Data from: Degree of host susceptibility in the initial disease outbreak influences subsequent epidemic spread

1. Disease epidemics typically begin as an outbreak of a relatively small,
spatially explicit population of infected individuals (focus), in which
disease prevalence increases and rapidly spreads into the uninfected,
at-risk population. Studies of epidemic spread typically address factors
influencing disease spread through the at-risk population, but the initial
outbreak may strongly influence spread of the subsequent epidemic. 2. We
initiated wheat stripe rust Puccinia striiformis f. sp. tritici epidemics
to assess the influence of the focus on final disease prevalence when the
degree of disease susceptibility differed between the at-risk and focus
populations. 3. When the focus/at-risk plantings consisted of partially
genetic resistant and susceptible cultivars, final disease prevalence was
statistically indistinguishable from epidemics produced by the focus
cultivar in monoculture. In these experimental epidemics, disease
prevalence was not influenced by the transition into an at-risk population
that differed in disease susceptibility. Instead, the focus appeared to
exert a dominant influence on the subsequent epidemic. 4. Final disease
prevalence was not consistently attributable to either the focus or the
at-risk population when focus/at-risk populations were planted in a
factorial set-up with a mixture (~28% susceptible and 72% resistant) and
susceptible individuals. In these experimental epidemics, spatial
heterogeneity in disease susceptibility within the at-risk population
appeared to counter the dominant influence of the focus. 5. Cessation of
spore production from the focus (through fungicide/glyphosate application)
after 1.3 generations of stripe rust spread did not reduce final disease
prevalence, indicating that the focus influence on disease spread is
established early in the epidemic. 6. Synthesis and applications. Our
experiments indicated that outbreak conditions can be highly influential
on epidemic spread, even when disease resistance in the at-risk population
is greater than that of the focus. Disease control treatments administered
shortly after the initial outbreak within the focus may either prevent an
epidemic from occurring or reduce its severity.