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, managing the field becomes a challenge. Tuber symptom 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 potatoes 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 to symptoms. Previous research has shown the potential for PMTV symptoms to develop with time in storage; therefore, the risk for longer-term storage with infected potatoes needs to be discussed. There are many unknowns, challenges and decisions that need to be addressed regarding PMTV, which is where the new SCRI grant will ultimately offer solutions and mitigate risk.
PVY
The “old” PVY seen in the industry was often the PVY strain “O.” But due to recombination of various strains of the virus, the industry is now dealing with multiple strains of PVY such as N, N:O, N-Wi, and NTN. Varieties react differently to infection by the different strains of PVY. This creates a large and complicated matrix on susceptibility to symptom development and impact on yield and quality. Add on the sensitivity of plant maturity, timing of aphid flights, and use of insecticides and crop oils, and management decisions to lessen risk for the disease get even more complicated.
Detection of PVY, whether out in the field or through the certification process, is a critical part of mitigating the risk of PVY on the crop. In addition, detection of PVY directly by tuber testing of seed potatoes for certification is a major objective of this new SCRI grant.
As fields are being watched and potatoes are being cut open for quality determinations, be on the watch for foliar, internal and external symptoms caused by these viruses. Don’t hesitate to send in samples to identify the cause of the symptoms to develop a management plan for the remainder of the season, the stored crop, or even next year’s potato crop. Stay tuned for more research-based information on how the industry manages PVY and PMTV now and into the future.
Nora Olsen is a professor and extension potato specialist based at the University of Idaho’s Kimberly Research & Extension Center. She can be contacted at norao@uidaho.edu.
Alex Karasev is a professor of entomology, plant pathology and nematology based at the University of Idaho’s Moscow campus. He can be reached at akarasev@uidaho.edu.