January 2006. The Secretariat of the Pacific Community and others have published two accounts on Citrus greening disease – now known as Citrus huanglongbing. One is a Pest Advisory Leaflet on this disease and its insect vector; the other is a paper in the journal Australasian Plant Pathology.
Davis RI, Gunua TG, Kame MF, Tenakanai D, Ruabete TK (2005) Spread of citrus huanglongbing (greening disease) following incursion into Papua New Guinea. Australasian Plant Pathology 34(4): 517???5247. Both have a strong quarantine focus. Both have colour photos of confirmed infected leaves: a surprisingly hard thing to find the literature.
There was a claim made in the late 1990s that this disease is present in four Pacific island countries. This claim was made by a group of researchers who conducted surveys and published their findings in a scientific journal. The information spread around the world and became accepted by many as fact.
However, besides PNG, there is no evidence today of a spreading HLB disease problem in any of the other Pacific Island Countries or Territories that SPC works for. The PNG HLB paper just published in Australasian Plant Pathology includes some disease surveillance data from other countries near PNG. This is some of the earliest evidence being gathered to prove HLB is absent from the other Pacific Islands that lie to the north and east of New Guinea.
Why go on at such length about this? Because it is imperative from the point of view of commercial and backyard citrus production that HLB and the Asian citrus psyllid (the vector of the Asian form of the pathogen) should remain near the very top of plant quarantine target lists.
Huanglongbing (HLB) was previously known in many countries as greening disease. It is caused by the bacterium ???Candidatus Liberibacter asiaticus??? and is vectored by the Asian citrus psyllid Diaphorina citri (Hemiptera: Psyllidae). A delimiting survey showed that the disease had become established in, and near the border town of, Vanimo in the Sandaun Province of Papua New Guinea (PNG) by late 2002. A campaign of quarantine containment and public awareness followed. A second survey undertaken 1 year later indicated that long-distance movement of the disease and its vector had not occurred. Out of a total of 120 trees indexed by polymerase chain reaction (PCR), 4/72 were HLB-positive in 2002 compared to 12/48 in 2003. The second survey found presumptive evidence for limited HLB disease cluster expansion and further independent introduction of infected planting material. HLB-positive samples were also screened for Citrus tristeza virus (CTV) infection using a double antibody sandwich enzyme-linked immunosorbent assay. The symptoms observed on leaves of orange (Citrus sinensis) and lemon (Citrus limon) infected by ???Ca. L. asiaticus??? alone and ???Ca. L. asiaticus??? plus CTV were similar. This is also the first verified record of CTV in PNG. No evidence was found for the presence of HLB in four Pacific Island countries (Cook Islands, Fiji Islands, Samoa and Tonga) to the east of PNG with 18 citrus trees tested negative by PCR.
Journal details at: http://www.australasianplantpathologysociety.org.au /