title: Quantitative resistance increases the durability of qualitative resistance to Leptosphaeria maculans in Brassica napus.
abstract: It has frequently been hypothesized that quantitative resistance increases the durability of qualitative (R-gene mediated) resistance but supporting experimental evidence is rare. To test this hypothesis, near-isogenic lines with/without the R-gene Rlm6 introduced into two Brassica napus cultivars differing in quantitative resistance to Leptosphaeria maculans were used in a 5-yr field experiment. Recurrent selection of natural fungal populations was done annually on each of the four plant genotypes, using crop residues from each genotype to inoculate separately the four series of field trials for five consecutive cropping seasons. Severity of phoma stem canker was measured on each genotype and frequencies of avirulence alleles in L. maculans populations were estimated. Recurrent selection of virulent isolates by Rlm6 in a susceptible background rendered the resistance ineffective by the third cropping season. By contrast, the resistance was still effective after 5 yr of selection by the genotype combining this gene with quantitative resistance. No significant variation in the performance of quantitative resistance alone was noted over the course of the experiment. We conclude that quantitative resistance can increase the durability of Rlm6. We recommend combining quantitative resistance with R-gene mediated resistance to enhance disease control and crop production.
authors.affiliation: INRA, Agrocampus Ouest, Univ. Rennes1, UMR1099 BiO3P (Biology of Organisms and Populations applied to Plant Protection), F-35653 Le Rheu, France. Hortense.Brun@rennes.inra.fr
authors.forename: Hortense
authors.initials: H
authors.lastname: Brun
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Chèvre
authors.forename: Bruce D L
authors.initials: BD
authors.lastname: Fitt
authors.forename: Stephen
authors.initials: S
authors.lastname: Powers
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Besnard
authors.forename: Magali
authors.initials: M
authors.lastname: Ermel
authors.forename: Virginie
authors.initials: V
authors.lastname: Huteau
authors.forename: Bruno
authors.initials: B
authors.lastname: Marquer
authors.forename: Frédérique
authors.initials: F
authors.lastname: Eber
authors.forename: Michel
authors.initials: M
authors.lastname: Renard
authors.forename: Didier
authors.initials: D
authors.lastname: Andrivon
mesh_terms: D000483:Alleles; D001203:Ascomycota / Q000235:genetics* / Q000472:pathogenicity*; D029688:Brassica napus / Q000235:genetics* / Q000382:microbiology*; D002352:Carrier Proteins / Q000235:genetics; D018556:Crops, Agricultural / Q000235:genetics / Q000382:microbiology; D017343:Genes, Plant; D005838:Genotype; D010935:Plant Diseases / Q000235:genetics* / Q000382:microbiology*
chemical_list: D002352:Carrier Proteins