Citrus Canker Bacterium

Xanthomonas citri is a highly destructive bacterial pathogen belonging to the Xanthomonas genus, recognized worldwide as the causative agent of citrus canker. This plant disease is a significant global concern due to its ability to severely impact the production of various citrus species, including sweet orange, grapefruit, and key lime.

The pathogen attacks all aerial parts of the host plant, including leaves, stems, and fruits. Initially, the disease presents as small, water-soaked spots that eventually develop into raised, corky, necrotic lesions. These lesions are typically surrounded by a yellow, chlorotic halo, which is a diagnostic feature used by agronomists during field inspections.

Regarding its biology and cycle, the bacterium enters the plant through natural openings like stomata or via wounds created by thorns, hail, or insect feeding. The infection cycle is highly dependent on environmental conditions, specifically warmth and high humidity. Rain splash is the primary mechanism for short-distance dispersal, while human activity and trade serve as vectors for long-distance geographical movement.

The economic impact of Xanthomonas citri is severe. Infected fruits are aesthetically unappealing and forbidden for export in most countries due to strict quarantine regulations. Heavy infestations cause premature leaf drop, fruit drop, and, in susceptible varieties, dieback of branches, which can significantly reduce the lifespan and productivity of entire commercial citrus orchards.

Effective management requires an integrated approach to mitigate the risks associated with this persistent pathogen:

• Strict quarantine regulations to prevent the introduction of contaminated plant material.
• Implementation of windbreaks to reduce rain splash and dispersal of the bacteria.
• Routine application of copper-based bactericides during active growth flushes.
• Sanitization protocols for tools, machinery, and clothing of field workers.
• Systematic monitoring and eradication of infected trees in nursery settings.