Potato Grower

May 2021

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36 POTATO GROWER | MAY 2021 Diggin' In Diggin' In Tackling the problem of evolving viruses Going Viral VIRUSES | By Nora Olsen & Alex Karasev Virus. This past year, we have been impacted by a virus pathogen more than we ever could have imagined. Historically, the potato industry has battled viruses for many years. Some viruses have subsided; others have persisted, changed or established a greater presence. Potato leaf roll virus (PLRV) was once the primary virus of concern, and then we were given (chemical) tools that made it almost nonexistent, at least for now. PVY was dominated by the O-strain of the virus, but now the major battle is against the N-Wi strain. Potato mop top virus (PMTV) has become more widely known and seen. PVY and PMTV are the focus of a new USDA Specialty Crop Research Initiative (SCRI) project to develop sustainable system-based management strategies for the two vector-borne, tuber-necrotic viruses. This multi- state, multi-year project encompasses multiple approaches to ultimately help the industry respond and develop economical and efficient means to manage the two viruses. Unfortunately, these two viruses are not easy problems to tackle. PMTV & TOBACCO RATTLE VIRUS Potato mop-top virus (PMTV) is vectored or transmitted by the powdery scab protist. Alone, powdery scab can be difficult to manage because it is persistent as resting spores for years in the soil. The presence of PMTV makes the task of managing powdery scab even more cumbersome. Once the soil becomes infected with both, man- aging the field becomes a challenge. Tuber symp- tom development can be nil or minimal although the virus may still be present. This creates the situation for asymptomatic potatoes — no visible symptoms, but the virus is present. Typical symptoms are dark brown arcs in the flesh of the tuber. Raised ring spots on the skin may also be observed. These are classic symptoms, but exceptions to the norm are often seen, especially in different growing regions and among various cultivars. This is a problem that can sneak up on you. Any tuber symptoms should be tested to identify whether you need to target management against PMTV or are you battling tobacco rattle virus ( also known as corky ring spot). If your po- tatoes are infected with tobacco rattle virus, your next action is for stubby root nematode control. Some varieties are prone to developing PMTV symptoms, whereas others are not as sensitive Classic tuber symptoms of potato mop-top virus. Note the multiple brown arcs. Foliar symptoms are not very common.

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