Bacterial diseases: Citrus canker

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Citrus canker in its Asiatic form (canker A) is a highly infectious disease that affects not only leaves and shoots but also fruit of susceptible citrus hosts, such as small-fruited acid lime and grapefruit. The causal agent is a rod-shaped, Gram-negative bacterium, Xanthomonas campestris pv. citri. Five pathotypes of X. c. pv. citri are known: A, B, C, D and E (Hartung and Civerolo, 1987, 1989). Pathotype A is the most common and is endemic throughout Pakistan, India, the islands of the Indian Ocean, Southeast Asia, China and Japan. It is most severe on small-fruited acid lime, grapefruit and P. trifoliata. Sour orange, lemon and sweet orange are moderately susceptible, while mandarin is moderately resistant. The pathotype identified in Oman is A (see Chapter 16). The same pathotype is probably also involved in Yemen, Saudi Arabia and the United Arab Emirates. Pathotype B occurs in Argentina, Paraguay and Uruguay. It is less severe than pathogen A and does not affect sweet orange or grapefruit. Pathotype C has been reported in Brazil as a very severe type on small-fruited acid lime, which also affects sour orange but no other citrus. Pathotype D is responsible for a leaf disease similar to canker A (see below for symptom description) discovered in Mexico in 1981, on small-fruited acid lime, Tahiti lime and grapefruit growing close to affected acid lime trees. No infection of the fruit has been reported. In 1984 Florida experienced an outbreak of an apparently new form of X. c. pv. citri, restricted almost entirely to nurseries. Isolates of this form have been classed as pathotype E. Strains belonging to group E do not produce raised lesions on diseased plants, in contrast to all strains belonging to groups A to D, but instead produce flat, water-soaked lesions of various sizes.

Diagnosis of citrus canker in the field is based on the presence of typical lesions on fruit, leaves and twigs. These lesions are similar for all strains of pathotypes A to D, although those of pathotype B are smaller than those of A, C or D. A leaf lesion develops first on the lower leaf surface about a week after infection and soon thereafter begins to grow on the corresponding upper surface, so that a lesion affects both the lower and upper surfaces of the leaf. The lesions or pustules become crater-like with raised margins and a sunken centre on both sides of the leaf (Figs 248 to 250). This is in contrast to the pustules of scab, a fungal disease of citrus, where a protuberance develops on the invaded side of the leaf, and a corresponding depression forms on the opposite side. Canker lesions on leaves are characteristically, but not specifically, surrounded by a yellow halo. Also, a water-soaked margin, detected with transmitted light, encircles the necrotic tissue, and is a most favourable tissue for isolation of the bacterium. Lesions or pustules on fruit and twigs are raised and cork-like (Fig. 251). As mentioned above, the lesions due to pathotype E are flat with necrotic centres.

The canker bacterium is spread by wind and rain. It develops more severely on the side of the tree exposed to wind, where wounds on thorn-injured leaves or twigs are more numerous and favour infection by the bacterium.

Control of canker in countries or regions where the disease is not present is by rigid restrictions on the importation of citrus plant material and fruit from areas where the disease is present. The presence of canker in Oman, the United Arab Emirates, northern Yemen and the Jizan area in Saudi Arabia is probably due to unwitting importation of citrus material from countries known to be infected by the canker bacterium.

In countries where canker is present, control requires appropriate cultural practices, such as the use of windbreaks and copper treatments, or even the replacement of very susceptible cultivars (grapefruit and small-fruited acid lime) by more resistant ones (sweet orange or mandarin).

Bibliography

Aubert, B. & Bové, J.M. 1980. Effect of penicillin or tetracycline injections of citrus trees affected by greening disease under field conditions in Reunion Island. In Proc. 8th Conf: IOCV, p. 103-108. Riverside, Univ. Calif.

Aubert, B., Bové, J.M. & Etienne, J. 1980. La lutte contre la maladie du "greening" des agrumes à l'île de la Réunion. Résultats et perspectives. Fruits, 35: 605-624.

Bar-Joseph, M. & Loebenstein, G. 1973. Effects of strain, source plants and temperature on the transmissibility of citrus tristeza virus by the melon aphid. Phytopathol., 63: 716-720.

Bar-Joseph, M., Garnsey, S.M. & Gonsalves, D. 1979. The closteroviruses: a distinct group of elongated plant viruses. Adv. Virus Res., 25: 93-168.

Bar-Joseph, M., Raccah, B. & Loebenstein, G. 1977. Evaluation of the main variables that affect citrus tristeza virus transmission by aphids. Proc. Int. Soc. Citricult., 1: 958-961.

Bar-Joseph, M., Garnsey, S.M., Gonsalves, D., Moscovits, D.E., Clark, M.F. & Loebenstein, G. 1979. The use of enzyme-linked immunosorbent assay for detection of aphid-borne citrus tristeza virus from Israel and Florida. Phytopathol., 69(2): 190-194.

Beñateña, H.N. & Portillo, M.M. 1984. Natural spread of psorosis in sweet orange seedlings. In Proc. 9th Conf: IOCV, p. 159-164. Riverside, Univ. Calif.

Bové, J.M. 1984. Wall-less prokaryotes of plants. Ann. Rev. Phytopathol., 22: 361396.

Bové, J.M. 1986a. Greening in the Arabian Peninsula: toward new techniques for its detection and control. FAO Plant Prot. Bull., 34(1): 7- 14.

Bové, J.M. 1986b. Witches' broom disease of lime. FAO Plant Prot. Bull., 34(4): 217218.

Bové, J.M. & Garnier, M. 1984. Citrus greening and psylla vectors of the disease in the Arabic Peninsula. In Proc. 9th Conf: IOCV, p. 109-114. Riverside, Univ. Calif.

Bové, J.M., Whitcomb, R.F. & McCoy, R.E. 1983. Culture technique for spiroplasmas from plants. In J.G. Tully & S. Razin, eds. Methods in mycoplasmology. p. 225234. New York, Academic Press.

Bové, J.M., Bonnet, P., Garnier, M. & Aubert, B. 1980. Penicillin and tetracycline treatments of greening disease-affected citrus plants in the glasshouse and the bacterial nature of the prokaryote associated with greening. In Proc. 8th Conf: IOCV, p. 91-97. Riverside, Univ. Calif.

Bové, J.M., Garnier, M., Mjeni, A.M. & Khayrallah, A. 1988. Witches' broom disease of small-fruited acid lime trees in Oman: first MLO disease of citrus. In Proc. 10th Conf: IOCV, p. 307-309. Riverside, Univ. Calif.

Bové, J.M., Saillard, C., Vignault, J.C. & Fos, A. 1984. Citrus stubborn disease in Iraq and Syria: correlation between symptom expression and detection of Spiroplasma citri by culture and ELISA. In Proc. 9th Conf: IOCV, p. 145-152. Riverside, Univ. Calif.

Bové, J.M., Calavan, E.C., Capoor, S.P., Cortez, R.E. & Schwarz, R.E. 1974. Influence of temperature on symptoms of California stubborn, South Africa greening, India citrus decline and Philippines leaf mottling diseases. In Proc. 6th Conf: IOCV, p. 12-15. Berkeley, Div. of Agric. Sci., Univ. Calif.

Bové, J.M., Carle, P., Garnier, M., Renaudin, J. & Saillard, C. 1989. Molecular and cellular biology of spiroplasmas. In R.F. Whitcomb & J.G. Tully, eds. The mycoplasmas, vol. V. p. 244-364. New York, Academic Press.

Calavan, E.C. 1961. Ferment gum disease (Rio Grande gummosis) in grapefruit. Calif: Citrog., 46: 231-232.

Calavan, E.C. 1980. Stubborn. In J.M. Bové & R. Vogel, eds. Description and illustration of virus and virus-like diseases of citrus. A collection of colour slides. Paris, IRFA SETCO-FRUITS.

Calavan, E.C. & Bové, J.M. 1989. Ecology of Spiroplasma citri. In R. F. Whitcomb & J.G. Tully, eds. The mycoplasmas, p. 425485. New York, Academic Press.

Calavan, E.C. & Christiansen, D.W. 1958. Production of ferment gum disease in Marsh grapefruit trees by fungus inoculation. Phytopathol., 48: 391. (Abstract only)

Calavan, E.C. & Wallace, J.M. 1954. Hendersonula toruloidea Nattrass on citrus in California. Phytopathol., 44: 635639.

Calavan, E.C., Olson, E.O. & Christiansen, D.W. 1972. Transmission of the stubborn pathogen in citrus by leaf-piece grafts. In Proc. 5th Conf: IOCV, p. 11-14. Gainesville, Univ. Fla. Press.

Calavan, E.C., Dewolfe, T.A., Roistacher, C.N., Carpenter, J.B. & Halsey, D. 19621963. Unpublished data on file in Dept. of Plant Pathology. Riverside, Univ. Calif.

Capoor, S.P., Rao, G. & Viswanath, S.M. 1967. Diaphorina citri Kuwayama, a vector of the greening disease of citrus in India. Indian J. Agric. Sci., 37: 572-576.

Catling, H.D. 1970. Distribution of the psyllid vectors of citrus greening disease with notes on the biology and bionomics of Diaphorina citri. FAO Plant Prot. Bull., 18: 8-15.

Catling, H.D. 1973a. Notes on the biology of the South African citrus psylla Trioza erytreae. J. Entomol. Soc. S. Afr., 36: 299306.

Catling, H.D. 1973b. Results of a survey for psyllid vectors of citrus greening disease in Reunion. FAO Plant Prot. Bull., 21: 78-82.

Chen, M.H., Miyakawa, T. & Matsui, C. 1973. Citrus likubin pathogens in salivary glands of Diaphorina citri. Phytopathol., 63: 194-195.

Chevalier, C., Saillard, C. & Bové, J.M. 1990. Spiralins of Spiroplasma citri and Spiroplasma melliferum: amino acid sequences and putative organization in the cell membrane. J. Bacteriol., 172(5): 6090-6097.

Childs, J.F.L. 1950. The cachexia disease of Orlando tangelo. Plant Dis. Rep., 34: 295298.

Childs, J.F.L. 1953. An actinomycete associated with gummosis disease of grapefruit trees. Phytopathol., 43: 101-103.

Childs, J.F.L. 1978. Rio Grande gummosis disease of citrus trees. Part 1. A brief review of the history and occurrence of Rio Grande gummosis. Plant Dis. Rep., 62: 390-394.

Cole, R.M. 1979. Mycoplasma and spiroplasma viruses: ultrastructure. In M.F. Barile & S. Razin, eds. The mycoplasmas, vol. 1. Cell biology, p. 385-410. New York, Academic Press.

Commonwealth Department of Health. 1982. Citrus dieback and greening. Canberra, Australian Government Publishing Service.

Corbett, M.K. & Grant, T.J. 1967. Purification of variegation virus. Phytopathol., 57: 137-143.

Da Graca, J.V. & Maharaj, S.B. 1991. Citrus vein enation virus, a probable luteovirus. In Proc. 11th Conf: IOCV, p. 391-394. Riverside, Univ. Calif.

Davino, M. & Garnsey, S.M. 1984. Purification, characterization and serology of a mild strain of citrus infectious variegation virus from Florida. In Proc. 9th Conf. IOCV, p. 196-203. Riverside, Univ. Calif.

Davis, R.M. 1980. Evidence for the involvement of Diplodia natalensis in Rio Grande gummosis of citrus. J. Rio Grande Val. Hort. Soc., 34: 55-60.

Duran-Vila, N., Pina, J.A., Ballester, J.F., Juarez, J., Roistacher, C.N., Rivera-Bustamante, R. & Semancik, J.S. 1988. The citrus exocortis disease: a complex of viroid-RNAs. In Proc. 10th Conf: IOCV, p. 152-164. Riverside, Univ. Calif.

EPPO. 1988. Data sheet on greening. EPPO Bull., 18: 497-507.

FAO. 1983. International plant quarantine treatment manual. FAO Plant Prod. and Prot. Paper, 50.

Fawcett, H.S. 1933. New information on psorosis or scaly bark of citrus. Calif: Citrog., 18: 326.

Fawcett, H.S. 1936. Citrus diseases and their control. 2nd ed. New York, McGraw-Hill.

Fawcett, H.S. & Bitancourt, A.A. 1943. Comparative symptomatology of psorosis varieties on citrus in California. Phytopathol., 33: 837-864.

Fawcett, H.S. & Klotz, L.J. 1939. Infectious variegation of citrus. Phytopathol., 29: 911-912.

Fawcett, H.S., Perry, J.C. & Johnston, J.C. 1944. The stubborn disease of citrus. Calif: Citrog., 29: 146-147.

Feldman, A.W. & Hanks, R.W. 1969. The occurrence of a gentisic glucoside in the bark and albedo of virus-infected citrus trees. Phytopathol., 59: 603-606.

Fos, A., Bové, J.M., Lallemand, J., Saillard, C., Vignault, J.C., Ali, Y., Brun, P. & Vogel, R. 1986. La cicadelle Neoaliturus haematoceps (Mulsant et Rey) est vecteur de Spiroplasma citri en Méditerranée. Ann. Inst. Pasteur/Microbiol., 137 A: 97-107.

Fudl-Allah, A.E.-S.A. & Calavan, E.C. 1974. Cellular morphology and reproduction of the mycoplasma-like organism associated with citrus stubborn disease. Phytopathol., 64: 1309- 1313.

Fudl-Allah, A.E.-S.A., Calavan, E.C. & Igwegbe, E.C.K. 1972. Culture of a mycoplasma-like organism associated with stubborn disease of citrus. Phytopathol., 62: 729-731.

Gadeau, A., Mouches, C. & Bové, J.M. 1982. Resistance of mollicutes to rifampicin. In 4th Int. Cong. Int. Organ. Mycoplasmol., p. P-127. Tokyo, 1-7 Sept.

Garnett, H.M. 1985. Isolation of the greening organism. Citrus & Subtrop. Fruit J., 611: 4-6.

Garnier, M. & Bové, J.M. 1977. Structure trilamellaire des deux membranes qui entourent les organismes prokaryotes associés à la maladie du "greening" des agrumes. Fruits, 32: 749-752.

Garnier, M. & Bové, J.M. 1983. Transmission of the organism associated with citrus greening disease from sweet orange to periwinkle by dodder. Phytopathol., 73: 1358- 1363.

Garnier, M., Clerc, M. & Bové, J.M. 1984. Growth and division of Spiroplasma citri: elongation of elementary helices. J. Bacteriol., 158(1): 23-28.

Garnier, M., Danel, N. & Bové, J.M. 1984a. Aetiology of citrus greening disease. Ann. Inst.Pasteur/Microbiol., 135 A: 169-179.

Garnier, M., Danel, N. & Bové, J.M. 1984b. The greening organism is a Gram-negative bacterium. In Proc. 9th Conf: IOCV, p. 1 15-125. Riverside, Univ. Calif.

Garnier, M., Latrille, J. & Bové, J.M. 1976. Spiroplasma citri and the organism associated with likubin: comparison of their envelope system. In Proc. 7th Conf: IOCV, p. 13-17. Riverside, Univ. Calif.

Garnier, M., Martin-Gros, G. & Bové, J.M. 1987. Monoclonal antibodies against the bacterium-like organism associated with citrus greening disease. Ann/lnst. Pasteur/ Microbiol., 138: 639-650.

Garnier, M., Gao, S., He, Y., Villechanoux, S., Gandar, J. & Bové, J.M. 1991. Study of the greening organism (GO) with monoclonal antibodies: serological identification, morphology, serotypes and purification of the GO. In Proc. 11th Conf: IOCV, p. 428-435. Riverside, Univ. Calif.

Garnsey, S.M. 1975. Purification and properties of citrus leaf-rugose virus. Phytopathol., 65: 50-57.

Garnsey, S.M. & Weathers, L.G. 1972. Factors affecting mechanical spread of exocortis virus. In Proc. 5th Conf: IOCV, p. 105-111. Gainesville, Univ. Fla. Press.

Godfrey, G.H. 1946. Infections wood necrosis and gummosis of citrus. Proc. Lower Rio Grande Val. Citrus Inst., 1: 66-70.

Grant, T.J. & Corbett, M.K. 1961. Mechanical transmission of infectious variegation virus in citrus and non-citrus hosts. In Proc. 2nd Conf: IOCV, p. 197-204. Gainesville, Univ. Fla. Press.

Green, G.C. & Catling, H.D. 1971. Weather-induced mortality of the citrus psylla Trioza erytreae (Del Guercio) a vector of greening virus in-some citrus producing areas of Southern Africa. Agric. Meteorol., 8: 305-307.

Gumpf, D.J. & Calavan, E.C. 1981. Stubborn disease of citrus. In K. Maramorosch & S.P. Raychaudhuri, eds. Mycoplasma diseases of trees and shrubs, p. 97-134. New York, Academic Press.

Haas, A.R.C., Klotz, L.J. & Johnston, J.C. 1944. Acorn disease in oranges. Calif: Citrog., 29: 168- 169.

Hartung, J.S. & Civerolo, E.L. 1987. Genomic fingerprints of Xanthomonas campestris pv. citri strains from Asia, South America and Florida. Phytopathol., 77(2): 282-285.

Hartung, J.S. & Civerolo, E.L. 1989. Restriction fragment length polymorphisms distinguish Xanthomonas campestris strains isolated from Florida Citrus Nurseries from X. c. pv. citri. Phytopathol., 79(7): 793-799.

Igwegbe, E.C.K. & Calavan, E.C. 1970. Occurrence of mycoplasma-like bodies in phloem of stubborn-infected citrus seedlings. Phytopathol., 60: 1525-1526.

Knorr, L.C. & Koo, R.C.J. 1969. Rumple - a serious rind collapse of lemons in Florida and in Mediterranean countries. In H.D. Chapman, ed. Proc. 1st Int. Citrus Symp., p. 1463-1472. Riverside, Univ. Calif

Koizumi, M. & Sasaki, A. 1980. Protection phenomena against tristeza in trees pre-inoculated with vein enation virus. In Proc. 8th Conf: IOCV, p. 48-50. Riverside, Univ. Calif.

Koizumi, M., Kano, T., Ieki, H. & Mae, H. 1988. China laurestine: a symptomless carrier of satsuma dwarf virus which accelerates natural transmission in the fields. In Proc. 10th Conf. IOCV, p. 348352. Riverside, Univ. Calif.

Laflèche, D. & Bové, J.M. 1970. Structures de type mycoplasme dans les feuilles d'orangers atteints de la maladie du greening. C. R. Acad. Sci. Ser. D, 270: 1915-1917

Lallemand, J., Fos, A. & Bové, J.M. 1986. Transmission de la bactérie associée à la forme africaine de la maladie du "greening" par le psylle asiatique Diaphorina citri Kuwayama. Fruits, 41(5): 341-343.

Lin, K.H. 1956. Observations on yellow shoot of citrus: aetiological studies of yellow shoot of citrus. Phytopathol. Sinica, 2: 1-42.

Markham, P.G. & Towsend, D. 1974. Transmission of Spiroplasma citri to plant. In J.M. Bové & J.F. Duplan, eds. Les mycoplasmes/mycoplasmas, p. 201-206. Coll. Inst. Nat. Sante Rech. Med., Paris, INSEAM.

Massonié, G., Garnier, M. & Bové, J.M. 1976. Transmission of Indian citrus decline by Trioza erytreae (Del Guercio), the vector of South African greening. In Proc. 7th Conf: IOCV, p. 18-20. Riverside, Univ. Calif.

McClean, A.P.D. 1974a, 1974b. Abnormal bud-union between some sweet oranges and rough lemon rootstock: evidence of cause by a transmissible pathogen. The tristeza virus complex. In Proc. 6th Conf IOCV, p. 203-210, p. 59-66. Berkeley, Div. Agric. Sci., Univ. Calif.

McClean, A.P.D. & Oberholzer, P.C.J. 1965. Citrus psylla, a vector of the greening disease of sweet orange. S. Afr. J. Agric. Sci., 8: 297-298.

McClean, A.P.D. & Schwarz, R.E. 1970. Greening or blotchy-mottle disease of citrus. Phytophylactica, 2: 177-194.

Moll, J.N. & Martin, M.N. 1973. Electron microscopy evidence that citrus psylla Trioza erytreae (Del Guercio) is a vector of greening disease in South Africa. Phytophylactica, 5: 41-44.

Moll, J.N. & Martin, M.N. 1974. Comparison of the organism causing greening disease with several plant pathogenic Gram-negative bacteria, rikettsia-like organisms and mycoplasma-like organisms. In J.M. Bové & J.F. Duplan, eds. Les mycoplasmes/mycoplasmas, p. 89-96. Coll. Inst. Nat. Santé Rech. Méd., Paris, INSEAM.

Moran, V.C. 1968. The development of citrus psylla Trioza erytreae on Citrus limon and four indigenous host plants. J. Entomol. Soc. S. Afr., 31: 391-402.

Mouches, C. & Bové, J.M. 1984. Electrophoretic characterization of mycoplasma proteins. In S. Razin & J.G. Tully, eds. Methods in mycoplasmology, p. 241-255. New York, Academic Press.

Mouches, C., Candresse, T., Gadeau, A., Barroso, G., Saillard, C., Wroblewski, H. & Bové, J.M. 1984. Expression of the Spiroplasma citri spiralin gene in Escherichia coli: use of the recombinant plasmid carrying this gene as a molecular probe. Isr. J. Med. Sci., 20: 773-777.

Navarro, L., Pina, J.A., Juarez, J. & Ballester-Olmos, J.F. 1992. Elimination of a bud-union abnormality of sweet orange grafted on rough lemon by shoot tip grafting in vitro. In Proc. 12th Conf: IOCV.

Nour-Eldin, F. 1956. Phloemdiscoloration of sweet orange. Phytopathol., 46: 238-239.

Nour-Eldin, F. 1968. Gummy bark of sweet orange. In J.F.L. Childs, ed. Indexing procedures for 15 virus diseases of citrus trees, p. 50-53. ARS/USDA Handbook.

Nour-Eldin, F. 1981. Gummy bark. In J.M. Bové & R. Vogel, eds. Description and illustration of virus and virus-like diseases of citrus. A collection of colour slides. Paris, IFRA SETCO-FRUITS.

Oldfield, G.N. & Calavan, E.C. 1980. Spiroplasma citri: non-rutaceous hosts. In J.M. Bové & R. Vogel, eds. Description and illustration of virus and virus-like diseases of citrus. A collection of colour slides. Paris, IRFA SETCO-FRUITS.

Olson, E.O. 1952. Investigations of citrus rootstock diseases in Texas. Proc. Rio Grande Val. Hort. Soc., 6: 28-34.

Olson, E.O. & Waibel, C.W. 1953. Rio Grande gummosis in relation to Diplodia infection in Texas citrus. J. Rio Grande Val. Hort. Soc., 7: 84-94.

Pande, Y.D. 1971. Biology of citrus psylla Diaphorina citri. Isr. J. Entomol., 6: 307311.

Reichert, l. & Perlberger, J. 1931. Little-leaf disease of citrus trees and its causes. Hadar, 4: 193- 194.

Reichert, 1. & Perlberger, J. 1934. Xyloporosis, the new citrus disease. Bull. Agric. Exp. Sta., Rehovot, Palestine, 12: 49.

Renaudin, J., Aullo, P., Vignault, J.C. & Bové, J.M. 1990. Complete nucleotide sequence of the genome of Spiroplasma citri virus SpV1-R8A2 B. Nucleic Acids Research, 18(5): 1293- 1294.

Renaudin, J., Bodin-Ramiro, C. & Bové, J.M. 1987. Spiroplasma citri virus SpV1-78, a non-lytic rod-shaped virus with single-stranded, circular DNA: presence of viral sequences in the spiroplasma genome. In Proc. 10th Conf: IOCV, p. 285-290. Riverside, Univ. Calif.

Roistacher, C.N. 1988. The cachexia and xyloporosis diseases of citrus - a review. In Proc. 10th Conf: IOCV, p. 116-124. Riverside, Univ. Calif.

Roistacher, C.N., Blue, R.L. & Calavan, E.C. 1973. A new test for cachexia. Citrograph, 58: 261-262.

Roistacher, C.N., Nauer, E.M., Kishaba, A. & Calavan, E.C. 1980. Transmission of citrus tristeza virus by Aphis gossypii reflecting changes in virus transmissibility in California. In Proc. 8th Conf: IOCV, p. 76-82. Riverside, Univ. Calif.

Ruggieri, G. 1955. Le arance impietrate. Rivista Agrumicoltura, I (2): 65-69.

Ruggieri, G. 1961. Observations and research on impietratura. In Proc. 2nd Conf: IOCV, p. 182-186. Gainesville, Univ. Fla. Press.

Saglio, P., Laflèche, D., Bonissol, C. & Bové, J.M. 1971a. Isolement et culture in vitro des mycoplasmes associés au "stubborn" des agrumes et leur observation au microscope électronique. C. R. Acad. Sci. Paris, 272: 1387-1390.

Saglio, P., Laflèche, D., Bonissol, C. & Bové, J.M. 1971b. Isolement, culture et observation au microscope électronique des structures de type mycoplasme associées à la maladie du stubborn des agrumes et leur comparaison avec des structures observées dans le cas de la maladie du greening des agrumes. Physiol. Veg, 9: 569-582.

Saglio, P., Lhospital, M., Laflèche, D., Dupont, G., Bové, J.M., Tully, J.G. & Freundt, E.A. 1973. Spiroplasma citri gen. and sp.n.: a mycoplasma-like organism associated with "stubborn" disease of citrus. Int. J. Syst. Bacteriol., 23: 191-204.

Saillard, C. & Bové, J.M. 1983. Application of ELISA to spiroplasma detection and classification. In S. Razin & J. G. Tully, eds. Methods in mycoplasmology, p. 471476. New York, Academic Press.

Saillard, C., Vignault, J.C., Bové, J.M., Raie, A., Tully, J.G., Williamson, D.L., Fos, A., Garnier, M., Gadeau, A., Carle, P. & Whitcomb, R.F. 1987. Spiroplasma phoeniceum sp. nov.: a new plant-pathogenic species from Syria. Int. J. Syst. Bacteriol., 37(2): 106- 115.

Salibe, A.A. 1977. The stem pitting effects of tristeza on different citrus hosts, and their economic significance. Proc. Int. Soc. Citricult., 3: 953-955.

Schwarz, R.E. 1968a. Indexing of greening and exocortis through fluorescent marker substances. In Proc. 5th Conf: IOCV, p. 118-124. Gainesville, Univ. Fla. Press.

Schwarz, R.E. 1968b. Thin-layer chromatographical studies on phenolic markers of the greening virus in various citrus species. S. Afr. J. Agric. Sci., 11: 797-801.

Schwarz, R.E. & Green, G.C. 1970. Citrus greening and the citrus psyllid Trioza erytreae, a temperature dependent agent-vector complex. Zeits. Pflanzenkr. Pflanzenschutz, 79: 490-493.

Schwarz, R.E. & Knorr, L.C. 1973. Presence of citrus greening and its psylla vector in Thailand. FAO Plant Prot. Bull., 21: 132138.

Semancik, J.S., Roistacher, C.N., Rivera-Bustamente, R. & Duran-Vila, N. 1988. Citrus cachexia viroid, a new viroid of citrus; relationship to viroids of the exocortis disease complex. J. Gen. Virol., 69(12): 3059-3068.

Solel, Z. & Salerno, M. 1989. Mal secco. In Compendium of citrus diseases, p. 18- 19. St Paul, Minnesota, APS Press.

Timmer, L.W. & Garnsey, S.M. 1980. Natural spread of citrus ringspot virus in Texas and its association with psorosis-like diseases in Florida and Texas. In Proc. 8th Conf: IOCV, p. 167-173. Riverside, Univ. Calif.

Uyeda, I. & Mink, G.I. 1983. Relationship among some ilar viruses: proposed revision of subgroup A. Phytopathol. 73.

Van den Berg, M.A., Van Vuuren, S.P. & Deacon, V.E. 1987. Cross-breeding and greening disease transmission of different populations of the citrus psylla Trioza erytreae. Phytophylactica, 19: 353-354.

Villechanoux, S., Garnier, M. & Bové, J.M. 1990. Purification of the bacterium-like organism associated with greening disease of citrus by immunoaffinity chromatography and monoclonal antibodies. Curr. Microbiol., 21 (3): 175- 180.

Villechanoux, S., Garnier, M., Laigret, F., Renaudin, J. & Bové, J.M. 1993. The genome of the non-cultured, bacterial-like organism associated with citrus greening disease contains the nusG-rp/KAJL-rpoBC gene cluster and the gene for a bacteriophage type RNA polymerase. Curr. Microbiol., 26: 161-166.

Villechanoux, S., Garnier, M., Renaudin, J. & Bové, J.M. 1992. Detection of several strains of the bacterium-like organism of citrus greening disease by DNA probes. Curr. Microbiol., 24: 89-95.

Vogel, R. & Bové, J.M. 1964. Stem pitting sur bigaradier et sur oranger tarocco en Corse: une maladie à virus. Fruits, 19: 264-276.

Vogel, R. & Bové, J.M. 1968. Cristacortis, a virus disease inducing stem pitting on sour orange and other citrus species. In Proc. 4th Conf: IOCV, p. 221-228. Gainesville, Univ. Fla. Press.

Vogel, R. & Bové, J.M. 1972. Relation of cristacortis to other citrus viruses. In Proc. 5th Conf: IOCV, p. 178-183. Gainesville, Univ. Fla. Press.

Vogel, R. & Bové, J.M. 1980. Pollen transmission to citrus of the agent inducing cristacortis and psorosis young leaf symptoms. In Proc. 8th Conf IOCV, p. 188190. Riverside, Univ. Calif.

Vogel, R. & Bové, J.M. 1988. Graft transmission from kumquat of an agent inducing bud-union crease in Parson's Special mandarin grafted on Volkamer lemon rootstock. In Proc. 10th Conf: IOCV, p. 367-369. Riverside, Univ. Calif.

Wallace, J.M. 1957. Tristeza and seedling yellows of citrus. Plant Dis. Rep., 41: 394397.

Wallace, J.M. 1978. Virus and virus-like diseases. In W. Reuther, E.C. Calavan & G.E. Carman, eds. The citrus industry, vol. IV. Crop production, p. 67-74. Riverside, Univ. Calif.

Wallace, J.M. & Drake, R.J. 1960. Woody galls on citrus associated with vein enation. Plant Dis. Rep., 44: 580-584.

Wallace, J.M. & Drake, R.J. 1968. Citrange stunt and ringspot, two previously unde-scribed virus diseases of citrus. In Proc. 4th Conf: IOCV, p. 177-183. Gainesville, Univ. Fla. Press.

Weathers, L.G. 1960. Yellow-vein disease of citrus and studies of interactions between yellow-vein and other viruses of citrus. Virology, 11: 753-764.

Weathers, L.G. 1961. Responses of citrus to concurrent infection with two or more unrelated viruses. In Proc. 2nd Conf: IOCV p. 187-196. Gainesville, Univ. Fla. Press.

Whitcomb, R.F. 1983. Culture media for spiroplasmas. In S. Razin & J.G. Tully, eds. Methods in mycoplasmology, p. 147159. New York, Academic Press.

Whitcomb, R.F., Chen, T.A., Williamson, D.L., Liso, C., Tully, J.G., Bové, J.M., Mouches, C., Rose, D.L., Coan, M.E. & Clark, T.B. 1986. Spiroplasma kunkelii sp. nov.: characterization of the etiological agent of corn stunt disease. Int. J. Syst. Bacteriol., 36(2): 170-178.

Wroblewski, H., Johansson, K.E. & Hjerten, S. 1977. Purification and characterization of spiralin, the main protein of the Spiroplasma citri membrane. Biochim. Biophys. Acta., 465: 275-289.

Yamada, S. & Sawamura, K. 1952. Studies on the dwarf disease of satsuma orange, Citrus unshiu Marcovitch (preliminary report). Hort. Div. Tokai-Kinki Agric. Exp. Stn., Bull, 1: 61-71.

Chapter 7: Citrus stubborn disease in the Syrian Arab Republic and natural transmission of its causal agent, Spiroplasma citri

Natural spread of S. citri in the Tadla region of Morocco
Stubborn in the Syrian Arab republic
Natural transmission of S. Citri in the Syrian Arab republic
Conclusion
Bibliography

Stubborn disease of citrus was observed in California in the early 1900s and first described in 1944 (Fawcett, Perry and Johnston, 1944). Its causal agent was first seen under the electron microscope in 1970 (Igwegbe and Calavan, 1970; Laflèche and Bové, 1970) and cultured in the same year (Saglio et al., 1971; Fudl-Allah, Calavan and Igwegbe, 1972). In 1972, the organism was fully characterized as being a mollicute (mycoplasma) with helical morphology and motility, and it was given the name Spiroplasma citri (Saglio et al., 1973).

Historically, S. citri was the first mollicute of plant origin that was obtained in culture and for which Koch's postulates could be fulfilled (Markham and Towsend, 1974). The work on S. citri led to the discovery of many more spiroplasmas. Today about 30 spiroplasmas besides S. citri are known, classified in 23 different serogroups (Bové, 1984; Tully, 1989).

The main vector of S. citri in California is the leafhopper Neoaliturus (ex-Circulifer) tenellus. This insect is not usually associated with citrus, which probably explains why it was not identified as a vector until 1976 (Oldfield et al., 1976), when techniques became available that made it possible to screen candidate vectors for the presence of

S. citri. This spiroplasma can be detected in plants as well as in insects by two major techniques - culturing of the spiroplasma and the use of ELISA (Saillard et al., 1980) (Tables 15 and 16). Both techniques have played a major role in the discovery of Neoaliturus haematoceps Mulsant and Rey as a major vector of S. citri in the Mediterranean area and the Near East (Fos et al., 1986). They were also useful in the discovery of a new plant pathogenic spiroplasma, S. phoeniceum (Saillard et al., 1987). Today, DNA-DNA hybridization and DNA amplification are even more promising for the detection of this group of pathogens, since the techniques appear to be at least 100 times more sensitive than previous methods.

Stubborn, like tristeza and greening, is of major concern to citrus growers because the disease is transmitted by insect vectors. Hence, trees propagated from healthy bud-wood will become reinfected when planted in areas where the pathogen and its insect vectors are both present. Obviously, information on natural transmission of stubborn in a given location is of paramount importance. For this reason, such studies were undertaken in Morocco in 1978 and in the Syrian Arab Republic in 1982. The results of these investigations are reported here.

MAP 4 Map of Morocco. Salsola kali,the host plant of Neoaliturus haematoceps and Neoaliturus tenellus, the two leafhopper vectors of the stubborn agent (Spiroplasma citri), was found north of Agadir all the way up to Kenitra. At Agadir only H. tenellus was captured on S. kali; at El Jadida, the two leafhopper species were present, and at Rabat and Kenitra, only M haematoceps was collected

TABLE 15 Detection of Spiroplasma citri in the Syrian Arab Republic: number of samples analysed by ELISA and culture

Even though accurate data are missing, citrus trees with severe stubborn symptoms appear most frequently in countries of the Mediterranean area and the Near East where summer temperatures are high. This is in keeping with the fact that S. citri also multiplies best at 32°C. This is certainly so in the Islamic Republic of Iran, Iraq, Morocco and Syria, where the diagnosis of this disease has been based not only on symptomatology, but also on the detection of S. citri by culture and ELISA (Bové, 1981; Bové et al., 1984). In California, the use of infected budwood was one of the main reasons for the early widespread distribution of stubborn. However, the subsequent availability of plant material certified free of infectious agents, including S. citri, has not resulted in the disappearance of stubborn from young orchards. This is because three leafhoppers were found to be the insect vectors of S. citri, namely, Neoaliturus tenellus, Scaphytopius nitridus and Scaphytopius acutus delongi (Oldfield and Kaloostian, 1978). In the Mediterranean area, the first evidence for natural spread of S. citri was obtained in Morocco between 1978 and 1981 (Bové, 1981; Nhami et al., 1980). Work in Syria from 1982 to 1986 resulted in the identification of the leafhopper N. haematoceps as a major vector of S. citri, and of Salsola kali as the preferred host plant of the leafhopper. The following account is an updated version of an earlier publication(Bové, 1986).

Natural spread of S. citri in the Tadla region of Morocco

The Tadla region of Morocco (of which the major town is Beni Mellal) is a hot depression at the western foot of the High Atlas mountain range (see Map 4), where citrus, sugar beet and cotton are grown in irrigated zones.

Many trees of Washington navel and Valencia late sweet oranges, although they were believed to be healthy, showed stubborn symptoms and were found to be infected with S. citri.

Observations made on periwinkle plants (Catharanthus roseus) growing as ornamentals in the area showed that many of these plants became diseased and died in the summer and autumn owing to S. citri-induced lethal wilting (Fig. 175). Experiments were then begun using periwinkles as indicator plants for S. citri infection. Plants exposed to natural contamination during the summer near stubborn-infected citrus orchards became infected with 5. citri (Fig. 176).

TABLE 16 Detection of Spiroplasma citri in fruit axes and various types of leaves from stubborn-affected sweet orange trees in the Syrian Arab Republic

Key:
-: assay was negative.
+: assay detected S. citri.
ND: not done.

In one experiment, as many as 16 percent of 165 exposed periwinkles became contaminated. Other periwinkles became infected with MLOs.

Out of many leafhopper species tested as potential vectors, only one yielded a S. citri culture. This insect was identified as N. haematoceps.

This same species was then found to be the dominant insect caught from July to September in two yellow traps placed in an experimental periwinkle bed, and some of these plants were found to be infected with S. citri the next autumn (Bové, 1981) All these observations suggested that N. haematoceps might be a major vector of S. citri.

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