Data from: 28 year temporal sequence of epidemic dynamics in a natural rust – host plant metapopulation

A long-term study of disease dynamics caused by the rust Uromyces
valerianae in 31 discrete populations of Valeriana salina provides a rare
opportunity to explore extended temporal patterns in the epidemiology of a
natural host-pathogen metapopulation. Over a 28-year period, pathogen
population dynamics varied across the metapopulation with disease
incidence (presence/absence), prevalence (% plants infected) and severity
(% leaf area covered by lesions) all showing strong population and year
effects, indicative of heterogeneity among years and host populations in
the suitability of conditions for the pathogen. Disease incidence within
individual host populations was significantly affected by host population
size, disease prevalence the previous year and the proximity of
neighbouring populations infected in the current year. After accounting
for these variables there was still a marked temporal component with
winter sea level having a significant effect; as did summer rainfall in
the second part of the study period (1997-2011). Disease prevalence was
also effected by host population size and disease prevalence in the
previous year. However, it was less affected by spatial aspects of disease
spread than was disease incidence. Winter sea level and June rainfall
significantly affected disease prevalence. Assessment of disease impact on
plant performance found strong variation in disease severity associated
with the aspect and positioning of host populations. Plants growing in
lower disease environments produced significantly more seeds than those
growing in high disease sites. Significant variation in reaction to
infection by U. valerianae was detected among plants within four
populations and between these different populations. Synthesis. The
epidemiology of U. valerianae was highly influenced by host population
size, previous disease and distance. After accounting for these factors,
there was a clear temporal signal of change in disease incidence linked to
winter sea level and summer rainfall. These patterns reinforce the
importance of considering interactions in multiple populations over long
periods of time in order to obtain a clear picture of the variability of
disease-induced selection pressures across time and space. The behaviour
of the pathogen fitted that predicted for a metapopulation with
considerable asynchrony in epidemiological patterns among demes.