title: Quantitative trait locus mapping reveals complex genetic architecture of quantitative virulence in the wheat pathogen Zymoseptoria tritici.
abstract: We conducted a comprehensive analysis of virulence in the fungal wheat pathogen Zymoseptoria tritici using quantitative trait locus (QTL) mapping. High-throughput phenotyping based on automated image analysis allowed the measurement of pathogen virulence on a scale and with a precision that was not previously possible. Across two mapping populations encompassing more than 520 progeny, 540 710 pycnidia were counted and their sizes and grey values were measured. A significant correlation was found between pycnidia size and both spore size and number. Precise measurements of percentage leaf area covered by lesions provided a quantitative measure of host damage. Combining these large and accurate phenotypic datasets with a dense panel of restriction site-associated DNA sequencing (RADseq) genetic markers enabled us to genetically dissect pathogen virulence into components related to host damage and those related to pathogen reproduction. We showed that different components of virulence can be under separate genetic control. Large- and small-effect QTLs were identified for all traits, with some QTLs specific to mapping populations, cultivars and traits and other QTLs shared among traits within the same mapping population. We associated the presence of four accessory chromosomes with small, but significant, increases in several virulence traits, providing the first evidence for a meaningful function associated with accessory chromosomes in this organism. A large-effect QTL involved in host specialization was identified on chromosome 7, leading to the identification of candidate genes having a large effect on virulence.
authors.affiliation: Plant Pathology Group, ETH Zürich, Universitätstrasse 2, Zürich, 8092, Switzerland.
authors.forename: Ethan L
authors.initials: EL
authors.lastname: Stewart
authors.affiliation: Plant Pathology Group, ETH Zürich, Universitätstrasse 2, Zürich, 8092, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Croll
authors.affiliation: Plant Pathology Group, ETH Zürich, Universitätstrasse 2, Zürich, 8092, Switzerland.
authors.forename: Mark H
authors.initials: MH
authors.lastname: Lendenmann
authors.affiliation: Plant Pathology Group, ETH Zürich, Universitätstrasse 2, Zürich, 8092, Switzerland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Sanchez-Vallet
authors.affiliation: Plant Pathology Group, ETH Zürich, Universitätstrasse 2, Zürich, 8092, Switzerland.
authors.forename: Fanny E
authors.initials: FE
authors.lastname: Hartmann
authors.affiliation: Plant Pathology Group, ETH Zürich, Universitätstrasse 2, Zürich, 8092, Switzerland.
authors.forename: Javier
authors.initials: J
authors.lastname: Palma-Guerrero
authors.affiliation: Plant Pathology Group, ETH Zürich, Universitätstrasse 2, Zürich, 8092, Switzerland.
authors.forename: Xin
authors.initials: X
authors.lastname: Ma
authors.affiliation: Plant Pathology Group, ETH Zürich, Universitätstrasse 2, Zürich, 8092, Switzerland.
authors.forename: Bruce A
authors.initials: BA
authors.lastname: McDonald
mesh_terms: D000483:Alleles; D001203:Ascomycota / Q000235:genetics* / Q000472:pathogenicity*; D002874:Chromosome Mapping; D015825:Chromosomes, Fungal / Q000235:genetics; D020869:Gene Expression Profiling; D015966:Gene Expression Regulation, Fungal; D056726:Genetic Association Studies; D040582:Inheritance Patterns / Q000235:genetics; D008126:Lod Score; D058977:Molecular Sequence Annotation; D010641:Phenotype; D040641:Quantitative Trait Loci / Q000235:genetics*; D014908:Triticum / Q000382:microbiology*; D014774:Virulence / Q000235:genetics
keywords: Mycosphaerella graminicola; QTL mapping; Zymoseptoria tritici; image analysis; quantitative virulence