2.2.92
DIFFERENCES BETWEEN MELAMPSORIDIUM RUSTS ON BIRCH AND ALDER LEAVES

T KURKELA1, M HANSO2 and J HANTULA1

1Finnish Forest Research Institute, PO Box 18, FIN-01301 Vantaa, Finland; 2Estonian Agricultural University, Faculty of Forestry, FR Kreutzwaidi 5, EE-2400 Tartu, Estonia

Background and objectives
Melampsoridium rust epidemics on alder leaves occurred in Estonia in 1996 and 1997, and in Finland in 1997. Rust fungus M. betulinum appears annually on birches in northern forests. Two Melampsoridium species has been described on alders, M. aini and M. hiratsukanum. In the literature, some confusion has occurred in identifying Melampsoridium species on alders and distinguishing them from birch rust. In this study we tested possibilities of distinguishing the rusts observed on birch and alder by morphological and/or PCR-based methods.

Materials and methods
The morphology of uredospores and variation of DNA at internal transcribed spacer regions (ITS) were studied in Melampsoridium rust samples collected from birch (Betula penduia and B. pubescens) and alder (Alnus glutinosa and A. incana) leaves in Estonia and Finland in the autumn of 1997.

Results and conclusions
The rust occurring on birch had longer uredospores, the average length in Estonian and in Finnish samples were 30 and 33 ;Ám respectively, and in alder rust the corresponding measures were 25 and 27nbsp;Ám. The breadth of the spores did not differ between the samples. Birch rust uredospores were not echinulated in their broader end. Alder rust spores had echinulation in both ends. The roundness of the spores was also a differentiating character. The average roundness index varied in alder rusts from 1.33 to 1.41 and in birch rusts from 1.46 to 1.60. The PCR-amplified ITS regions from alder and birch rusts could be separated by denaturing gradient gel electrophoresis. Our conclusion is that the rusts we observed on A. glutinosa and A. incana are different from M. betulinum at species level and they are morphologically similar to M. hiratsukanum.