Overlapping niches of Beauveria bassiana in a conifer forest

There is limited information on the spatial distribution and diversity of Beauveria bassiana s.l. in above-ground locations. The occurrence of B. bassiana s.l. in a conifer forest was assessed in October, March and June 2006 through collection of samples from soil, branches and bark and isolation onto selective media. The density of B. bassiana s.l. was greater in soil (up to mean (SE) 148.9 (15.5) CFUs per gram) compared to bark (up to mean (SE) 28.8 (14.8) per gram). For branch samples the mean (SE) number of CFUs ranged from 0.0 (0.0) to 42.3 (9.9) per 2 cm low branch and from 0 (0) to 37.3 (16.9) per 2 cm mid branch. In all samples B. bassiana s.l. showed a temporal decline from October to June and was completely absent from the conifer branch samples in June. More extreme environmental conditions above-ground compared to below-ground are likely to be the major factor contributing to this decline. Molecular analyses (Inter Simple Sequence Repeat PCR (ISSR-PCR)) indicated that B. bassiana s.l. is genetically diverse and there appears to be distinct isolates associated with microhabitats and time; there were separate genetically related clusters of isolates originating from the soil or tree location and separate clustering of October, March and June isolates. Some isolates were ubiquitous in above and below-ground locations. The occurrence of B. bassiana s.l. isolates above and below-ground suggests that this fungus occupies various overlapping niches. The heterogeneous nature of the conifer forest provides a model system for studying the population dynamics of this fungus