Infection biology of the invasive alder rust pathogen Melampsoridium hiratsukanum in the Eastern Italian Alps

The hetero-macro-cyclic rust fungus Melampsoridium hiratsukanum was accidentally introduced into Northern European countries at the end of the past century, probably from Asia, with infected plant material. In a couple of decades, this rust has spread pervasively southwards, infecting species of Alnus in severa! European countries. In Italian alpine valleys, where the fungus arrived about ten years ago, it colonized aggressively grey alder (Alnus incana), inducing yearly a heavy defoliation in early summer. M. hiratsukanum was always found, in the countries where it was reported, on its telial hosts (Alnus sp.), while it was never observed on its aecial host (Larix sp.). This induced some authors to hypothesize that this full-cyclic rust fungus can also survive in alder buds, re-infecting the same broadleaf host in a reduced cycle. Since in alpine valleys the larch grows spontaneously, often intermingled with alder, a study was undertaken to ascertain whether aecia that are found in spring on this conifer also belonged to this rust and not solely to the other rusts (species of Melampsora), which occur sympatrically in the same valleys and have also larch as their secial host. To this purpose, infected alder leaves hearing uredinia and larch needles with aecia were collected for the laboratory analysis. Micro-morphological and molecular (DNA-based) identification proved the rust propagules found on both the conifer and the broadleaf hosts to belong to M. hiratsukanum. This demonstrates that the rust fungus has established in the Eastern Italian Alps, where it has found an ideai habitat for its survival and reproduction