Reproductive consequences of a gall-inducing fungal pathogen (Exobasidium vaccinii) on Rhododendron calendulaceum (Ericaceae)
We investigated the reproductive consequences of a gall-inducing fungal pathogen (Exobasidium vaccinii) on its host plant, Flame Azalea (Rhododendron calendulaceum (Michx.) Torr.) in southwestern Virginia. The percentage of infected plants ranged from 10 to 90% among the four study sites. There was a high degree of consistency in the pattern of prevalence between years at both the site and individual plant level within sites; plants and sites that showed high gall loads in 1997 were similarly infected in 1998. Infection rates and gall loads were higher in 1997 compared with 1998. All measures of reproduction were negatively affected by galls. Individuals infected in 1997 were less likely to flower the next season. Diseased inflorescences produced fewer flowers, smaller individual flowers, and had a lower probability of producing fruit. At the individual host level, the probability of fruit production was negatively correlated with the gall load on that individual. Finally, branches that were diseased in 1997 were more likely to die the following year, while healthy branches had a high probability of producing leaves and (or) flowers. Our results demonstrate that the fungal galls produced by E. vaccinii have immediate negative consequences to the reproductive process of R. calendulaceum.