First record of Melampsoridium hiratsukanum on alder in Norway

In September 2001, the uredineal sori of a rust were found on alder trees (Alnus incana) in Ã…s parish, Akershus, in southeastern Norway. Further examination of these sori, which always occured on the lower side of the infected leaves, revealed urediniospores measuring 25-31 × 12-14 μm, which were uniformly echinulate and which had apical spines. From this morphology Melampsoridium hiratsukanum was identified (Culture reference Lye No. 25356). M. betulinum is also known to occur on Alnus glutinosa in Ã…s (Roll-Hansen & Roll-Hansen, 1981) and a germination test with fresh urediniospores revealed 4-6 bizonate pores, similar to those reported for M. betulinum. However, this rust lacks spines in the apical region of its urediniospores and it is the presence of spines in the apical region that distinguishes these rust species (Kaneko & Hiratsuka, 1981). M. alni, an Asian rust of Alnus spp., was also ruled out as it too lack spines at the apical region of the urediniospores and has only two germ pores, one at each end (Kaneko & Hiratsuka, 1981).

M. hiratsukanum often causes considerable damage to foliage, that can easily be seen from a distance. Leaves turn either greyish-green or a golden colour, and the margins curl inwards. Sometimes leaves may drop prematurely but to a much lesser extent than experienced with M. betulinum on Betula spp. M. hiratsukanum does not attack alder until late summer or early autumn, with severe attacks occurring mainly in September and October. The long term effects of the rust on the host are therefore less severe.

During 2002 and 2003, Alnus species were examined for rusts throughout much of Norway. M. hiratsukanum was found on Alnus incana at about 400 localities, from sea-level to 870 m above sea level. The rust was also found on Alnus glutinosa at 8 locations. It was not found on Alnus viridis; a rare alder, recently introduced to Norway. So far, the northern limit of M. hiratsukanum in Norway is at 66° North (Luktvasslimo in Vefsn parish in Nordland county). The species was also common in Sweden, in areas near the Norwegian border.

M. hiratsukanum was first described on Alnus hirsuta from Hokkaido in Japan in 1927. It has now become well established in Europe, being first noted in Estonia in 1996 and in 1997 in Finland (Kurkela et al., 1998). Other recent new records include Hungary (Szabo, 2002) and Poland (Piatek et al., 2001). This is the first record for this disease in Norway.