A Fungal Symbiont of the Redbay Ambrosia Beetle Causes a Lethal Wilt in Redbay and Other Lauraceae in the Southeastern United States S. W. Fraedrich, Southern Research Station, USDA Forest Service, Athens, GA 30602; T. C. Harrington, Depart- ment of Plant Pathology, Iowa State University, Ames 50011; R. J. Rabaglia, Forest Health Protection, USDA Forest Service, Arlington, VA 22209; M. D. Ulyshen, Southern Research Station, USDA Forest Service, Athens, GA 30602; A. E. Mayfield, III, Florida Department of Agriculture and Consumer Services, Division of Forestry, Gainesville 32608; J. L. Hanula, Southern Research Station, USDA Forest Service Athens, GA 30602; J. M. Eickwort, Florida Department of Agriculture and Consumer Services, Division of Forestry, Gainesville 32608; and D. R. Miller, Southern Research Station, USDA Forest Service, Athens, GA 30602 fungi have been assigned to the anamor- ABSTRACT phic genera Ambrosiella or Raffaelea Fraedrich, S. W., Harrington, T. C., Rabaglia, R. J., Ulyshen, M. D., Mayfield, A. E., III, Hanula, (3,22), and subsequent phylogenetic stud- J. L., Eickwort, J. M., and Miller, D. R. 2008. A fungal symbiont of the redbay ambrosia beetle ies have found close relationships between causes a lethal wilt in redbay and other Lauraceae in the southeastern United States. Plant Dis. these anamorphs and the ascomycetaceous 92:215-224. genera Ceratocystis and Ophiostoma (7,24,40). Many bark beetles, including Extensive mortality of redbay has been observed in the coastal plain counties of Georgia and ambrosia beetles, have mutualistic associa- southeastern South Carolina since 2003 and northeastern Florida since 2005. We show that the tions with species in these genera of asco- redbay mortality is due to a vascular wilt disease caused by an undescribed Raffaelea sp. that is a fungal symbiont of Xyleborus glabratus, an exotic ambrosia beetle. Trees affected by the disease mycetes, and it is thought that the ambro- exhibit wilt symptoms that include a black discoloration of the sapwood. Redbay trees and con- sia beetle symbionts are asexual tainerized seedlings died within 5 to 12 weeks after inoculation with the Raffaelea sp. When derivatives of Ceratocystis and Ophio- redbay seedlings were challenged with X. glabratus, the beetles tunneled into 96% of the plants, stoma (22). 70% died, and the Raffaelea sp. was recovered from 91%. X. glabratus and the Raffaelea sp. Redbay is an attractive, aromatic, ever- have also been associated with mortality of sassafras, and the Raffaelea sp. has been isolated green tree that is common in forests of the from wilted pondberry and pondspice. Additional inoculation studies have shown that the Raf- Atlantic and Gulf Coastal Plains of the faelea sp. is pathogenic to sassafras, spicebush, and avocado, but not to red maple. Female adults southeastern United States (5). Confusion of X. glabratus have paired mycangia near the mandibles, and the Raffaelea sp. is routinely iso- currently exists regarding the taxonomy of lated from the heads of beetles. The fungus is apparently introduced into healthy redbay during P. borbonia and other possible taxa in the beetle attacks on stems and branches. The wilt currently affecting redbay and sassafras repre- southeastern United States (6). Some bota- sents a major threat to other members of the Lauraceae indigenous to the Americas, including nists recognize swampbay (P. palustris avocado in commercial production. (Raf) Sarg.) as an additional Persea spe- cies (10,41), but others consider swampbay (P. borbonia var. pubescens (Pursh) Little) Extensive mortality of redbay (Persea stems and branches of many affected trees, to be a variety of redbay (8,29) or do not borbonia (L.) Spreng.) has been observed and several species of ambrosia beetles recognize it as a distinct species or variety in the lower coastal plains of South Caro- (Coleoptera: Curculionidae, Scolytinae) (5,14,38). In this paper, we refer to redbay lina and locations around Savannah, GA were also found in symptomatic redbay as P. borbonia sensu lato without attempt- since 2003. Initial reports of the mortality samples, including Xyleborinus gracilis ing to discern species or varietal differ- suggested that the problem might be Eichhoff, Ambrosiodmus obliquus Le- ences, except in a pathogenicity test where drought related, but direct evidence for this Conte, and Xyleborus glabratus Eichhoff. we obtained seedlings from a commercial was lacking and no explanation was pro- The two former beetles are native to the nursery that listed the seedlings as swamp- vided for the localized nature of the mor- southeastern United States, but X. glabra- bay (P. palustris). Species in the genus tality. During a site visit to Hilton Head tus is an exotic beetle reported only once Persea are members of the family Lau- Island, SC in November 2004, many dead before in the United States at Port Wen- raceae, which includes many important redbay trees were found, as well as live tworth, GA in 2002 (37). The beetle is species of plants worldwide, including trees exhibiting varying levels of branch native to Southeast Asia (e.g., India, Japan, avocado (P. americana Mill.). dieback. Stems and branches of affected and Taiwan), where it is often associated Redbay in the broadest sense can toler- trees had streaks of black discoloration in with plant species in the family Lauraceae ate a wide variety of sites ranging from the sapwood, and a fungus was consis- (e.g., Lindera latifolia Hk.f and Litsea xeric to mesic to swampy, and the species tently isolated from the discolored sap- elongata (Nees) Hk.f.) (50). is suitable for many landscape applications wood. Beetle entrance holes were noted in Little is currently known about the biol- (16). Redbay is regarded as a minor-use ogy of X. glabratus, although we assume hardwood, and the wood is occasionally that it is typical of other ambrosia beetles, used for interior finishing, cabinets, and Corresponding author: Stephen Fraedrich which do not consume wood but build furniture (5). Trees are small to medium E-mail: [email protected] gallery systems in wood to cultivate sym- size and are reported to grow as much as Accepted for publication 14 September 2007. biotic fungi as food for their larvae (28). 18 to 21 m high and 60 to 90 cm in diame- Many xylem-inhabiting ambrosia beetles ter (5). The fruit is eaten by songbirds, and some bark beetles carry their symbi- wild turkey, and other animals and deer doi:10.1094/ PDIS-92-2-0215 otic fungal associates in spore-bearing sacs browse on the foliage (5). Redbay also This article is in the public domain and not copy- serves as a primary larval host for the pala- rightable. It may be freely reprinted with custom- called mycangia, which can vary greatly in ary crediting of the source. The American Phyto- morphology and location among beetle medes swallowtail (Papilio palamedes pathological Society, 2008. species (22,45). The majority of ambrosia Drury) (43). Plant Disease / February 2008 215 Insects and diseases have not caused se- July 2005 at the Timucuan Ecological and of sterile water was placed into the wound. rious damage to redbay in the past (5,16). Historic Preserve (National Park Service) Inoculation points on all seedlings were Since our initial evaluations on Hilton on Fort George Island (Duval County), FL. wrapped with Parafilm M (Pechiney Plas- Head Island, many additional sites with Redbay mortality on the site was first ob- tic Packaging, Menasha, WI). Seedlings redbay mortality have been found and served during the fall of 2004, and ap- were placed in a growth chamber with a evaluated in Georgia, Florida, and South proximately one-third of the largest diame- 16-h photoperiod and day and night tem- Carolina. The vascular discoloration, X. ter redbay were dead by July 2005. Five peratures were set at 28 and 25°C, respec- glabratus, and the unidentified fungus (0.08-ha) circular plots were established tively. After 9 weeks, disease symptoms have been associated with dead and dying along a 1.1-km section of park road where were evaluated and pieces of stem tissue redbay trees in coastal areas of South dead and wilting redbays were observed. from 10 to 20 cm above the inoculation Carolina, Georgia, and northeast Florida. Plot centers were established approxi- points were surface sterilized and plated on In addition, mortality of sassafras (Sassa- mately 20 m from the road and at least 70 CSMA. fras albidum (Nuttall) Nees), another m apart and all were located within the A second test was established in June member of the Lauraceae, has been ob- same hardwood hammock forest type 2006 to assess possible variation in patho- served in several coastal counties of Geor- dominated by live oak (Quercus virginiana genicity among isolates. Ten isolates of the gia and X. glabratus and the unidentified Mill.), redbay, red cedar (Juniperus virgin- unknown fungus were obtained from fungus were associated with these trees. iana L.), southern magnolia (Magnolia symptomatic redbay and sassafras trees at The objectives of this study were to: i) grandiflora L.), and cabbage palm (Sabal various locations within the known range assess the distribution and determine the palmetto (Walter) Lodd. ex Schult. & of the disease. Seedlings were 2 to 3 years cause of the mortality of redbay in the Schult.f.). In each plot, every redbay with a old and averaged 82 cm high and 12 mm in southeastern United States; ii) evaluate the diameter at breast height (dbh; diameter at diameter at groundline. Inoculum for each pathogenicity of the unidentified fungus to 1.4 m high) greater than 2.5 cm was tagged isolate was produced as previously de- redbay and other members of the Lau- and visually rated for crown condition (i.e., scribed, and inoculum concentrations for raceae found in the southeastern United foliage primarily green, wilting, or brown).