Hop latent viroid: First report of vector transmission in hemp (Cannabis sativa)

Since the 2018 U.S Farm Bill reintroduced industrial hemp (Cannabis sativa L., < 0.3 % dry weight THC) back into the agricultural landscape, the crop has faced an influx of pests and pathogens. Among them, hop latent viroid (HLVd) has risen to the highest threat level. Hop Latent Viroid (HLVd) is a single-stranded, 256 bp circular RNA molecule that can cause leaf chlorosis, stunted growth, and reduced yield and quality of cannabinoids and terpenes. Losses due to HLVd in C. sativa (hemp and marijuana, >0.3% THC) are estimated to be upwards of $4 billion per year. HLVd is known to be transmitted mechanically, but there is currently no information regarding any possible insect vectors. Here we evaluated vector transmission by two common hemp pests, cannabis aphids (Phorodon cannabis) and western flower thrips (Frankliniella occidentalis). We hypothesize that both insects will transmit HLVd, but with different transmission efficiencies. Vector competence was evaluated in acquisition and transmission assays to determine the ability of the insects to uptake, maintain, and transmit HLVd to healthy hemp plants. Further, accumulation of HLVd in specific tissues, including salivary glands, alimentary canal, and carcass was performed to confirm virus progression through the insect body. Knowledge of insect vectors will provide hemp growers with a better understanding of this disease and develop targeted management strategies to avoid economic losses.