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An assay for quantitative virulence in R hynchosporium commune reveals an association between effector genotype and virulence
Author(s) -
Stefansson T. S.,
Willi Y.,
Croll D.,
McDonald B. A.
Publication year - 2014
Publication title -
plant pathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.928
H-Index - 85
eISSN - 1365-3059
pISSN - 0032-0862
DOI - 10.1111/ppa.12111
Subject(s) - virulence , biology , pathosystem , genetics , quantitative trait locus , heritability , genotype , pathogen , gene
Detailed knowledge of the evolutionary genetics of virulence is needed to understand and predict host–pathogen dynamics. This study used a virulence assay based on digital image analysis and treated virulence as a quantitative rather than a binary trait. Such quantitative data may better reflect the genetic underpinning of virulence in many pathogen systems and provide better resolution in statistical investigations. A greenhouse experiment based on a common garden design was conducted to measure virulence (% of leaf area covered by lesions) of 126 genetically distinct isolates of the barley scald pathogen, R hynchosporium commune , originating from nine field populations around the world. Virulence in this pathosystem was found to be a quantitative trait with a continuous distribution in all populations. By comparing population genetic differentiation for virulence and neutral microsatellite markers (i.e. a Q ST / G ST comparison), evidence that virulence is under stabilizing selection across populations was found. Heritability values were high and ranged from 0·52 to 0·96 with a mean heritability of 0·84. Virulence was positively correlated with spore production as predicted by the trade‐off theory of virulence evolution. Furthermore, an association analysis between virulence and sequence haplotypes of three known necrosis‐inducing effector genes ( NIP 1 , NIP 2 and NIP 3 ) revealed a significant effect of NIP 2 haplotypes and NIP 1 deletions. Overall, the results support a quantitative model for virulence in the R . commune –barley pathosystem and very high evolutionary potential for this trait.