Exobasidium rostrupii

Exobasidium rostrupii is a specialized fungal plant pathogen belonging to the kingdom Fungi, phylum Basidiomycota, class Exobasidiomycetes, and genus Exobasidium. This fungus is primarily recognized as the causal agent of leaf gall disease on various species of the Ericaceae family, most notably on cowberry (Vaccinium vitis-idaea).

The disease is characterized by the formation of hypertrophied leaf tissues and gall-like deformities. Infected leaves often change color, shifting from green to various shades of yellow, pink, or red, and eventually develop a dense white powdery coating on the leaf surface, which corresponds to the fungal sporulation stage.

The life cycle of the pathogen involves the dispersal of basidiospores via wind, rain splashes, or insect vectors. Upon landing on a susceptible host leaf, the spores germinate and penetrate the tissue, establishing a mycelial network. The infection can be systemic, allowing the fungus to persist within the plant's tissues for multiple growing seasons.

Favorable conditions for the development and spread of Exobasidium rostrupii include high humidity, persistent leaf wetness, and moderate temperatures. It is commonly found in environments with poor air circulation or in marshy, shaded regions where environmental conditions support the longevity and germination efficiency of the fungal spores.

The economic impact is significant as the disease reduces the photosynthetic area of the plant, leading to stunted growth and a considerable decrease in fruit yield. Management strategies focus on sanitation, such as the pruning and destruction of symptomatic plant parts, complemented by the application of copper-based or other systemic fungicides before the onset of the bloom phase.