New data on pathotype distribution and mefenoxam tolerance of Plasmopara halstedii in Hungary

Abstract

Sunflower downy mildew (Plasmopara halstedii) is one of the major diseases that can be controlled by using resistant cultivars and seed dressings; however, several isolates have developed tolerance to some fungicides and the resistance has also been overcome by new pathotypes. We aimed to examine the pathotype distribution in Hungary and to test the pathotypes' mefenoxam sensitivity. The isolates, which provided the basis of the research were collected from different regions of Hungary between 2014 and 2017 and, later, their pathotypes were identified. According to our results, pathotype 704 was one of the most widespread in Hungary, but pathotype 730, pathotype 724 and pathotype 700 were also detected. Seven out of ten isolates caused relatively high disease rates on the mefenoxam-treated and inoculated sunflower plants with P. halstedii. The pathogen has a high genetic variability which enhances the possibility to develop fungicide resistance. Furthermore, this variability can easily contribute to the breakdown of the resistant genes of the resistant hybrids. Both features can reduce the effectiveness of management; therefore, the continuous monitoring of this oomycete is very important.

Keywords

• fungicide tolerance
• helianthus annuus
• metalaxyl-m
• sunflower downy mildew
• virulence phenotype