Olive knot

The causal agent of this plant disease is Pseudomonas savastanoi, a rod-shaped, gram-negative bacterium. It is widely recognized as the primary pathogen responsible for olive knot disease, characterized by the development of galls and tumor-like growths on various parts of the plant.

This pathogen primarily targets the olive tree (Olea europaea), though it can also affect other related plant species. The bacteria produce phytotoxins and plant hormones that interfere with the host's normal development, leading to severe structural damage and internal transport disruption.

The most distinctive symptoms are the formation of knots or galls on stems, branches, and occasionally leaves. These galls begin as small, smooth swellings, but as the disease progresses, they become hardened, dark, and fissured, significantly altering the tree's appearance and weakening its physical structure.

The disease thrives in environments with high humidity and frequent rainfall. Transmission is facilitated by wind and water splashing, which carry the bacteria into host tissues through wounds caused by pruning, mechanical harvesting, frost, or hail. Once inside, the bacteria colonize the plant's vascular tissue.

The economic impact of olive knot is substantial, as it leads to reduced growth vigor, lower olive yields, and poor oil quality. Over time, severe infections can cause dieback of major branches, significantly shortening the lifespan and productivity of affected olive groves.

Control and prevention strategies are essential for maintaining healthy orchards:

• Sterilizing all pruning tools with a disinfectant between trees to prevent cross-contamination.
• Performing pruning operations during dry periods to limit bacterial entry.
• Applying copper-based fungicides immediately after pruning or severe weather events to protect open wounds.
• Removing and burning heavily infected branches to reduce the overall bacterial inoculum in the orchard.