An overview of pathogens associated with biotic stresses in hemp crops in Oregon, 2019-2020

Authors: Rivedal, Hannah; FUNKE, CASSANDRA - Oregon State University; FROST, KENNETH - Oregon State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2021
Publication Date: 4/4/2022
Citation: Rivedal, H.M., Funke, C.N., Frost, K.E. 2022. An overview of pathogens associated with biotic stresses in hemp crops in Oregon, 2019-2020. Plant Disease. 106(5):1334-1340. https://doi.org/10.1094/PDIS-11-21-2415-SR.
DOI: https://doi.org/10.1094/PDIS-11-21-2415-SR

Interpretive Summary: Hemp (Cannabis sativa) is a newly approved crop for production in the United States. However, this means that there can often be production challenges, like diseases, that growers and researchers have never seen previously in a new hemp crop. In Oregon, this risk of production challenges is high as hemp acreage has increased by approximately 24,000% in the last five years. This increase in production has resulted in a greater number of observed hemp diseases including those caused by fungi and viruses. This special report documents diseases observed affecting field and greenhouse-grown hemp plants submitted to the Hermiston Agricultural Research and Extension Center Plant Clinic of Oregon State University in 2019 and 2020. We identified diseases caused by fungi, viruses and virus-like organisms affecting hemp. The fungal diseases we identified have all been documented previously in other American hemp growing regions. The viruses that we found to be most prevalent were beet curly top virus (BCTV) and hop latent viroid. Based on the prevalence of beet leafhopper insects, the insects that spread BCTV, field-grown hemp yields in western production regions may be affected by BCTV. Increasing hemp acreage in the landscape may have importance for other crops affected by BCTV, because this virus can infect and reduce yields in hundreds of other crops like cucurbits, tomatoes, peppers, and beets. Virus and virus-like diseases could be a limiting factor for hemp production in some regions of the United States.

Technical Abstract: Hemp (Cannabis sativa) acreage in Oregon has increased by approximately 24,000% in the last five years resulting in a greater number of observed hemp diseases. This special report documents diseases observed affecting field and greenhouse-grown hemp plants grown in Oregon and submitted to the Hermiston Agricultural Research and Extension Center Plant Clinic of Oregon State University in 2019 and 2020, with a focus placed on virus and virus-like diseases. Symptoms and signs were used to select 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 viruses, viroids, and phytoplasmas using polymerase chain reaction (PCR), or reverse transcriptase-PCR. Diseases with fungal or oomycete, and virus causes accounted for 26.5%, and 42.9% of submissions, respectively; simultaneous infection of viral and fungal or oomycete pathogens were detected from 6.1% of submissions. Curtoviruses and hop latent viroid (HLVd) were the predominant pathogens detected from field and indoor grown hemp. Worland-like strains of Beet curly top virus (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 prevalence, field-grown hemp in western production regions may be affected by curly top disease and increasing hemp acreage in the landscape may have importance for 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.