Leprosis

Scientific name

[Virus] Citrus leprosis virus (CiLV)

Other common names

Nailhead rust, nailhead spot, scaly bark, lepra explosiva

Disease cycle

Citrus leprosis virus (CiLV) is transmitted by the false spider mites in the genus Brevipalpus (Acari: Tenuipalpidae). Brevipalpus mites occur on citrus around the world but do not alone cause significant damage unless the mite population is extremely high. Multiple species of Brevipalpus mites may transmit the virus; however, there has been misidentification of the mites found in association with the virus. Brevipalpus obovatus, B. californicus, and a closely related species of B. phoenicis (which has not been identified at this point) have been associated with CiLV. All three species have been collected from citrus in the United States. The disease only spreads when both infected trees and the vectorvector:
an organism that does not cause diseases itself but which carries the disease-causing microorganism from one host to another
is present. The virus does not appear to move systemically in the hosthost:
an organism that is infected with or fed upon by a pathogenic or parasitic organism
plant with the exception of short distances along the mid-vein or secondary veinlets.

All active life stages of the mite are equally able to transmit the virus, yet there is no transovarial transmission of the virus (virus moving from female to offspring). Newly hatched mites must feed on infected plant tissue in order to acquire the virus. The virus multiplies in the mites; therefore the mite may spread the virus throughout its life.

Symptoms

Leaf - foliar lesions are shallow but visible on both sides. Each lesionlesion:
any defined area of living tissue that has been structurally modified as a result of a disease or damaging process
is produced in association with the feeding by the mite vectorvector:
an organism that does not cause diseases itself but which carries the disease-causing microorganism from one host to another
. Symptoms appear 1-2 months after inoculation. Typical lesions are circular with a dark-brown central mite feeding spot. The overall lesionlesion:
any defined area of living tissue that has been structurally modified as a result of a disease or damaging process
size may vary from 10-30 mm with the central mite feeding spot ranging 2-3 mm in diameters. The feeding spot is surrounded by a chlorotic halo with 1 -3 concentric rings. Lesions may coalesce to form larger erratically shaped lesions. Under high temperature conditions the center of the lesionlesion:
any defined area of living tissue that has been structurally modified as a result of a disease or damaging process
may crack.

Fruit - fruit lesions only affect the outer rind. Lesions appear as flat or depressed spots 10-20 mm wide with a 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
center. It is common for a single fruit to exhibit up to 30 lesions covering a significant portion of the rind. Lesions on green fruit initially appear as yellow circles with a central mite feeding spot. Over time the lesionlesion:
any defined area of living tissue that has been structurally modified as a result of a disease or damaging process
becomes brown or blackish, sometimes depressed. Infected fruit tend to change color early and become susceptible to various rots. CiLV also induces premature fruit drop which greatly reduces yield. Infected trees may have copious amounts of fruit on the ground.

Stem - on young stems, symptoms appear as small, chlorotic, shallow lesions that become darker brown or reddish. On bark and twigs lesions become corkier as they age and may progress into conspicuous scaling bark symptom. Lesions may coalesce which may lead to girdling of the stem and result in die back.

Regulatory information

This disease does not occur in the United States.

Host range

Hosts of the Citrus leprosis virus (CiLV) are only known to occur in the genus Citrus. Recorded hosts include Mexican lime, sour orange, rough lemon, Persian lime, lemon, citron, mandarins, mandarin hybrids, sweet oranges and grapefruits. Sweet oranges and grapefruits are considered the most susceptible; other listed varieties exhibit various levels of resistance and may not show conspicuous symptoms.

Distribution

As of publication Citrus leprosis virus exists in Argentina, Brazil, Colombia, Uruguay, Paraguay, Venezuela, Panama, Honduras, Guatemala, Costa Rica, Nicaragua, El Salvador, and Mexico. Leprosis was found in Florida in the 1920's but no longer occurs in Florida and is considered an exotic disease throughout the United States.

Easily confused with

CiLV leaf symptoms may be confused with measles, pesticide injury or insect damage. CiLV fruit symptoms may be confused with citrus canker. On the trunk CiLV bark scaling symptoms can appear similar to citrus psorosis. However, the psorosis virus causes wood staining while CiLV does not.