Xylella

Xylella is a genus of plant-pathogenic bacteria that infects the xylem of a wide range of plant species. The best-studied member is Xylella fastidiosa, a Gram-negative, rod-shaped bacterium that colonizes water-conducting vessels and moves systemically within its host, causing hydraulic failure and symptoms such as leaf scorch, wilting, and dieback. Xylella is primarily transmitted by xylem-feeding insects and can spread through contaminated plant material, making movement of plants a key factor in its distribution.

Xylella fastidiosa comprises multiple subspecies with varying host ranges. X. f. subsp. fastidiosa is associated with Pierce’s disease in grapevines in the Americas, while X. f. subsp. pauca is linked to olive quick decline syndrome (OQDS) in southern Italy and to infections in some other regions. Other subspecies infect a variety of hosts, including almond, citrus, coffee, oleander, and ornamental plants. The pathogen is typically restricted to the xylem, where it disrupts water transport and induces vascular occlusions.

Notable impacts and management strategies vary by region and crop. In North America, Pierce’s disease causes significant losses in grape production. In Europe, the outbreak of OQDS in Italy prompted regulatory responses, surveillance, and eradication efforts to contain spread. Because there is no universal cure, management focuses on preventing spread, removing infected plants, controlling vectors, enforcing quarantines, and, in some crops, deploying resistant varieties or tolerant rootstocks.

Detection and research rely on molecular tools such as PCR-based assays and sequencing, complemented by serology and field surveillance. Ongoing work aims to refine vector management, understand host range, and develop effective resistance strategies.