Gladiolus Rust Caused by Uromyces transversalis Makes First Nearctic Appearance in Florida

The most serious rust pathogen of gladiolus (Gladiolus × hortulanus), Uromyces transversalis, has been listed as an exotic pathogen of concern for the United States for more than 80 years (4). Native to South Africa, the pathogen was reported in the Western Hemisphere for the first time in Brazil (2) and Argentina (1). Reports of gladiolus rust in several central Mexican states from 2004 to 2005 (3; http://www.pestalert.org/espanol/oprDetail.cfm?oprID=138 ) and interceptions at Mexican border stations and in Brazilian imports in 2005 at the port of Miami, FL collectively raised the alert level in the United States to high. In April 2006, the Hawaii Department of Agriculture notified the USDA of rust-infected gladiolus in a cut-flower shipment that was traced back to a 1,400-acre (565 ha) farm in Manatee County, FL. Inspection at the farm yielded samples that were quickly confirmed as U. transversalis by FDACS-DPI and USDA plant pathologists. The disease was identified in eight residential gardens near the commercial find and in another 700-acre (285 ha) farm in remote Hendry County, 100 miles to the southeast. In May 2006, gladiolus rust was detected in residential and commercial gladiolus in San Diego County, CA (see companion publication). On the advice of a USDA-assembled panel of experts, strict rust management guidelines and fallow host-free periods were implemented with the ultimate goal of eradication. Subsequent summer, fall, and now winter surveys in the infested commercial and residential areas have uncovered diminishing amounts of rust, with last traces detected on 9 September 2006. Commercial planting resumed at both farms in late summer, and crops remained rust free under weekly inspection until 15 February 2007 in Manatee County and 29 March 2007 in Hendry County. To insure a rust-free product, cut flowers are carefully inspected and foliage stripped at the packinghouse. Eradication will be attempted once more with a fallow host-free period before the 2007 season. U. transversalis is an autoecious rust that mainly infects Gladiolus spp., but has been known to infect other members of the Iridaceae: Anomatheca, Crocosmia, Melasphaerula, Tritonia, and Watsonia. Amphigenous uredinia form in transverse lines across gladiolus foliage and also on flower spikes under heavy disease pressure. The isolate present in Florida fits the literature description of U. transversalis in every respect (uredinia 0.5 to 1.5 mm in diameter, subglobose to ellipsoid verruculose yellow-amber urediniospores, 15 to 28 × 14 to 20 μm with wall 1.5 to 2.5 μm thick; telia also amphigenous, 0.5 to 1.3 μm in diameter, dark brown-black, subglobose to pyriform smooth amber teliospores, 20 to 30 × 15 to 20 μm with wall 1.5 to 2.0 μm thick, 4 to 6 μm thick at apex, pale brown to hyaline pedicel 30 to 40 μm long, yellow-brown paraphyses in pustule) ( http://nt.ars-grin.gov/fungaldatabases/new_allView.cfm?whichone=all&thisName=Uro myces%20transversalis&organismtype=Fungus ). Urediniospores initiated typical foliar lesions on transplanted gladiolus samples kept in the FDACS-DPI quarantine greenhouse during the diagnostic process. References: (1) J. R. Hernandez and J. F. Hennen. Sida 20:313, 2002. (2) G. P. B. Pitta et al. Biologica 47:323, 1981. (3) G. Rodriguez-Alvarado et al. Plant Dis. 90:687, 2006. (4) J. A. Stevenson. Page 82 in: Foreign Plant Diseases. USDA Fed. Hortic. Board Bureau Plant Ind. Government Printing Office, Washington DC, 1926.