Huanglongbing (Citrus Greening Disease) and Pathways toward Genetic Management of the Disease

Citrus Huanglongbing (HLB or citrus greening disease), associated with a phloem-limited, insect-vectored bacterium Candidatus Liberibacter asiaticus, has decimated citrus production where ever it has been found in the world. In Florida alone, citrus production has been reduced to one-third of what it was in just 10 years since the disease was first found. The manifestation of disease is complex, as a consequence of perturbations in many aspects of plant metabolism, anatomy and physiology. There are no citrus accessions or sexually compatible germplasm resources that confer resistance to the disease, but there is a tremendous degree of variation in types and severity of symptoms and tree responses. The most sensitive citrus types decline severely and frequently die, while more tolerant types appear to overcome some of the deleterious effects of disease, and some even remain productive regardless of the infection. Genomic tools have been exploited to understand the nature of the host-pathogen interactions in these diverse citrus accessions. Transcriptomic, proteomic, metabolomic and bioinformatic approaches have shed light on some fundamental differences among diverse citrus accessions; these studies will be reviewed, and possible pathways toward genetic management of HLB will be highlighted.