Infection of the Anther-smut Microbotryum violaceum in Populations of Silene dioica : Variation in Floral Morphology, Patterns of Spore Deposition and Pathogen-Pollinator Mediated Selection

摘要

The anther-smut Microbolryum violaceum (Brandenburger and Schvinn) G. Demi, and Oberw.) causes a systemic infection of its host Silene dioica (L.) Clairv. , resulting in sterility and production of teliospores (dispersal propagules) in flowers. These spores are transmitted to healthy plants mainly by flower visitors. The behavioral responses of flower visitors to a variation in floral characters, are not only likely to affect rales of pollen export/import, but also the rate of spore deposition and probability of disease. In a transplantation experiment, using plants from four different populations, we tested for correlation between variation in female floral morphology and patterns of spore and pollen deposition, and a resulting risk of disease. The source populations in this experiment were located on four islands in Skeppsvik archipelago in northern Sweden, and represented a gradient of disease incidence from completely healthy (Island 1) , low incidence (Island 2) to high incidences (Islands 3 and 4) of disease. Fifty plants from each population were transplanted to the center of the population on Island 4. There were significant differences among the transplants in floral characters, i. e. corolla size, style length and ovule number. Plants from the non-diseased population had larger flowers and longer styles than plants from the highly diseased populations. Numbers of pollen grains and spores deposited on flowers were strongly and positively con-elated. We found that plants originating from the non-diseased population captured approximately 4 times more pollen and 9 times more spores per flower than the individuals from the resident population (Island 4, population 4) . The incidences of disease among plants from the four populations differed significantly, and was 37% , 20% , 18% and 0 for populations 1,2,3 and 4 respectively. In a survey of ten populations we found a significant negative correlation between the mean style length ( positively correlated with corolla size and ovule number) among healthy plants and incidence of disease in these populations . The potentiality for pathogen-pollinator mediated selection on floral characters and consequences for gene flow between populations of Silene dioica are discussed.