Citrus leprosis virus no longer occurs in the USA
Citrus leprosis is an important disease in South and Central America where it causes economic losses in citrus orchards (e.g. in Brazil and Argentina). The main symptoms include lesions on leaves, fruit, and twigs, causing premature fruit drop, defoliation and death of twigs or small branches leading to serious tree decline. In addition, the disease is always associated with the presence of mites. Until the 1990s, the absence of systemic infection and the failure to transmit leprosis by either grafting or mechanical means led to suppose that it was caused by mite salivary toxins. It was then demonstrated that the disease was caused by Citrus leprosis virus (unassigned Rhabdovirus, CiLV – EPPO A1 List) and that it was transmitted by mites in the genus Brevipalpus (Acari: Tenuipalpidae), in particular by Brevipalpus californicus, B. phoenicis, and B. obovatus.
In the USA, citrus leprosis was only recorded in Florida1) where it nearly destroyed the Florida citrus industry prior to 1925, according to reports published from 1906 to 1968. This was supported with pictures showing the typical symptoms of the disease. However, since the 1960s the disease has not been observed in Florida. More recently, a study showed that CiLV no longer occurred in Florida and could not be detected in the citrus-growing areas of Texas (Childers et al., 2003). Samples showing suspect symptoms were collected in 1997 from Florida (orange and grapefruit leaves) and from Texas in 1999 and 2000 (grapefruit and orange fruits). These tissue samples were observed in transmission electron microscopy and no virus particles were observed. In 2001 and 2002, 24 555 orange trees (Citrus sinensis) were inspected across Florida and no symptoms were observed. The authors concluded that citrus leprosis no longer exists in Florida and remains absent from Texas based on: 1) lack of leprosis symptoms on leaves, fruit, and twigs in citrus crops surveyed, 2) failure to find virus particles or inclusion bodies in suspect samples, 3) absence of any other documented reports on the presence of characteristic leprosis symptoms. Although it is not known exactly why CiLV is no longer found in Florida, it is supposed that the following factors contributed to its disappearance by breaking the virus-mite vector cycle of the disease: 1) several frost periods between 1934 and 1962, 2) successful control of mite vectors (extensive use of wettable sulfur until the early 1960s combined with pruning of leprosis-infected branches and use of more resistant cultivars). Finally, USDA-APHIS confirmed to the EPPO Secretariat that active surveillance was continuing in the US citrus-growing areas (using survey methodologies developed by USDA-ARS), and that all survey results to date were negative for CiLV.
The situation of Citrus leprosis virus in the USA can be described as follows: Absent, the disease was observed in the past in Florida (until the 1960s) but is no longer found.
1) According to Rodrigues et al. (2003) there is an old record of leprosis in Mississippi in 1923 but the disease has not been reported since.
Childers CC, Rodrigues JC, Derrick KS, Achor DS, French JV, Welbourn WC, Ochoa R, Kitajima EW (2003) Citrus leprosis: its status in Florida and Texas: past and present. Experimental and Applied Acarology 30, 181–202.
Chung KR, Brlansky RH (2006) Citrus diseases exotic to Florida: Citrus leprosis. Fact Sheet PP-226. University of Florida, IFAS Extension, 3 pp. http://edis.ifas.ufl.edu/pdffiles/PP/PP14800.pdf
Rodrigues JCV, Kitajima EW, Childers CC, Chagas CM (2003) Citrus leprosis virus vectored by Brevipalpus phoenicis (Acari: Tenuipalpidae) on citrus in Brazil. Experimental and Applied Acarology 30, 161-179.
NAPPO Phytosanitary Alert System. Pest Alert of 2001-03-21. Citrus leprosis virus (CiLV) Bitancourt. http://www.pestalert.org/viewArchPestAlert.cfm?rid=46&keyword=leprosis
Personal communication with H. Hartzog, APHIS-USDA (2009-01).