Molecular Plant Pathology - Pathogen Profiles
Xanthomonas citri: breaking the surface
Asha M. Brunings and Dean W. Gabriel
Plant Molecular and Cell Biology Program, University of Florida,
Gainesville, FL 32611, USA
Gammaproteobacteria; Xanthomonadales; Xanthomonadaceae, Xanthomonas.
||Gram-negative, obligately aerobic,
straight rods, motile by a single polar flagellum, yellow pigment.
||X. campestris, X.
axonopodis, X. oryzae, X. albilineans.
||Affects Rutaceous plants, primarily
Citrus spp., Fortunella spp., and Poncirus spp.,
world-wide. Quarantined pathogen in many countries. Economically important
hosts are cultivated orange, grapefruit, lime, lemon, pomelo and citrus
||On leaves, first appearance is as
oily looking, 2-10 mm, similarly sized, circular spots, usually on
the abaxial surface. On leaves, stems, thorns and fruit, circular lesions
become raised and blister-like, growing into white or yellow spongy
pustules. These pustules then darken and thicken into a light tan to brown
corky canker, which is rough to the touch. On stems, pustules may coalesce
to split the epidermis along the stem length, and occasionally girdling of
young stems may occur. Older lesions on leaves and fruit tend to have more
elevated margins and are at times surrounded by a yellow chlorotic halo
(that may disappear) and a sunken centre. Sunken craters are especially
noticeable on fruit, but the lesions do not penetrate far into the rind.
Defoliation and premature abscission of affected fruit occurs on heavily
Typical, naturally occurring citrus canker lesions from a relatively
causing premature leaf and fruit abscission.
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