Brief Summary of Minutes of Annual Meeting

1. Seed certification:
   1. Assessed in-season spread of PVY in winter post-harvest grow-out tests and determined that this was not an issue.
   2. Lab tests to replace winter post-harvest grow-out tests were initiated in one certification program. Comparison to field results generally suggested similar levels of pathogen identification, although some cases had better detection in the lab. An added benefit of this new testing program is the detection of PVY in varieties for which foliar symptoms are difficult to discern.
   3. Increase of the sample size for pathogen detection in seed lots led to a reduction in the confidence interval, an improvement in the ability to distinguish similar prevalence levels, and an improvement of the confidence in the estimate of prevalence.
   4. Initial tests using a high throughput tuber testing method showed promise and will be a focus for future optimization and validation.
   5. Continuation of grower education for seed production and the certification process, as isolation of seed growers from commercial growers is important.
   6. Economic analyses determined that testing 400 tubers from a seed lot was sufficient to generate a fairly accurate identification of PVY infection levels.
   7. Analyses of seed lots for PMTV and TRV for three years show an increasing trend of PMTV-positive lots across different cultivars and seed origins, which is cause for concern. Diagnostics will continue in the future.

2. Tuber Quality:
   1. PMTV symptom development in storage varies by cultivar and year, though overall symptoms tend to increase in storage.
   2. PVY infection led to reduced tuber yields, lower specific gravity in tubers, and generally no fry color differences compared to healthy tubers.
   3. TRV-infection has little impact on symptom development across different cultivars or times in storage.
   4. The PVY^Wilga strain depresses tuber yield overall across different cultivars, though chip color does not appear to change unless symptoms are visible in the tuber.

3. Diagnostics:
   1. Successful demonstration of use of FTA cards for sampling tubers for PVY, PMTV, and TRV. These cards can be stored long-term and allow the repeated testing of samples from the cards. This method will decrease the dependence on winter grow-out tests and will improve the current sampling and reporting methods by increasing accuracy of disease levels in seed.
   2. A method to detect PMTV and Spongospora subterranean from soil was developed which has a detection limit of 100 spore propagules, respectively.
   3. The occurrence of stubby root nematodes that vector TRV was demonstrated in multiple states. The genetic diversity and evolutionary relationship of the most prevalent vector Paratrichodorus allius with three other stubby root nematode species were characterized, and a one-step multiplex PCR assay was developed for the first time for rapid detection of these four stubby-root nematode species to improve the detection efficiency of this nematode in infested potato fields.
   4. TRV and PMTV strain differentiation was analyzed from collection across the US. For PMTV, US isolates were found to share high sequence identity (>97%). Results suggest that PMTV in the US may be from a single introduction into the country. For TRV, US isolates tend to cluster together when compared to isolates collected around the world.

4. Cultivar Development and Evaluation:
   2018. Potato virus Y demonstration plots were part of three industry field days in Washington, Wisconsin, and Maine in 2018. A similar field day was held in Washington in 2016.  Presentations from the 2016 field day were given by the researchers involved at state and national meetings explaining the difficulties in identifying PVY in seed potato crops.
   2019. In an effort to breed for resistance to PVY, PMTV, and TRV, potato hybrids were generated with resistant parents and true potato seed. Replicated trials identified ~26 clones with extreme resistance conferred by specific genes.
   2020. Two genetic markers for PMTV resistance (one on chromosome 2 and one on chromosome 3), and one marker for TRV (on chromosome 9) were identified.
   2021. An initial pilot study assessed tuber yield as a function of days of growth before PVY  Results show that the earlier the plant was infected, the larger the yield loss. At some point yield loss was not significant.

5. Disease management:
   1. Analyzed different chemicals for their effects on Spongospora subterranean and showed that many chemicals do not significantly reduce soil inoculum levels, tuber lesion development, or PMTV incidence.
   2. For aphid control, it was determined that weekly paraffinic oil applications resulted in the lowest overall post-harvest test readings (2009-2018), and biweekly applications further reduced PVY in daughter tubers.

Babujee, L., Witherell, R.A., Mikami, K., Aiuchi, D., Charkowski, A.O., and Rakotondrafara, A.M. (2019) Optimization of an isothermal recombinase polymerase amplification method for real-time detection of Potato virus Y O and N types in potato. Journal of Virological Methods. 267: 16-21.

Chikh-Ali, M., Rodriguez-Rodriguez, M., Green, K.J., Kim, D.-J., Chung, S.-M., Kuhl, J.C, and Karasev, A.V. (2019) Identification and molecular characterization of recombinant Potato virus Y (PVY) in potato from Korea, PVY^NTN strain. Plant Disease 103: 137-142.

DeBlasio, S.L., Rebelo, A.R., Parks, K., Gray, S.M. and Heck, M.C. (2018) Disruption of chloroplast function through downregulation of phytoene desaturase enhances the systemic accumulation of an aphid-borne, phloem limited virus. Molecular Plant-Microbe Interactions. 31: 1095-1110.

DeBlasio, S.L., Xu, Y., Johnson, R.S., Rebelo, A.R., MacCoss, M.J., Gray, S.M., and Heck, M. (2018) The interaction dynamics of two Potato leafroll virus movement proteins affects their localization to the outer membranes of mitochondria and plastids. Viruses. 10: 1-26.

Duellman, K.M. and Marshall, J.M. 2018. Importance of Potato Volunteers as PVY Reservoirs in Idaho, 2018. 102nd Annual Meeting of the Potato Association of America, Boise ID (Poster)

Fulladolsa, A.C., Charkowski, A., Cai, X., Whitworth, J, Gray, S., and Jansky, S. (2019) Germplasm with resistance to Potato virus Y derived from Solanum chacoense: Clones M19 (39-7) and M20 (XD3). American Journal of Potato Research, published on-line March 15, 2019 (https://link.springer.com/article/10.1007/s12230-019-09719-6).

Green, K.J., Brown, C.J., and Karasev, A.V. (2018) Genetic diversity of Potato virus Y (PVY): sequence analyses reveal ten novel PVY recombinant structures. Archives of Virology 163: 23-32.

Gray, S.M., and Power, A.G. (2018) Anthropogenic influences on emergence of vector-borne plant viruses: the persistent problem of Potato virus Y. Current Opinion in Virology. 33: 177-183.

Huang, D., Yan, G. P., Gudmestad, N., Whitworth, J., Frost, K., Brown, C., Weimin, Y., Agudelo, P., and Crow, W. (2018) Molecular characterization and identification of stubby root nematode species from multiple states in the United States. Plant Disease. 102: 2101-2111.

Huang, D., Yan, G. P., Gudmestad, N., Ye, W., Whitworth, J., Frost, K., Crow, W., and Hajihassani, A. (2019) Developing a one-step multiplex PCR assay for rapid detection of four stubby-root nematode species Paratrichodorus allius, P. minor, P. pororus and Trichorodorus obtusus. Plant Disease. 103: 404-410.

Inglis, D.A., Gundersen, B., Beissinger, A., Benedict, C., and Karasev, A.V. (2019) Potato virus Y in seed potatoes sold at garden stores in western Washington: prevalence and strain composition. American Journal of Potato Research, published on-line February 13, 2019 (http://dx.doi.org/10.1007/s12230-018-09695-3).  

Olaya, C., Adhikari, B., Raikhy, G., Cheng, J., and Pappu, H.R. (2019) Identification and localization of Tospovirus genus-wide conserved residues in 3D models of the nucleocapsid and the silencing suppressor proteins. Virology Journal. 16: 1-15.

Nalam, V., Louise, J., and Shah, J. (2019) Plant defenses against aphids, the pest extraordinaire. Plant Science. 279: 96-107.

Pinheiro, P.V., Wilson, J.R., Xu, Y., Zheng, Yi, Rebelo, A.R., Fattah-Hosseini, S., Kruse, A., Santos Dos Silva, Xu, Y., Kramer, M., Giovannoni, J., Fei, Z., Gray, S. and Heck, M., (2019). Plant viruses transmitted in two different modes produce differing effects on small RAN-mediated processes in their aphid vector. Phytobiomes. Online 20 March 2019, https://doi.org/10.1094/PBIOMES-10-18-0045-R

Shakir, N., Hameed, S., Karasev, A.V., and Zafar, Y. (2018) Occurrence of Potato virus Y (PVY) recombinants, strain PVY^NTN, infecting tobacco in Pakistan. Plant Disease 102: 2385-2385.

Wenninger, E.J., Dahan, J., Thornton, M., and Karasev, A.V. (2019) Associations of the potato psyllid and “Candidatus Liberibacter solanacearum” in Idaho with the non-crop host plants bittersweet nightshade and field bindweed. Environmental Entomology 48: in press (https://doi.org/10.1093/ee/nvz033).

Xu, Y., Da Silva, W.L, Qian, Y., and Gray, S.M. (2018) An aromatic amino acid and associated helix in the C-terminus of the potato leafroll virus minor capsid protein regulate systemic infection and symptom expression. PLoS Pathogens. 14: e1007451.

Zeng, Y., Fulladolsa, A.C., Houser, A., and Charkowski, A.O. (2019) Colorado seed potato certification data analysis shows mosaic and blackleg are major disease of seed potato and identifies tolerant potato varieties. Plant Disease. 103: 192-199.