Comparative studies of conidium morphology of Marssonina species pathogenic to poplars on agar and host tissue

Comparative morphological studies of Marssonina species conducted on leaf discs of poplar and 15%V8 agar under defined laboratory conditions established that features of conidium morphology (shape, mean length and breadth dimensions, and septum location) were valid differential criteria enabling delimitation of three species M. brunnea, M. castagnei, and M. populi. Further, within each species the existence of large conidium variants or "L-forms" was demonstrated. "L-forms" were stable mutants which, apart from length and breadth dimensions, were morphologically similar to their parents.