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Keywords:

  • Silene acaulis;
  • Microbotryum violaceum;
  • anther smut disease;
  • gynodioecy;
  • evolution of plant breeding systems;
  • functional gender;
  • plant pathogens

Summary

  • • 
    Sex-dependent infection rates could change the effective sex ratio of a population. Here, I tested whether females and hermaphrodites of Silene acaulis were equally likely to be infected by Microbotryum violaceum, a fungus that sterilizes the host, and whether sex allocation in hermaphrodites differed between low and high disease plots.
  • • 
    Sex ratios of healthy and diseased plants were estimated in five natural plots. Fitness gained through seed production was estimated by measuring seed quantity and quality for each sex morph in eight plots for 2 yr; four plots had 1–5% disease frequency and four plots had 18–25% disease frequency.
  • • 
    Sex ratios of healthy and diseased plants did not differ in five plots. The proportion of fitness hermaphrodites gained through ovules varied from 25 to 48%, indicating that this population is near the cosexual end of gynodioecy. Variation in functional gender of hermaphrodites was not explained by sex-dependent infection rates.
  • • 
    Spatial heterogeneity in resources and microclimate seems to be important in explaining both disease frequency and variation in seed production by females and hermaphrodites.