Abstract
The use of single-site fungicides to control plant pathogens in the agroecosystem can be associated with an increased selection of resistance. The evolution of resistance represents one of the biggest challenges in disease control. In vineyards, frequent applications of fungicides are carried out every season for multiple years. The agronomic risk of developing fungicide resistance is, therefore, high. Plasmopara viticola, the causal agent of grapevine downy mildew, is a high risk pathogen associated with the development of fungicide resistance. P. viticola has developed resistance to most of the fungicide classes used and constitutes one of the most important threats for grapevine production. The goals of this review are to describe fungicide resistance evolution in P. viticola populations and how to conduct proper monitoring activities. Different methods have been developed for phenotyping and genotyping P. viticola for fungicide resistance and the different phases of resistance evolution and life cycles of the pathogen are discussed, to provide a full monitoring toolkit to limit the spread of resistance. A detailed revision of the available tools will help in shaping and harmonizing the monitoring activities between countries and organizations.
Highlights
The use of single-site fungicides to control plant pathogens in the agroecosystem can be associated with an increased selection of resistance
Downy mildew, caused by the oomycete Plasmopara viticola, is one of the major threats for grapevine production, due to the quantitative and qualitative yield losses that are associated with severe disease epidemics [1]
Grapevine is a perennial plant with a life expectancy of decades; it is cultivated in monoculture, with a period of susceptibility to P. viticola of several months that varies each year
Summary
Downy mildew, caused by the oomycete Plasmopara viticola, is one of the major threats for grapevine production, due to the quantitative and qualitative yield losses that are associated with severe disease epidemics [1]. Only these plants were treated, with a mush made with copper sulphate and lime, to discourage people from eating the grapes This observation led to the development of the “Bordeaux mixture” to control downy mildew [7]. The dithiocarbamates and phthalimides were the first chemical classes employed against P. viticola Members of these classes (e.g., zineb and captan), showed similar or higher control than the Bordeaux mixture [13,14]. The success of these fungicides was mainly caused by the higher return on investment and the absence of phytotoxicity, the latter often observed when using copper compounds [15,16]. The substantial difference between systemic and cytotropic active ingredients is that the former can translocate inside the tissues of the plant (mainly through xylem vessels) and protect the newly formed vegetation, whereas the latter redistribute only locally [23]
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