Rapid emergence of boscalid resistance in Swedish populations of Alternaria solani revealed by a combination of field and laboratory experiments

Abstract Early blight, caused by Alternaria solani , is a common potato disease worldwide. Reduced field efficacy of the fungicide boscalid against this has been reported in several countries. Boscalid resistance mostly studied with in-vitro and/or greenhouse experiments. Field studies validating phenomenon are largely missing. Here, for first time Scandinavia, we validated Swedish population A. both and laboratory. trials between 2014 2017 Nymö showed significant reduction year. The target regions genes encoding succinate dehydrogenase subunits (Sdh) B, C D samples collected from Nymö, additional fields south-eastern central Sweden, were analysed substitutions associated loss sensitivity. In 2014, SdhC-H134R mutation was found at sites low frequency, while, 2017, majority had either SdhB-H278Y or substitution. No mutations detected gene SdhD subunit. Spore germination tests high sensitivity (EC 50 < 1 ?g mL ?1 ) isolates lacking substitutions. This supported decrease their radial growth rate, 0.1 to 10 boscalid. However, mutated EC > 100 rates hardly decreased concentrations above 1–10 . These results add current knowledge development indicate that early blight management southeast Sweden should no longer rely on