EFFECTS OF THE ANTHER-SMUT-FUNGUS MICROBOTRYUM-VIOLACEUM ON HOST LIFE-HISTORY PATTERNS IN SILENE-LATIFOLIA (CARYOPHYLLACEAE)

This study investigated the role of genetic variation among host plant s and fungal pathogen on disease prevalence and pathogen-induced pheno typic changes. Four different maternal sibships of Silene latifolia sh owed no difference in susceptibility to disease by the anther smut fun gus Microbotryum violaceum after inoculation of an infectious mixture containing haploid sporidia of both mating types into the growing rose tte. Three different combinations of sporidia were used. Two selfing c ombinations, one using fungus collected from the same population as th e host plants, one from a second population, and one cross between str ains from the two populations were generated. The three sporidia combi nations did not differ in their success in infecting the host plant an d sporulating in the flowers. However, this fungal disease altered hos t plant phenotype in several important ways. Disease retarded flowerin g in those male plants that initiated flowering in their first season, and it increased the number of flowers produced by both male and fema le plants. Different fungal strains differentially augmented Bower pro duction, indicating that there is genetic variability for important fi tness-related life-history traits in natural populations of the fungus M. violaceum in Europe. Furthermore, in this short-lived perennial ho st plant, diseased plants were more likely than were healthy ones to i nitiate flowering in their first growing season. Since this shift from vegetative growth to reproduction should enhance fungal reproductive success, we interpret this as a manipulation of the host plant phenoty pe by the fungus. In addition we found a significantly female-biased s ex ratio across the four maternal sibships in this study and higher in fection rates for female plants than males.