Validation of sugar beet varietal resistance against Cercospora leaf spot under greenhouse conditions

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most destructive foliar disease in sugar beet. Although CLS is traditionally managed through fungicide applications, integrated management is recommended in practice due to increased fungicide resistance and loss of fungicide efficacy. The implementation of varieties that are resistant to CLS is important for integrated pest management. Currently, resistant varieties have been reported to show delayed disease onset and reduced disease development in the field. However, studies that investigating the resistance phenotype of varieties under greenhouse conditions are limited. In this study, we evaluated, under greenhouse conditions, the resistance properties of three sugar beet varieties that had previously been tested in the field. To identify incubation conditions that allow discrimination between varieties with different levels of resistance, inoculated plants were incubated for varying lengths of time after inoculation. As in field trials, differentiation between susceptible and resistant varieties was possible based on disease development under greenhouse conditions. The varietythat performed best in field trials was also the best in greenhouse trials, with high reproducibility. In contrast, a second resistant varietythat showed less resistance in field trials also performed more variably in greenhouse trials, depending on the incubation time. A higher overall disease development was closely associated with longer incubation, but no single treatment consistently discriminated all three tested varieties across two independent experiments. Therefore, assessing disease resistance to CLS in a greenhouse can provide additional information but cannot replace field trials under natural infection conditions.