Systemic Aquired Resistances: Citrus Canker
Xanthomonas axonopodis pv. citri (Xac) is the causal agent of one
of the most serious citrus diseases worldwide, Asiatic citrus canker (Khalaf et al.,
In United States, Florida had experienced three major outbreaks of Asiatic citrus
canker during 1910, 1984, and 1995 and become a potential threat to $8.5 billion
citrus industry (Schubert et al., 2001).
Citrus occupied an area of 576,577 acre in 2008 and was lowest since 1996 exhibited
a decline of 281110 acres out of which 87000 acres were destroyed under canker eradication
program and 65,000 acres were abandoned due to heavy losses (Lowe, 2009).
In terms of varietal impact, lime industry in Miami-Dade County was completely destroyed
and Grapefruit acreage was declined to 56,881 (2008) from 146,915 (1994) due to
its high susceptibility for canker (Anonymous, 2009).
Disease Spread and Symptoms
The canker bacterium gains entry through stomates and wounds and within 5 days built
up a population (3-4 log units per lesion) to act as a source of inoculum for further
disease proliferation (Gottwald and Graham, 1992).
This inoculum is spread by rain and in association with higher wind speed (≥ 18
mph) enhanced the magnitude of disease and caused infection in larger area (Gobel
et al., 2003).
Symptoms of the disease are characterized by raised, brown eruptant lesions surrounded
by water-soaking and yellow halos. Severe infection on young leaves and fruits causes
leaf abscission and pre-mature fruit drop with enormous production losses (Veniere
et al., 2003).
- Khalaf et al., 2007. New insights into the resistance of Nagami kumquat to canker
disease. Physiol. Mol. Plant Pathol. 71: 240-250.
- Schubert et al., 2001. Meeting the challenge of eradicating citrus canker in Florida-again.
Plant Dis. 85: 340-356.
- Lowe, D. 2009. Citrus canker: Current situation, management, and economic impact
in Florida 1995-2009. International workshop on citrus quarantine pests. Villahermosa,
- Gottwald, T. R., Graham, J. H. 1992. A device for precise and nondisruptive stomatal
inoculation of leaf tissue with bacterial pathogens. Phytopathology 82: 930-935.
- Anonymous. 2009. Citrus Summary 2007-2008. Florida Agricultural Statistic Service,
USDA NASS, FL.
- Gobel et al., 2003. Lipid peroxidation during the hypersensitive response in potato
in the absence of 9-Lipoxugenases. J. Biol. Chem. 278: 52834-52840.
- Verniere et al., 2003. Disease development and symptom expression of Xanthomonas
axonopodis pv. citri in various citrus plant tissues. Phytopathology 93: 832-843.
- Durrant and Dong, 2004. Systemic acquired resistance Annual Review of Phytopathology,
42: 185-209. Physiol. Mol. Plant Pathol. 71: 240-250.