Specificity and seasonal prevalence of anther smut disease Microbotryum on sympatric Himalayan Silene species

Abstract

Host sympatry provides opportunities for cross-species disease transmission and compounded disease effects on host population and community structure. Using the Silene-Microbotryum interaction (the castrating anther smut disease), eleven Himalayan Silene species were assessed in regions of high host diversity to ascertain levels of pathogen specificity. We also investigated disease prevalence, seasonal dynamics of infection and flowering patterns in five co-blooming Silene species. We identified several new Microbotryum lineages with varying degrees of specialization that is likely influenced by degrees of host divergence and ecological similarities (i.e. shared pollinator guilds). Affected species had 15%-40% of plants infected by anther smut. Flowering was seasonally overlapping among host species (except for the species pair S. asclepiadea and S. atrocastanea), but diseased flowering onset was earlier than healthy plants, leading to dramatic seasonal shifts in observed disease prevalence. Overlapping distributions and flowering provides opportunities for floral pathogen movement between host species, but host specialization may be constrained by the plant phylogenetic relatedness, adaptation to micro-habitats and difference in pollinator/vector guilds.

Keywords: Silene-Microbotryum interaction; anther smut fungus; disease prevalence; flowering phenology; host specificity; pollinator-transmitted pathogen; sympatry.