Hemp virome revealed, and the ecology of beet curly top virus in hemp in Colorado

Hemp (Cannabis sativa L.), is a rapidly growing industry in the United States. Colorado is one of the biggest hemp growing states having over doubled its acreage from 35,950 in 2018 to over 75,000 in 2019. However, the crop has been understudied in the U.S. since its production declined in the late 1950s and information on the biological and agricultural factors affecting hemp under current conditions is limited. Disease identification and management is an increasing challenge for hemp growers across the country. For instance, beet curly top virus (BCTV), which is transmitted by the beet leafhopper, was recently shown to infect hemp plants in Colorado. Since its initial detection, we have confirmed the virus from 9 counties in Colorado, with several fields reporting disease incidence levels above 50%. We found BCTV-Worland and BCTV-CO strains and many mixed infections. Using next generation-based metagenomics we have characterized the virome of hemp. Life history assays were performed in BCTV viruliferous and non-viruliferous beet leafhopper to understand the impact-if any, the virus has on vector survival and fecundity. A survey of beet leafhopper and BCTV was performed in hemp to understand their abundance and seasonality in Colorado. The results of this research will improve diagnostics through the development of and accessibility of species-specific primers. Accurate and efficient identification of viruses and viroids will help target control strategies through integrated pest management and interruption of transmission cycles, in turn reducing yield losses.