| Abstract: | A collection of 42 isolates of Melampsora allii-populina was established. Fourteen isolates were collected from various poplar cultivars over several French localities and 28 isolates from the alternate hosts (Allium spp., Arum spp. and Muscari comosum) obtained from nature or after inoculation. These isolates were inoculated in the laboratory on a large range of poplar cultivars belonging to several species. No isolate proved pathogenic on all cultivars and many qualitative interactions were observed between isolates and cultivars. This is the first evidence for the existence of physiological races within this fungus. No link was found between pathogenicity on poplar and on the alternate hosts. Among the inoculated cultivars, at least three were susceptible to all isolates (Beaupre, Candicans and Robusta), whereas the following showed qualitative reactions to the inoculated isolates: Altichiero, Carpaccio, Cima, Fritzi Pauley, I 154, Isieres, Luisa Avanzo, NL 2842, Rap and Spijk. Race-specific resistance to M. allii-populina (i.e. resistance to some races of the pathogen, but not to the others) has been found in two North American species (Populus deltoides and Populus trichocarpa) which have never coevolved with this fungus. The results are discussed in comparison with Melampsora larici-populina. |
