Evaluation of the sensitivity of Leptosphaeria maculans isolates causing phoma stem canker in oilseed rape in the Czech Republic to boscalid and dimoxystrobin fungicides

Abstract

Phoma stem canker, caused by Leptosphaeria spp. is generally managed with demethylation inhibitor (DMI) fungicides in the Czech Republic. However, there have been reports of resistance to DMIs in L. maculans populations. Fungicide resistance management recommends the application of fungicides with different modes of action, either as mixtures or in rotation with other fungicide classes. The objective, therefore, was to evaluate the efficacy of boscalid, dimoxystrobin and a mixture of boscalid and dimoxystrobin, belonging to the succinate dehydrogenase inhibitor and quinone outside inhibitor fungicide groups, respectively, on L. maculans isolates. A total of 41 and 285 isolates were tested using the mycelial growth and microtitre plate assays, respectively. The EC50 values for the mycelial growth plate method ranged from 0.026-0.984 µg/mL and 0.097-1.653 µg/mL for boscalid and boscalid + dimoxystrobin, respectively. For dimoxystrobin, the EC50 range was wide, between 0.053-95.59 µg/mL. The EC50 values for the microtitre plate assay ranged from 0.001 496-0.836 3 µg/mL and 7.3 × 10-4-2.801 µg/mL for boscalid and dimoxystrobin, respectively. The results also showed that the L. maculans conidia were more sensitive to boscalid and dimoxystrobin than mycelia.

Keywords

• fungicide resistance
• blackleg disease
• dmi
• sdhi
• qoi