4:45:00 PM-5:00:00 PM        Lessons learned from a grower supported mail-away PVY test project
Chakradhar Mattupalli, Washington State University

               Potato virus Y (PVY) is the leading cause of seed lot rejections by seed potato certification programs in the U.S., as well as a significant disruptor for seed potato supply chain as certification process currently requires breaking tuber dormancy resulting in certification results to be delivered close to when the seed is shipped for replanting. Motivated to provide expedited results based on the detection of PVY directly from tubers, a grower supported mail-away PVY test project with 17 cooperators from 12 U.S. states involving 103 seed lots representing 36 cultivars was implemented in 2022. Onsite trained farm personnel used mail-away test kit materials to sample potato tuber tissues onto Whatman Flinders Technology Associates Plantsaver® (FTA) cards and shipped them to an ISO-certified molecular diagnostic laboratory for PVY detection using a reverse-transcription quantitative real-time polymerase chain reaction (RT-qPCR) assay. The mean turn-around time to process and report seed lots by the diagnostic lab was 12-days. The RT-qPCR results were then compared to the PVY levels that cooperators provided from their respective state seed certification programs for their seed lots. To account for differences in the state seed certification standards, seed generation levels, and privacy concerns, a one percent PVY threshold level was adopted to compare results from both sources. With this one percent threshold limit, an agreement was observed for 88 % of seed lots (n=96). A survey of the cooperators indicated labor constraints to adopt the diagnostic protocol but also showed an interest in testing for additional potato pathogens besides PVY. The mail-away PVY test project provided a template for implementing a high-throughput molecular diagnostic protocol for direct tuber testing for PVY with a short turnaround time as well as a roadmap for responding rapidly to existing and emerging potato pathogens.

3:45:00 PM-4:00:00 PM             Dormant tuber testing for potato virus Y: comparison to the winter grow-out test
Lisa Tran, University of Idaho

               Six seed potato lots were subjected to direct dormant tuber testing (DDTT) followed by a winter grow-out (WGO). 400-tuber samples of potato cultivars Chieftain, Dakota Russet, Pacific Russet, Ranger Russet, Russet Burbank, and Russet Norkotah were sampled in pools of five, extracted, and PVY was detected using RT-qPCR. The same tubers were subjected to Rindite treatment and shipped to Hawaii for a regular winter grow-out (WGO) conducted by the Idaho Crop Improvement Association, the seed certification agency for the state. Once the plants reached approximately 1 ft in height, leaf samples were collected from each plant and shipped to the seed certification lab, where they were pooled in five (different composite samples from DDTT) and tested for the presence of PVY using ELISA methodology. The six potato seed lots tested by DDTT methodology produced PVY infection rates between 0 and 6.6%; the same tubers from these six seed lots tested by winter grow-out (WGO)/ELISA leaf assay produced rates between 0 and 17.5% PVY infection. There was a close correlation between the DDTT and WGO data, with both methods producing similar results. One-way ANOVA analysis determined that the mean PVY% produced by DDTT is not significantly different compared to WGO. The WGO may have a lower accuracy simply due to reduced plant emergence during the grow-out. 

4:00:00 PM-4:15:00 PM             Can a Fast and Furious Vine Kill Speed at Late Tuber Maturity Make a Difference in Blackspot Bruise Incidence?
Pamela Hutchinson

               Field research was conducted at the University of Idaho Aberdeen Research and Extension Center in 2021, 2022, and 2023 with sulfuric acid, diquat, or pyraflufen ethyl for a fast, medium, and slow vine-kill speed, respectfully, when natural potato vine senescence was less than 10% or approximately 40%, representing early or late tuber maturity timing. Ranger Russet, a late-maturing variety relatively susceptible to bruise, and Russet Burbank were used. Vine kill was 95% or greater within three days after application of sulfuric acid at either timing to either variety. Otherwise, Russet Burbank vine-kill was faster with diquat or pyraflufen ethyl than when the same were applied to Ranger Russet early or late. Tubers were collected 2 weeks after vine-kill reached 95% in a given treatment and placed in 50 F storage for 24 hours. Nontreated plots were also harvested at the same time. A weight was then dropped on the stem and bud ends, tubers were stored at 70 to 80 F for 48 hours, and then peeled and assessed visually for bruising. Overall, bruise incidence was less for Russet Burbank than it was for Ranger Russet, regardless of tuber maturity at time of application. As expected, Ranger Russet tuber bruise incidence was relatively greater with late-maturity vine-kill, than it was when vine-kill was at early-maturity. However, when fast-kill, sulfuric acid was applied at late maturity, bruising was less compared to bruising with slow- or medium-kill speed at the same timing, or to bruising on tubers from nontreated controls. Implications are that even though Blackspot bruise incidence will likely be higher for a susceptible variety, such as Ranger Russet, when vine-kill occurs at late- rather than early-maturity, incidence will not be as high at that late-maturity timing when vine-kill is fast than when it is slower.         

4:15:00 PM-4:30:00 PM            Reduced fungicide applications for managing early blight/ brown spot on disease resistant cultivars.
Jeff Miller, Miller Research

               Early blight, brown spot, and white mold are the most common foliar diseases in southern Idaho and can cause significant yield reductions if not managed. Russet cultivars differ in their susceptibility to these foliar diseases, but work has not been done evaluating how this variation in susceptibility would affect the performance of a standard fungicide program. Field trials were conducted in 2022 and 2023 with Clearwater Russet and Dakota Russet comparing three different fungicide programs that varied by the number of applications to a non-treated check. The trial was arranged as a two-way factorial (variety x fungicide program) with four replications. The fungicide programs were: 1) standard (four foliar applications), 2) reduced foliar (two foliar applications), and 3) one in-furrow and one foliar application (1 IF-1Fol). Early blight and brown spot severity were visually rated together and the number of white mold lesions were counted from all plants in the center two rows of each four-row plot. In 2022, early blight/brown spot (EB/BS) severity was low and fungicide programs did not reduce disease severity or increase yield. In 2023, EB/BS severity was high and the reduced foliar and 1 IF-1Fol programs were not as effective as the standard program for EB/BS control or for improving late-season plant vigor. White mold incidence was low both years and all treatments were similar. All fungicide programs numerically increased yield. Dollar return was significantly increased by all programs over the non-treated control and all fungicide programs were similar. Interactions between variety and fungicide program were not observed. In both years, using the reduced foliar or 1 IF-1Fol did not result in lower yield or dollar return compared to the standard program for Dakota and Clearwater. Reduced foliar programs could save growers time and money while still providing protection against these common foliar diseases.

4:30:00 PM-4:45:00 PM             Impact on yield in seedborne potato virus Y field studies
Nora Olsen, University of Idaho

               "Virus infection and seed potato quality are known to influence crop yield and productivity, but the extent of yield loss due to seedborne potato virus Y (PVY) and the impact from other seed quality factors remain unclear. Two trials were conducted to evaluate the impact of mother tuber seed size and seedborne PVY on yield. Trial one was conducted over two growing seasons with Russet Norkotah (60% seedborne PVY in year one and 11% in year two) and one growing season with Umatilla Russet (26% seedborne PVY). Plots were planted from predetermined seed tuber size categories: a) single drop (42 to 112 g), b) small (113 to 169 g), c) medium (170 to 282 g), and d) large (283 to 340 g). Trial two was conducted one year with field plots planted from seed lots with low (0%), medium (5%), and high (8%) seedborne PVY Russet Burbank, low (3%) and high (34%) seedborne PVY Ranger Russet, and low (2%) and high (11%) seedborne PVY Russet Norkotah. Visual evaluations for PVY symptoms, stem number per plant, and yield profile were conducted for both trials. In trial one, visual seedborne PVY incidence did not significantly differ between plants based upon seed size category for either year, cultivar, or seedborne PVY level, however seed size influenced yield and stem number per plant. In trial two, the high seedborne PVY lot significantly reduced total yield by 14% in Russet Burbank and 13% in Russet Norkotah compared to the low PVY lots. Ranger Russet total yield was not significantly impacted by higher levels of seedborne PVY infection. PVY was a yield limiting factor in these studies, however, interactions between cultivar, PVY level, and other seed qualities need to be considered when estimating crop productivity.

"