M A R C H 2 0 1 8 POTATO GROWER 27 North Dakota Certified Seed Potatoes 2017 Crop Winter Grow Out Results by Kent Sather, North Dakota State Seed Departement Director A post-harvest winter test is a requirement for North Dakota certi- fied seed potato lots that will again be re-certified during the 2018 growing season. Tuber samples taken from harvested seed lots of the 2017 crop provide an estimate of virus incidence that may be pres- ent in the next generation of seed potatoes. Samples are grown in a warm climate, and trained inspec- tors record any virus infected plants. Primary viruses recorded are Potato Virus Y (PVY or Mosaic) and Potato Leaf Roll Virus (PLRV). Eligibility to re-certify seed lots depends on tolerance limitations stated in North Dakota rules and regulations for certification of seed potatoes. No more than 0.5% virus is allowed in a seed lot that will be planted for re-certification. Samples were taken by North Dakota certified seed potato grow- ers during harvest and submitted to North Dakota State Seed Department (NDSSD) staff in Grafton, North Dakota, then shipped to Florida. North Dakota’s post-harvest test plot is planted near Homestead, Florida and man- aged by Alger Farms, LLC. The 12 acre plot was planted November 14- 20, 2017 by NDSSD staff. Inspections were completed January 1-16, 2018. North Dakota certified seed growers submitted 364 seed lots, represent- ing 8,000 acres of the 11,912 acres passing the 2017 summer inspec- tions. Based on North Dakota’s win- ter test disease tolerances, sample lots representing 5,711 acres were deemed eligible for recertification in 2018. The only factor causing ineligibility of the remaining 2,287 acres was PVY incidence greater than the 0.5% tolerance. Table 1 shows a comparison of eligi- ble acres by percent and represented acres with zero PVY recorded at the winter test. The 2017 crop eligible acres were down by 11% compared to the previous year. In addition, the samples with no PVY recorded were down by 11%. Certified seed growers will need to be discerning in replanting seed lots. Less acreage is available for recertification, and of those acres, there may be slightly more PVY incidence in the seed. PVY is a virus that can easily be spread from field to field, vectored by aphids. This is a community dis- ease, and difficult to control. Isolation of seed potato fields con- tinues to be a factor in reducing dis- ease spread. Seed lots planted far from other commercial and seed potato fields that may be infected with PVY tend to have zero or very low levels of PVY. However, as seed lots are increased over generations, exposure to disease increases. PVY levels within the seed lot increase, potentially causing rejection from the certification process. This was confirmed in our inspection results as older generation lot had higher percent of ineligible acreage due to PVY. An electronic version of the North Dakota Approved Seed List for Recertification based on the 2017 Crop winter test inspections can be found at www.ndseed.com under the Potato Directory tab. Crop Year Total Acres Represented Eligible Acres % Eligible Acres Acres 0 PVY % 0 PVY 2014 9,007 6,850 76 4,126 46 2015 8,820 7,209 81 5,742 65 2016 8,338 6,797 82 4,881 58 2017 8,000 5,711 71 3,721 47