Abstract
Beet curly top virus (BCTV) in sugar beet is an important yield limiting disease problem in semi-arid production areas of the western U.S. BCTV is transmitted exclusively by the insect beet leafhopper, Circulifer tenellus. Resistant sugar beet cultivars remain a primary control measure, however most commercial cultivars only contain low to moderate levels of resistance because the resistance is thought to be quantitatively inherited and is difficult to maintain in parental lines used to create commercial hybrids. This is further complicated by the fact the mutation rate of BCTV far exceeds the breeding timeline of sugar beet. Methods to screen sugar beet germplasm for new and novel traits of resistance is complicated by the fact that the virus is transmitted by the beet leafhopper which is difficult rear and maintain in the laboratory setting. Field evaluations for BCTV resistance in sugar beet has traditionally been limited to areas in the western U.S. that are conducive to beet leafhopper habitats during the growing season and carry the BCTV virus. Beet leafhoppers are also known to co-currently carry and transmit multiple variants of the BCTV virus (Severe, Cal-Logan, etc.) at the same time which further complicates the interpretation of screening outcomes in field trials. To expedite the screening of sugar beet germplasm for new and novel sources of resistance traits, we have developed an agroinfiltration shuttle vector system (Agrobacterium t.) that bypasses the need for the beet leafhopper to transmit the BCTV virus into sugar beet seedlings. Once agroinfiltrated into the plant, the BCTV full-length virus is mobilized and replicated de novo resulting in systemic and persistent BCTV disease symptoms in the seedling. Methods to use this agroinfiltration vector system as a high-throughput method to screen USDA sugar beet plant introductions (PI lines) or other sugar beet lines of interest will be discussed.