Hemp (Cannabis sativa) acreage in Oregon has increased by approximately 240 times in the last 5 years, and a greater number of hemp diseases have been observed. This special report documents pathogens, particularly those causing virus and virus-like diseases, that have been detected from field and greenhouse-grown hemp crops in Oregon, based on plant samples submitted to the Hermiston Agricultural Research and Extension Center Plant Clinic of Oregon State University in 2019 and 2020. Symptoms and signs were used to evaluate disease types and determine diagnostic assays used on each submission. Plants with signs or symptoms of fungal or oomycete infection were cultured to isolate pathogenic organisms and plants with symptoms suspected to be caused by virus infection were assayed for the presence of Beet curly top virus (BCTV), viroids, and phytoplasmas using PCR, or reverse transcription (RT)-PCR. Diseases with fungal or oomycete, and virus causes accounted for 26.5 and 42.9% of submissions, respectively; coinfection of viral and fungal or oomycete pathogens were detected from 6.1% of submissions between 2019 and 2020. BCTV, a curtovirus, and hop latent viroid (HLVd) were the predominant pathogens detected from field and indoor grown hemp. Worland-like strains of BCTV represented 93% of all curtovirus detections. Eighty percent of HLVd detections occurred from plants that originated from indoor growing facilities. Based on BCTV vector, beet leafhopper, prevalence, field-grown hemp in western production regions may be affected by curly top and increasing hemp acreage in the landscape may have potential implications on other crops affected by curtoviruses. Virus and virus-like diseases could be a limiting factor for hemp production in some regions of the United States.

Winter squash (Cucurbita maxima) is produced in Oregon’s Willamette Valley for edible seeds, processing, and fresh markets. Recently, prominent cultivar Golden Delicious has experienced significant yield losses due to a soilborne disease. Symptoms include stunting, root and crown rot, vascular discoloration, and late-season vine collapse. To identify potential causal pathogens, 64 fields were surveyed during 2014 to 2016 to characterize the fungal community associated with surface-disinfested root, crown, and stem tissue of diseased and healthy squash. Over 10,000 fungal isolates were identified morphologically, and 1,783 isolates were identified to species by sequencing of internal transcribed spacer and translation elongation factor 1 alpha genomic regions. Fungal communities were analyzed for association with the presence or absence of field symptoms using multivariate community analyses (indicator species analysis, multiresponse permutation procedure, and nonmetric multidimensional scaling). Although no fungal species were consistently associated with disease, five species were consistently isolated from plants regardless of the presence of symptoms and were capable of causing disease in a greenhouse pathogenicity trial: Fusarium oxysporum, F. solani, F. culmorum, Plectosphaerella cucumerina, and Setophoma terrestris. Results from community analyses confirmed that some fungi were more common in specific tissues (e.g., P. cucumerina in stems and crown, F. solani in roots and crown). Symptom severity tended to be greater in fields with a prior history of squash production, although a few fields with no prior history of squash had above average symptom ratings. The results from this study suggest that the five most common fungi may take on greater disease significance when they co-occur in a host.

Winter squash (Cucurbita maxima cultivar Golden Delicious) produced in Oregon’s Willamette Valley for edible seed production has experienced significant yield losses because of a soilborne disease. The symptoms associated with this disease problem include root rot, crown rot, and vascular discoloration in the stems, leading to a severe late season wilt and plant collapse. Through field surveys, Fusarium oxysporum, F. solani, F. culmorum-like fungi, Plectosphaerella cucumerina, and Setophoma terrestris were identified to be associated with diseased tissues, and each produced symptoms of root rot, crown rot, or stem discoloration in preliminary pathogenicity trials. In this study, 219 isolates of these species were characterized by molecular identity analyses using BLAST of the internal transcribed spacer and translation elongation factor 1 alpha genomic regions and by pathogenicity testing in outdoor, large-container trials. Molecular identity analyses confirmed the identity of isolates at 99 to 100% similarity to reference isolates in the database. In pathogenicity experiments, F. solani produced the most severe symptoms, followed by F. culmorum-like fungi, F. oxysporum, P. cucumerina, and S. terrestris. Some treatments of mixed-species inoculum produced symptom severity greater than what was expected from individual species. In particular, the mixture of F. culmorum-like fungi, F. oxysporum, and P. cucumerina and the mixture of F. culmorum-like fungi, F. solani, and S. terrestris had symptom ratings as high as that of F. solani by itself. Results indicate that this soilborne disease is caused primarily by Fusarium solani, but interactions between the complex of F. solani, F. culmorum-like fungi, F. oxysporum, and P. cucumerina can exacerbate disease severity.

Fusarium sambucinum is an ascomycete that has been isolated from a broad range of plant hosts, including hop (Humulus lupulus L.), where it acts as a causal agent of Fusarium canker, a disease that can impact cone quality and yield in severe cases. Current diagnostic methods rely on isolation of the fungus from plant tissue, a time- and resource-intensive process with limited sensitivity, complicated by the potential presence of other Fusarium spp. that have been reported on hop. Our objective was to develop a rapid and sensitive diagnostic tool to detect and quantify F. sambucinum in plant tissues. Using a modified random amplified polymorphic DNA PCR assay, we identified a F. sambucinum-specific marker that serves as the target in a TaqMan (hydrolysis) probe quantitative PCR (qPCR) assay that can be used to detect F. sambucinum DNA in a background of plant DNA. When used to screen 52 isolates of F. sambucinum and isolates representing 13 other Fusarium spp., the assay was robust in detecting F. sambucinum while discriminating between F. sambucinum and closely related Fusarium spp., including F. venenatum. Furthermore, this assay reliably detects as little as 1 pg of F. sambucinum DNA in a background of total DNA from plant tissue. Within-sample comparisons of this qPCR assay with traditional cultural isolation methods demonstrated the greater sensitivity of the qPCR-based method for detection of F. sambucinum. When used to screen 220 asymptomatic stem samples, the qPCR assay detected F. sambucinum in 100 samples (45.5%); by comparison, F. sambucinum was detected in only 3 samples (1.4%) by culturing methods. Moreover, quantification of F. sambucinum DNA was possible for 60 of these samples, indicating the utility of the qPCR assay for early detection. This assay should be useful in diagnostic and epidemiological applications to detect and quantify F. sambucinum from multiple hosts and environmental samples.

Potato (Solanum tuberosum cv. Norkotah) tubers with symptoms of soft rot were submitted to Oregon State University, Hermiston Agricultural Research and Extension Center Plant Clinic in 2019. One su...

Choke disease, which is caused by Epichloë typhina, was first reported in orchardgrass seed production fields in the Willamette Valley, Oregon in 1997 and has continued to persist in the system. The disease can cause up to 30% losses in seed yield. Unlike many Epichloë species that are seed transmitted, it is unclear how infection of orchardgrass by E. typhina occurs in the field, or how the disease spreads within plants. In this study, the overall incidence of choke on trap plants placed in a choke-infested field was 41% in 2018 and 9% in 2019. Similar incidence of infection occurred when exposed before (39%) or after (43%) swathing in 2018. Contrary to our hypothesis, plants sprayed with an artificial honeydew had a significantly lower incidence of infection (32%) when compared to the controls (48%). An examination of the spread of E. typhina within tillering plants revealed that development of infected tillers was greater than development of uninfected tillers, which could contribute to the gradual increase in choke in fields over time. These studies contribute to a better understanding of how choke is spread within plants and in orchardgrass seed production fields, which is an important step towards developing control methods to reduce choke in orchardgrass seed production fields.