title: Erosion of quantitative host resistance in the apple×Venturia inaequalis pathosystem.
abstract: Theoretical approaches predict that host quantitative resistance selects for pathogens with a high level of pathogenicity, leading to erosion of the resistance. This process of erosion has, however, rarely been experimentally demonstrated. To investigate the erosion of apple quantitative resistance to scab disease, we surveyed scab incidence over time in a network of three orchards planted with susceptible and quantitatively resistant apple genotypes. We sampled Venturiainaequalis isolates from two of these orchards at the beginning of the experiment and we tested their quantitative components of pathogenicity (i.e., global disease severity, lesion density, lesion size, latent period) under controlled conditions. The disease severity produced by the isolates on the quantitatively resistant apple genotypes differed between the sites. Our study showed that quantitative resistance may be subject to erosion and even complete breakdown, depending on the site. We observed this evolution over time for apple genotypes that combine two broad-spectrum scab resistance QTLs, F11 and F17, showing a significant synergic effect of this combination in favour of resistance (i.e., favourable epistatic effect). We showed that isolates sampled in the orchard where the resistance was inefficient presented a similar level of pathogenicity on both apple genotypes with quantitative resistance and susceptible genotypes. As a consequence, our results revealed a case where the use of quantitative resistance may result in the emergence of a generalist pathogen population that has extended its pathogenicity range by performing similarly on susceptible and resistant genotypes. This emphasizes the need to develop quantitative resistances conducive to trade-offs within the pathogen populations concerned.
authors: INRA, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, SFR 4207 QUASAV, 49071 Beaucouzé Cedex, France; AgroCampus-Ouest, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France; Université d'Angers, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France. Electronic address: valerie.caffier@angers.inra.fr.
authors: Valérie
authors: V
authors: Caffier
authors: INRA, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, SFR 4207 QUASAV, 49071 Beaucouzé Cedex, France; AgroCampus-Ouest, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France; Université d'Angers, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France.
authors: Pauline
authors: P
authors: Lasserre-Zuber
authors: CTIFL - Centre Technique Interprofessionnel des Fruits et Légumes, Centre de Lanxade, 24130 Prigonrieux, France.
authors: Michel
authors: M
authors: Giraud
authors: CRRG - Centre Régional de Ressources Génétiques, Ferme du Héron, 59650 Villeneuve d'Ascq, France.
authors: Matthieu
authors: M
authors: Lascostes
authors: CRRG - Centre Régional de Ressources Génétiques, Ferme du Héron, 59650 Villeneuve d'Ascq, France.
authors: René
authors: R
authors: Stievenard
authors: INRA, Unité Expérimentale Horticole N°34 0449, Centre d'Angers-Nantes, 49071 Beaucouzé Cedex, France.
authors: Arnaud
authors: A
authors: Lemarquand
authors: Plant Breeding, Wageningen University and Research Centre, Droevendaalsesteeg 1, P.O. Box 16, 6700 AA Wageningen, The Netherlands.
authors: Eric
authors: E
authors: van de Weg
authors: INRA, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, SFR 4207 QUASAV, 49071 Beaucouzé Cedex, France; AgroCampus-Ouest, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France; Université d'Angers, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France.
authors: Pascale
authors: P
authors: Expert
authors: INRA, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, SFR 4207 QUASAV, 49071 Beaucouzé Cedex, France; AgroCampus-Ouest, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France; Université d'Angers, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France.
authors: Caroline
authors: C
authors: Denancé
authors: INRA, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, SFR 4207 QUASAV, 49071 Beaucouzé Cedex, France; AgroCampus-Ouest, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France; Université d'Angers, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France.
authors: Frédérique
authors: F
authors: Didelot
authors: INRA, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, SFR 4207 QUASAV, 49071 Beaucouzé Cedex, France; AgroCampus-Ouest, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France; Université d'Angers, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France.
authors: Bruno
authors: B
authors: Le Cam
authors: INRA, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, SFR 4207 QUASAV, 49071 Beaucouzé Cedex, France; AgroCampus-Ouest, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France; Université d'Angers, UMR1345 Institut de Recherche en Horticulture et Semences - IRHS, 49045 Angers, France.
authors: Charles-Eric
authors: CE
authors: Durel
mesh_terms: D001203:Ascomycota; D060467:Disease Resistance / Q000235:genetics*; D005838:Genotype; D054884:Host-Pathogen Interactions / Q000235:genetics*; D015994:Incidence; D027845:Malus / Q000235:genetics* / Q000382:microbiology*; D010935:Plant Diseases / Q000235:genetics* / Q000382:microbiology*
keywords: Aggressiveness; Apple scab; Durability; Epistasis; Malus×domestica; Partial resistance