Abstract
European grapevine, Vitis vinifera, carries no major resistances against Plasmopara viticola, the causal agent of grapevine downy mildew. The introgression of quantitative trait loci conferring resistance to P. viticola (Rpv) 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 P. viticola, 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 Rpv loci. A set of 16 cultivars carrying different combinations of Rpv loci, was challenged with five P. viticola isolates, obtained from susceptible or Rpv3.1+V. vinifera cultivars. Based on the severity of sporulation, different host and pathogen phenotypes might be distinguished, which could be related to the presence of different Rpv loci. The hormonal responses before and during some interactions were compared to assess the resistance mechanisms underlying Rpv3.1, Rpv10, and Rpv12 and the infection mechanisms of the different isolates. This paper reports on the strength of some of the commonly used Rpv loci, single or stacked. The isolates derived from Rpv3.1+ hosts, GREPv1 and GPHPv1, were able to sporulate intensely on cultivars carrying Rpv3.1, without triggering necrosis. Moreover, Rpv10 was not able to efficiently halt the development of the Rpv3.1-breaking isolate GPHPv1. Cultivars carrying Rpv12, however, were resistant to all five P. viticola 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 Rpv3- and Rpv10-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 P. viticola. A standardized phenotyping assay may be used to determine P. viticola 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.
Highlights
The obligatory biotrophic pathogen Plasmopara viticola, the causal agent of grapevine downy mildew, is considered one of the most economically important oomycetes (Kamoun et al, 2015)
This study provides an indication of the diversity in virulence of P. viticola isolates in a vineyard with a high occurrence of these Rpv loci
The disease severity index (DSI) clustered the isolates into three isolate groups (IGs)
Summary
The obligatory biotrophic pathogen Plasmopara viticola, the causal agent of grapevine downy mildew, is considered one of the most economically important oomycetes (Kamoun et al, 2015). The only grapevine species endemic in Europe, carries no resistance to this pathogen, except for a minor locus identified in Chardonnay (Bellin et al, 2009). Breeding of new cultivars resistant to the pathogen is being explored as a promising strategy to minimize chemical control. Controlled grapevine breeding was first launched in Europe following the introduction of phylloxera and powdery and downy mildews during the mid to late 19th century (Töpfer et al, 2011). Mildew resistances are still among the first criteria in a breeding program to select prime candidates from the seedling mass, before the evaluation of their viticultural performance and wine quality
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
