Candidatus Liberibacter Species and Associated Plant Diseases


Currently, seven species of Liberibacter have been described. Most Liberibacters have not been cultured in artificial medium except Liberibacter crescens. Liberibacters are causal agents of multiple devastating plant diseases including citrus Huanglongbing and potato zebra chip. Importantly, pathogens, and psyllid vectors, are expanding worldwide, leading to spread of corresponding diseases and potential new diseases with host jump of psyllids, threatening the production of many important crops. It is critical to understand the interactions among the pathogens, psyllid vectors, and the hosts, as well as epidemiology of the diseases to design efficient, environment friendly and sustainable disease management strategies.

Key Concepts

  • Candidatus Liberibacters are gram‐negative, uncultured, plant‐associated bacteria.
  • Liberibacters cause serious diseases on many plants, including devastating diseases such as citrus Huanglongbing and potato zebra chip.
  • Liberibacter pathogens are transmitted by psyllids in nature, and the pathogens and psyllid vectors are expanding worldwide.
  • Diseases caused by Liberibacters can be confirmatively diagnosed by quantitative polymerase chain reaction (qPCR) with pathogen‐specific primers.
  • Molecular mechanisms of pathogenesis of Liberibacter remain largely unknown due to the difficulty in culturing these bacteria.
  • The diseases may be controlled via reducing the inoculum sources and limiting the spread of psyllid vectors.

Keywords: Liberibacter; psyllid; phloem; Huanglongbing; HLB; greening; zebra chip

Figure 1. Valencia sweet orange trees showing the symptoms characteristic of Huanglongbing (HLB) disease including yellow shoot; blotchy mottling leaves; upright, harden and small leaves; twig dieback; premature and smaller fruit; and preharvest fruit drop. (a) A young HLB‐diseased tree, (b) a mature HLB‐diseased tree, (c) typical HLB leaf symptoms showing blotchy mottle symptom, small and upright leaf, corky vein and secondary zinc deficiency, (d) branches showing dieback and leaf fall off, (e) top showing branch dieback, leaf fall off. Pictures a–e are by Nian Wang and Jinyun Li. (f) Asian citrus psyllid (D. citri) feeding on citrus plants. Photograph taken by Dr. Yuanchun Wang, Citrus Research and Education Center, University of Florida.
Figure 2. Zebra chip disease symptoms. (a) A potato field showing zebra chip‐diseased potato plants. (b) Beginning symptoms of ZC showing leaf curling and smaller leaves in the terminal. (c) ZC symptoms at a later stage. (d) An adult potato psyllid Bactericera cockerelli feeding on potato leaf. (e) A nymph of potato psyllid feeding on potato leaf. (f) Zebra chip‐diseased potato tuber with internal necrosis (right two) and healthy tuber (left). (g) Fried potato chips from healthy (upper) and zebra chip‐diseased plant tubers (bottom). Courtesy of Kay Ledbetter and Charlie Rush.


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Further Reading

Bové JM (2006) Huanglongbing: a destructive, newly‐emerging, century‐old disease of citrus. Journal of Plant Pathology 88: 7–37.

Gottwald TR, da Graça JV and Bassanezi RB (2007) Citrus Huanglongbing: the pathogen and its impact. Plant Health Progress (online). DOI: 10.1094/PHP-2007-0906-01-RV.

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Li J, Pang Z, Trivedi P, et al. (2017) ‘Candidatus Liberibacter asiaticus’ encodes a functional salicylic acid (SA) hydroxylase that degrades SA to suppress plant defenses. Molecular Plant‐Microbe Interactions 30 (8): 620–630.

Lin H and Civerolo EL (2014) Comparative genomics of the Liberibacteral plant pathogens. In: Gross DC, Lichens‐Park A and Kole C (eds) Genomics of Plant‐Associated Bacteria, pp. 203–233. Berlin: Springer‐Verlag.

Nelson WR, Munyaneza JE, McCue KF and Bové JM (2013) The Pangaean origin of “Candidatus Liberibacter” species. Journal of Plant Pathology 95: 455–461.

Rigano LA, Malamud F, Orce IG, et al. (2014) Rapid and sensitive detection of Candidatus Liberibacter asiaticus by loop mediated isothermal amplification combined with a lateral flow dipstick. BMC Microbiology 14: 86.

Wang N, Stelinski LL, Pelz‐Stelinski KS, Graham JH and Zhang Y (2017) Tale of the Huanglongbing disease pyramid in the context of the citrus microbiome. Phytopathology 107 (4): 380–387. PHYTO‐12‐16‐0426‐RVW.

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Li, Jinyun, and Wang, Nian(Oct 2017) Candidatus Liberibacter Species and Associated Plant Diseases. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0027201]