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Disease Note.

Another Outbreak of Bacterial Canker on Citrus in Florida. T. S. Schubert, Florida Department of Agriculture & Consumer Services - Division of Plant Industry, PO Box 147100, Gainesville 32614-7100 . J. W. Miller, Florida Department of Agriculture & Consumer Services - Division of Plant Industry, PO Box 147100, Gainesville 32614-7100; and D. W. Gabriel, University of Florida, PO Box 110680, Gainesville 32611-0680. Plant Dis. 80:1208. Accepted for publication 6 August 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1208A.

In late September 1995. bacterial canker caused by the Asian strain of Xanthomonas axonopodis pv. citri (syn. X. campeslris pv. citri) was discovered on residential citrus (Citrus spp.) in Dade County, FL. As of July 1996, delimiting surveys identified an infested area of about 47 sq. mi. (12,173 ha). The infested area is enclosed by a 170 sq. mi. (44,030 ha) quarantine area in which all citrus propagation, movement, and sales are prohibited. The quarantine area is located primarily west, southwest, and south of the Miami International Airport. Several small isolated outbreaks have been detected just north of Miami in Hialeah. Under an eradication order of the Florida Department of Agriculture and Consumer services and in cooperation with USDA-APHIS, 99% of known infected trees were destroyed by June 1996. More than 9,000 infected trees had been removed. Also, all green growth was pruned from another 8,000+ adjacent exposed trees (symptomless trees within 125 ft [38 in] of infected trees) to reduce epiphytic inoculum and eliminate undetected incipient infections. All infected citrus were in residential settings. Some backyard unregistered containerized citrus were heavily infected. No citrus canker has been found in any of the registered commercial nurseries within the quarantine area. No citrus canker has been found in any commercial groves. All citrus in the quarantine area is now on a schedule for inspection at 90- to 180-day intervals, depending on proximity to known infections. Similar quarantine, eradication, and inspection procedures effectively eradicated a canker outbreak on the Central Florida Gulf Coast from 1986 to 1992. No information is available about the origin of the inoculum responsible for the current outbreak of citrus canker. Total DNA fingerprinting and restriction fragment length polymorphism comparisons of 10 strains from the recent outbreak indicate they are clonal but recognizably different from isolates archived from the 1986 canker outbreak. Strains from the earlier outbreak were also clonal. The evidence suggests that the two outbreaks resulted from two separate introductions of genetically distinct strains of Xanthomonas axonopodis pv. citri.