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.

The first report of Plasmopara halstedii race 337 in the Russian Federation

“…Mefenoxam is quite effective among a limited number of fungicides against P. halstedii. However, the biotypes that are resistant to mefenoxam have spread worldwide (Molinero-Ruiz et al 2008;Körösi et al 2021). In the Russian Federation, resistance to mefenoxam was detected among isolates of the pathotypes 710, 730 and 734 (Iwebor et al 2019).…”

New and High Virulent Pathotypes of Sunflower Downy Mildew (Plasmopara halstedii) in Seven Countries in Europe

“…Among the less virulent ones, pathotype 700 continued to be dominant, while pathotypes 100 and 330 seem to have disappeared. In addition, Körösi et al [ 8 ] pointed out that pathotype 704 was rather widespread in Hungary between 2014 and 2017. From our findings, a further shift in the composition of the pathotypes could be detected from 2016, with an almost 80% occurrence of more virulent pathotypes.…”

“…The reason for the appearance and spreading of new P. halstedii pathotypes could be the result of several factors, including mainly the presumed high allele frequency of either the Pl 6, the more and more advanced and newest tolerance genes in the new sunflower hybrids supplied by international breeding and seed companies, and the more frequent favorable weather conditions for P. halstedii in the concerned period. In addition to the above, the appearance of mefenoxam-tolerant P. halstedii pathotypes [ 8 ], short crop rotations, and the spread of minimum tillage systems may accelerate the emergence of increasingly aggressive pathotypes.…”

“…There are only a few active ingredients such as mefenoxam that are effective enough against P. halstedii. The widespread and exclusive use of this chemical resulted in a descending efficiency and has led to the development of resistance or tolerance in the pathogen worldwide [ 6 , 7 , 8 ].…”

Efficacy of some plant resistance inducers against several sunflower downy mildew (Plasmopara halstedii (Farl.) Berl. et de Toni) isolates

“…Previously, mefenoxam, a phenyl amide active ingredient, provided efficient control against the disease for a long time (Albourie et al 1998). However, P. halstedii rapidly developed mefenoxamtolerant genotypes in several countries (Albourie et al 1998;Gulya 2000;Iwebor et al 2022;Körösi et al 2020;Molinero-Ruiz et al 2003). The introduction of new fungicides, therefore, is crucial for effectively managing ARTICLE Efficacy of some plant resistance inducers against several sunflower downy mildew (Plasmopara halstedii (Farl.)…”