Citrus Variegated Chlorosis

Citrus Variegated Chlorosis


 

History of Citrus Variegated Chlorosis

Citrus Variegated Chlorosis (CVC) is a bacterial disease caused by a subspecies of the Xylella fastidiosa bacterium, which lives in the xylem of the plant and limits the function of the vascular system. This bacterium is transmitted plant-to-plant by several species of large leafhopper insects called sharpshooters and through grafting. CVC was first discovered in Brazil in 1987 and is currently found in Brazil, Argentina, Costa Rica, and Paraguay. Sweet orange cultivars are highly susceptible to CVC. Grapefruit, mandarins, mandarin hybrids, and limes show less severe symptoms. CVC tolerant varieties are Rangpur lime, lemon, citron, and pummelo. CVC causes trees to have reduced vigor and growth. Tree death is not common from CVC, but production is greatly reduced.

Other subspecies of the causal agent are present in the United States, although this subspecies has yet to be found here. The alternate host range for this disease is unknown. Some hosts infected with X. fastidiosa show no symptoms of disease, making this bacteria and host range hard to study. Some hosts are known for example, as other subspecies of this bacterium cause Pierce’s disease in grapes and other scorch-type diseases in plants such as coffee and almond. This makes regulations difficult to design and enforce for non-citrus plant material, since it is not known how many species of plants can carry this pathogen. Another challenge with studying this bacterium is that it is difficult to culture in a lab setting and requires a very specific medium in which to grow. There is a long latent period, up to one year or longer, from when the infection occurs, and the tree starts to exhibit symptoms. During this latent period, the bacterium can be transmitted, and the spread of the disease can go undetected for some time.

How to Report a Suspected Find

If you suspect you may have Citrus Variegated Chlorosis, please contact your local Florida Department of Agriculture and Consumer Service's CHRP office for further diagnostic testing. Do not move infected plant material out of the area.

Fruit Symptoms

Fruit quality and production is greatly affected by CVC. Fruit fail to grow properly and prematurely ripen, they remain small and hard and have a high acid content. This renders the fruit unusable resulting in profit loss for the grower. The fruit does remain on the tree and will color change normally. The fruit may also exhibit signs of sunburn damage. CVC also causes off-season bloom and abnormal fruit set to occur as trees become more severely affected.

Leaf and Stem Symptoms

Symptoms can occur on one branch or in the entire canopy of the tree. Although the bacterium is living in the vascular tissue, stems are considered asymptomatic, but the tree can have twig dieback in the canopy. Leaf symptoms include severe chlorosis between veins and lesions. In the early stages, leaf lesions can resemble zinc deficiency. Lesions become gummy, reddish to brown in color and occur on the underside of the leaf. These lesions correspond to the yellow chlorotic areas on the upper side of the leaf. The symptoms of CVC are most pronounced in younger leaves but can also be expressed in older leaves. As the infection becomes more severe, tree health declines and the thinning of the canopy will occur.

Spread

The bacterium that causes CVC is transmitted by sharpshooters (leafhoppers, Cicadellidae), tree hoppers (Membracidae), and spittlebugs (Cercopidae). In Brazil, 11 species of sharpshooters are known to transmit CVC. There are two of these species currently found in Florida; the glassy-winged sharpshooter, Homalodisca vitripennis, and the blue-winged sharpshooter, Oncometopia nigricans. The presence of these insects in Florida increases the potential risk of an infection, if the pathogen should enter the state.

CVC can also be transmitted through grafting, making the use of clean budwood essential to reducing the spread of the disease. In Brazil, the main source of infection was from the use of diseased budwood, but with the implementation of undercover greenhouses in the early 2000’s, this is no longer the case. It is also believed that natural root graphs between adjacent trees can spread the disease within the grove. Studies have shown that the pathogen is not transmitted through seed.

Regulations and Management

Although the complete host range of X. fastidiosa, subspecies pauca, is still unknown, it is important to keep up regulations and restrictions on the plant material that enters the United States and Florida, especially from those countries known to have this disease. The use of clean budwood from registered sources and the planting of disease-free nursery resets, is essential to limiting the spread of this pathogen should it enter Florida. The current Florida nursery industry is well structured to be able to produce clean trees for the citrus industry should CVC arrive in Florida. Growers in Brazil prune out diseased wood on mild to moderately affected trees to reduce inoculum sources. In cases of severe symptoms, the entire tree is removed. Educational resources and identification tools should be utilized by grove workers, managers, and other industry professionals to increase awareness and knowledge of this disease.

Publications

Appel, D.N. 2004. Citrus variegated chlorosis; pathway analysis: Intentional introduction of Xylella fastidiosa. Special report by the National Agricultural Biosecurity Center Consortium for the USDA Animal and Plant Health Inspection Service. pp.34.

Hartung, J.S., Beretta, J., Brlansky, R.H., Spisso, J., and Lee, R.F. 1994. Citrus variegated chlorosis bacterium: axenic culture, pathogenicity, and serological relationships with other strains of Xylella fastidiosa, Phytopathology 84:591-597.

He, C.-X., Li, W.B., Ayres, A.J., Hartung, J.S., Miranda, V.S., and Teixeira, D.C. 2000. Distribution of Xylella fastidiosa in citrus rootstocks and transmission of citrus variegated chlorosis between sweet orange plants through natural root graphs. Plant disease 84:622-626.

Li, W.B., Pria, Jr., W.D., Teixeira, D.C, Miranda, V.S., Ayres, A.J., Franco, C.F., Costa, M.G., He, C.-X., Costa, P.I., and Hartung, J.S. 2001 Coffee Leaf Scorch caused by a strain of  Xylella fastidiosa from citrus. Plant Disease 85:501-505.

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Links

Resources

If you would like to obtain laminated identification sheets or copies of the other various educational materials, please contact Jamie Burrow, 863-956-8648 or jdyates@ufl.edu

Contacts

Megan Dewdney, Ph.D. Plant Pathologist 863.956.1151  mmdewdney@ufl.edu
Ozgur Batuman, Ph.D. Plant Pathologist 239.658.3400  obatuman@ufl.edu
Ron Brlansky, Ph.D. Professor Emeritus, Plant Pathology 863.956.1151 rhby@ufl.edu
Jamie Burrow Extension Program Coordinator 863.956.8648  jdyates@ufl.edu
Amit Levy, Ph.D. Plant Pathologist 863.956.1151  amitlevy@ufl.edu
Jawwad Qureshi, Ph.D. Entomologist 772.468.3922  jawwadq@ufl.edu
Phil Stansly, Ph.D. Entomologist 239.658.3400  pstansly@ufl.edu
Lukasz Stelinski, Ph.D Entomologist 863.956.1151  stelinski@ufl.edu 

Florida Multi-County Citrus Extension Agents