1:00:00 PM-1:15:00 PM
Epidemiology and control of potato virus Y (PVY) in Kenya
John Onditi, USDA and Kenya Agricultural and Livestock Research Organization (USDA)

               Potato virus Y (PVY) is the most important virus of potato (Solanum tuberosum L.) crops worldwide. Virus prevalence surveys are one of the options for obtaining information that can be used in virus control. A potato leaf sampling survey was therefore conducted in the major potato growing regions in Kenya to help in identifying cultivars with low virus prevalence (virus resistant) after several years of replanting uncertified seed in areas with high virus pressure. An interview with farmers during the survey indicated that farmers had limited knowledge of virus transmission and control. Enzyme Linked Immunosorbent assay (ELISA) test results on sampled leaves indicated high virus prevalence in virus susceptible cultivars and low virus prevalence on resistant cultivars like Shangi, Kenya Karibu, Sherekea and Unica. Similarly, regions where farmers planted virus resistant cultivars had lower virus prevalence as compared to regions where farmers planted virus susceptible cultivars. The result on resistance in cultivars were further confirmed by the data obtained from controlled greenhouse PVY inoculation experiments. This study provided a basis for increasing awareness of farmers on potato virus control and recommending use of virus resistant cultivars as a ready option for virus control.

1:15:00 PM-1:30:00 PM             
Genome characterization of six recombinant variants of potato virus Y from North American potato cultivars grown in China
Alexander Karasev, University of Idaho

               China is one of the potato-growing countries with a great diversity of PVY recombinants described, however, this diversity was addressed primarily for the local potato cultivars, and not studied in cultivars of North American origin. A total of 26 leaf potato samples from four North American potato cultivars, Blazer Russet, Ranger Russet, Russet Burbank, Shepody, and from unknown cultivar(s) were collected in June-July 2018 from potato originating in four provinces of China, Hebei, Inner Mongolia, Shaanxi, and Ningxia and pressed onto FTA cards. PVY-positives were typed to strain using RT-PCR. Six of the isolates representing unusual banding patterns were selected for the whole genome sequencing and characterization. The coding complete sequences 9,609-9,634 nt-long encoded a single open reading frame characteristic of potyviruses. The six sequenced PVY isolates represented three distinct recombinants of PVY, N-Wi, SYR-I, and SYR-II. Interestingly, three of the recombinants had shifted recombination junction points accounting for unusual banding patterns in RT-PCR typing.

1:30:00 PM-1:45:00 PM
Dynamics of potato virus Y infection pressure and strain composition in Colorado
Mohamad Chikh-Ali, Colorado State University

               The San Luis Valley (SLV), Colorado, is the second-largest fresh potato growing region in the United States, which accounts for about 95% of the total production in Colorado. Potato virus Y (PVY) is the leading cause of seed potato rejection in the SLV causing a constant decline in seed potato production over the past two decades. To help potato growers control PVY, we monitored the dynamics of PVY infection pressure over the growing seasons of 2022 and 2023 (May through August) using tobacco bait plants exposed weekly to natural field infection. PVY infection dynamics were slightly different between the two seasons, but July and August had the highest infection in both years. The first PVY infection was detected in the second half of June which coincides with the emergence of potato crops in the valley. PVY infection increased toward the beginning of August and then declined toward the end of the season. Three PVY strains were identified in tobacco bait plants and potato fields, PVYO, PVYN-Wi and PVYNTN. Unlike other producing areas of the United States, PVYO is still the major strain infecting potato crops in Colorado comprising ~40% of total PVY strain composition. This could be explained by the prevalence of the potato cultivar Russet Norkotah, that lacks any identified N genes, including the Nytbr that controls PVYO, which imposes no negative selection against this strain. The current study demonstrated the usefulness of bait plants to understand PVY epidemiology and develop more targeted control practices of PVY.

1:45:00 PM-2:00:00 PM             
New Directions and Updates from the Oregon State University-HAREC Entomology Program
Josephine Antwi, Oregon State University

               Hermiston Agricultural Research and Extension Center at Oregon State University (OSU-HAREC) recently hired Josephine Antwi as the new irrigated crop entomology, extension specialist. Josephine will lead the development, implementation, and evaluation of extension and research programs in arthropod pests management to support sustainable irrigated farming systems. In this presentation, Josephine will introduce herself to the PAA community and share some of her visions and goals for the entomology program. She will provide an update on ongoing research projects in her program, including the area-wide insect pest monitoring program in eastern Oregon, insect field trials to complement the plant breeding program at HAREC, and greenhouse trials to test pest control alternatives on potatoes. These projects are in their early phases but are designed to deliver research-based solutions to support growers, stakeholders, local industry, and extension agents in the region. Josephine also hopes to use this presentation as a starting point to establish more collaborations within the PAA community.

2:00:00 PM-2:15:00 PM             
Modeling of Successful Management Strategies to an Evolving PVY Threat in New Brunswick, Canada
Tyler D. B. MacKenzie, PhD, Agricultural Certification Services, Inc. - Potatoes New Brunswick

               Potato virus Y (PVY) is concerning to the potato industry worldwide, including in New Brunswick (NB), Canada. Seed potato crops in NB have had low average levels of PVY since the early 2010's, constrained by a mandatory post-harvest virus testing program with strict PVY caps. Industry-wide, annual average PVY ranged 0.43% to 1.1% between 2013 and 2021. In 2022 PVY surged, due in part to an unusual abundance of aphids, including the highest Green Peach Aphid levels—PVY's most efficient vector—recorded in recent years. PVY levels recovered substantially in 2023, dropping in half despite ongoing challenges. Statistical modeling of individual fields before, during and recovering from this PVY surge allowed analysis of how diverse factors can quantifiably impact post-harvest PVY levels, such as: planted PVY inoculum, aphid populations, weather, the declining trend in number of specialized seed growers while amalgamating seed and processing operations, and varied grower practices on individual farms. Growers could reduce PVY by on average 50-75% by adopting specific management practices including planting low-PVY seed, applying weekly mineral oil foliar sprays at >2L/acre, tank-mixed with diverse insecticides, and timing of planting, spray initiation, and crop topkill to minimize aphid exposure. These strategies worked to maintain acceptably low PVY levels even through the 2022 PVY surge. In NB, the PVY threat is evolving, through large changes in PVY strain populations, first in 2015 with the replacement of PVY(O) by PVY(NTN), now with the rapid expansion of PVY(N-Wi), with consecutive years of unprecedented GPA abundance, and perhaps related significant recent climatic shifts, particularly in overwinter temperatures. While some PVY management decisions are regionally specific, many successful strategies identified here are applicable more widely, and our comprehensive monitoring, statistical analysis and grower-engaged approach is a model for a well-managed seed potato industry adaptive to evolving threats from PVY.

2:15:00 PM-2:30:00 PM
Developing the Quality Seed Potato Sector in the East African Community: Policies and Investments Priorities
Kalpana Sharma, International Potato Center

               Potato is one of the fastest growing staple food crops in the East African Community (EAC) region and rank among the top five strategic staple crops for food and income security. Over the last 20 years, potato production across the EAC partner states has more than doubled, increasing from 1.6 to 3.4 million ton - an increase that has resulted from expansion of acreage under potatoes rather than from improved productivity. This indicates that innovations and technologies such as new varieties, use of high-quality seed, and good agricultural practices either have not been adopted or that adoption has failed to reach the necessary threshold to increase productivity in the subsector. Low productivity and the use of quality seed potatoes by less than 4% of farmers in the EAC remain key bottlenecks in the region; if such issues can be addressed, potato yields can be significantly increased. To unlock the potential of the region’s potato sector, the EAC with the support from development partners, provided an enabling framework to support the seed potato trade. This includes mapping out regional strategies and action plans, developing the capacities of member countries’ national plant protection organizations in implementing sanitary and phytosanitary measures, and developing and harmonizing regional seed potato standards. This paper presents recommendations for key policy and investment priorities that aimed at increasing the availability and supply of sufficient and affordable quality seed potatoes for internal use by EAC countries, with the surplus being traded to other EAC partner states. Results and recommendations focus on three pragmatic intervention areas: (1) policies, regulations, and markets; (2) infrastructure and technology investment; and (3) technical capacity development- which can ultimately boost yields and unlock the potential of potato.

2:30:00 PM-2:45:00 PM
Utilization of reverse transcription quantitative PCR (RT-qPCR) as a screening tool at the US Potato Genebank to detect Potato Spindle Tuber Viroid (PSTVd) in true seeds of potato germplasm
Gunnar Knox, University of Wisconsin-Madison

               The Potato Spindle Tuber Viroid (PSTVd) is a serious disease affecting potatoes, tomatoes and other Solanaceous crops. This viroid is highly contagious, transmitted by seed and cannot be eliminated by traditional therapies. Though symptoms in wild potato species are relatively mild, infections can be severe in commercial ones causing stunting, malformation, and cracking of tubers. It is therefore classified as a high-risk plant quarantine disease worldwide. The US Potato Genebank (USPG) expects that each germplasm sample sent to users is free of PSTVd, so detection methods have been adopted. In the past, the USPG commonly tested every single seedlot before growing them as parents for seed increase and after, when seedlings were ~2-inch tall were tested again by dot-blot assays. However, positive controls were not included as comparisons because of the high risk of growing them on site. A few years ago, suspicions of false negatives prompted us to assess reliability of the dot-blot test by growing known positives under isolation and testing them. Results showed that detection of known positives was only ~32%. This study shows our efforts to find an alternative test and adopting/developing true seeds as sampling materials. The method evaluated was reverse transcription quantitative PCR (RT-qPCR) because of its advantages of speed, high sensitivity, and specificity. The procedure to extract RNA from botanical seeds worked well and allowed to (a) eliminate risks of spreading infection since plants were never grown, (b) speed up germplasm screening through bulk samples of 10 accessions (~250 seeds) and (c) be cost-effective as 10 accessions were examined at once. The RT-qPCR always detected known positives, even when diluted 9:1 with known negatives. Results supported RT-qPCR as a reliable method to expedite screening and enhance secure germplasm distribution. In addition, research into transmission, detection, and maybe elimination of PSTV could be possible.

2:45:00 PM-3:00:00 PM
Litchi tomato (Solanum sisymbriifolium) as an asymptomatic carrier of tomato chlorotic dwarf viroid
Alexander Karasev, University of Idaho

               The solanaceaous weed Solanum sisymbriifolium (litchi tomato or sticky nightshade) is considered a potential biological control tool when used as a trap crop to manage the potato cyst nematode. In 2018-2019, tomato scions grafted onto two S. sisymbriifolium rootstocks originating either from healthy-looking greenhouse stocks or from tissue culture-maintained plants were examined for the presence of viruses and virus-like agents due to severe symptoms of stunting, foliar deformation, and chlorosis, exhibited by tomatoes grafted onto the greenhouse-maintained rootstocks of S. sisymbriifolium. High throughput sequencing was used to examine the virome of the tomato scions and the greenhouse- and tissue culture-maintained rootstocks. In the symptomatic tomato scions and the two S. sisymbriifolium rootstock samples, a 487-nt contig was found, corresponding to an ~1.35 tomato chlorotic dwarf viroid (TCDVd) genome with 99.7% identity. Asymptomatic tomatoes and S. sisymbriifolium plants from tissue culture were found negative for TCDVd. Given the very mild or asymptomatic infection of TCDVd in the latter, molecular diagnostic methods should be used to screen S. sisymbriifolium lines for the presence of this viroid to avoid inadvertent spread of TCDVd. This is the first report of TCDVd infection in S. sisymbriifolium, and also the first report of the TCDVd occurrence in Idaho.