Beet Curly Top Virus Revisited: Factors Contributing to Re-emergence in California

Beet curly top virus (BCTV), transmitted by the beet leafhopper (Circulifer tenellus) has caused significant problems to irrigated agriculture in the western United States since the late 1800s. Although managed annually through an intensive leafhopper eradication program, BCTV re-emerged in 2001 as a serious threat to agriculture in California's San Joaquin Valley. BCTV infects a broad range of crop hosts including sugarbeet, pepper, tomato, bean, spinach, and cucurbits, as well as numerous weeds. Although many strains of BCTV have been identified over the years, molecular characterization of BCTV in sugarbeet has demonstrated that the virus primarily exists as genetic variants of three strains known as CFH, Worland, and California/Logan. Studies conducted in the early 1990s determined that most sugarbeets were infected with either CFH or Worland strains, but little information exists on strain distribution among weed hosts. Data collected in California and other states has focused on molecular characterization of BCTV isolated from weed hosts, as well as sugarbeet and selected other crops. ELISA for universal detection of BCTV, as well as PCR using strain specific primers have been used to identify BCTV strains infecting crop and weed hosts from both fields and overwintering grounds of the beet leafhopper. Strain identification coupled with sequence analysis provides insight into variability in virus population structure over broad areas, as well as over time.