Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2007
Publication Date: 10/10/2007
Citation: Strausbaugh, C.A., Gillen, A.M., Camp, S., Shock, C.C., Eldredge, E.P., Gallian, J.J. 2007. Relationship of beet curly top foliar ratings to sugar beet yield. Plant Disease. 91:1459-1463. 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 beets can be caused by Beet severe curly top virus 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 beets with resistance became generally available in 1935. Since that time, host resistance has been the primary means of control for curly top in sugar beets. In order to maintain resistance to curly top, cultivars and germplasm must be screened annually. However, plants in the screening nurseries are only scored visually and yields are not assessed. Thus, studies were conducted to assess whether the curly top disease ratings made under inoculated conditions in curly top nurseries correlate with disease ratings and yield measured under commercial sugar beet production conditions. Under moderate natural infection pressure, curly top ratings in commercial cultivars were found to correlate with those taken in inoculated nurseries. Regression analyses showed that yield response was related to the ratings. For each unit increase in rating (increasing susceptibility), root yield decreased 2.6 to 3.1 tons per acre. Thus, curly top nurseries should be a reliable means to select resistant cultivars for commercial cultivation.
Technical Abstract: Sugar beet varieties were evaluated for disease resistance to Beet severe curly top virus (BSCTV) and closely related virus species to establish if disease ratings made in inoculated nurseries correlated with disease ratings and yield in sugar beet crops exposed to natural disease outbreaks. Cultivars were planted both in inoculated curly top nurseries in Kimberly, ID, and in commercial variety trials in irrigated fields near Ontario, OR and Nampa, ID. Plants were evaluated for curly top using a disease index (DI) scale of 0 (no symptoms) to 9 (dead). Moderate disease pressure in the Ontario (mean DI = 3.8) and Nampa (mean DI = 4.1) fields resulted in significant differences among commercial hybrids for DI, root yield, sugar content, and estimated recoverable sugar. Disease ratings from both commercial fields were positively correlated (r = 0.91 and 0.82, P < 0.0001) with ratings from the inoculated nurseries. In commercial fields, root yield was negatively related to DI (r squared = 0.47 and 0.39, P < 0.0004). For each unit increase in DI (increasing susceptibility), root yield decreased 5.76 to 6.93 t/ha. Thus, curly top nurseries can be used reliably to select curly top resistant cultivars for commercial cultivation.