Potato virus Y (PVY) in Seed Potato Certification

Abstract

In the EU and many other countries worldwide, seed potatoes require certification to be marketed. In most of the European national and international seed potato regulations, the tolerances for viruses are at present based on a combination of virus incidence and symptom severity. Historically all severe viruses were usually the origin of severe virus diseases, and mild viruses, in general, were seen to cause mild diseases. However, the situation has changed, especially for the most economically important virus, Potato virus Y (PVY), which is considered a severe virus. Investigation of PVY-infected potato leaf samples from Bavarian potato seed certification found that the "classical" O and the N strains, predominantly responsible for severe virus diseases, represented less than 1% of the infections present. Ca. 99% of the PVY infections were comprised of the new recombinant strains PVY NTN and PVY N W. The ratio between these recombinants differed substantially. Differences in susceptibility of particular cultivars to certain PVY strains seem to be one reason for that. Therefore, the ratio of the recombinants may depend upon which cultivars are favoured in different potato growing areas or countries.In greenhouse tests, PVY NTN and PVY N W were associated with both severe and mild disease symptoms. In corresponding field tests, the symptom severity differed considerably. Furthermore, there was no correlation detected between virus concentration and symptom severity.These results will contribute to a worldwide discussion on the elimination of the criterion virus symptom severity from potato seed certification during the forthcoming months. The discussion follows amendments made to international seed potato regulation documents. National regulations must be aligned by the EU member states until January 2016.

The movement of potato virus Y (PVY) in the vascular system of potato plants

“…In fact, while there may be cases where PVY NTN was not detected in progeny tubers, due to a low titer of the virus, PVY N-Wilga was detected in almost all progeny tubers, suggesting that the titer of PVY N-Wilga virus particles was higher in those tubers. This information might explain why PVY N-Wilga strains are increasing in prevalence in some European countries (Dupuis et al 2013;Dupuis and Schwaerzel 2011;Rigotti et al 2011;Lindner et al 2015).…”

Resistance of Potato Cultivars as a Determinant Factor of Potato virus Y (PVY) Epidemiology

“…In Switzerland, the prevalence of PVY N-Wi was at about 17% in 2008 (Rigotti et al 2011). It was comparable/slightly higher in the USA and Canada, with 18% and 33%, respectively, in 2006, but it was much higher in Germany, with 63% in 2011 (Lindner et al 2015). The prevalence of PVY N-Wi seems to have increased in Switzerland by 12% from 2003 to 2008 (Rigotti et al 2011) and in Canada by 9% from 2004 to 2006 (Gray et al 2010).…”

“…The prevalence of PVY N-Wi seems to have increased in Switzerland by 12% from 2003 to 2008 (Rigotti et al 2011) and in Canada by 9% from 2004 to 2006 (Gray et al 2010). PVY N-Wi seems to have been relatively stable in Germany, with an increase of 4% from 2009 to 2011 (Lindner et al 2015) and to have decreased in the USA by 9% from 2004 to 2006 (Gray et al 2010). Since then, this percentage has significantly increased to reach 47% in 2012 (+ 23% since 2009), PVY N-Wi becoming the most prevalent strain in the USA (Stewart Gray, personal communication).…”

“…The PVY recombinant strains, PVY NTN and PVY N-Wi , spread rapidly during the last 30 years into European seed-potato production and almost replaced the historical strains (Kerlan et al 2011). The spread of PVY N-Wi was more recent than the spread of PVY NTN , as this strain was first reported in Poland in the early 1990s (Chrzanowska 1991) and has since been reported in several countries, including France (Glais et al 2005;Rolland et al 2008), the USA, Canada (Gray et al 2010), Spain (Blanco-Urgoiti et al 1998), Germany, the UK (Schubert et al 2007;Lindner et al 2015), the Netherlands (van der Vlugt et al 2007), Belgium (Kamangar et al 2014) and Switzerland (Rigotti et al 2011). In Switzerland, the prevalence of PVY N-Wi was at about 17% in 2008 (Rigotti et al 2011).…”

“…The prevalence of PVY N-Wi seems to increase in the countries where periodic PVY strain monitoring has been performed. The following hypothesis have been proposed to explain the increase of the prevalence of PVY N-Wi strains: climate change and changes in cultural practices (Rolland et al 2008), a higher transmission rate of PVY N-Wi strains by aphids (Verbeek et al 2010), a faster translocation of PVY N-Wi than PVY NTN (Dupuis 2017), a faster spread in the field (Dupuis et al 2014), a lower expression of symptoms by PVY N-Wi -infected plants, which are then less susceptible to being eliminated from fields by roguing (Chrzanowska 1991;Glais et al 2005), acquisition of an enhanced pathogenicity (Bellstedt and Visser 2016) and finally, a shift in the cultivars that are produced, with the progressive introduction of cultivars susceptible to PVY N-Wi and resistant to other PVY strains (Lindner and Billenkamp 2005;Lindner et al 2015;Funke et al 2017). Indeed, it was shown through surveys in Germany and the USA that the susceptibility of the cultivars varies among PVY strains.…”