title: The jack of all trades is master of none: a pathogen's ability to infect a greater number of host genotypes comes at a cost of delayed reproduction.
abstract: A trade-off between a pathogen's ability to infect many hosts and its reproductive capacity on each host genotype is predicted to limit the evolution of an expanded host range, yet few empirical results provide evidence for the magnitude of such trade-offs. Here, we test the hypothesis for a trade-off between the number of host genotypes that a fungal pathogen can infect (host genotype range) and its reproductive capacity on susceptible plant hosts. We used strains of the oat crown rust fungus that carried widely varying numbers of virulence (avr) alleles known to determine host genotype range. We quantified total spore production and the expression of four pathogen life-history stages: infection efficiency, time until reproduction, pustule size, and spore production per pustule. In support of the trade-off hypothesis, we found that virulence level, the number of avr alleles per pathogen strain, was correlated with significant delays in the onset of reproduction and with smaller pustule sizes. Modeling from our results, we conclude that trade-offs have the capacity to constrain the evolution of host genotype range in local populations. In contrast, long-term trends in virulence level suggest that the continued deployment of resistant host lines over wide regions of the United States has generated selection for increased host genotype range.
authors.affiliation: Department of Ecology, Evolution and Behavior, University of Minnesota, Saint Paul, Minnesota, 55108; Department of Biology, University of Virginia, Charlottesville, Virginia, 22904. elb5m@virginia.edu.
authors.forename: Emily
authors.initials: E
authors.lastname: Bruns
authors.forename: Martin L
authors.initials: ML
authors.lastname: Carson
authors.forename: Georgiana
authors.initials: G
authors.lastname: May
mesh_terms: D000222:Adaptation, Physiological; D018554:Avena / Q000235:genetics / Q000382:microbiology*; D001487:Basidiomycota / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology; D005075:Biological Evolution; D056084:Genetic Fitness; D005838:Genotype; D058507:Host Specificity; D054884:Host-Pathogen Interactions / Q000235:genetics*; D010935:Plant Diseases / Q000382:microbiology*; D013172:Spores, Fungal / Q000235:genetics / Q000472:pathogenicity; D014481:United States; D014774:Virulence / Q000235:genetics*
keywords: Gene for gene; Puccinia coronata; host range; life history; trade-offs; virulence