Estimation of sugar beet lines and cultivars infection to Scrobipalpa ocellatella Boyd. (Lepidoptera: Gelechiidae) larvae under field condition with natural infection

In order to evaluate the infection rate of different sugar beet lines and cultivars to S. ocellatella, 24 sugar beet lines and cultivars were evaluated under natural infection in the field in Karaj, in 2013.Considering the presence of several generations of the pest, the infection rate treatments were evaluated during the growing season (eight stages, every 10days). After last sampling on 16 September, treatments were classified to four groups (low, medium, high, and very high infection) based on standard deviation distance from mean. The commercial varieties Paya, Marak, and 7K43 were placed in low infection group, whereas Rosire, Dorothea and the male line of Jolgeh in the very high infection group. Based on field observations, the first symptoms of the pest infection were emerged at 6-8-leaf stage early July; however, the infection percentage was low early July (less than 0.34-1.37%) and increased to more than 50% in August. In general, it is recommended that in sugar beet breeding programs, the resistance potential of the cultivars be used for damage control.