A fungal pathogen in time and space: the population dynamics of Beauveria bassiana in a conifer forest

The fungal entomopathogen Beauveria bassiana is ubiquitous in below-ground systems; however, there is a dearth of information on the above-ground diversity, temporal and spatial distribution of this fungus. Therefore, we assessed its occurrence in a conifer forest (Pseudotsuga monziesii and Pinus nigra var. maritima) using selective media to isolate B. bassiana from soil, branch and bark samples collected in October 2005, March and June 2006. Fungal density was the highest at all locations in October, declining in March and June, and absent from conifer branches in June. This above-ground decline most likely resulted from more extreme environmental conditions compared with those below ground. Molecular analyses (ISSR-PCR) indicated that B. bassiana is genetically diverse, comprising both distinct microhabitat-specific and seasonal isolates. The occurrence of dissimilar above- and below-ground isolates suggests that B. bassiana occupies various overlapping niches in these systems.