The Frequency of the Fungal Pathogen Exobasidium splendidum in Two Natural Stands of the Host Vaccinium vitis-idaea in the Subarctic Timberline Area

Abstract

We examined the host-pathogen system of an evergreen dwarf shrub Vaccinium vitis-idaea and its fungal pathogen Exobasidium splendidum in two habitats, a cleared forest (disturbed habitat), and an untouched forest (undisturbed habitat). Our aims were to find out how environmental factors, plant community characters, and the characters of V. vitis-idaea vary among the two habitats and whether these characters correlate with the frequency of E. splendidum. Our results suggest that environmental factors in the disturbed habitat are more favorable for the disease through increased growth of the host V. vitis-idaea and possibly by increased growth and reproduction of the pathogen. The high emergence rate of new V. vitis-idaea ramets in the disturbed habitat resulted in a younger ramet age structure as compared with the undisturbed habitat. Consequently, the ratio of growing to nongrowing ramets was higher in the disturbed habitat. We consider growth to be a prerequisite for V. vitis-idaea becoming infected. Thus, a low amount of growing ramets may be seen as a characteristic of undisturbed V. vitis-idaea stands, which buffers the plant against E. splendidum. On the other hand, shoot and ramet death caused by E. splendidum may induce compensatory growth in V. vitis-idaea, thus supporting the survival of the fungus.