We investigated relationships between an evergreen dwarf shrub Vaccinium vitis-idaea and infection frequency of its annual specific pathogenic fungus Exobasidium splendidum, and environmental conditions in six boreal and subarctic populations in Finland during 1998–2002. The aim was to explore how environmental factors and plant characteristics influence the infection frequency of the rare pathogen in nature. Climate data, soil organic matter, and plant characteristics were recorded along with annual demographic observations on V. vitis-idaea ramet dormancy, growth, flowering and fungal infection. Infection frequency of E. splendidum in V. vitis-idaea populations varied between 0 and 4.8% and increased with decreasing temperatures. Along with low air temperature, high concentration of NH4 , low concentration of P, high cover of bare ground, and high density of V. vitis-idaea were positively associated with the frequency of E. splendidum in V. vitis-idaea populations. Diseased ramets were at greatest risk of being reinfected by the fungus. The results indicate that both environmental factors and plant characteristics can constrain the distribution of the rare pathogen. Although an observational study of this kind does not allow us unequivocally to identify causality underpinning complex plant-pathogen-environment relationships, we can speculate that a further decrease in the frequency of E. splendidum infections will occur under climate warming.
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Vol. 40 • No. 3