title: Rapid and multiregional adaptation to host partial resistance in a plant pathogenic oomycete: evidence from European populations of Plasmopara viticola, the causal agent of grapevine downy mildew.
abstract: Crop pathogens evolve rapidly to adapt to their hosts. The use of crops with quantitative disease resistance is expected to alter selection of pathogen life-history traits. This may result in differential adaptation of the pathogen to host cultivars and, sometimes, to the erosion of quantitative resistance. Here, we assessed the level of host adaptation in an oomycete plant pathogenic species. We analysed the phenotypic and genetic variability of 17 Plasmopara viticola isolates collected on Vitis vinifera and 35 isolates from partially resistant varieties (Regent and genotypes carrying the Rpv1 gene). Cross-inoculation experiments assessed two components of aggressiveness and a life-history trait of the pathogen: disease severity, sporangial production and sporangia size. The results contribute evidence to the emergence of P. viticola aggressive isolates presenting a high level of sporulation on the partially resistant Regent. By contrast, no adaptation to the Rpv1 gene was found in this study. The erosion of Regent resistance may have occurred in less than 5years and at least three times independently in three distant wine-producing areas. Populations from resistant varieties showed a significant increase in sporangia production capacity, indicating an absence of fitness costs for this adaptation. The increase in the number of sporangia was correlated with a reduction in sporangia size, a result which illustrates how partial plant disease resistance can impact selection of the pathogen's life-history traits. This case study on grapevine downy mildew shows how new plant pathogen populations emerge in agro-ecosystems by adapting to partial host resistance. This adaptive pattern highlights the need for wise management of plant partial disease resistance to ensure its sustainability over time.
authors.affiliation: INRA, Institut des Sciences de la Vigne et du Vin, UMR1065 Santé et Agroécologie du Vignoble, F-33883 Villenave d'Ornon, France; Université de Bordeaux, ISVV, UMR1065 SAVE, F-33883 Villenave d'Ornon, France. Electronic address: delmotte@bordeaux.inra.fr.
authors.forename: François
authors.initials: F
authors.lastname: Delmotte
authors.affiliation: INRA, UMR 1131 Santé de la Vigne et Qualité du Vin, F-68000 Colmar, France; Université de Strasbourg, UMR 1131 Santé de la Vigne et Qualité du Vin, F-68000 Colmar, France.
authors.forename: Pere
authors.initials: P
authors.lastname: Mestre
authors.affiliation: INRA, UMR 1131 Santé de la Vigne et Qualité du Vin, F-68000 Colmar, France; Université de Strasbourg, UMR 1131 Santé de la Vigne et Qualité du Vin, F-68000 Colmar, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Schneider
authors.affiliation: Staatliches Weinbauinstitut, Merzhauser Strasse 119, 79100 Freiburg, Germany.
authors.forename: Hanns-Heinz
authors.initials: HH
authors.lastname: Kassemeyer
authors.affiliation: University of Pécs, Research Institute for Viticulture and Oenology, H-7634 Pécs, Pázmány Péter u.4, Hungary.
authors.forename: Pál
authors.initials: P
authors.lastname: Kozma
authors.affiliation: INRA, Institut des Sciences de la Vigne et du Vin, UMR1065 Santé et Agroécologie du Vignoble, F-33883 Villenave d'Ornon, France; Université de Bordeaux, ISVV, UMR1065 SAVE, F-33883 Villenave d'Ornon, France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Richart-Cervera
authors.affiliation: INRA, Institut des Sciences de la Vigne et du Vin, UMR1065 Santé et Agroécologie du Vignoble, F-33883 Villenave d'Ornon, France; Université de Bordeaux, ISVV, UMR1065 SAVE, F-33883 Villenave d'Ornon, France.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Rouxel
authors.affiliation: INRA, Institut des Sciences de la Vigne et du Vin, UMR1065 Santé et Agroécologie du Vignoble, F-33883 Villenave d'Ornon, France; Université de Bordeaux, ISVV, UMR1065 SAVE, F-33883 Villenave d'Ornon, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Delière
mesh_terms: D060467:Disease Resistance; D005843:Geography; D054884:Host-Pathogen Interactions; D009868:Oomycetes; D027843:Vitis / Q000382:microbiology*
keywords: Aggressiveness; Erosion of quantitative host resistance; Fungal plant pathogen; Life-history traits; Regent grape cultivar; Vitis vinifera