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   Xanthomonas axonopodis pv.citri (micro-organism)   
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      Citrus canker (Photo: Timothy Schubert, Florida Department of Agriculture and Consumer Services, United States, http://www.invasive.org/) - Click for full size   Cultivating Xanthomonas axonopodis pv. citri  (Photo: Jeffrey W. Lotz, Florida Department of Agriculture and Consumer Services, http://www.invasive.org/) - Click for full size   Citrus canker (Photo: Jeffrey W. Lotz, Florida Department of Agriculture and Consumer Services, http://www.invasive.org/) - Click for full size
    Taxonomic name: Xanthomonas axonopodis pv.citri
    Synonyms:
    Common names: citrus canker (English)
    Organism type: micro-organism
    Xanthomonas axonopodis pv.citri is a bacteria affecting citrus trees that thrives in areas with high temperatures, heavy rainfall, and high winds. In areas with these characteristics, X. axonopodis pv.citri causes citrus canker, which imparts heavy economic losses on citrus industries. It is spread through the inadvertent translocation of infected citrus fruits and seedlings to uninfected areas. Locally, X. axonopodis pv.citri is spread with the help of the Asian citrus leaf miner, which exposes the bacteria for spread by wind and rainfall.
    Description
    FDACS (2002) describes the appearance of leaves and fruit of infected plants as brown with raised lesions surrounded by oily, water-soaked yellow rings. Old lesions in leaves may fall out, creating a shot-hole effect. Masses of rod-shaped bacteria streaming from the edges of thinly cut lesion sections can be observed in infected citrus plants.

    Please see PaDIL (Pests and Diseases Image Library) Species Content Page Bacteria: Citrus canker (canker A) for high quality diagnostic and overview images.

    Similar Species
    Alternaria limicola, Xanthomonas campestris

    More
    Occurs in:
    agricultural areas, urban areas
    Habitat description
    Xanthomonas axonopodis pv.citri has been found in all types of citrus, including oranges, sour oranges, grapefruit, tangerines, lemons, and limes (FDACS, 2002). X. axonopodis pv.citri is unlikely to be found in regions where temperature increases while rainfall decreases because the disease prefers high temperatures and heavy rainfall (Gabriel, 2002).
    General impacts
    Xanthomonas axonopodis pv.citri causes the citrus tree to continually decline in health and fruit production until ultimately it produces no fruit at all and kills the tree (FDACS, 2002). Gabriel (2002) notes that the disease causes major economic losses to the citrus industry and is a nuisance to people with ornamental citrus trees. In the United States, Florida is at high risk because of its high humidity throughout the year, seasonal hurricanes, and frequent thunderstorms that are accompanied by high wind gusts. The 8.5 billion dollar citrus industry is critical to the well being of Florida's economy (FDACS, 2002).
    Geographical range
    Xanthomonas axonopodis pv.citri is found in southern Asia, Japan, Middle East, Africa, South America, and North America (Gabriel, 2002). [Biostatus (native vs. alien) in each location was not found.]
    Introduction pathways to new locations
    Agriculture:
    For ornamental purposes:
    Ignorant possession: The disease could be carried in plants or on equipment.
    Nursery trade: Contaminated plants may be exchanged through the nursery trade industry.


    Local dispersal methods
    Agriculture (local):
    For ornamental purposes (local):
    On animals (local): Wind-driven rain and overhead irrigation systems used in heavy wind can spread the disease from plant to plant.
    Other (local): The Asian citrus leaf miner (Phyllocnistis citrella), an invasive in Florida, increases the spread of X. axonopodis by exposing the disease for easier spread by wind and rainfall.
    Translocation of machinery/equipment (local): Contaminated equipment could spread the disease throughout an orchard from a single infected tree.
    Management information
    Preventative measures: The best preventive measure is to catch the infection early before it spreads extensively. Gabriel (2002), however, points out that because of increasing levels of international travel, and in spite of rigorous quarantine measures, the disease is likely to be reintroduced into citrus orchards repeatedly because of people inadvertently bringing infected citrus fruits and seedlings to uninfected places.

    Physical: According to Gabriel (2002), X. axonopodis pv.citri' distribution and survivability is strongly influenced by the ecological conditions surrounding its host. The Asian citrus leaf miner (Phyllocnistis citrella), an invasive in Florida, increases the spread of X. axonopodis pv.citri by exposing the disease for easier spread by wind and rainfall. FDACS (2002) states that no chemical compound is known to destroy the bacteria within the plant tissue. So in order to eradicate the disease, the infected and exposed trees must be cut down and disposed of properly. When an infected tree is found, all trees within 1,900 feet of it must also be cut down. Researchers determined that approximately 95% of the trees that became diseased were up to 1,900 feet away from a single disease-positive tree.

    The American Phytopathological Society (APS) offers on its website illustrated lessons to introduce the symptoms and signs, pathogen biology, disease cycle, epidemiology, disease management, and scientific, economic and social significance of major plant diseases. Please follow this link Citrus canker for details.

    Reproduction
    According to Campbell et al. (1999), bacteria reproduce asexually using binary fission. Binary fission is a type of cellular division in which each dividing daughter cell receives a copy of the single parent chromosome.
    Reviewed by: C. Vernière, Fruit Department, Centre de coopération International de recherche Agronomique pour le Développement CIRAD, Montpellier - France
    Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Saturday, 24 December 2005


ISSG Landcare Research NBII IUCN University of Auckland