Old virus new host: Ecology and management of beet curly top virus (BCTV) in hemp

Hemp production has increased significantly in recent years; however, the crop has been understudied in the U.S. since production declined in the late 1950s. Disease identification and management is an increasing challenge for hemp growers across the country. Curly top disease caused by beet curly top virus (BCTV) has been identified as an emerging disease of hemp. Hence, we were motivated to understand 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 presence of emerging and established virus and viroid sequences in hemp. Season-long surveys for beet leafhopper (Circulifer tenellus) vector and BCTV incidence revealed positive association between vector and virus incidence. Several weed species were found to be infected with BCTV in areas surrounding hemp. Evaluation of an F2 population of hemp lines derived from parental lines that differ in cannabinoid production revealed range of susceptibility to BCTV. Data presented here have important implications for the epidemiology and management of 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.