Changing Faces

Published online: Mar 30, 2022 Articles, Seed Potatoes Nora Olsen, Alex Karasev & Jonathan Whitworth
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This article appears in the April 2022 issue of Potato Grower.

Researchers, extension personnel, and the potato industry are partnering on a four-year project to tackle the issue of viruses in the potato industry. The “Potato Virus Initiative: Developing Solutions” is a federally funded Specialty Crop Research Initiative (SCRI), multi-state research and extension-based program with the mission to develop sustainable, system-based management strategies and decisions aids. Specific focus is being placed on potato mop-top virus and potato virus Y (PVY) by enhancing diagnostic and detection methods, breeding for resistance, and creating applied solutions for direct use by the potato industry to create economical and efficient means to manage the viruses.

One part of the project is directly related to PVY since the virus unfortunately continues to trouble and complicate the potato industry. Presence of the disease can be a major reason for seed lot rejection or downgrade, seriously affecting seed potato production in the U.S. (especially in the past 20 years), and occasionally affecting tuber yield and quality of the commercial potato production.

The dynamics of PVY strain abundance and composition in the Pacific Northwest were monitored as part of the federal SCRI-funded project on tuber necrotic viruses. Based on the testing of more than 10,000 foliar samples during Idaho seed certification winter grow-out evaluations and seed lot trials in Washington State, a dramatic shift in the PVY strain composition was revealed in the Pacific Northwest between 2011 and approximately 2016. During this time period, the prevalence of the ordinary, PVYO strain in seed potatoes dropped eight- to tenfold, concomitantly with the rise of recombinant strains PVYN-Wi and PVYNTNa, which together accounted for 98% of all PVY positives by 2021. The two most prevalent PVY strains, N-Wi and NTN, tend to be asymptomatic in the leaves or express mild, transient leaf symptoms in the currently most widely grown potato cultivars.

Why is it important to know the dominant PVY strains in your area and seed lot? In order to assess the risk of PVY on yield and quality, you will need to know the variety response to PVY infection and to a particular PVY strain. To add another layer of complexity, there are isolates within each strain that may impact how the variety reacts to the infection. Recent research has identified the risk factor for commonly grown varieties and the effect of PVY strain on quality, especially for the risk of internal or external tuber symptoms. This research was done on over 60 varieties. Notable findings:

  • Russet Norkotah did not show necrotic tuber symptoms when infected with five different PVY strains.
  • Russet Burbank may show tuber symptoms if infected with NTN and N:O, depending on the isolate, but not from the other PVY strains.
  • Ranger Russet may show tuber symptoms when infected with O and NTN, and N:O and N-Wi, depending on the isolate tested.

These results indicate that there is a variety-to-virus strain interaction, and that even isolates within a strain can react differently.

Changes in PVY strain prevalence create the need for adjustments in diagnostic services, potato certification, and breeding programs developing PVY resistance. Breeding for resistance is a major goal of the SCRI-funded project, and shifts in PVY strain popularity complicate the breeding goal. The best resistance to PVY comes from an Ry gene, which provides broad-scale resistance across multiple PVY strains. Russet varieties with the Ry gene are Payette Russet and Castle Russet. 

Seeing how relatively quickly the Pacific Northwest shifted from having the PVYO strain be the most dominant, to the recombinant strains PVYN-Wi and PVYNTNa, emphasizes the need for continual monitoring of PVY strains dominant in the industry and to evaluate the risk of variety-specific yield and quality issues based on PVY strain infection.

 

Prevalence of six PVY strains circulating in Washington and Oregon Columbia Basin commercial potato fields

Season

O

N:O

N-Wi

NTN

NE-11

N

Unclassified

2011

63%

0%

27%

8%

1%

0%

1%

2012

31%

3%

37%

13%

6%

6%

4%

2013

17%

2%

47%

21%

10%

0%

3%

2014

16%

2%

59%

6%

8%

0%

9%

2015

7%

9%

53%

24%

1%

0%

7%

2016

6%

4%

76%

12%

0%

0%

2%

2017

9%

2%

69%

18%

1%

0%

2%

2018

2%

4%

66%

26%

0%

0%

3%

2019

7%

8%

61%

24%

0%

0%

1%

2020

1%

5%

77%

17%

0%

0%

0%

2021

0%

2%

78%

20%

0%

0%

0%

Results from this long-term project have been published in the journal Plant Disease and the American Journal of Potato Research.

Nora Olsen (norao@uidaho.edu) is an extension potato specialist with the University of Idaho. Alex Karasev (akarasev@uidaho.edu) is a UI plant virologist. Jonathan Whitworth (jonathan.whitworth@usda.gov) is a potato pathologist with USDA’s Agricultural Research Service based in AberdeenIdaho.