Mal secco of citrus

Plenodomus tracheiphilus is a fungal pathogen within the Kingdom Fungi, primarily known as the causal agent of "Mal secco," a systemic vascular disease that affects citrus species. This pathogen is highly destructive and considered a significant threat to citrus production in the Mediterranean region and other citrus-growing areas worldwide.

The disease primarily impacts lemon trees, though it also affects other citrus cultivars, including citron and bergamot. The fungus colonizes the xylem, producing spores and toxins that cause the browning and eventual necrosis of the inner wood. As the vascular system becomes clogged, the tree suffers from systemic wilting, leading to leaf drop and "dieback" starting from the terminal branches.

The life cycle of the pathogen is driven by the production of pycnidiospores. These spores are dispersed by water splashes, wind, and pruning tools. Infection occurs through wounds created by mechanical injury, insect bites, or pruning, especially when these injuries are exposed to high humidity and cool to moderate temperatures ranging from 15°C to 25°C.

Environmental conditions play a critical role in the epidemiology of Plenodomus tracheiphilus. Outbreaks are most frequent during periods of prolonged rainfall or heavy fog, which facilitate the spread of spores. The pathogen can survive for extended periods within infected twigs and branches, acting as a permanent reservoir for reinfection if the material is not properly managed.

Management of the disease relies heavily on integrated control strategies, as chemical control of established infections is rarely effective. Key preventive measures include:

• Planting resistant or tolerant cultivars.
• Strict adherence to orchard sanitation practices.
• Thorough disinfection of pruning tools between trees.
• Prompt removal and destruction of symptomatic branches or entire trees.
• Implementation of phytosanitary regulations to prevent the introduction of the pathogen into new areas.