Gaultheria procumbens L. is an ericaceous perennial and hardy shrub. Over the last years, German plant growers have suffered from enormous losses up to collapses of the whole crop due to the appearance of Colletotrichum gloeosporioides (Penz.). Several disease symptoms like lesions on stems and partially on leaves, shoot wilting and dieback were observed. Increasing expansion of this pathogen and lack of effective fungicides require new genetic sources for resistance breeding. A plant seedling assay gives information about the resistance behaviour to the fungus in an early growth stage. Twenty monoconidial isolates collected from Gaultheria species were surveyed for their growth, morphological diversity and virulence spectrum on G. procumbens in order to select representative isolates for resistance screening. The isolates differed in growth rate and virulence variability. Three types of virulence were obtained: weakly virulent, virulent and highly virulent. Within a testing period of only 6 weeks it was possible to realise a selection of pathogenic isolates.