Citrus canker

Citrus canker is a severe bacterial disease caused by the pathogen Xanthomonas citri subsp. citri. It affects all aerial parts of citrus trees, including leaves, stems, and fruits, causing significant economic losses in commercial citrus production. Due to its high transmissibility and impact, it is considered a quarantine pest in most countries worldwide.

The host range includes almost all commercially grown citrus species, such as lemons, oranges, grapefruit, and limes. The pathogen relies on wounds to enter the plant tissues, which are often caused by storms, thorns, or insect feeding, particularly by the citrus leafminer. Once established, the bacteria multiply rapidly within the intercellular spaces of the host tissue.

Symptoms are easily identifiable as raised, necrotic lesions or pustules surrounded by a characteristic yellow halo. As the infection progresses, these pustules can merge, leading to defoliation, twig dieback, and fruit drop. In addition to reducing overall yields, the lesions ruin the external appearance of the fruit, making them unmarketable for international trade.

Environmental conditions play a critical role in the development and spread of citrus canker. The bacteria thrive in warm and humid conditions, spreading mainly through rain splashes, wind-driven rain, and human activities. The movement of contaminated equipment, clothing, and untreated nursery stock are the primary pathways for long-distance dissemination of the disease.

Management of citrus canker is heavily dependent on exclusion and eradication. Once the disease is introduced into an area, it is extremely difficult to eradicate. Preventive strategies include the use of disease-free rootstocks, establishing windbreaks to minimize wind-driven rain movement, and implementing rigorous sanitation protocols for pruning tools and machinery. Copper-based sprays are commonly used as a prophylactic measure to protect healthy tissues from bacterial colonization.