Molecular and genetic analyses of geographic variation in isolates of Phoma macrostoma used for biological weed control.

Molecular and genetic approaches were used to evaluate the genetic relatedness among isolates of the fungus Phoma macrostoma Montagne originating from Canada and Europe and to other species in the genus Phoma. Distinct differences were observed in genetic variation among nine species of the genus Phoma. Randomly amplified polymorphic DNA (RAPD) revealed the presence of intraspecific genetic variation among the isolates of P. macrostoma, with the isolates being used for biological weed control being distributed in a distinct phylogenetic cluster. Additional variation within the biocontrol isolate cluster in P. macrostoma was revealed by pulsed field gel electrophoresis (PFGE), which showed that biocontrol isolates generated two different chromosomal profiles, however the profiles did not relate to their Canadian ecozone origin. Mating studies showed that biocontrol isolates of P. macrostoma from Canada did not produce sexual reproductive structures and were incapable of crossing. These studies also confirmed that no obvious differentiation exists among the biocontrol isolates of P. macrostoma from Canadian Ecozones 3 and 4.