First Documentation of Life Cycle Completion of the Alien Rust Pathogen Melampsoridium hiratsukanum in the Eastern Alps Proves Its Successful Establishment in This Mountain Range

Abstract

Melampsoridium hiratsukanum is an alien rust fungus which has spread pervasively throughout several European countries following introduction into North Europe at the end of the 20th century. The authenticity of several records of the Melampsoridium species infecting alder (Alnus spp.) in the northern hemisphere is questionable, due to the misidentification and confusion that surround many of the older reports. Given this complicated taxonomic history, and since a M. hiratsukanum-like rust is strongly impacting Alnus incana stands in the Alps, probably affecting the bank protection role of this species along rivers, the unambiguous identification of this pathogen was a pressing epidemiological and ecological issue. In this study, field surveys, light (LM) and scanning electron microscopy (SEM), and molecular characterization were put together in an attempt to solve the conundrum. Field monitoring data, LM and SEM analyses of key taxonomic traits (length of ostiolar cells of uredinium, uredinio-spore shape and size, spore echinulation, number and position of germ pores) and ITS-rDNA sequence-based identification, convergently and unambiguously connected the rust that is causing the current epidemic to the non-native M. hiratsukanum. We documented the completion of the M. hiratsukanum life cycle on its two taxonomically unrelated broadleaf/conifer hosts. This is the first report of M. hiratsukanum from naturally infected Larix decidua in Europe.

Endophytic fungi of hazelnut (Corylus avellana)

“…share many of the endophytic fungi which could be identified by means of high-throughput DNA sequencing (Küngas et al 2020). Even the leaf rust agent Melampsoridium hiratsukanum, known as an obligate biotroph pathogen developing its life cycle between alder and larch (Moricca et al 2021), was detected in all sampled hazelnut organs. As a general trait in this study, the kind of plant organ resulted to correlate to the pattern of the associated endophytic species better than the tree species.…”

The Good, the Bad, and the Useable Microbes within the Common Alder (Alnus glutinosa) Microbiome—Potential Bio-Agents to Combat Alder Dieback

“…The fungus Septoria alnifolia has been known to form leaf spots, stem cankers, and stem breakage on Alder trees [ 84 ]. Furthermore, a rust fungus, Melampsoridium hiratsukanum , causing yellow–brown spotting on Alder leaves, followed by early leaf fall, crown thinning, and/or death, has been identified [ 85 ]. The fungal pathogen Mycopappus alni tends to cause brown blotches on leaves and defoliation of Alder trees [ 86 ].…”

Alien Invasive Pathogens and Pests Harming Trees, Forests, and Plantations: Pathways, Global Consequences and Management

“…This rust is currently causing heavy defoliation, stunted growth and death to riparian Alnus incana (L.) Moench trees in the eastern Alps, threatening the stability of some riverbanks. In this mountain range the fungus has also found Larix europea L. to be a suitable alternate host on which to complete its life cycle [81].…”

“…Furthermore, phytosanitary inspectors may face plant material that has been attacked, but which has already been abandoned by its phytophages; therefore, they have to track the pest only on the basis of the traces left behind, which becomes a more difficult task. It is also true, on the other hand, that the reproductive structures of many forest pathogens can be observed on infected plant material, and these are of a great diagnostic value [81]. Furthermore, when the reproductive structures (e.g., fruiting bodies) are not present on the host surface, they can still be obtained in the laboratory by using a moist chamber; alternatively, the isolation from infected plant material into pure culture can permit the growth and identification of the causal agent.…”