Kretzschmaria root rot

Pathogen and disease type: Kretzschmaria root rot, caused by the fungus Kretzschmaria deusta (formerly Ustulina deusta), is a destructive disease that leads to white rot in the roots and the basal stem of trees. It acts as a white rot pathogen, efficiently decomposing the lignin and cellulose within the wood, which results in significant structural weakening of the host plant.

Host range: This fungus primarily attacks a wide range of hardwood tree species, including beech, oak, and maple. Within agricultural systems, it is particularly destructive to Citrus species. It exploits stressed or damaged root systems, leading to severe decline in the health and productivity of citrus orchards.

Symptoms and signs: The disease is identified by the presence of flat, crust-like, carbonaceous fruiting bodies that appear charcoal-black at the base of the tree or on major buttress roots. Inside the wood, the fungus creates a bleached, white rot pattern often delineated by thin, irregular black lines. Infected trees may exhibit reduced vigor, premature leaf drop, and dieback of the canopy as the root system fails.

Conditions for development and severity: The fungus thrives in moist, poorly drained soils, particularly in environments where roots are prone to mechanical injury. Spores are primarily airborne, allowing them to infect fresh wounds. The severity of this disease is high, as it often goes undetected until structural integrity is severely compromised, frequently leading to tree collapse.

Protection and prevention measures: Effective management relies heavily on preventative cultural practices rather than curative chemical treatments. Key strategies include:

• Avoiding mechanical damage to the roots or trunk base during cultivation.
• Ensuring proper soil drainage to prevent moisture buildup.
• Promptly removing and destroying infected trees and their root systems to reduce inoculum levels.
• Quarantining affected areas to prevent the spread of the fungus to healthy neighbors.