Beet Curly Top Virus (BCTV) is a single-stranded circular DNA virus that infects more than 300 hundred plants, most notably sugar beets. BCTV was discovered in 1888 in the western United States, and it nearly wiped out sugar beet production in Idaho until resistant crops were developed in 1935.
BCTV was first described in hemp in 2019, and studies are limited. Still, researchers at Colorado State University have observed a wide range of symptoms in hemp, which may be due to genetic differences in plant response to the virus or differences in the strains of the virus.
Mild cases produce slight yellowing and molting at the base of the leaf. More severe infections produce the “classic” BCTV symptoms found in other crops: whole plants will become pale yellow, often with some slight upward leaf curling, and become generally stunted. Other hemp plants may show stunting along with strong twisting of the new growth, which may turn yellow.
Researchers have also seen some strange symptoms that are unique to hemp. For example, some plants show strong leaf curling, only to later outgrow most of the symptoms. Other plants will show leaf twisting and stunting in the main stem, but side stems appear normal. However, in those cases, BCTV is detected in both symptomatic and asymptomatic tissue.
The beet leafhopper is the only insect vector capable of spreading BCTV to other plants. All BCTV infections in hemp occur when a leafhopper that is carrying BCTV feeds on a hemp plant. The leafhoppers pick up the virus while feeding on other infected plants, BCTV does not cause disease in the insect.
Farmers have struggled with preventing BCTV for generations due to the mobility of the leafhoppers and the fact that the virus can spread in just hours. Insecticides are ineffective, but reflective mulches that deter insects may be helpful. Also, because hemp is not the beet leafhoppers’ preferred food crop, hemp farmers can reduce the likelihood of their occurrence by making sure favored food plants are not nearby, if possible.
Punya Nachappa, PhD of Colorado State University appeared on the CannMed Coffee Talk Podcast to discuss her team’s paper that identified several different viruses in Colorado hemp samples, most notably Beet Curly Top Virus. The conversations covers:
Medicinal Genomics offers a variety of PathoSEEK qPCR assays for plant pathogens, including Beet Curly Top Virus. DNA can be extracted from infected fan leaves using the Leaf Punch Lysis, and the detection assay can be run on the Agilent AriaMX and BioRad CFX96. .