Liberibacter

Liberibacter is a genus of fastidious, Gram-negative bacteria in the family Rhizobiaceae. Members are primarily phloem-restricted plant pathogens transmitted by phloem-feeding insect vectors, notably psyllids.

The best known species are Liberibacter asiaticus, Liberibacter africanus, and Liberibacter americanus, all associated with citrus Huanglongbing (HLB), or citrus greening, a devastating disease causing leaf mottling, fruit deformation, and tree decline. Liberibacter solanacearum (often cited as Candidatus Liberibacter solanacearum) is associated with zebra chip disease in potatoes and other solanaceous crops. Liberibacter crescens is the only member that has been cultivated in vitro; other species have not been routinely cultured.

Biology and transmission: The bacteria inhabit the phloem of host plants and are transmitted by phloem-feeding psyllids; for citrus, the primary vector is the Asian citrus psyllid, Diaphorina citri. Transmission is persistent and circulative. The pathogens are not easily cultured in standard media, and detection relies on molecular methods such as PCR targeting 16S rRNA or other genes; serology exists.

Impact and management: HLB has caused substantial economic losses in citrus-growing regions worldwide. Management focuses on vector control, removal of infected trees, use of disease-free planting stock, and quarantine measures; breeding for tolerance or resistance is ongoing. Research continues into genome biology, host–pathogen interactions, and better diagnostic methods to enable early detection and containment.

Taxonomy notes: The genus is named Liberibacter; the species names reflect geography and disease associations. Taxonomic status of some "Candidatus" designations reflects that many Liberibacter are not readily cultured.