Brown root rot

Brown root rot, caused by the basidiomycete fungus Phellinus noxius, is a devastating disease affecting the root systems of various tree species worldwide. This pathogen is known for causing rapid white rot of woody tissues, leading to a compromised structural integrity of the plant and eventual systemic failure.

The host range of Phellinus noxius is extensive, encompassing both wild and cultivated plant species. Among the most susceptible and economically critical crops affected are cocoa (cacao), rubber trees, coffee, and numerous tropical fruit species, which are frequently subjected to severe mortality in infested plantations.

Symptoms of the disease are typically observed through the crown of the tree, showing signs of nutrient deficiency, chlorosis, and general decline. A diagnostic feature is the presence of a dark brown to black mycelial sheath covering the bark of the roots and the base of the trunk, often associated with a crust-like growth of fungal tissue.

The development of the disease is favored by warm, humid environments, where the fungus can survive for many years in decaying stumps or root residues. Transmission occurs primarily through root-to-root contact, as the fungus spreads via dense mycelial rhizomorphs that navigate through the soil profile to find new, healthy hosts.

Managing Brown root rot is challenging due to the pathogen's ability to persist in the soil. Integrated pest management strategies are essential for controlling the spread:

• Prompt removal of diseased trees and thorough excavation of root material.
• Physical isolation of infected zones by trenching to prevent root contact.
• Avoidance of replanting susceptible species in sites known to be heavily infested.
• Application of microbial biocontrol agents such as Trichoderma species to suppress pathogen activity.