Alder bacterial canker

Alder bacterial canker is a serious tree disease caused by the bacterium Brenneria alni. This phytopathogen belongs to the family Pectobacteriaceae and is specifically associated with the genus Alnus. It is classified as a vascular and cortical pathogen that disrupts the transport of nutrients within the tree by inducing necrosis in the bark and underlying tissues.

The disease primarily affects various species of alder, which are common in wetlands, riparian corridors, and forest ecosystems. While healthy trees can sometimes withstand infection, those suffering from drought stress, flood damage, or mechanical injuries are significantly more susceptible to colonization by Brenneria alni.

The most distinctive symptom of this disease is the presence of longitudinal cracks in the bark, accompanied by the bleeding of dark, viscous exudate. This liquid contains high concentrations of bacteria. Beneath the damaged bark, the inner tissues (cambium and phloem) exhibit extensive reddish-brown discoloration and necrosis, which progressively prevents the flow of water and nutrients to the crown.

The spread of the disease is highly dependent on environmental conditions, particularly moisture availability. Rainfall facilitates the spread of bacteria from infected sites to new wound areas on the stem. Insects and contaminated forestry tools are also significant vectors for the transmission of the pathogen, allowing it to bypass the plant's natural external barriers.

Management of alder bacterial canker focuses on containment and prevention. There are no systemic pesticides currently available to cure infected trees, making sanitation the most effective approach. This includes the removal and destruction of severely affected trees to reduce inoculum pressure, and the rigorous disinfection of pruning equipment to prevent human-assisted spread between healthy and infected populations.