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Citrus Huanglongbing (HLB), commonly referred to as citrus greening, is one of the major disease challenges of citrus. In Uganda, there was limited information on Liberibacter spp., the causal organisms of HLB disease, and its psyllid vectors despite the presence of HLB symptoms on citrus. The objective of this study was to identify the Liberibacter spp. and psylla vector species responsible for HLB in Uganda. Other native plant species that could be hosts to pathogens and the psyllid vectors, but are not in the citrus genus, were also investigated. A survey was conducted in 15 citrus growing districts, and symptomatic citrus leaf samples collected, as well as citrus psyllid nymphs and adults for isothermal detection of pathogens in the laboratory. Two types of bacterial pathogens responsible for HLB were detected, namely Candidatus Liberibacter africanus (CLaf), known as the African type; and Candidatus Liberibacter asiaticus (CLas), known as the Asian type. CLaf was found in Mukono and Wakiso districts in Central Uganda and in Mbarara in Western Uganda; while CLas was found in Budaka and Tororo districts in Eastern Uganda. Citrus psyllids, which are the major known disease vectors were present in seven out of the fifteen districts. Psyllid vector identification by morphological means indicated Trioza erytreae, the African psyllid to be the insect vector. Psyllids were common on tangerines (66.7%), Sour Orange (13.3%) and Rough Lemon (13.3%); and least on Washington Navel (6.7%). Three non-citrus plants, Stephania abyssinica (Dill. & A. Rich) walp var. tomentella (Oliv.) Deils (Menispermaceae), Diospyros mespiliformis (Ebenaceae) and Ficus spp (Moraceae) were found to be alternative host plants for the psyllid.

Huanglongbing (HLB) has become the most serious threat to the citrus industry worldwide. Although the disease first emerged in the southeastern part of Asia, it is now well established in Brazil, Florida and California, which are the world's most important citrus production areas. The disease is associated with three insect-vectored, obligate intracellular bacteria of the genus 'Candidatus Liberibacter'. These bacteria reside in the host phloem cells and they are transmitted by psyllids. Early pathogen detection is important to protect free areas from pathogen introduction. Unfortunately, the disease has a long incubation period, during which the pathogen is at low concentration and non-systemically distributed. This makes diagnostic and eradication difficult. Agdia has recently developed a new, rapid, molecular detection technique, AmplifyRP ® , allowing PCR-level sensitivity detection within minutes, in the field. AmplifyRP ® uses a recombinase-polymerase methodology for DNA amplification at a single temperature. In contrast to conventional or real-time PCR, AmplifyRP ® has no DNA purification requirements, requires no thermocycling, and results can be read using small, user-friendly devices. A portable fluorescence reader or a lateral flow device (similar to Agdia's ImmunoStrip ®) can be used to visualize results in as little as 30 minutes, compared to several hours for conventional PCR. AmplifyRP ® eliminates the need for expensive PCR equipment, a large number of chemicals reagents, and the need for technically trained staff. Given its characteristics, AmplifyRP ® is the ideal tool to monitor HLB progression by early detection of Ca. Liberibacter in citrus trees or in vector insects.

No abstract

Huanglongbing (HLB) disease is found throughout Asia, in Brazil, Mexico, the USA, and parts of Africa and has seriously affected citrus production in many regions. The three species of the Candidatus Liberibacter which have been identified are Candidatus Liberibacter asiaticus, Candidatus. L. americanus, and Candidatus L. africanus.We discuss here improvements in the AmplifyRP™ platform which allow for easy, accurate, and specific detection and identification of the three causative species of HLB. The singlecomponent test systems allow for the use of either purified nucleic acid preps or crude extracts prepared from psyllids or plant tissue. Comparisons with other detections will be discussed.