Arthuriomyces peckianus

Systematic position and nature of the pathogen. Arthuriomyces peckianus is a specialized basidiomycete fungus belonging to the order Pucciniales (rust fungi). It acts as an obligate parasite that specifically infects members of the Rosaceae family, particularly the genus Rubus. The pathogen is distinguished by its systemic nature, meaning it colonizes the vascular system and internal tissues of the host plant, rather than just the surface.

Diseases and host plants. This fungus is the primary causal agent of the disease known as orange rust of raspberry and blackberry. It affects both commercial cultivars and wild Rubus species. The infection is systemic, establishing itself within the roots, crowns, and canes of the host, which ensures that the plant remains infected for its entire remaining lifespan once the pathogen has taken hold.

Biology and life cycle. The pathogen exhibits a monocyclic and endocyclic life cycle. The fungus overwinters as perennial mycelium within the roots and buds of the host plant. During the spring growth flush, the mycelium grows systematically into the developing shoots. This leads to the production of characteristic bright orange aecia on the undersides of the leaves, which release spores that facilitate the spread of the infection to nearby healthy plants.

Conditions for development and economic impact. The pathogen thrives in cool, moist conditions during the spring, which are optimal for spore production and secondary spread. The economic impact is severe; infected plants typically become stunted, fail to produce fruit, and eventually succumb to the infection. Because the mycelium is internal, the disease cannot be effectively managed with localized treatments, often necessitating the removal of entire plants.

Protection and control measures. Since there is no curative treatment for a systemically infected plant, control strategies are focused on sanitation and prevention:

• Prompt removal and destruction of symptomatic plants, including the entire root system.
• Use of high-quality, disease-free nursery stock for new plantings.
• Avoiding planting near wild bramble populations that may harbor the pathogen.
• Monitoring the plantation during early spring to identify and rogue out diseased canes before spores are released.