Microsatellite markers for cultivation-independent monitoring of persistenceof the entomopathogenic fungus Beauveria bassiana in soil samples

Abstract: If bulk DNA extracted from soil samples should be monitored for the occurrence andpersistence of a particular strain of an entomopathogenic fungus, strain specific molecularmethods are needed. Here, we report on the applicability of five Beauveria bassiana specificmicrosatellite (SSR) markers for amplification of strain specific bands in the B. bassiana isolateATCC 74040, which is present in the commercial product Naturalis. Discriminatory power ofthese markers was initially determined on B. bassiana DNAs from a world-wide collection of thisentomopathogen. Single clearly separated peaks were evident in chromatograms after capillaryelectrophoresis, which had a characteristic size for most of the respective B. bassiana isolates.These microsatellite markers were accordingly applied for monitoring the establishment andpersistence of B. bassiana isolate ATCC 74040 in the field. Experiments were conducted in acommercial nursery on a 100m by 25m field planted with Paeonia spp. Two defined plots withinthis field each with a size of 2m x 2m were treated with a 3% Naturalis-water suspension. Soilsamples were taken before and after inoculation with B. bassiana. From the treated plots soil wastaken and analysed 4, 10 and 19 weeks, respectively, after Naturalis application. Beauveriabassiana was successfully established and isolated from soil samples up to a period of 19 weeksafter inoculation as indicated by the amplification of B. bassiana strain specific SSR profilesfrom soil DNA preparations.