Poster Session: Disease Control and Pest Management - Genetics of Resistance

210-P

Discriminatory concentration assay to detection of low and high benzimidazole resistant isolates of Cercospora beticola.
N. R. TRKULJA (1), N. S. Dolovac (1), A. G. Milosavljevic (1), E. L. Pfaf-Dolovac (1)
(1) Institute for Plant protection and environment, Belgrade, Serbia

The appearance of populations of Cercospora beticola resistant to benzimidazoles is recorded wherever sugar beet grows. Designing methods which have the ability to provide faster data of the benzimidazole sensitivity of C. beticola is very useful to improve the management of disease. We have selected five isolates from each sensitivity group, sensitive, low-resistant (167-ß-tubulin mutation) and high-resistant (198-ß-tubulin mutation). Each isolate was grown for 10 days at 25°C in dark on potato dextrose agar medium amended with carbendazim and thiophanate-methyl at 0, 0.1, 1, 10, 50, 100, 500, and 1000 μg ml–1, afterwards colony growth was measured. The discriminatory concentration (DC) was defined as the concentration at which C. beticola isolates could clearly be separated into two groups, inhibited or not inhibited by the carbendazim or thiophanate-methyl. Appropriate DC for separation of sensitive from resistant isolates was 1 μg ml–1 for both carbendazim and thiophanate-methyl. Determined DC adequate to separate low-resistant from high-resistant isolates was 10 μg ml–1 and 100 μg ml–1 of carbendazim and thiophanate-methyl respectively. DC is very quick and useful method for resistance detection for large number of isolates, especially in case of single point mutation as well as resistance to benzimidazole fungicides. We propose using defined DC as method for detection of benzimidazole resistance of C. beticola.