An Overview of Pathogens Associated with Biotic Stresses in Hemp Crops in Oregon, 2019 to 2020

Abstract

Hemp (Cannabis sativa) acreage in Oregon has increased by approximately 240 times in the last five 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 polymerase chain reaction (PCR), or reverse transcription (RT)-PCR. Diseases with fungal or oomycete, and virus causes accounted for 26.5%, and 42.9% of submissions, respectively; co-infection 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.

First Year Survey of Arthropods in California Hemp

“…Although the species was not confirmed in this study, beet leafhopper, Circulifer tenellus (Hemiptera: Cicadellidae), is a species of concern for hemp in California since it can transmit beet curly top virus (Severin, 1931). So far, beet curly top virus has been confirmed in hemp in Arizona (Hu et al, 2020), Colorado (Giladi et al, 2020), and Oregon (Rivedal et al, 2021). Symptoms in hemp include stunted growth and yellowing of leaves (Giladi et al, 2020), potentially leading to yield loss.…”

New Insights into Hop Latent Viroid Detection, Infectivity, Host Range, and Transmission

“…HLVd was first described in 1988 [ 12 , 31 ] using PAGE electrophoresis, HPLC, blotting, and nucleic acid hybridization techniques. A decade after this, end-point PCR was employed for HLVd detection using viroid-specific primers and has since become a popular and feasible tool for the accurate detection and quantification of viroid loads in infected tissues [ 38 , 40 , 43 , 70 , 71 , 72 , 73 ]. Biological indexing is no longer beneficial for discriminating between infected and healthy hemp plants due to a lack of characteristic symptoms of novel versus existing viruses and viroids.…”

“…HLVd is among several viral and subviral agents that attack hemp and cause several types of losses in product quality and total yield, such as HSVd, hemp streak virus, hemp mosaic virus, cannabis cryptic virus, and beet curly top virus [ 3 , 70 , 73 , 74 ]. Disease symptoms can be significantly affected by pathogen population within the same niche, and synergism or superinfection exclusions are among the widely known types of interactions among viral pathogens within plants [ 75 , 76 , 77 , 78 ].…”

Challenges to Cannabis sativa Production from Pathogens and Microbes—The Role of Molecular Diagnostics and Bioinformatics

“…Subsequently, diagnostic methods using RT-PCR with specific primers have been developed to detect these viruses [ 3 , 33 , 34 , 35 , 36 , 37 , 38 ]. Recent studies have also reported spiroplasma/phytoplasma pathogens affecting hemp, including Spiroplasma citri and Candidatus Phytoplasma trifolii, which were detected using specific PCR primers [ 39 , 40 ]. Cannabis cryptic virus (CCV) has also been reported in cannabis plants, without causing any apparent symptoms [ 22 , 23 ].…”

“…A similar situation may be taking place with the virus/viroid pathogens, but preliminary evidence may suggest an evolving suite of these pathogens may be found infecting these crops in the future. The applications of the molecular diagnostic and bioinformatics methods described in this study should provide useful information to address the evolving challenges facing cannabis and hemp crops as a result of these evolving multiple and assorted pathogens, which could become a limiting factor to production in certain regions [ 64 ].…”