Examples of leprosis. Citrus leprosis research update

By Ron Brlansky, William Schneider, John Hartung and Avijit Roy

itrus leprosis is one of the oldest citrus diseases, but is also one of the most important emerging citrus diseases in South America and Central America. It is apparently spreading northward toward the United States. CThe disease causes leaf, twig and fruit lesions with severe defoliation, girdled limbs, premature fruit drop, death of twigs and reduction in both fruit quality and yield, as well as possible tree death within three to five years. The disease is currently not present in the United States, but it was first reported from Florida in the 1860s and resulted in serious impacts on citrus production. After 1926, the incidence of the disease in Florida began to decline. By the 1950s, citrus leprosis was present only in isolated areas on the east coast of Florida, and since 1968, surveys have not found it in Florida. The cause of citrus leprosis has always been considered to be a virus transmitted by species. Virus particles were reported in 1972 in the cell nucleus, and in the cytoplasm in 1995. The viruses were similar in structure but different in size, and thus were considered to be different. However, each virus caused essentially the same symptoms on citrus, and both were transmitted by flat . With the spread of citrus leprosis northward from South America into Central America and Mexico, work recently began in our lab group for the detection and diagnosis of citrus leprosis and to test transmission by endemic Brevipalpus (flat) mites, respectively. The research is funded by grants from the U.S. Department of Agriculture- and Plant Health Inspection

20 Citrus Industry August 2015 Service and the Citrus Research and Development Foundation. Start Research in our labs and by others has shown that citrus leprosis disease is caused by a complex of viruses, and that five different viruses currently rs present in South America, Central America and North America (Mexico) Field Ready Line can cause the disease. The finding that five different viruses are associated Fast with the disease was made possible by Grow Gall using modern molecular technology ons (next-generation sequencing) and the associated analysis. The new techniques have made the identification and characterization of these unknown When performance viruses quicker. counts, start The citrus leprosis-associated with the best. viruses are present in either the cyto- Call us today! plasm or the nucleus of the cells, which is a big difference at the cellular level. However, the symptoms produced in citrus by most of them are very similar. The characterized citrus leprosis- associated viruses found in the cytoplasm are citrus leprosis virus C (CiLV-C), citrus leprosis virus C2 (CiLV-C2) and hibiscus green spot Finish virus 2 (HGSV-2). The characterized nuclear viruses are citrus leprosis virus N (CiLV-N) and citrus necrotic spot virus (CiNSV). All of these viruses cause similar leaf, twig and fruit lesions, and do not move systemically in the infected plant.

The diversity of viruses is also matched by a previously unexpected IslandGroveAgProducts.com Bert Sheffield 352.274.3835 diversity in the flat mites associated [email protected] with the disease. So far, two species of Brevipalpus (flat) mites are involved. Mites collected from CiLV-C and CiLV-N infected citrus groves in

Mexico were identified as B. yothersi and B. californicus, respectively. Only B. yothersi was detected from CiLV-C2 Lab and CiLV-N in citrus infected with Technologies for improved wear resistance both viruses in the Orinoco region of and corrosion resistance of stainless steel Colombia. It has now been found that materials both cytoplasmic viruses (CiLV-C and

CiLV-C2) replicate in the Brevipalpus ����� �� �� ��e ������ e��� flat mites. ����� ��� Recent sequence analysis of these cytoplasmic leprosis viruses has revealed a close relationship with virus sequences found in mosquitoes. This

Citrus Industry August 2015 21

“My business is strong suggests that the genus , to because Farm Credit was which these viruses belong, may have there when I needed them.” originally evolved in mites and that citrus may actually be a secondary host. Flat mites collected from Florida were identified as B. yothersi; however, transmission tests (in quarantine) with CiLV-C from Colombia were negative. Further transmission tests are required with Florida Brevipalpus mites since citrus leprosis has not been present since the 1950s. Marty McKenna, third generation citrus grower, walking and As mentioned above, citrus leprosis working the land his grandfather planted. virus was present in Florida in the 19th and 20th centuries, but rather Loans made for farmers by farmers, since 1916. 866.824.5626 mysteriously disappeared. Fortunately, Farm Credit is the nation’s leading provider of credit FarmCreditFlorida.com a sweet orange specimen with leprosis to agriculture and rural America. symptoms was collected by University of Florida Professor Knorr in Volusia County, Fla. in 1948, and was deposited at the USDA herbarium in Beltsville, Md. for safekeeping. We used a portion Available Now: of this specimen for next-generation Ruby Red/Sour 7,000 sequencing and analysis, and were Hamlin/Sour 1,500 able to obtain the genomic sequence Valencia/Sour 1,500 Eric Nething (813) 477-4023 of a member of the CiLV-N group of Robles/Sour 500 viruses. The genome of the Florida [email protected] Sunburst/Sour 500 CiLV-N virus is noticeably different Doug Holmberg (813) 335-8800 Hamlin/Carrizo 500 from the other strains of CiLV-N that [email protected] Valencia/Carrizo 5,000 Navel/Carrizo 1,000 are widespread today. Presumably, the Lee/Carrizo 500 Florida strain – designated CiLV-N0 – Rootstocks Hamlin/SWG 8,000 is not extinct but survives elsewhere, Available: Valencia/SWG 15,000 and primers and assays have been Red Navel/SWG 1,000 Sour orange x639 developed to detect it. Honey Bell/SWG 1,000 Swingle us802 Ruby Red/F83 1,000 Specific detection methods are now Carrizo us812 Honey Bell/F83 500 in place for diagnosis of the known Cleo us897, us942 viruses that cause citrus leprosies, and plans are to combine them into a multiplex assay. A recovery plan is 13430 Hobson Simmons Rd., Lithia, FL 33547 in place with the USDA in case the disease should be introduced into the United States.

Ron Brlansky is a professor emeritus at the University of Florida, CREC, Lake Alfred; William Schneider is a research plant pathologist with the USDA Agricultural Research Service Foreign Disease-Weed Science Research Unit, Fort Detrick, Md.; John Hartung is a research plant pathologist with the USDA ARS Molecular Plant Pathology Laboratory, Beltsville, Md.; Avijit Roy is a research molecular biologist with the USDA ARS FDWSRU, Fort Detrick, Md. 22 Citrus Industry August 2015