First Occurrence of Laurel Wilt Disease Caused by Raffaelea lauricola on Redbay Trees in Mississippi

Abstract

Laurel wilt is a lethal, nonnative vascular wilt disease of redbay (Persea borbonia), sassafras (Sassafras albidum), and other trees in the Lauraceae (1,4). It is caused by a fungus (Raffaelea lauricola) and transmitted by the redbay ambrosia beetle (Xyleborus glabratus), a nonnative insect first detected in Georgia in 2002 (1,2). Since introduction of the pathogen and vector (presumably from Asia), laurel wilt has caused extensive mortality to redbays in Georgia, Florida, and South Carolina (1). In June 2009, a landowner in Gautier, MS reported dead redbay trees. Signs and symptoms were identical to those reported for laurel wilt along the Atlantic Coast (wilted, bronze red foliage, and dark gray-to-black vascular discoloration) (1). Infected trees have subsequently been confirmed in and near the Pascagoula River Basin. Size of infected redbays ranged from 5 to 20 cm (diameter at breast height). No heavily decomposed or fallen redbays were noted. Many individual specimens exhibited extensive drying of stem wood and dry, wilted, light brown foliage. This indicates that introduction to the area may have occurred within the last 3 years. X. glabratus adults were collected (30°26′44.45″N, 88°39′41.83″W) in a Lindgren funnel trap baited with phoebe and manuka oil lures. Beetle identification was confirmed by USDA-APHIS, and voucher specimens were submitted to the Smithsonian National Museum of Natural History and the Mississippi Entomological Museum. Symptomatic redbay wood chips from the same location were surface sterilized and plated on cycloheximide-streptomycin malt agar and R. lauricola was isolated. A 1,026-bp portion of 18S rDNA (GenBank No. GQ996063) was amplified by PCR and sequenced using primers NS1 and NS4. BLASTn searches revealed perfect homology to R. lauricola isolate PL 697 (GQ329704). Two isolates of R. lauricola were recovered and prepared into separate spore suspensions (1 × 108 CFU/ml). Each isolate was inoculated into two healthy redbays. The inoculated redbays were placed in a growth chamber with two water-only controls. All inoculated plants, and none of the controls, exhibited wilt symptoms and died within 20 days. R. lauricola was recovered from the discolored sapwood of the inoculated plants, completing Koch's postulates. A model prediction for the natural dispersion of X. glabratus and R. lauricola estimated that these organisms may not reach Mississippi for 10 to 15 years (3). The current detection of laurel wilt in Mississippi is substantially ahead of this estimate. Currently, no records of laurel wilt have been reported from western Georgia, all of Alabama, or the panhandle of Florida. Confirmed locations in Mississippi are in Jackson County, along the Interstate 10 corridor and the Pascagoula River drainage. Due to the relatively large extent of the infestation (~64 km2, including hundreds of infected trees) eradication is not being attempted. Surveys, remote sensing, and phylogeographic analysis are underway to delineate the extent of infestation and discover the mode of introduction. The current outbreak of laurel wilt in Mississippi is likely the result of human transport of infested wood, either from Asia as a separate, new introduction or from previously infested areas in the southeastern United States. References: (1) S. W Fraedrich et al. Plant Dis. 92:215, 2008. (2) T. C. Harrington et al. Mycotaxon 104:399, 2008. (3) F. Koch and W. Smith. Environ. Entomol. 37:442, 2008. (4) J. A. Smith et al. Plant Dis. 93:198, 2009.

Supercooling in the Redbay Ambrosia Beetle (Coleoptera: Curculionidae)

“…As X. glabratus moves outside the range of redbay and swampbay, LWD has caused extensive sassafras mortality Smith et al 2009;Riggins et al 2011;Bates et al 2013). Disjunct populations are established in coastal counties of Mississippi and Alabama (Riggins et al 2010;Formby et al 2012), and in Marengo County, an interior county of Alabama (Bates et al 2013). Marengo County, Alabama is ~200 km from the nearest infestation site and exceeds a previous temporal estimation of invasion by 12 yr (Koch & Smith 2008).…”

Laurel Wilt in Natural and Agricultural Ecosystems: Understanding the Drivers and Scales of Complex Pathosystems

“…As this disease has spread, others have noted large jumps in its distribution. Riggins et al [172] reported a laurel wilt outbreak in Mississippi, over 500 km from the nearest known outbreak, and a recent finding in Texas was 300 km from the nearest known occurrence [16]. The above findings have been on redbay, but sassafras has also been impacted.…”

First Records ofXyleborus glabratus(Coleoptera: Curculionidae) in Alabama and in Harrison County, Mississippi

“…Stands of redbay throughout these areas have been decimated by laurel wilt disease. Both laurel wilt disease and infestations of X. glabratus have also been reported from Jackson County, Mississippi (Riggins et al 2010), far to the west of the contiguously infested areas in South Carolina, Georgia, and Florida. This represents the largest range expansion of X. glabratus in North America, and it is unclear if the beetles in Mississippi and Alabama originated from populations occurring along the Atlantic coast or represent a separate introduction from Asia.…”

“…We selected these locations because they are adjacent or near the previously reported Jackson County, Mississippi (Riggins et al 2010) and contain healthy populations of redbay. As a result of this monitoring program, X. glabratus was collected in Mobile County, Alabama and Harrison County, Mississippi for the first time.…”