Aureobasidium pullulans

Systematic position and nature of the pathogen
Aureobasidium pullulans is a ubiquitous microfungus belonging to the kingdom Fungi, phylum Ascomycota. It is widely recognized in agriculture not only as a saprotroph living on plant surfaces but also as an opportunistic phytopathogen. Its ability to switch nutritional strategies makes it a complex organism to manage, as it can colonize healthy tissue and cause significant economic losses in various horticultural sectors.

Affected crops and diseases
This pathogen is primarily known for causing surface blemishes, often described as black staining or soot-like spots, on various fruits including apples, pears, grapes, and strawberries. While it often colonizes the surface without penetrating deeply, the aesthetic damage is severe enough to render fresh produce unmarketable. Furthermore, it creates lesions that facilitate the entry of other, more aggressive decay-causing fungi.

Biology and development cycle
The life cycle of Aureobasidium pullulans is characterized by a remarkable polymorphism, producing yeast-like cells, chlamydospores, and hyphae. This flexibility allows the fungus to adapt quickly to diverse environments, including the phyllosphere of host plants. The primary dispersal of the pathogen is mediated by conidia, which are easily disseminated by wind, rain splashes, and insect activity across orchard environments.

Developmental conditions and impact
The growth of this fungus is heavily favored by high relative humidity (above 85%) and moderate temperatures ranging from 15°C to 25°C. In the field, extended periods of rain during the pre-harvest phase significantly increase the risk of infection. The economic impact is twofold: immediate loss of quality at harvest and decreased shelf life due to subsequent decay development during storage and logistics.

Control and management measures
Effective management of this pathogen requires a multi-pronged approach:

• Strict sanitation practices in orchards and storage facilities to reduce inoculum loads.
• Optimization of storage conditions, focusing on low humidity and proper air circulation to suppress fungal growth.
• Application of preventive fungicides during critical infection periods in the growing season.
• Minimizing physical injuries to fruit skin during harvest and sorting processes.
• Utilization of biological control agents that act as competitive microorganisms against the pathogen.