Integrated Plant Genetics Inc.
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Gainesville, FL 32653

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Citrus Canker In-Depth

I. Economic Hosts

II. Pathogens

III. Disease

IV. Symptoms and Signs:

V. Disease

VI. Symptoms and Signs:

VII. Pathogenicity:

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 [2]. 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

XII. References

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