title: Quantitative resistance affects the speed of frequency increase but not the diversity of the virulence alleles overcoming a major resistance gene to Leptosphaeria maculans in oilseed rape.
abstract: Quantitative resistance mediated by multiple genetic factors has been shown to increase the potential for durability of major resistance genes. This was demonstrated in the Leptosphaeria maculans/Brassica napus pathosystem in a 5year recurrent selection field experiment on lines harboring the qualitative resistance gene Rlm6 combined or not with quantitative resistance. The quantitative resistance limited the size of the virulent isolate population. In this study we continued this recurrent selection experiment in the same way to examine whether the pathogen population could adapt and render the major gene ineffective in the longer term. The cultivars Eurol, with a susceptible background, and Darmor, with quantitative resistance, were used. We confirmed that the combination of qualitative and quantitative resistance is an effective approach for controlling the pathogen epidemics over time. This combination did not prevent isolates virulent against the major gene from amplifying in the long term but the quantitative resistance significantly delayed for 5years the loss of effectiveness of the qualitative resistance and disease severity was maintained at a low level on the genotype with both types of resistance after the fungus population had adapted to the major gene. We also showed that diversity of AvrLm6 virulence alleles was comparable in isolates recovered after the recurrent selection on lines carrying either the major gene alone or in combination with quantitative resistance: a single repeat-induced point mutation and deletion events were observed in both situations. Breeding varieties which combine qualitative and quantitative resistance can effectively contribute to disease control by increasing the potential for durability of major resistance genes.
authors.affiliation: INRA, UMR 1349 IGEPP, BP35327, F-35653 Le Rheu Cedex, France. Electronic address: Regine.Delourme@rennes.inra.fr.
authors.forename: R
authors.initials: R
authors.lastname: Delourme
authors.affiliation: INRA, UMR 1349 IGEPP, BP35327, F-35653 Le Rheu Cedex, France. Electronic address: Lydia.Bousset@rennes.inra.fr.
authors.forename: L
authors.initials: L
authors.lastname: Bousset
authors.affiliation: INRA, UMR 1349 IGEPP, BP35327, F-35653 Le Rheu Cedex, France. Electronic address: Magali.Ermel@rennes.inra.fr.
authors.forename: M
authors.initials: M
authors.lastname: Ermel
authors.affiliation: INRA, UMR 1349 IGEPP, BP35327, F-35653 Le Rheu Cedex, France. Electronic address: Philippe.Duffe@rennes.inra.fr.
authors.forename: P
authors.initials: P
authors.lastname: Duffé
authors.affiliation: INRA, UMR 1349 IGEPP, BP35327, F-35653 Le Rheu Cedex, France. Electronic address: Anne-Laure.Besnard@rennes.inra.fr.
authors.forename: A L
authors.initials: AL
authors.lastname: Besnard
authors.affiliation: INRA, UMR 1349 IGEPP, BP35327, F-35653 Le Rheu Cedex, France. Electronic address: Bruno.Marquer@rennes.inra.fr.
authors.forename: B
authors.initials: B
authors.lastname: Marquer
authors.affiliation: INRA, UR 1290 BIOGER, BP 01, F-78850 Thiverval-Grignon, France. Electronic address: Isabelle.Fudal@versailles.inra.fr.
authors.forename: I
authors.initials: I
authors.lastname: Fudal
authors.affiliation: INRA, UR 1290 BIOGER, BP 01, F-78850 Thiverval-Grignon, France. Electronic address: Juliette.Linglin@versailles.inra.fr.
authors.forename: J
authors.initials: J
authors.lastname: Linglin
authors.affiliation: INRA, UR 1052 GAFL, Domaine Saint Maurice, CS 60094, F-84143 Montfavet Cedex, France. Electronic address: joel@paca.inra.fr.
authors.forename: J
authors.initials: J
authors.lastname: Chadœuf
authors.affiliation: INRA, UMR 1349 IGEPP, BP35327, F-35653 Le Rheu Cedex, France. Electronic address: Hortense.Brun@rennes.inra.fr.
authors.forename: H
authors.initials: H
authors.lastname: Brun
mesh_terms: D000483:Alleles; D001203:Ascomycota; D005075:Biological Evolution; D029688:Brassica napus / Q000235:genetics* / Q000382:microbiology*; D060467:Disease Resistance / Q000235:genetics*; D014644:Genetic Variation; D018598:Minisatellite Repeats; D009154:Mutation; D010935:Plant Diseases / Q000235:genetics*; D011110:Polymorphism, Genetic; D012621:Seasons
keywords: Brassica napus; Leptosphaeria maculans; Qualitative resistance; Quantitative resistance; Resistance durability; Virulence