Clinal resistance structure and pathogen local adaptation in a serpentine flax-flax rust interaction

Our plain-English summary of Clinal resistance structure and pathogen local adaptation in a serpentine flax-flax rust interaction, by Y.P. Springer (Evolution; International Journal of Organic Evolution, 2007).

The study

• Author: Y.P. Springer
• Journal: Evolution; International Journal of Organic Evolution
• Published: 2007;61(8):1812-22
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Because disease resistance is a hallmark signature of pathogen-mediated selection pressure on hosts, studies of resistance structure (the spatial distribution of disease resistance genes among conspecific host populations) can provide valuable insights into the influence of pathogens on host evolution and spatial variation in the magnitude of their effects. To date few studies of wild plant-pathogen interactions have characterized resistance structure by sampling across the host's biogeographic range, and only a handful have paired such investigations with studies of disease levels under natural conditions. I used a greenhouse cross-inoculation experiment to characterize genetic resistance of 16 populations of California dwarf flax (Hesperolinon californicum) to attack by multiple samples of the rust fungus Melampsora lini. I documented a latitudinal cline in resistance structure, manifest across the host's biogeographic range, which mirrored almost identically a cline in infection prevalence documented through field surveys of disease in study populations. These results provide empirical evidence for clinal patterns of antagonistic selection pressure, demonstrate that such patterns can be manifest across broad biogeographic scales, and suggest that rates of disease prevalence in wild plant populations may be tightly linked to the distribution of host resistance genes. Tests for local adaptation of the fungus revealed evidence of the phenomenon (significantly greater infection in sympatric plant-fungal pairings) as well as the potential for substantial bias to be introduced into statistical analyses by spatial patterns of host resistance structure.

In plain English

This plant ecology study does not concern asbestos or human health. The author grew seedlings of California dwarf flax (Hesperolinon californicum) from 16 wild populations spanning the plant's range in northern California, with 22 maternal lines per population. In a greenhouse, the seedlings were inoculated with 10 samples of the rust fungus Melampsora lini collected from wild populations in 2003 and 2004. Resistance to infection was low in northern populations and rose gradually toward the south. This closely matched infection levels recorded in field surveys: about 60% of the variation in field disease prevalence could be explained by greenhouse-measured resistance. Fungus samples infected plants from their own population significantly more than plants from other populations (mean infection score 2.09 versus 1.64). The author took this as evidence that the fungus was locally adapted. However, the north-to-south pattern in plant resistance distorted distance-based tests of local adaptation: plant population explained 84.4% of the variation in infection and distance explained 2.0%. The author noted that some fungal samples may have contained more than one strain.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Greenhouse cross-inoculation experiment (plant ecology), compared with field disease survey data
• Who was studied: Seedlings of California dwarf flax (Hesperolinon californicum) from 16 populations in northern California, 22 maternal lines per population (352 maternal lines in total), mostly grown from seed collected in 2002
• Exposure: Inoculation with 10 samples of the rust fungus Melampsora lini, collected from two flax populations in 2003 and eight in 2004. No asbestos exposure was studied.
• Main results:
  • Genetic resistance to rust followed a north-to-south gradient across the plant's range: low in northern populations, increasing gradually to high levels in the south.
  • Across the 16 populations, greenhouse-measured resistance explained approximately 60% of the variation in disease prevalence measured in the field.
  • Plants paired with fungus from their own population had significantly higher mean infection scores than plants paired with fungus from other populations (2.09 versus 1.64 in the entire dataset, P = 0.0009).
  • There was no relationship between the mean resistance of plant populations and the mean virulence of the fungal samples from those populations.
  • When fungal samples were moved north, infection rose with distance between plant and fungal populations. In the adjusted analysis, plant population explained 84.4% of the variation in infection, fungal population 13.5%, and distance 2.0%.
• The authors' conclusion: The author concluded that the results suggest rates of disease prevalence in wild plant populations may be tightly linked to the distribution of host resistance genes.
• Limitations the authors state:
  • Spores were bulk-sampled, so some fungal samples may have contained more than one strain (pathotype).
  • Local adaptation could not be tested within individual plant populations because fungal samples were not replicated at that scale.
  • In southern populations it is unclear whether lower infection reflects less fungus being present or greater plant resistance.
  • Interpretation assumes a gene-for-gene resistance mechanism, which has not been shown directly for this plant.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Serpentine Group, Disease Level.

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