Spread of Anther-Smut Disease (Ustilago Violacea) and Character Correlations in a Genetically Variable Experimental Population of Silene Alba

Abstract

1 The anther-smut fungus Ustilago violacea produces spores in diseased flowers of the dioecious plant Silene alba; spores are transferred to healthy plants by insect pollinators. 2 To study the ecological and genetic determinants of disease spread and its demographic consequences, an experimental population of S. alba was created that contained both anther-smut inoculated plants (as an inoculum source) and uninoculated plants which were the progeny of crosses between genotypes with high or low disease resistance. 3 Genetic analyses confirmed that variation in resistance is heritable. 4 Total disease incidence increased over the 3-year study, but rates of establishment of new infections decreased and estimates of the latent period increased each year. By the end of the study, the remaining healthy plants were more likely to be from resistant parents, suggesting that changes in genetic structure of the healthy plants may contribute to the decline in new infections over time. 5 Diseased plants were significantly more likely than healthy plants to die during the first winter of the study but there was no difference in the second year. A compilation of several data sets suggests that diseased plants have higher mortality than healthy plants only in winters with overall high plant survivorship. 6 Phenotypic correlations revealed that plants with early flowering dates and high rates of flower production are more likely to become diseased. 7 There was evidence for a genetic correlation between disease resistance and flowering date in males, such that early flowering families were more prone to infection. Such a relationship suggests that resistance could have a fitness cost, since earlier flowering plants are likely to have high fitness in the absence of disease.