Poplar and squill rust

Melampsora rostrupii is a specialized fungal pathogen belonging to the Basidiomycota phylum, responsible for causing rust disease on leaves. It is an heteroecious parasite, meaning it requires two distinct host species to complete its complex life cycle: trees from the genus Populus (poplar) and herbaceous plants from the genus Scilla (squill).

The primary host range includes various poplar species, such as white and black poplar, as well as spring-flowering squill plants. The life cycle is cyclical, with the fungus overwintering as dormant stages on the plant debris of its hosts, specifically the squill, which serves as the source of primary inoculum in the early spring.

Clinical signs of the infection begin as bright yellow or orange pustules known as aecia on the foliage of squill plants. During the summer, the pathogen develops uredinia on poplar leaves, which appear as rusty-colored powdery spots. These uredinia produce vast amounts of urediniospores that facilitate the rapid secondary spread of the disease among poplar populations.

Environmental conditions play a critical role in the development and proliferation of this pathogen. High atmospheric humidity, dew, and frequent rainfall are essential for spore germination and infection establishment. Areas where poplars and squills grow in close proximity are at significantly higher risk of severe outbreaks, especially during cool and wet growing seasons.

The economic and ecological impact of Melampsora rostrupii includes premature defoliation, which severely stresses the trees, reduces annual growth, and impairs their overall health. Integrated pest management strategies are crucial:

• regular removal and destruction of fallen leaves to eliminate overwintering spores;
• careful monitoring of urban and forest plantations;
• application of systemic fungicides during the early stages of disease development to curb widespread infection.