The aim of the present study was to examine the genetic variation among European-registered and native strains of Phlebiopsis gigantea used as a practical biological agent against root rot in conifers. The high degree of genetic similarity between the P. gigantea strain used in product formulations and the P. gigantea native strain is crucial for product efficiency against the root rot pathogen H. annosum in the forest. Random amplified microsatellite (RAMS) markers were used to detect variation among registered (British and Finnish) and indigenous (Polish) P. gigantea isolates. Data were evaluated with using two tests: Band Sharing Index (BSI) and genetic similarity. Higher precision in genetic similarity assessments between isolates resulted from the genetic distance based on UPGMA data, proving strong similarity between six indigenous isolates (PL1, PL2, PL3, PL6, PL7, and PL12), four British (FC14, FC15, FC16, and FC17) and two Finnish and Swedish (VF8 and VF10) isolates. One Polish PL12 isolate was genetically analogous to the registered FC16 from Great Britain, proving their high reciprocal RAMS similarity. Results indicated that there is little reason to fear that foreign isolates pose an invasive threat to non-native forest environments.

Key words: Phlebiopsis gigantea isolates, RAMS, biological control, genetic similarity.