Beet Curly Top Virus Genetic Diversity, Impact on Cannabinoids, Potential Seed Transmission, and Vector Biology in Hemp

Beet curly top virus (BCTV) has emerged as a major threat to hemp production in the western United States. Despite this concern, little is known about BCTV biology in hemp. This study investigated the incidence and genetic variability of BCTV strains, its impact on cannabinoid profiles, potential for seed transmission, and vector survival on hemp. Field surveys across five states revealed four distinct BCTV strains, with BCTV-CO and BCTV-Wor being the most prevalent. In addition, BCTV-PeCT was detected for the first time in hemp samples from Oregon, Colorado, and New Mexico, while BCTV-PeYD was detected exclusively in New Mexico. Genetic analysis showed high nucleotide diversity and widespread recombination among hemp-associated BCTV strains, consistent with active genetic exchange in BCTV. Furthermore, BCTV was detected in surface-disinfected seeds (77% in Elite genotype, 18% in 791 genotype), and in a small number of seedlings in grow-out experiments (0.98% in Elite, 0.87% in 791). Additional seed dissection experiments in Elite, revealed BCTV presence in 41% of embryos, 72% of endosperm, and 5% of seed coats, demonstrating potential for seed transmission in hemp rather than surface contamination. BCTV infection reduced cannabinoid levels in one hemp genotype but not in another, indicating genotype-specific effects of BCTV on cannabinoid production. Finally, beet leafhoppers, the exclusive vector of BCTV, were unable to survive on hemp beyond seven days indicating that the insect cannot complete its lifecycle on hemp. These findings provide a foundational understanding of BCTV evolutionary dynamics and host interactions in hemp, with implications for disease management.