title: Slow erosion of a quantitative apple resistance to Venturia inaequalis based on an isolate-specific Quantitative Trait Locus.
abstract: Quantitative plant resistance affects the aggressiveness of pathogens and is usually considered more durable than qualitative resistance. However, the efficiency of a quantitative resistance based on an isolate-specific Quantitative Trait Locus (QTL) is expected to decrease over time due to the selection of isolates with a high level of aggressiveness on resistant plants. To test this hypothesis, we surveyed scab incidence over an eight-year period in an orchard planted with susceptible and quantitatively resistant apple genotypes. We sampled 79 Venturia inaequalis isolates from this orchard at three dates and we tested their level of aggressiveness under controlled conditions. Isolates sampled on resistant genotypes triggered higher lesion density and exhibited a higher sporulation rate on apple carrying the resistance allele of the QTL T1 compared to isolates sampled on susceptible genotypes. Due to this ability to select aggressive isolates, we expected the QTL T1 to be non-durable. However, our results showed that the quantitative resistance based on the QTL T1 remained efficient in orchard over an eight-year period, with only a slow decrease in efficiency and no detectable increase of the aggressiveness of fungal isolates over time. We conclude that knowledge on the specificity of a QTL is not sufficient to evaluate its durability. Deciphering molecular mechanisms associated with resistance QTLs, genetic determinants of aggressiveness and putative trade-offs within pathogen populations is needed to help in understanding the erosion processes.
authors.affiliation: IRHS, Agrocampus-Ouest, INRA, Université d'Angers, SFR 4207 QuaSaV, 49071 Beaucouzé, France. Electronic address: valerie.caffier@angers.inra.fr.
authors.forename: Valérie
authors.initials: V
authors.lastname: Caffier
authors.affiliation: IRHS, Agrocampus-Ouest, INRA, Université d'Angers, SFR 4207 QuaSaV, 49071 Beaucouzé, France.
authors.forename: Bruno
authors.initials: B
authors.lastname: Le Cam
authors.affiliation: IRHS, Agrocampus-Ouest, INRA, Université d'Angers, SFR 4207 QuaSaV, 49071 Beaucouzé, France.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Al Rifaï
authors.affiliation: IRHS, Agrocampus-Ouest, INRA, Université d'Angers, SFR 4207 QuaSaV, 49071 Beaucouzé, France.
authors.forename: Marie-Noëlle
authors.initials: MN
authors.lastname: Bellanger
authors.affiliation: IRHS, Agrocampus-Ouest, INRA, Université d'Angers, SFR 4207 QuaSaV, 49071 Beaucouzé, France.
authors.forename: Morgane
authors.initials: M
authors.lastname: Comby
authors.affiliation: IRHS, Agrocampus-Ouest, INRA, Université d'Angers, SFR 4207 QuaSaV, 49071 Beaucouzé, France.
authors.forename: Caroline
authors.initials: C
authors.lastname: Denancé
authors.affiliation: IRHS, Agrocampus-Ouest, INRA, Université d'Angers, SFR 4207 QuaSaV, 49071 Beaucouzé, France.
authors.forename: Frédérique
authors.initials: F
authors.lastname: Didelot
authors.affiliation: IRHS, Agrocampus-Ouest, INRA, Université d'Angers, SFR 4207 QuaSaV, 49071 Beaucouzé, France.
authors.forename: Pascale
authors.initials: P
authors.lastname: Expert
authors.affiliation: IRHS, Agrocampus-Ouest, INRA, Université d'Angers, SFR 4207 QuaSaV, 49071 Beaucouzé, France.
authors.forename: Tifenn
authors.initials: T
authors.lastname: Kerdraon
authors.affiliation: UE0449 Unité Expérimentale Horticole, INRA, SFR 4207 QuaSaV, 49071 Beaucouzé, France.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Lemarquand
authors.affiliation: IRHS, Agrocampus-Ouest, INRA, Université d'Angers, SFR 4207 QuaSaV, 49071 Beaucouzé, France.
authors.forename: Elisa
authors.initials: E
authors.lastname: Ravon
authors.affiliation: IRHS, Agrocampus-Ouest, INRA, Université d'Angers, SFR 4207 QuaSaV, 49071 Beaucouzé, France.
authors.forename: Charles-Eric
authors.initials: CE
authors.lastname: Durel
mesh_terms: D000483:Alleles; D001203:Ascomycota; D060467:Disease Resistance / Q000235:genetics*; D020022:Genetic Predisposition to Disease; D005838:Genotype; D015994:Incidence; D027845:Malus / Q000235:genetics* / Q000382:microbiology*; D010935:Plant Diseases / Q000235:genetics* / Q000382:microbiology*; D040641:Quantitative Trait Loci
keywords: Aggressiveness; Apple scab; Durability; Malus×domestica; Quantitative resistance; Venturia inaequalis