Xanthomonas axonopodis pv.citri: factors
affecting successful eradication of citrus canker
James H, Graham1, Tim R. Gottwald2, Jaime Cubero1
and Diann S. Achor1
1 Citrus Research and Education Center, University of Florida,
700 Experiment Station Road, Lake Alfred, FL 33850, USA
2 USDA-ARS, Horticultural Research Laboratory 2001 South Rock
Road, Ft. Pierce, FL 34945, USA
||Bacteria, Proteobacteria, gamma
subdivision, Xanthomodales, Xanthomonas group, axonopodis
DNA homology group, X. axonopodis pv. citri (Hasse).
negative, slender, rodshaped, aerobic, motile by a single polar flagellum,
produces slow growing, non-mucoid colonies in culture, ecologically
obligate plant parasite.
||Causal agent of Asiatic citrus
canker on most Citrus spp. and close relatives of Citrus in
the family Rutaceae.
||Distinctively raised, necrotic
lesions on fruits, stems and leaves.
||Bacteria exude from lesions during
wet weather and are disseminated by splash dispersal at short range,
windblown rain at medium to long range and human assisted movement at all
||Severe infections cause
defoliation, blemished fruit, premature fruit drop, die-back of twigs and
general debilitation of the tree.
||Citrus canker is not present in all
subtropical to tropical regions of citriculture in the world, so
considerable regulatory efforts are expended to prevent the introduction
and spread of X. axonopodis pv. citri into areas in the Americas,
Australia and elsewhere, with climates conducive to the disease.
||Limited strategies exist for
suppression of citrus canker on more susceptible cultivars. Blemished
fruit are unmarketable and exposed fruit are restricted in market access.
The economic impact of loss of markets is much greater than that from
yield and quality reductions of the crop.
Scanning electron microscopy of infections by Xanthomonas
axonopodis pv. citri on the abaxial leaf surface of grapefruit
(Citrus paradisi). (A) Bacterial egress from a stomatal opening 5
days after infiltration of the leaf mesophyll with 105 cfu/mL.
(B) Eruption of infected mesophyll tissues through the epidermis to form a
pustule 30 days after inoculation. (C) Bacteria embedded in a matrix of
extracellular polysaccharide (EPS) from the surface of the lesion in (B).
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