Citrus variegated chlorosis (CVC)

Scientific name

[Bacterium] Xylella fastidiosa Wells et al.

Disease cycle

CVC is a systemicsystemic:
spreading internally throughout the plant body; may refer to a pathogen or chemical
disease that only survives in plant xylemxylem:
the plant vascular tissue that conducts water and dissolved minerals upwards from the roots to the rest of the plant
or within its vectorvector:
an organism that does not cause diseases itself but which carries the disease-causing microorganism from one host to another
. X. fastidiosa has been shown to move from seed to seedling in sweet orange. CVC has a latency period of 9-12 months before symptoms occur. Natural spread of X. fastidiosa occurs by several species of sharpshooter leafhoppers in the order Hemiptera. At least 11 species of sharpshooter have been shown to vectorvector:
an organism that does not cause diseases itself but which carries the disease-causing microorganism from one host to another
CVC. Some of these species currently occur in the United States. Sharpshooters are xylemxylem:
the plant vascular tissue that conducts water and dissolved minerals upwards from the roots to the rest of the plant
feeders and acquire X. fastidiosa within two hours of feeding. Sharpshooters have a high rate of feeding and retain infectivity indefinitely. Sharpshooters do not pass X. fastidiosa onto the next generation. Sharpshooters have an extensive hosthost:
an organism that is infected with or fed upon by a pathogenic or parasitic organism
range and may undergo one to several generations per year.

Symptoms

Leaf - foliar symptoms of CVC are very similar to nutrient deficiency and other diseases; therefore, it is difficult to rely on foliar symptoms alone for identification. Early leaf symptoms resemble zinc deficiency with interveinal chlorotic areas on the upper surface. Early symptoms may be limited to a single branch. As the leaf matures, gummy lesions become visible on the lower leaf surface corresponding to chlorotic areas on the upper surface of the leaf. The chlorotic areas gradually enlarge toward the leaf margin, and the lesions on the underside of the leaf may become dark brown or necroticnecrotic:
a cell, group of cells, or tissue that has suffered a rapid destruction and quick death; typically localized and may be caused by injury, radiation, chemicals, toxic substances, or microbiological interactions
. Leaves may be smaller than normal. Leaf symptoms are most pronounced on mature leaves (behind the new flush).

Fruit - blossom and fruit occur at the normal time, but fruit thinning does not occur. This results in clusters of 4-10 early maturing fruit. Fruits of infected trees may exhibit sunburn damage because of defoliation at branch terminals. In addition, fruit may change color early, have hard rinds, lack juice, and have an acidic flavor. Fruit symptoms of CVC are more easily recognized from a distance.

Whole tree - affected trees may exhibit reduced vigor and growth, and show abnormal flowering and fruit set. Newly affected trees may only exhibit symptoms on one limb or branch, and then symptoms may spread to the entire canopy. Older trees may only show symptoms on the extremities of the branches. Severely diseased trees frequently posses upper crown branches with defoliation at terminal twigs and small leaves and fruit.

Host range

Xylella fastidiosa can infect most of the citrus cultivars, species and hybrids, yet the severity of symptoms is variable. Sweet oranges are the most susceptible. Grapefruit, mandarins, mandarin hybrids, lemons, limes, kumquat and trifoliate orange are moderately susceptible, showing less severe symptoms. Rangpur lime, citron, and pummelo are less susceptible.

Distribution

CVC is found throughout South America.

Easily confused with

Foliar symptoms may be confused with nutrient deficiency, anthracnose, and greasy spot.