8:00am-8:15am
Characterizing Colorado potato beetle insecticide resistance through genetic mechanisms   
Emma Terris, University of Wisconsin-Madison

Insect pest control continues to be a crucial avenue of research as pests threaten food security, sustainable agricultural practices, and on-farm economics. Understanding chemical options and efficacy in potato agroecosystems is important for growers, considering the destructive capabilities of the most prominent commercial potato pest, the Colorado potato beetle (CPB). CPB can be a devastating pest and is well known for its rapid adaptive evolution to resist whole suites of insecticides, using various mechanisms (target-site, penetration, metabolic, and microbial resistance). In this project bioassays were used to characterize the spread and distribution of insecticide resistance evolution among CPB across potato production states, as it pertains to a neonicotinoid, imidacloprid (AdmirePro), as well as a novel and currently unregistered compound, Plinazolin (isocycloseram). Both compounds act on specific nervous system sites, however, Plinazolin represents a potentially new mode of action and target site to which most, if not all CPB populations would be regarded as highly susceptible. Further examination of the underlying genetic mechanisms of CPB resistance through RNA-sequencing compares the  differential expression of metabolic detoxification genes among these different active ingredients, each of which were tested across a diverse set of CPB populations. This project implicates the expected performance of new chemical control strategies through examining expression of gene families involved in metabolic detoxification.

8:15am-8:30am
Impact of new Sdh mutations in Alternaria solani on the management of potato early blight
Julie Pasche, North Dakota State University

               The early blight pathogen, Alternaria solani, impacts potato yield in the midwestern US annually. The application of foliar fungicides is the major input for early blight management. Resistance to single-site mode of action fungicides has been a major concern in A. solani for more than two decades. Five mutations in the Sdh gene of A. solani have been previously identified that resulted in reductions in the efficacy of SDHI (FRAC group 7) fungicides. We have detected four novel mutations in the SdhB and SdhD subunits of Sdh gene, along with co-occurrence of two mutations in single isolates. In vitro sensitivity of new A. solani mutant isolates varied from reduced sensitivity to high resistance to SDHI fungicides fluopyram and pydiflumetofen. In vitro resistance factors of the mutated A. solani isolates for fluopyram and pydiflumetofen ranged from 2 to >500 and 1.6 to >100, respectively. In vivo greenhouse evaluations supported the results from in vitro assays. Disease control by fluopyram and pydiflumetofen was significantly reduced in 12 and 8 of 12 Sdh mutant A. solani isolates respectively, with loss of disease control ranging from 20.4% to 65.8% for fluopyram and 2.7% to 84.9% for pydiflumetofen as compared to the baseline isolates. In vitro and in vivo results were highly correlated in both SDHI fungicides fluopyram (r =0.820; p=0.0002) and pydiflumetofen (r=0.695, P=0.0041). Results from both in vitro (r = 0.877; P <.0001) and in vivo greenhouse assays (r = 0.859; P <.0001) indicated cross sensitivity in a majority of isolates between the two SDHI fungicides fluopyram and pydiflumetofen. These results aid in our understanding of SDHI fungicide resistance and will improve grower recommendations for the effective management of early blight.

8:30am-8:45am
Thiamin priming to control early blight in potato: investigation of its effectiveness and molecular mechanisms
Aymeric Goyer, Oregon State University

               Thiamin applied on foliage can induce plant immunity and is effective in controlling fungal, bacterial, and viral diseases. However, the effectiveness of thiamin against potato pathogens has been seldom investigated. Here, we tested the effect of thiamin foliar application against Alternaria solani, a necrotrophic fungus that causes the potato early blight disease, on potato plants grown in a greenhouse. Foliar applications of thiamin reduced lesion size by ~33% when applied at a concentration of 10 mM, which we found was optimal. However, the effect of thiamin on lesion size was short lived; while we observed a reduction of lesion size when leaves were inoculated 4 h after thiamin treatment, there was no effect when inoculations were done 24 h after thiamin treatment. In addition, we found that the effect of thiamin on lesion size was restricted to the site of application and was not systemic. We also investigated changes in gene expression by RNA sequencing to shed light on the potential molecular mechanisms involved in thiamin-induced defense response against A. solani. Gene expression was analyzed in thiamin- and mock-treated plants 12, 24, and 48 h after inoculation with A. solani or without pathogen. Gene ontology (GO) enrichment analysis showed that GO terms associated with photosynthesis and lipid metabolism were enriched in both mock-treated plants infected with A. solani and plants treated with thiamin without pathogen infection. Furthermore, we identified specific genes coding for major latex protein-like proteins, fatty acid desaturases, and terpene biosynthesis enzymes that may play important roles in thiamin-mediated defense. Our results indicate that thiamin-induced resistance in potato to early blight may involve modification of lipid metabolism and photosynthetic processes. These pathways have not been reported before in thiamin-mediated resistance in other plant-pathosystems.

8:45am-9:00am
Pink rot of potato – studies into the causal agent Phytopthora erythroseptica and its alternative host species
Ronika Thapa   University of Tasmania

               Pink rot in potato is distinguished by the intense salmon-pink colour (Chambers, 1958); that develops in infected tuber tissue when they are cut and left exposed to air for 20 to 30 minutes (Cullen et al., 2007). P. erythroseptica-causing tuber rots are economically more significant each year than any other disease impacting the quality of tubers (Gudmestad et al., 2007). P. erythroseptica has the ability to infect a range of both solanaceous and non-solanaceous plants. Basing P. erythroseptica identification on morphological characteristics is notoriously difficult due to intraspecific variation, the overlap of morphological characters between Phytophthora species. The development of PCR primers to detect potato pathogens (Tooley et al 1997) has enabled accurate and reliable identification of P. erythroseptica. In Tasmania, lupins (Lupinus spp.) are used in potato crop rotations.  Lupins have been identified overseas from both natural infections and artificial inoculations as alternative hosts of P. erythroseptica (Morgan & Johnson 1965; Trapero-Casas et al 2000) but the host status of the lupin varieties planted in Tasmania and Australia is unknown. This study focuses on identifying the alternative host species of the pathogen.

9:00am-9:15am            
Spongospora subterranea f. sp. subterranea (Sss) affects plant susceptibility to subsequent pathogen infections under controlled environment conditions
Ibrahim Kutay Ozturk, University of Maine        

               Spongospora subterranea f. sp. subterranea (Sss) is a soilborne potato pathogen responsible for causing powdery scab on tubers and galls on roots, reducing root water uptake through colonizing root hairs, and vectoring of Potato mop-top virus (PMTV). However, effects of Sss on overall plant susceptibilities against subsequent infections of potato pathogens above ground have not been previously reported. This study aimed to investigate the effects of Sss on root and tuber disease expression, yield, and susceptibilities to subsequent late blight and white mold infections across six potato varieties. Sss-infected Silverton plants had 28.3% less total tuber yield and 29% fewer tubers compared to non-infected Silverton plants. We did not find a correlation across the varieties between root colonization and root gall formation. Sss-infected Silverton plants were more susceptible to hemibiotrophic late blight and less susceptible to necrotrophic white mold. Sss infection also increased susceptibilities of Goldrush and Atlantic plants to white mold. We also evaluated prevalence of asymptomatic Sss infections across the six varieties. Between 50% to 92% of the asymptomatic tubers tested positive for Sss DNA, depending on the variety. Further research is required to understand the possibility and extent of these asymptomatic infections to the spread of Sss in the field. These findings highlight the complexity of Sss-host interactions and gives precedence that the lack of disease expression does not necessarily indicate resistance of a variety to Sss.

9:15am-9:30am            
Contiguous draft genome of Powdery Scab Pathogen Spongospora subterranean
Shengwei Hu, Oregon State University

               Powdery scab, caused by Spongospora subterranea f. sp. subterranea (Sss), is a globally prevalent soil-borne disease impacting potato cultivation. This biotrophic pathogen induces raised pustules on potato tubers, diminishing marketability and fresh market quality. Additionally, powdery is a vector of potato mop-top virus (PMTV). Previous attempts at whole genome sequencing of Sss resulted in a highly fragmented genome. Two distinct DNA extraction methods were used to isolate high molecular weight DNA: (i)from the sporosori obtained by gently scraping powdery scab lesions (OSU1) and sieving peeled skin (OSU2) from infected potato tubers grown in Klamath Falls, and (ii) from root galls (WSU1 and WSU2) collected from ‘Umatilla Russet’ potatoes with initial inoculum from mid-south Washington. Whole genome sequencing of all four DNA libraries was carried out using the PacBio Sequel II System HiFi sequencing workflow.  A meticulous sequencing reads decontamination procedure utilizing Diamond blast preceded the assembly of sequencing data via Hifiasm. BRAKER3 was employed to predict genes within assembled genomes, leveraging RNA-Seq evidence and the Eukaryota protein data. The comprehensive contiguous genome and comparison analysis of OSU and WSU genomes will offer a vital resource for unraveling its genetic intricacies and potential applications in disease management.

9:30am-9:45am
Consistency of Biological Control of Postharvest Fusarium Dry Rot Across Potato Cultivars, Storage Temperatures and Disease Pressures—Second Year Results
Patricia J. Slininger      USDA National Center for Agricultural Utilization Research              

               Biocontrol of Fusarium dry rot by a dried Pseudomonas fluorescens triculture was investigated across two harvest years to examine factors impacting control consistency.  In one-ton bins each treatment, having 4 replicate mesh bags of 20 tubers, was embedded among bulk tubers.  Three-way ANOVA was conducted to study the impact of post-harvest control agent, cultivar, and Fusarium level. Control agents included water, Archive(TM), biocontrol agent (BCA), or BCA rehydrated 16 h with nutrients. Cultivars were Clearwater Russet, Russet Burbank, Ranger Russet and Russet Norkotah, in increasing dry rot resistance order.  A BCA-Archive mixture was also applied to Clearwater Russet.  Temperature dependence of efficacy in Clearwater was studied with each treatment stored in 4 boxes of 20 tubers.  After cultivation, BCA was air dried on Kenite 700 carrier and stored two weeks at 4 C. In parallel lab and small pilot trials, tubers were sprayed 0.1 mL/oz tuber with Fusarium sambucinum (F.s.) at 1 x 10e5 or 5 x 10e5 conidia/mL, dried 15-30 min, wounded, and treated at 0.06 mL/oz.  BCA sprays contained ~10e9 cfu/mL. Ten-tuber lab treatments were incubated 28 d at 14.3 or 18.3 C, for suberization, while 80-tuber pilot treatments were stored 96 d at 5.6 or 8.9 C.  At lab scale, BCA significantly reduced dry rot in all cultivars at both F.s. inoculations but only in Norkotah (low F.s.) and Clearwater (high F.s.) at 1-ton bin scale. In box studies, Clearwater at 5.6 C, developed less disease than at 8.9 C, and tubers treated with BCA, especially when rehydrated with nutrients, had lower disease severity and incidence of >5% severity than the untreated control. In lab assays dry rot was less at 18.3 than 14.3 C. The BCA was not as effective as Archive, but data showed biocompatibility of the two products and indicated beneficial use in mixture.