AUTHOR=Heyman Lisa , Höfle Rebecca , Kicherer Anna , Trapp Oliver , Ait Barka Essaid , Töpfer Reinhard , Höfte Monica 

TITLE=The Durability of Quantitative Host Resistance and Variability in Pathogen Virulence in the Interaction Between European Grapevine Cultivars and Plasmopara viticola

JOURNAL=Frontiers in Agronomy

VOLUME=3

YEAR=2021

URL=https://www.frontiersin.org/journals/agronomy/articles/10.3389/fagro.2021.684023

DOI=10.3389/fagro.2021.684023

ISSN=2673-3218

ABSTRACT=<p>European grapevine, <italic>Vitis vinifera</italic>, carries no major resistances against <italic>Plasmopara viticola</italic>, the causal agent of grapevine downy mildew. The introgression of quantitative trait loci conferring resistance to <italic>P. viticola</italic> (<italic>Rpv</italic>) from American and Asian donor species has resulted in a range of resistant cultivars. In light of the perennial nature of grapevine and the high evolutionary potential of <italic>P. viticola</italic>, the durability of this quantitative resistance is an important challenge. Durability of host resistance and variability in pathogen virulence may be evaluated by describing interactions between pathogen isolates and grapevine cultivars in terms of <italic>Rpv</italic> loci. A set of 16 cultivars carrying different combinations of <italic>Rpv</italic> loci, was challenged with five <italic>P. viticola</italic> isolates, obtained from susceptible or <italic>Rpv3.1</italic><sup>+</sup><italic>V. vinifera</italic> cultivars. Based on the severity of sporulation, different host and pathogen phenotypes might be distinguished, which could be related to the presence of different <italic>Rpv</italic> loci. The hormonal responses before and during some interactions were compared to assess the resistance mechanisms underlying <italic>Rpv3.1, Rpv10</italic>, and <italic>Rpv12</italic> and the infection mechanisms of the different isolates. This paper reports on the strength of some of the commonly used <italic>Rpv</italic> loci, single or stacked. The isolates derived from <italic>Rpv3.1</italic><sup>+</sup> hosts, GRE<italic>Pv</italic>1 and GPH<italic>Pv</italic>1, were able to sporulate intensely on cultivars carrying <italic>Rpv3.1</italic>, without triggering necrosis. Moreover, <italic>Rpv10</italic> was not able to efficiently halt the development of the <italic>Rpv3.1</italic>-breaking isolate GPH<italic>Pv</italic>1. Cultivars carrying <italic>Rpv12</italic>, however, were resistant to all five <italic>P. viticola</italic> isolates. Phytohormones might be implicated in the basal resistance against this pathogen, but during the early defense response, no significant hormonal responses to the isolates were observed. The isolate-specificity of the <italic>Rpv3</italic>- and <italic>Rpv10</italic>-mediated resistance suggests that these loci do not result in the most sustainable resistance. Furthermore, the isolate-specific behavior of the pathogen emphasizes the need for a characterization system for <italic>P. viticola</italic>. A standardized phenotyping assay may be used to determine <italic>P. viticola</italic> pathogen phenotypes or measure the durability, strength, and isolate-specificity of the host quantitative resistances. The characterization of both components of the pathosystem may lead to an increased understanding of the resistance mechanisms, beneficial for a durable deployment of resistance genes.</p>