Details on Melampsora medusae in New Zealand
In a paper describing the Melampsora and Marssonina pathogens of poplars and willows in New Zealand, it is recalled that in 1973 the poplar rusts Melampsora larici-populina and Melampsora medusae (EPPO A2 quarantine pest) were introduced into the country. It was felt that they first entered Australia on illegally imported cuttings and were then transported by wind to New Zealand. By 1975, M. larici-populina was widespread in New Zealand. In contrast, M. medusae had largely disappeared, although it remained in several locations where isolated trees of Populus deltoides (cv. Angulata) were grown. In 1984, the disease was no longer seen in these locations. In 1990, M. medusae reappeared in Hamilton and has persisted there on several P. deltoides x P. trichocarpa cultivars. In 1991 in North Island, a severe outbreak of poplar rust was observed on new 'rust resistant' cultivars. Studies showed that the pathogen was an interspecific hybrid of M. larici-populina and M. medusae named M. medusae-populina (see EPPO RS 94/180). It was thought that this hybrid rust first arose in Australia by hyphal fusion or cross-fertilization of pycnia. This hybrid rust failed to overwinter in New Zealand after this first finding, but it reappeared in April 1998 in North Island.
Sources
Spiers, A.G. (1998) Melampsora and Marssonina pathogens of poplars and willows in new Zealand.
European Journal of Forest Pathology, 28(4), 233-240.