Hemp (Cannabis sativa L.) production has increased significantly in recent years; however, the crop has been understudied in the U.S. since its production declined in the late 1950s. Disease identification and management is an increasing challenge for hemp growers across the country. In 2019, beet curly top virus (BCTV) was first reported in hemp in Colorado. Hence, we were motivated to understand the diversity and prevalence of BCTV strains infecting hemp in Colorado. We detected BCTV at high incidence rate (81%) in leaf samples from 12 counties. Two different strains of BCTV, Worland (Wor) and Colorado (CO) were present as a single or mixed infection in hemp leaf samples. Phylogenetic analysis revealed BCTV sequences from hemp formed a distinct group along with BCTV strains CO and Wor. To determine other potential viral and viroid pathogens in hemp, we performed next generation sequencing (NGS). Virome analysis revealed the presence of both virus and viroid sequences that had high nucleotide sequence identity with GenBank accessions for cannabis cryptic virus, cannabis sativa mitovirus, citrus yellow vein associated virus, opuntia-like virus and hop latent viroid. In contrast, tobacco streak virus sequences were highly variable compared to sequences in GenBank suggesting a possible new genotype of this virus. The data presented here has important implications for the epidemiology and management of the various diseases of hemp and will lead to the development of integrated pest management strategies designed to interrupt transmission cycles and facilitate efficient crop production.

No abstract

Hemp (Cannabis sativa) or industrial hemp is a rapidly growing industry in the United States. However, the crop has been poorly studied in the US since its production declined in the late 1950s, and information on the biological and agricultural factors affecting hemp is limited. With the passage of the 2014 Farm Bill, hemp is no longer considered an illegal plant and is now a legal agricultural crop in the US. Within the bill, Section 7606 (Legitimacy of Industrial Hemp Research) provided a formal definition of the crop as "the plant Cannabis sativa L. and any part of such plant, whether growing or not, with a delta-9-tetrahydrocannabinol (THC) concentration of not more than 0.3 percent on a dry weight basis". In addition, the 2018 Farm Bill addressed many issues that had previously impeded development of the crop. Currently, 46 US states have enacted laws removing barriers to its production. In 2019, hemp production was 206, 965 hectares with 16,877 grower licenses across 34 states, according to "US Hemp Report" (www.votehemp.com). This is a greater than 455% increase over 2018 licensed acreage. Colorado, the leading state in hemp production increased production from 4,873 licensed hectares (346 growers) in 2017 to 12,525 licensed hectares (835 growers) in 2018. The US retail sales of hemp products was reported at $1.2 billion in 2018. The most profitable market for North American hemp is oilseed production and cannabidiol (CBD), a nonintoxicant cannabinoid with promising therapeutic use as a pharmaceutical product. Current CBD sales are estimated at $190 million and are projected to reach $2.5 billion by 2022. As we enter this new era of hemp production, plant diseases associated with the crop in the US and associated disease management needs are essentially undescribed. The emergence of phytopathogens and their spread is a rising concern as hemp production increases. Therefore, there is an urgent need to identify emerging and established hemp viruses and viroids, elucidate their diversity and distribution, develop early pathogen detection tools, and provide hemp growers, industry and other stakeholders information and resources to make timely management decision and minimize crop loss.

No abstract