Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2008
Publication Date: 10/8/2008
Citation: Strausbaugh, C.A., Wintermantel, W.M., Gillen, A.M., Eujayl, I.A. 2008. Curly top survey in the Western United States. Phytopathology. 98(11):1212-1217. Interpretive Summary: Curly top is a considerable problem on a number of important crops in arid growing regions of the western United States. Curly top on sugar beet can be caused by Beet severe curly top virus (BSCTV) or a number of other closely related species transmitted by the beet leafhopper. Curly top almost eliminated the sugar beet industry in southern Idaho until beet with resistance became generally available in 1935. Since that time, host resistance has been the primary means of control for curly top in sugar beet. During the 1950s to the 1970s a broad range of curly top isolates were described, and some were noted to have increased in severity. Since then new Curtovirus species have been identified in the western U.S. on other crops and curly top losses in sugar beet have increased in areas of the western U.S. Thus, a survey was conducted for two years which showed that BSCTV and Beet mild curly top virus (BMCTV) were widely distributed in the western U.S. Only a few isolates of Beet curly top virus (BCTV) were found in the survey. Phylogenetic analysis indicated that the isolates from all three curly top species (BSCTV, BMCTV, and BCTV) formed three distinct groups, which supports the prior literature. Given the wide host range of the viruses responsible for curly top, frequent co-infections, and genetic diversity within and among species, establishing better host resistance and controlling curly top will continue to be a challenge.
Technical Abstract: Curly top in sugar beet continues to be a challenging disease to control in the western United States. To aid in development of host resistance and management options, the Curtovirus species composition was investigated by sampling 246 commercial fields along with nursery and field trials in the western U.S. DNA was isolated from leaf samples and the species were identified using species-specific PCR primers for the C1 gene. Amplicons from 79 isolates were also sequenced to confirm identifications. Beet severe curly top virus (BSCTV) and Beet mild curly top virus (BMCTV) were widely distributed throughout the western U.S., while only a few isolates of Beet curly top virus (BCTV) were found. In phylogenetic analysis, BSCTV, BMCTV, and BCTV isolates formed distinct groups in the dendrogram. Seven isolates not amplifiable with species-specific primers did amplify with curly top coat protein primers, indicating novel Curtovirus species or strains may be present. Given the wide host range of the viruses responsible for curly top, frequent co-infections, and genetic diversity within and among species, establishing better host resistance and controlling curly top will continue to be a challenge.