The Characterization of Pathotypes in Grapevine Downy Mildew Provides Insights into the Breakdown of Rpv3, Rpv10, and Rpv12 Factors in Grapevines

Abstract

We describe a standard method for characterizing the virulence profile of Plasmopara viticola, the causal agent of grapevine downy mildew. We used 33 European strains to inoculate six grapevine varieties carrying the principal factors for resistance to downy mildew (Rpv1; Rpv3.1; Rpv3.2; Rpv5, Rpv6; Rpv10 and Rpv12) and the susceptible Vitis vinifera cv. Chardonnay. For each interaction, we characterized the level of sporulation by image analysis and the intensity of the grapevine hypersensitive response by visual score. We propose a definition for the breakdown of grapevine quantitative resistances combining these two traits. Among the 33 strains analyzed, 29 are virulent on at least one resistance factor. We identified five different pathotypes across the 33 strains analyzed: two pathotypes overcoming a single resistance factor (vir3.1 and vir3.2) and three complex pathotypes overcoming multiple resistance factors (vir3.1-3.2; vir3.2-12; vir3.1-3.2-10). Our findings confirm the widespread occurrence of P. viticola strains overcoming the Rpv3 haplotypes (29 strains). We also detected the first breakdown of resistance to the Rpv10 by a strain from Germany and the breakdown of Rpv12 factors by a strain in Hungary. The pathotyping method proposed here and the associated differential host range lay the groundwork for the early detection of resistance breakdown in grapevines. This approach will also facilitate the monitoring of the evolution of P. viticola populations at large spatial scales. This is an essential step forward to promoting durable management of the resistant grapevine varieties currently available.

Quantification of grapevine yield losses as a function downy mildew severity on foliage and cluster

“…Such data are needed to better estimate the parameters of the foliage-cluster transfer function, and to test, for example, how they depend on cultivars. Indeed, if all Vitis vinifera are susceptible to DM, differences in susceptibility to attack between (and within) cultivars exist (Boso and Kassemeyer, 2008; Gaforio et al, 2015; Paineau et al, 2022). Deriving robust foliage-cluster transfer functions grasping inoculum exchange between foliage and clusters is an important step for improving the protection strategies of grapevine against DM.…”

Effects of pathogen sexual reproduction on the evolutionary and epidemiological control provided by deployment strategies for two major resistance genes in agricultural landscapes

“…In recent years, breeders have been developing programs for breeding resistance to grapevine downy mildew, resulting in the creation of several resistant varieties, with the aim of lowering rates of fungicide application on grapevines. However, P. viticola has already been shown to have a high evolutionary potential, as demonstrated by the rapid emergence of fungicide resistance (Blum et al, 2010; Chen et al, 2007) and the breakdown of some of the resistances deployed (Peressotti et al, 2010; Delmas et al, 2016; Paineau et al, 2022). All the model parameters used in the simulations are listed in Table 2.…”

Crossing Plasmopara viticola strains in controlled conditions to uncover the genomic bases of downy mildew resistance breakdown in grapevine

“…We selected two parental strains of interest, respectively INRAE-Pv1419 (P1) and INRAE-PV412 (P2). They both overcome Rpv3-mediated resistance, and INRAE-Pv1419 also overcome Rpv10-mediated resistance (Paineau et al, 2022). They were crossed and their progeny was recovered as described in Figure 1.…”