| Abstract: | Leaf discs from seedlings of six clones of B. pendula Roth and two clones of B. pubescens Ehrh. were inoculated with two urediniospore isolates of M. betulinum Kleb. The field collection iso-lates were obtained from B. pendula and B. pubescens growing in the field. The B. pendula rust was more specialized than the B. pubescens rust. The clones of B. pubescens showed partial resis-tance against the B. pendula rust, while the B. pubescens isolate was compatible to both birch species. Some interclonal variation was also found in both birch species. The results support an earlier suggestion by Klebahn that M. betulinum has two formae speciales. |
