in Northern Ireland, UK is Transient, actionable, under eradication.