PVY has re-emerged over the last decade as a serious threat to potato production. Contributing factors include:
Emergence of new strains that cause mild or absent foliar symptoms. Prior to the early 2000s, PVYO was the most prevalent strain found throughout all US potato production regions. PVYO, in general, induces observable foliar symptoms in most potato cultivars. Since 2002, new strains of PVY, commonly referred to as PVYNTN (the tuber necrotic strain) or PVYNWi (Wilga strain, similar to PVYNO), have been rapidly displacing PVYO in all production areas. In general, these new strains cause mild symptoms in most potato cultivars. A lack of easily observable symptoms makes it difficult or impossible to detect infected plants during inspection by certification personnel or by rouging crews. Additionally, these new strains, especially PVYNTN, cause serious damage to potato tubers of certain cultivars, manifested as potato tuber necrotic ringspot disease or PTNRD.
Popularity of cultivars that exhibit mild or transient foliar symptoms. Many of the cultivars released have not been adequately tested against the changing strains of PVY. This disconnect between pathology and breeding has led to the release of cultivars that are tolerant to PVY infection, i.e. they are easily infected, but show mild or transient symptoms. A list of these cultivars is available at Oregon Seed Certification Service under Latent Variety List . A lack of easily observable symptoms makes it difficult or impossible to detect infected plants during inspection by certification personnel or by rouging crews. Despite having few or no symptoms, these cultivars often harbor high levels of PVY and thus serve as sources of inoculum for new infections.
Climate change has altered the range and migration patterns of aphids. Warmer and longer growing seasons, especially in the northern latitudes, has allowed aphids to move further north and pushed seasonal flights later in the growing season. In some areas of the US, later aphid flights means more late season spread of virus. Mature plants of many potato varieties are still susceptible to infection, especially tuber infection. Virus introduced to mature plants often does not manifest noticeable infections in the foliage, but bulking tubers will become infected and subsequently generate infected plants if used as seed potatoes.