Over the last several years, readers of this column have seen quite a number of publications, by myself and others, on the subject of potato virus Y (PVY). This virus disease is present everywhere potatoes are produced and, with the continuing decline in potato leaf roll virus (PLRV), has become the most important virus disease of potato on a worldwide basis. The recent influx of new strains of PVY into North America, including the so called PVY"NTN" or "tuber necrotic strains," has rendered this virus even more prominent.
With the help of a Specialty Crops Research Initiative (SCRI) grant, I and a team of fellow scientists from across the United States are currently performing extensive research on PVY, with particular emphasis on the new strains. The grant is entitled "Development of comprehensive strategies to manage Potato Virus Y in potato and eradicate the tuber necrotic variants recently introduced into the United States." I invite you to access our website at www.potatovirus.com. There is a wealth of information contained on the website about the project and about the virus. PVY management guidelines for seed producers are also available.
You would think that with all the attention being paid to PVY these days, we might be seeing some progress in reducing the amount of virus in seed potatoes. While information on this subject can be hard to come by, I recently encountered a couple sources of information I think you'll find interesting because they show direct evidence that we are starting to see a reduction of PVY levels in our seed.
The first of these sources is the results from the Washington Commercial Seed Lot Trial. Planted each summer in Othello, Wash., this trial consists of 200 tuber samples of seed potatoes purchased for use in commercial fields in the Columbia Basin of Washington-Oregon. The samples are collected and submitted to Washington State University Researchers for inclusion in the grow-out trials by the commercial grower who bought them. Participation is completely voluntary. This year's results were impressive. In samples of 167 seed lots originating from nine different states and five different Canadian provinces in the trials last season, there were only eight seed lots in the entire trial that contained more than 10 percent PVY! All but one of these eight seed lots were either Shepody or Russet Norkotah, two varieties that are notorious for PVY problems.
Another information source was the report given this spring to Idaho Seed Potato Producers by the Idaho Crop Improvement Association (ICIA), the agency that certifies seed potatoes in Idaho. The report contains a table listing the amount of PVY that was found in Idaho seed lots during the winter grow-outs in California over the last seven years. Remember that the ICIA, at the behest of the seed producers themselves, determines PVY levels in all seed lots in the California grow-outs using the ELISA test and no longer relies on visual symptoms.
When the testing program began with the 2007 seed crop, 60 percent of the 551 seed lots in the winter grow-out had at least one PVY infected plant in them. The number of seed lots with more than 2 percent PVY (the level above which the seed lot is no longer eligible be replanted in the seed program or "recertified") was 27 percent. In the 2010 crop (653 lots), the percentage of seed lots with any PVY had dropped to 40 percent and the percentage of seed lots ineligible for recertification had dropped to only 8 percent! I'd call that progress!
It shouldn't surprise any of you that our SCRI virus group recommends using ELISA for determining PVY levels in seed lots during winter grow-outs. It's the best way to get accurate PVY readings and avoid planting problem seed lots back into your seed program. PG