AbstractInoculation of a range of poplar species and clones with conidia ofMarssoninaspecies in the laboratory resulted in the identification oftwo formae specialesofM. brunnea, and established thatM. castagneiwas not specifically pathogenic toP. alba. Poplars infected withM. brunnea, M. castagneiandM. populiexhibited an overlapping range of symptoms, varying from discrete spots to blotches. The dendritic lesion symptom was peculiar toM. populiand was host specific.