Report of an interspecific hybrid of Melampsora medusae and M. larici-populina in New Zealand
Studies were carried out in New Zealand on poplar rusts as an outbreak appeared in March 1991 on 'resistant' cultivars. Microscopic examination of urediniospores revealed that the causal agent shared morphological features of both M. larici-populina and M. medusae (EPPO A2 quarantine pest). Both rusts have been introduced into New Zealand from Australia. The authors thought that this 'new rust' could have arisen in Australia by hybridization between M. larici-populina and M. medusae. The host range of the hybrid rust is closer to M. medusae, as it does not attack Populus nigra (Lombardy poplar). However, the rust failed to overwinter, either on Larix decidua or on poplars in New Zealand. The authors concluded that this was the first report of an interspecific hybrid between two apparently separate Melampsora species pathogenic to poplars, which may be more closely related than thought before, and proposed to call it M. medusae-populina sp nov. Further studies are needed to obtain DNA fingerprints of the hybrid and its parents and field studies should be carried out in Australia to determine whether the hybrid is present.
Sources
Spiers, A.G.; Hopcroft, D.H. ( 1994) Comparative studies of the poplar rusts Melampsora medusae, M larici-populina and their interspecific hybrid M. medusae-populina.
Mycological Research, 98 (8), 889-903.