Orange spots on leaves of mountain ash caused by mountain ash-juniper rust fungus (Gymnosporangium cornutum) in Petiayarvi, north from Saint Petersburg. Russia, July 17, 2015
Unnamed Road, Leningradskaya oblast', Russia, 188732Synonyms: Aecidium cornutum, Caeoma cornutum, Ceratitium cornutum, Gymnosporangium aurantiacum, Gymnosporangium juniperi, Gymnosporangium juniperinum, Roestelia cornuta.
Common names: mountain ash-juniper rust, rowan crown.
Russian names: Rzhavchina listev ryabiny, Rzhavchina ryabiny.
Gymnosporangium cornutum is a species of fungus that belongs to the family Gymnosporangiaceae. It is a heteroecious rust fungus that infects members of the Cupressaceae and Rosaceae families. In St. Petersburg, Leningrad Oblast, and north-western Russia, G. cornutum has been found on Juniperus communis and other coniferous hosts, as well as on species of Sorbus and Crataegus. The fungus produces characteristic horn-shaped telial horns on the underside of juniper leaves, while aecidial stage develops on the leaves of rosaceous plants.
Orange spots on leaves of mountain ash caused by mountain ash-juniper rust fungus (Gymnosporangium cornutum) in Petiayarvi, north from Saint Petersburg. Russia, July 17, 2015Unnamed Road, Leningradskaya oblast', Russia, 188732The fungus Gymnosporangium cornutum was observed in Leningrad Oblast and north-western Russia, specifically on the leaves of mountain ash trees. In Petiayarvi, located north of Saint Petersburg, orange spots were noted on the leaves, which are characteristic of infection by the mountain ash-juniper rust fungus. This observation was made on July 17, 2015. The presence of G. cornutum in this region suggests that the fungus is able to thrive in the local climate and environment. The infection was likely facilitated by the proximity of juniper plants, which serve as an alternate host for the fungus. The observation highlights the importance of monitoring fungal infections in natural ecosystems, particularly in regions where the fungus may be expanding its range or increasing in prevalence. Further study is needed to understand the full impact of G. cornutum on mountain ash populations in this region.
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