HOST-PATHOGEN DYNAMICS IN EXPERIMENTAL POPULATIONS OF SILENE ALBA AND USTILAGO-VIOLACEA .1. ECOLOGICAL AND GENETIC-DETERMINANTS OF DISEASE SPREAD

1 To investigate the influence of within and among season factors on spread of anther-smut disease (Ustilago violacea), experimental populations of susceptible and resistant plants of (Silene alba) were established in a natural setting. 2 Frequency and density of diseased plants were both important predictors of percentage infection at the end of the growing season, but their relative importance varied across years. 3 Host families that were the progeny of relatively susceptible parents had consistently higher infection levels than families derived from more resistant parents. 4 Late flowering individuals or those producing fewer flowers were at lower risk of becoming infected. Male plants experienced a higher rate of infection because they initiated flowering earlier and produced more flowers than females. 5 There was greater over-wintering mortality of diseased plants than healthy plants in years when overall mortality was low but not in years in which mortality was high. 6 Host plants infected late in the season were more likely to recover than hosts infected early. 7 We conclude that detailed knowledge of within season environmental and genetic factors influencing disease spread does not adequately describe host-pathogen dynamics; epidemiological studies must also consider across season dynamic processes such as disease-induced mortality, host recovery, and recruitment.