Citrus canker affects all aboveground plant parts, with initial symptoms on leaves appearing as tiny, slightly raised blister-like lesions. With time, foliar lesions turn grey, then tan/brown, a water soaked margin appears and the entire lesion is usually surrounded by a chlorotic margin. The centre of the lesion becomes characteristically raised, and spongy or corky. Lesions arising from stomatal infection are typically visible from both sides of the leaf (unlike these of scab – Elsinoe spp.). A shot-hole effect can also eventuate, after the centre of the lesion becomes crater-like and falls out. As the disease becomes more severe on foliage, defoliation generally occurs. A similar symptom to the above is observed on twigs and fruit, however chlorotic margins are not found on twig lesions. Severe infections can result in fruit abscission, and twig dieback due to girdling. Twigs not to be killed by girdling by the pathogen can harbour lesions for many years, with the old lesions tending to be raised corky patches in the otherwise smooth bark. Lesions can be associated with physical injuries to the host, in particular those caused by Asian citrus leaf miner (Phyllocnistis citrella Stainton) (Schubert et al. 2001).
The bacterium is an aerobic, gram-negative rod measuring 0·5–0·75 × 1·5–2·0 µm. It is motile by one polar flagellum. Carbohydrates are metabolised by oxidation. Growth on 2% sucrose-peptone agar is yellow and copiously mucoid. Gelatin, casein and starch are hydrolysed. Nitrite is not formed from nitrate, and aesculin is hydrolysed (Hayward and Waterston 1964).
- Specimen Contact
- Dr Jose R. Liberato
- Liberato JR, Miles AK, Rodrigues Neto J & Gambley C
- 17/05/2006 01:53 AEST
- Last Updated
- 21/10/2011 09:32 AEST
- Liberato JR, Miles AK, Rodrigues Neto J & Gambley C (2006) Citrus canker (canker A) (Xanthomonas axonopodis pv. citri ) Updated on 10/21/2011 9:32:02 AM Available online: PaDIL - http://www.padil.gov.au.
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