Economic implications Need more information? Citrus greening reduces the quantity and quality of citrus fruit and eventually the infected trees become – to report occurrence or suspected occurrence of the disease – unproductive. An infected tree produces fruit that is unsuitable for sale as fresh fruit or for juice making. Directorate: Plant Health Citrus Division: Early Warning Systems It is a quarantine pest in the countries where it is not Tel: 012 319 6384 yet present. The spread of this disease within a previ- Email: [email protected] ously pest-free country can hamper the opportunity of greening that country to access potential citrus markets which – for awareness and promotion enquiries – may import only from citrus greening pest-free areas. Citrus greening, therefore, negatively affects access Directorate: Food Import and Export Standards ‘Candidatus Liberibacter africanus’ to major international citrus markets, such as the Division: Plant Health Promotion United States of America and the European Union. Tel: 012 319 6295 ‘Candidatus Liberibacter asiaticus’ Email: [email protected] ‘Candidatus Liberibacter americanus’ Legislative implications In terms of the Agricultural Pests Act, 1983 (Act No. 36 of 1983), Control Measures R.110 of 27 January Description 1984 (as amended), movement of citrus propagation Citrus greening, also known as yellow dragon disease material from one area to another within the Republic or Huanglongbing, is one of the most serious bacterial of South Africa is prohibited unless the movement is diseases of citrus. There are three known forms of authorised by means of a permit or the material is citrus greening causing bacteria, namely the Afri can certified as pest free. The Department of Agriculture, form (‘Candidatus Liberibacter africanus’), the Asian Forestry and Fisheries renders inspection services form (‘Candida tus Liberi bacter asiaticus’) and the and issues permits to ensure compliance with the ap- Ame rican form (‘Candidatus Liberibacter americanus’). plicable control measures. The African form is heat sensitive and symptoms are The abovementioned interventions will assist in pre- produced under relatively cool conditions (20–24 °C) venting the further spread of citrus greening. 2012 while the Asian form develops under both cool and warm temperatures (up to 32 °C). Little is known about Printed and published by Sources of information Department of Agriculture, Forestry and Fisheries temperature requirements of the American form. APHIS Factsheet, 2007, Citrus Greening: Questions and Answers, Obtainable from United States Department of Agriculture. Resource Centre Origin and global distribution J.V. DA GRACA, 1991, Citrus greening disease, Phytopathology, Directorate Communication Services Citrus greening probably originated in China in the 29: 109–136. Private Bag X144 PRETORIA 1900s. UNIVERSITY OF FLORIDA, 2005, Citrus greening—Another Threat to 0001 Agriculture, UF-IFAS, USA.

PIETERSEN, G., ARREBOLA, E., BREYTENBACH, J.H.J., KORSTEN L., LE ROUX, H.F., LA GRANGE H., LOPES, S.A., MEYER J.B., PRETORIUS M.C., SCHWERDTFEGER, M., VAN VUUREN S.P. & YAMAMOTO, P. 2010. A survey agriculture, for “Candidatus Liberibacter” species in South Africa confirms the forestry & fisheries presence of only “Ca. L. africanus” in commercial Citrus. Plant Department: Disease, 94: 244–24. Agriculture, Forestry and Fisheries REPUBLIC OF SOUTH AFRICA The Asian form (‘Candidatus Liberi bac ter asiaticus’) is teristic of greening. Other symptoms include twig die- However, cultivars such as lime (C. aurantifolia), pom- the most severe and geo graphically widespread. It back, poor flowering and stunted growth. elo (C. grandis), and trifoliate orange (Ponicirus trifoli- occurs throughout Asia, the Indian subcontinent and ate) are tolerant to the disease. In general, most citrus Fruit from diseased trees is small, often abnormal and neighbouring islands, the Saudi Ara bian peninsula, species and their relatives are susceptible. typically some green colour remains even on ripe fruit. Brazil, southern Florida, California, Cuba, Mauritius, Greening-affected fruit taste bitter, medicinal and Reunion and Ethiopia. sour. Seeds usually abort, and fruit formation is poor. Identifi cation methods The African form (‘Candidatus Liberi bac ter africanus’) Symp toms vary according to the time of infection, The only definitive method of diagnosis on trees sus- is less severe and is more restricted geographically. It stage of disease, tree species and tree maturity. pected to be infected by the citrus greening pathogen is found in Africa, south of the Sahara. (Huanglongbing) is polymerase chain reaction (PCR) Transmission in an author ised plant diagnostic laboratory. In South The American form (‘Candidatus Liberi bacter ameri- This disease is primarily spread by two species of Africa, this can be done by the Department of Agri cul- ca nus’) is so far known to occur in Brazil, Cuba, Flor i- ture, Forestry and Fisheries’ diagnostic laboratories in psyllid insect, namely the Asian citrus psyllid (Dia pho r- da, Belize, Mexico and Dominican Republic. Stellenbosch. ina citri) and the African citrus psyllid (Trioza erytreae). Both species transmit the citrus greening pathogen Symptoms from infected trees to healthy trees as they feed on Control methods Citrus plants affected by citrus greening bacteria may the plants. Citrus greening can also be transmitted by Control of citrus greening can be achieved through an not show symptoms for years following infection. grafting infected budwood, by dodder, and, possibly, integrated approach which includes eradicating in- Initial symptoms on a tree include the appearance of by infected seed. fected plant material, introducing clean nursery seed- yellow shoots. As the bacteria move within a tree, the lings, adhering to regulatory measures and eliminating entire canopy progressively develops a yellow colour. Host range insect vectors by means of systemic insecticides (as The three forms of bacteria produce similar symp- Citrus greening in South Africa is largely a disease of they are sap feeders). toms. sweet orange (Citrus sinensis), with valencias show- Treating affected trees with injections of antibiotics The most characteristic foliar symptoms of citrus ing more distinct leaf symptoms than navels. It is also alleviates the symptoms, but does not cure the dis- greening are blotchy mottling of the leaves and yellow- particularly severe on mandarins (C. reti culata) and eased plants. Prompt elimination of diseased trees is ing of leaf veins and shoots. Young leaves may display tangelos (C. sinensis x C. reticulata), but less on strongly advised. symptoms that can be misdiagnosed as signs of zinc lemon (C. limon), grapefruit (C. paradisi) and sour deficiency. Older leaves take on the mottling charac- orange (C. aurantium).

Typical blotchy mottling Feeding damage to citrus Infected orange Nymph of AdultAd lt Asian A i citrus it Adult of the African citrus Nymph of African citrus psylid symptoms of citrus leaves caused only by the the Asian psyllid psyllid greening on citrus spp African citrus psyllid, citrus psyllid Trioza erytreae