Citrus Canker In-Depth
I. Economic Hosts
IV. Symptoms and Signs:
VI. Symptoms and Signs:
Recovery of X. citrion agar media is not generally a problem, and these
strains do not lose virulence readily upon subculturing. Bacteria may be grown in
liquid culture or scraped off a freshly streaked agar plate and suspended in tap
water for inoculation into citrus. Recovery of X. campestris pv. aurantifolii
strains on agar media can be a serious problem. Once cultured, bacteria may be
harvested for inoculation as above. If axenic culturing of bacteria proves
difficult, the lesions should be excised and ground in a mortar and pestle in
several milliliters of tapwater. After debris has settled, the crude bacterial
suspension may be directly inoculated.
Pathogenicity tests should be conducted on younger leaves using control strain(s)
if possible. For either direct inoculations from citrus, or inoculations from
culture, the bacterial suspension should be drawn into a tuberculin syringe
(without a needle), the blunt end of the syringe appressed gently, but firmly
against the abaxial citrus leaf surface (to one side of the mid-vein), and the
slurry forced into the stomata until about two cm2 of the leaf is water congested.
The congestion is transient and disappears within a few minutes. A control strain
grown under the same conditions as the test strain(s) should be inoculated into
the same leaf, on the other side of the mid-vein. Six different strains may be
conveniently inoculated onto the same leaf, three on each side of the mid-vein.
The key diagnostic symptom is tissue hyperplasia (cankers). Symptoms are
generally first observed beginning four days after inoculation as a raised margin
surrounding a slighly chlorotic region. Over time, the raised margin becomes
pronounced, roughened and corky, while the central region of the lesion becomes
necrotic and collapsed. After several weeks, the necrotic lesions may split and
the leaves abscise. If pathotype C of X. campestris pv. aurantifolii is
inoculated on an incompatible host, the hypersensitive response appears within
48 hours, and leaves typically abscise several days later. On Mexican lime,
cankers should be observed.
X. campestris pv. aurantifolii strains are reportedly difficult to isolate and
culture directly from citrus tissue; these strains may be cultured initially on
1% sucrose, 0.5% peptone, 0.05% K2HPO4, 0.03% MgSO4 and Difco purified agar .
After initial culturing, however, these strains appear to adapt to other media
and may be routinely cultured on TY-MOPS or other nutrient media.
VIII. Storage of Organism
IX. Reported Host Range
X. Geographical Range and Spread
XI. Suggested Taxonomic Keys
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