Your are here:

Citrus huanglongbing

Scientific Name
Liberibacter asiaticus
Scientific Author
(Bacteria: a-Proteobacteria)

Page menu options:

Diagnostic Images

Image Options
Diagnostic Images (10)
Diagnostic Notes

The symptoms are similar to nutrients deficiencies and other disorders and the disease can be difficult to detect in unthrifty trees. A sectoral chlorosis (yellow of one branch or one part of the canopy) in the early stages is the clearest indication of citrus greening disease. Chlorotic blotching of leaves and swollen or corky leaf veins are two key visual guides, especially when they occur in combination. However, after time, the chlorotic blotching can become less obvious and zinc deficiency-like symptoms (yellow on green vein banding) become more prominent. In a period of one year infected tree can decline noticeably, with extensive yellowing of foliage and little or no fruit set (Davis et al. 2005). If the infection occurs soon after the propagation, the whole tree can show symptoms, otherwise, the pathogen and the symptoms are often partially confined at the beginning. Initially, the tree got a yellow shoot appearance. Afterwards, a progressive yellowing of the entire canopy occurs. Primarily, leaves show yellowing along the veins and, sometimes, a blotchy-mottle. Secondary symptoms consist of small, upright leaves with a variety of chlorotic patterns resembling zinc and iron deficiencies. The fruits are often small, lopsided and poorly coloured and contain aborted seeds. Its juice is abnormally bitter. Chronically infected trees are sparsely foliated and show extensive twig dieback (Graça 1991, Garnier & Bové 2000, Crop Protection Compendium 2005).

The pathogen:

Citrus huanglongbing (greening) is caused by three phloem limited species of the a-Proteobacteria, ‘Candidatus Liberibacter asiaticus’, ‘Candidatus Liberibacter africanus’ and ‘Candidatus Liberibacter americanus’. Neither of the three species has been cultured. Detection of them is based on PCR amplification of their 16S rRNA gene with specific primers (Davis et al. 2005, Teixeira et al. 2005, Hung et al. 2004, Subandiyah et al. 2000, Jagoueix et al. 1996). ‘Ca L. africanus’ and ‘Ca. L. asiaticus’ are transmitted by the psyllid insects, Trioza erytreae and Diaphorina citri, respectively (Graça 1991). Long-distance spread occurs via infected and infested plant material. ‘Ca. L. asiaticus’ is usually found causing huanglongbing in warmer climatic conditions than those in which ‘Ca. L. africanus’ is found.
More Information
Specimen Contact
Dr Richard I. Davis
Davis RI & Liberato JR
02/06/2006 12:18 AEST
Last Updated
27/07/2016 08:01 AEST
Davis RI & Liberato JR (2006) Citrus huanglongbing (Liberibacter asiaticus) Updated on 7/27/2016 8:01:02 AM Available online: PaDIL -
Image Use
Free for use under the Creative Commons Attribution 3.0 Australia License