[Bacterium] Xanthomonas axonopodis pv. citri (Hasse) Vauterin et al. Synonyms: Xanthomonas campestris pv. citri
Different strains of citrus canker have been reported throughout the world. The Asiatic strain (A-strain) is the most widespread and severe form. Strains can be differentiated by molecular tests and host range.
Asiatic citrus canker
Citrus canker is not vectored by any organism but is spread by wind-driven rain. However, wounds caused by feeding of the Asian citrus leaf miner (Phyllocnistis citrella Stainton) may serve as an entry point for the bacterium if citrus canker inoculum is present.
Leaf - typical citrus canker lesions on leaves will range from 2-10 mm in size and will have raised concentric circles on the underside of the leaf. Frequently lesions will be surrounded by a water-soaked margin and a yellow halo. As a canker lesion ages, it may lose it palpable roughness, but the concentric circles will still be visible with a hand lens (on the underside of the leaf). The yellow halo eventually changes to dark brown or black and the water-soaked margin surrounding the lesion may diminish. The middle of the lesion (on underside of leaf) will be corky in texture with a volcano or pimple-like point. With the exception of very young lesions, lesions always penetrate through both sides of the leaf. In the presence of damage, the lesion may follow the contours of the damage and therefore may not be circular. In older lesions, a saprophytic white fungus may grow over the center of the lesion. The center of a lesion may fall out producing a shot hole appearance.
Fruit - typical citrus canker lesions on fruit will range from 1-10 mm in size. Larger lesions usually penetrate a few millimeters into the rind. Fruit lesions may vary in size and may coalesce. Fruit lesions consist of concentric circles. On some varieties these circles are raised with a rough texture on other varieties the concentric circles are relatively flat like the surface of a record. The middle of the lesion will be corky in texture with a volcano or pimple like point. The center of a lesion may crack and has a crusty material inside that resembles brown sugar. Frequently on green fruit a yellow halo will be visible; however it will not be visible on ripened fruit. Lesions may have a water-soaked margin and the water-soaked margin is especially evident on smaller lesions. In the presence of damage the lesion may follow the contours of the damage therefore not being circular. In older lesions a saprophytic white fungus may grow over the center of the lesion.
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Citrus canker affects multiple genera in the family Rutaceae. Citrus canker is most severe on grapefruit, key/Mexican lime, lemons, and kaffir lime.
Citrus canker is thought to have originated in southeast Asia. Different strains of citrus canker are widespread throughout many tropical and subtropical areas of the world. In the United States and its territories citrus canker is only found in Florida as of 2009.
On leaves, citrus canker may be confused with citrus bacterial spot (CBS), greasy spot, citrus scab, and leprosis. On fruit, citrus canker may be confused with alternaria, citrus scab, damage, and leprosis.