First Report of Laurel Wilt Disease Caused by Raffaelea lauricola on Sassafras in Florida and South Carolina

Laurel wilt disease, caused by Raffaelea lauricola (T.C. Harr., Fraedrich & Aghayeva sp. nov.), which is a fungal symbiont of the nonnative redbay ambrosia beetle (Xyleborus glabratus Eichhoff), has caused widespread mortality of native redbay (Persea borbonia (L.) Spreng) in Georgia, South Carolina, and Florida since 2002. The disease has been noted on other species in the Lauraceae including sassafras in Georgia (1), and more recently, on avocado and camphor in Florida (4). Since 2005, wilted shoots, branch dieback, and tree death have been observed in sassafras trees (Sassafras albidum (L.)) in Liberty, McIntosh, Chatham, Effingham, Bulloch, Evans, and Screven counties in Georgia; Bamberg, Beaufort, Charleston, Colleton, Hampton, and Orangeburg counties in South Carolina; and Putnam County in Florida. Symptomatic sassafras trees ranged from 1 to 12 m high and 2.5 to 25 cm in diameter at breast height. In contrast to red bay trees that retain wilted foliage, symptomatic sassafras defoliate rapidly as trees wilt and die. Multiple symptomatic ramets originating from a common root system have been observed. Removal of bark from stem and root sections from wilted trees revealed black-to-brownish staining in the sapwood, characteristic of laurel wilt. Wood chips from symptomatic areas of branches and roots were surface sterilized and plated on cycloheximide-streptomycin malt agar as previously described (1) and R. lauricola was routinely isolated. Small subunit (18S) sequences from rDNA were amplified by PCR and sequenced using primers NS1 and NS4 (3) for isolates from sassafras from Florida and South Carolina. BLASTn searches revealed homology to Raffaelea sp. C2203 (GenBank Accession No. EU123076, 100% similarity) described by Fraedrich et al. (1) from redbay and later named R. lauricola (2). The small subunit rDNA sequences for these isolates have been deposited into GenBank ( http://www.ncbi.nlm.nih.gov/Genbank/index.html ) and assigned Accession Nos. EU980448 (Florida) and GQ329704 (South Carolina). Koch's postulates have been completed with R. lauricola on this host previously (1). Laurel wilt on sassafras often was geographically isolated from other symptomatic hosts in Georgia and South Carolina and appears to occur on this host independently of proximity to redbay. Further studies to determine the epidemiology of laurel wilt on sassafras, potential resistance, and impact on sassafras life history and distribution are needed. Given the clonal nature of sassafras, the disease would appear to have the potential to move through roots of trees once established in a stand. References: (1) S. W Fraedrich et al. Plant Dis. 92:215, 2008. (2) T. C. Harrington et al. Mycotaxon 104:399, 2008. (3) M. A. Innis et al. PCR Protocols, A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990. (4) J. A. Smith et al. Plant Dis. 93:198, 2009.

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First Report of Laurel Wilt Disease Caused by Raffaelea lauricola on Pondspice in Florida

Plant Disease ◽

10.1094/pdis-06-11-0528 ◽

2011 ◽

Vol 95 (12) ◽

pp. 1588-1588 ◽

Cited By ~ 14

Author(s):

M. Hughes ◽

J. A. Smith ◽

A. E. Mayfield ◽

M. C. Minno ◽

K. Shin

Keyword(s):

Small Subunit ◽

Wilt Disease ◽

Spore Suspension ◽

Ambrosia Beetle ◽

Laurel Wilt ◽

Mature Adult ◽

Raffaelea Lauricola ◽

Laurel Wilt Disease ◽

Redbay Ambrosia Beetle ◽

Small Subunit Rdna

Laurel wilt is a fungal vascular disease of redbay (Persea borbonia (L.) Spreng) and other plants in the family Lauraceae in the southeastern United States (1). The disease is caused by Raffaelea lauricola T. C. Harr., Fraedrich & Aghayeva, which is vectored by the exotic redbay ambrosia beetle (Xyleborus glabratus Eichhoff) (2). Pondspice (Litsea aestivalis (L.) Fern.) is an obligate wetland shrub listed as endangered in Florida and Maryland and threatened in Georgia (4). On 29 August 2008, 369 of 430 (85%) pondspice trees observed at St. Marks Pond in St. John's County, Florida were dead and/or dying (4). Stem samples were collected from plants with wilted and reddened foliage, entrance holes with boring dust characteristic of ambrosia beetle attack, and dark discoloration in the outer sapwood. Discolored stem sections were surface disinfested for 30 s in a 5% sodium hypochlorite solution and then plated onto cycloheximide streptomycin malt extract agar (1). Smooth, cream-buff, submerge hyphae with uneven margins resembling R. lauricola (2) was observed growing from all sapwood pieces. DNA was extracted from a single isolate (PL 392) and the 18s small subunit rDNA was PCR amplified and sequenced with primers NS1 and NS4 (3), resulting in a 1,026-bp amplicon. A BLASTn search showed identical homology to R. lauricola strain PL 159 (GenBank Accession No. EU257806). The 18s small subunit rDNA sequence was deposited into GenBank (FJ514097). In May 2011, a spore suspension was made by flooding a single-spore culture plate of isolate PL 392 with 2 ml of sterile water, collecting the spores by pipette, and quantification by hemacyometer to 1.5 × 106 spores/ml. Pathogenicity tests were conducted on 1 to 1.5 m tall pondspice plants. Six saplings were wounded by a 3/32-inch drill bit, with four receiving 50 μl of the spore suspension and two serving as water-inoculated controls. All plants were kept in a greenhouse under ambient temperature. Within 21 days, all fungal-inoculated saplings displayed complete canopy wilt, typical of laurel wilt. R. lauricola was later recovered from all four infected plants, completing Koch's postulates. To determine if the vector can reproduce in pondspice, infected stem sections were placed in a plastic rearing box indoors at room temperature, and both callow and mature adult female X. glabratus emerged in October and November 2008. Although laurel wilt has been previously observed on pondspice in South Carolina and Georgia (1), this is the first confirmation of the disease on pondspice in Florida and the first confirmation of the vector from stem material of this host. References: (1) S. W. Fraedrich et al. Plant Dis. 92:215, 2008. (2) T. C. Harrington et al. Mycotaxon 104:399, 2008. (3) M. A. Innis et al. PCR Protocols, A Guide to Methods and Applications. Academic Press. San Diego, CA, 1990. (4) J. A. Surdick and A. M. Jenkins. Pondspice (Litsea aestivalis) Population Status and Response to Laurel Wilt Disease in Northeast Florida. Florida Natural Areas Inventory, Tallahassee, FL, 2009.

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First Report of Laurel Wilt Disease Caused by Raffaelea lauricola on Camphor in Florida and Georgia

Plant Disease ◽

10.1094/pdis-93-2-0198b ◽

2009 ◽

Vol 93 (2) ◽

pp. 198-198 ◽

Cited By ~ 28

Author(s):

J. A. Smith ◽

L. Mount ◽

A. E. Mayfield ◽

C. A. Bates ◽

W. A. Lamborn ◽

...

Keyword(s):

South Carolina ◽

Resistance Mechanisms ◽

Small Subunit ◽

Residential Areas ◽

Laurel Wilt ◽

Xyleborus Glabratus ◽

Raffaelea Lauricola ◽

Redbay Ambrosia Beetle ◽

Persea Borbonia ◽

Branch Dieback

Laurel wilt is a recently described (1) vascular disease of redbay (Persea borbonia (L.) Spreng) and other plants in the family Lauraceae. The wilt is caused by Raffaelea lauricola, a fungus vectored by the nonnative redbay ambrosia beetle (Xyleborus glabratus Eichhoff) (1,2). Since 2003, laurel wilt has caused widespread mortality of redbay in Georgia, South Carolina, and Florida (1) and has recently been found on avocado in Florida (4). Since June of 2007, wilted shoots and branch dieback have been observed in several camphor trees (Cinnamomum camphora (L.) Sieb.) in residential areas of McIntosh and Glynn counties in Georgia and Baker County in Florida. Symptomatic camphor trees ranged from 4.5 to 12 m high and occurred in areas where redbay mortality due to laurel wilt has been frequently observed during the last 2 to 3 years. In some camphor trees, only the smaller branches (<2 cm in diameter) were wilting or dead, whereas in other trees (e.g., Baker County, Florida), the larger branches and substantial portions of the crown were also symptomatic. Rapid wilt that affects entire trees that is usually observed in redbay, has not been observed in camphor. Some camphor trees in residential areas of Jekyll Island, Georgia (Glynn County), where extensive wilt of redbay has occurred, have exhibited only localized wilt of some shoots or branches and other camphors remain asymptomatic. Removal of bark from wilted branch sections revealed black-to-brownish staining in the sapwood, characteristic of laurel wilt. Although no evidence of ambrosia beetles was observed on these samples, more extensive surveys are needed to determine the role of this vector in laurel wilt of camphor. Wood chips from symptomatic areas of branches were surface sterilized and plated on cycloheximide-streptomycin malt agar as previously described (1,4) and R. lauricola was routinely isolated. Small subunit (18S) sequences from rDNA were amplified by PCR and sequenced using primers NS1 and NS4 (3). BLASTn searches revealed homology to R. lauricola C2203 (GenBank Accession No. EU123076, 100% similarity, e-value of 0.0, and a total score of 1,886). The small subunit rDNA sequence for this isolate has been deposited into GenBank ( http://www.ncbi.nlm.nih.gov/Genbank/index.html ) and has been assigned Accession No. EU 853303. The presence of laurel wilt in camphor provides an opportunity to understand the pathogen distribution and possible resistance mechanisms in this host, which could have implications for efforts to remediate the impacts of the disease in redbay and other species in the Lauraceae 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) M. A. Innis et al. PCR Protocols, A Guide to Methods and Applications. Academic Press. San Diego, CA, 1990. (4) A. E. Mayfield, III et al. Plant Dis. 92:976, 2008.

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California Laurel Is Susceptible to Laurel Wilt Caused by Raffaelea lauricola

Plant Disease ◽

10.1094/pdis-92-10-1469a ◽

2008 ◽

Vol 92 (10) ◽

pp. 1469-1469 ◽

Cited By ~ 17

Author(s):

S. W. Fraedrich

Keyword(s):

South Carolina ◽

West Coast ◽

Persea Americana ◽

Malt Extract ◽

Natural Ecosystems ◽

The West ◽

Laurel Wilt ◽

Raffaelea Lauricola ◽

Redbay Ambrosia Beetle ◽

Branch Dieback

Extensive mortality of redbay (Persea borbonia (L.) Spreng.) has been observed in the southeastern United States since 2003. The mortality is due to laurel wilt caused by Raffaelea lauricola T. C. Harr., Fraedrich & Aghayeva, a fungal symbiont of the recently introduced redbay ambrosia beetle (RAB), Xyleborus glabratus Eichhoff (1,2). The wilt is known to affect other members of the Lauraceae including sassafras (Sassafras albidum (Nuttall) Nees) and avocado (Persea americana Mill.) (1,3). Two inoculation experiments were conducted to evaluate the susceptibility of California laurel (Umbellularia californica (Hook. & Arn.) Nutt.) to R. lauricola. Seedlings, averaging 73 cm high and 13 mm in diameter, were wounded with a drill bit (2.8 mm) to a depth of one-half the diameter of the stems. In each experiment, 10 seedlings were inoculated with one of two isolates of R. lauricola (five seedlings per isolate) obtained as previously described (1) from wilted redbays on Hilton Head Island, South Carolina and Fort George Island, Florida. In the first experiment, seedlings were inoculated with spore suspensions (0.1 ml) ranging from 1.9 to 2.3 × 106 spores/ml and produced as previously described (1). In the second experiment, seedlings were inoculated with mycelial plugs obtained from the edge of 10-day-old cultures growing on malt extract agar (MEA). Five seedlings in each experiment served as controls and were inoculated with sterile deionized water or plugs of sterile MEA. Inoculation points were wrapped with Parafilm M (Pechiney Plastic Packaging, Menasha, WI). Seedlings were grown in growth chambers (daytime temperature 26°C, nighttime 24°C, and a 15-h photoperiod) for 13 to 15 weeks. At the end of the first experiment, 7 of 10 seedlings inoculated with R. lauricola exhibited wilt that appeared as a dieback of a few to the majority of branches. Nine of the ten seedlings exhibited sapwood discoloration and the fungus was isolated from eight of these seedlings. At the end of the second experiment, 8 of 10 seedlings exhibited wilt that again appeared as a dieback of a few branches to most branches. All seedlings with wilt exhibited sapwood discoloration and the fungus was recovered from these seedlings. Two seedlings inoculated with R. lauricola exhibited no symptoms of disease and the fungus was not recovered. Control seedlings remained healthy in both experiments with no evidence of wilt or sapwood discoloration and R. lauricola was not isolated. These results indicate that California laurel is susceptible to laurel wilt caused by R. lauricola. Furthermore, the disease on California laurel may appear as a branch dieback affecting individual branches one at a time rather than a rapid wilt of the entire crown as is often observed in redbay (1). Currently, the RAB is not known to occur on the West Coast and it is also not known if this beetle is capable of attacking and producing brood on California laurel. Nonetheless, if the RAB and R. lauricola become established on the West Coast, laurel wilt could pose a serious threat to natural ecosystems as well as the avocado industry in California. References: (1) S. W. Fraedrich et al. Plant Dis. 92:215, 2008. (2) T. C. Harrington et al. Mycotaxon 104:399, 2008. (3) A. E. Mayfield, III et al. Plant Dis. 92:976, 2008.

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First Report of Raffaelea canadensis Causing Laurel Wilt Disease Symptoms on Avocado in California

Plant Disease ◽

10.1094/pdis-03-11-0203 ◽

2011 ◽

Vol 95 (9) ◽

pp. 1189-1189 ◽

Cited By ~ 3

Author(s):

A. Eskalen ◽

V. McDonald

Keyword(s):

Wilt Disease ◽

Persea Americana ◽

Ambrosia Beetle ◽

Necrotic Tissue ◽

Laurel Wilt ◽

Disease Symptoms ◽

First Report ◽

Raffaelea Lauricola ◽

Laurel Wilt Disease ◽

Redbay Ambrosia Beetle

Laurel wilt disease is a newly described vascular disease of redbay (Persea borbonia (L.) Spreng.) and other members of the Lauraceae family in the southeastern United States. The disease, caused by the fungus Raffaelea lauricola and vectored by a nonnative redbay ambrosia beetle (Xyleborus glabratus Eichhoff), was first detected in Georgia in 2003 (1). Laurel wilt has caused extensive mortality of native redbay in Georgia, Florida, South Carolina, and recently, Mississippi. The avocado, Persea americana, is in the Lauraceae family and has been shown to be susceptible to the laurel wilt pathogen in Florida (3). The potential spread of this pathogen into California is of concern to the commercial avocado industry. During a survey in 2010 in a Temecula, CA avocado orchard with a history of root rot, an avocado (cv. Hass) tree with a diameter at breast height (DBH) of 45 cm was found to be showing typical laurel wilt disease symptoms. The crown was approximately 80% declined and exhibited dead branches without leaves. Black-to-brown discolored sapwood under the bark and many ambrosia beetle exit holes within 1 to 1.5 m up the bole were also observed. A Raffaelea sp. was consistently isolated from symptomatic branch tissue (from two different branches) plated onto cycloheximide-streptomycin malt agar (2) and incubated at room temperature for 2 weeks. Small subunit (18S) sequences of rDNA (approximately 1,150 bp) of three Raffaelea isolates were amplified using primers NS1 and NS4 (4) and deposited into GenBank under Accession Nos. JF327799, JF327800, and JF327801. A BLASTn search of all three sequences revealed high homology (98, 99, and 98% respectively) to an accession of R. canadensis associated with a species of ambrosia beetle (GenBank Accession No. AY858665). Pathogenicity testing was conducted by pipetting 50 μl of a 105 conidia per ml suspension of each of two isolates (UCR1080 and UCR1081) into five 2-mm-diameter holes on each of two avocado (cv. Hass) trees (10 to 15 cm DBH). Isolate UCR1080 was inoculated into three holes on Tree 1 and two holes on Tree 2. Isolate UCR1081 was inoculated into two holes on Tree 1 and three holes on Tree 2. Sterile water was used as a control in five 2-mm-diameter holes on each tree. Holes were drilled to the cambium within 1 to 2 m up the bole using a 0.157-cm electric drill. Four months later, phloem tissue was peeled back, lesion lengths were measured, and pieces of necrotic tissue were cultured for completion of Koch's postulates. R. canadensis was consistently reisolated from necrotic tissue but not from control treatments. To our knowledge, this is the first report of R. canadensis associated with wilt on avocado in California. R. canadensis is closely related to R. lauricola, however, its impact on the California avocado industry is unknown at this time. References: (1) S. W. Fraedrich et al. Plant Dis. 92:215, 2008. (2) T. C. Harrington et al. Mycotaxon 111:337, 2010. (3) A. E. Mayfield et al. Plant Dis. 92:976, 2008. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990.

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

Plant Disease ◽

10.1094/pdis-94-5-0634c ◽

2010 ◽

Vol 94 (5) ◽

pp. 634-634 ◽

Cited By ~ 13

Author(s):

J. J. Riggins ◽

M. Hughes ◽

J. A. Smith ◽

A. E. Mayfield ◽

B. Layton ◽

...

Keyword(s):

South Carolina ◽

Atlantic Coast ◽

Signs And Symptoms ◽

Wilt Disease ◽

Laurel Wilt ◽

Jackson County ◽

Stem Wood ◽

Raffaelea Lauricola ◽

Pascagoula River ◽

Redbay Ambrosia Beetle

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.

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Entomopathogenic fungi as biological control agents for the vector of the laurel wilt disease, the redbay ambrosia beetle, Xyleborus glabratus (Coleoptera: Curculionidae)

Biological Control ◽

10.1016/j.biocontrol.2014.10.009 ◽

2015 ◽

Vol 81 ◽

pp. 44-50 ◽

Cited By ~ 33

Author(s):

D. Carrillo ◽

C.A. Dunlap ◽

P.B. Avery ◽

J. Navarrete ◽

R.E. Duncan ◽

...

Keyword(s):

Biological Control ◽

Entomopathogenic Fungi ◽

Wilt Disease ◽

Ambrosia Beetle ◽

Biological Control Agents ◽

Laurel Wilt ◽

Xyleborus Glabratus ◽

Laurel Wilt Disease ◽

Redbay Ambrosia Beetle

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Potential Economic Impact of Laurel Wilt Disease on the Florida Avocado Industry

HortTechnology ◽

10.21273/horttech.20.1.234 ◽

2010 ◽

Vol 20 (1) ◽

pp. 234-238 ◽

Cited By ~ 32

Author(s):

Edward A. Evans ◽

Jonathan Crane ◽

Alan Hodges ◽

Jason L. Osborne

Keyword(s):

Regional Economy ◽

Impact Analysis ◽

Control Measure ◽

Wilt Disease ◽

Persea Americana ◽

Economic Losses ◽

Laurel Wilt ◽

Raffaelea Lauricola ◽

Laurel Wilt Disease ◽

The Impact

This article describes and provides preliminary estimates of the potential economic losses that could result from an incursion of the recently discovered exotic laurel wilt disease caused by Raffaelea lauricola, in the main avocado (Persea americana) growing area of Florida. Estimates are provided for the direct losses as well as the indirect or “spillover” losses that could occur across the rest of the regional economy. The Impact Analysis for Planning (IMPLAN) input-output multipliers were used in assessing the regional impacts. The results of the investigation indicate that the direct loss to the industry in terms of lost sales, property damage, and increased management costs could range from $356 million in a do-nothing situation to about $183 million if damage control measure were 50% effective. If increased management costs and decreased property values are ignored, the adverse impact on the regional economy could range from $54 million in a do-nothing situation to $27 million in a case in which the treatments result in only a 50% reduction in avocado production.

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First Report of Laurel Wilt Disease Caused by a Raffaelea sp. on Avocado in Florida

Plant Disease ◽

10.1094/pdis-92-6-0976a ◽

2008 ◽

Vol 92 (6) ◽

pp. 976-976 ◽

Cited By ~ 35

Author(s):

A. E. Mayfield ◽

J. A. Smith ◽

M. Hughes ◽

T. J. Dreaden

Keyword(s):

South Carolina ◽

Small Subunit ◽

Persea Americana ◽

Ambrosia Beetle ◽

Sodium Hypochlorite Solution ◽

Potential Threat ◽

Laurel Wilt ◽

Xyleborus Glabratus ◽

Residential Neighborhood ◽

Redbay Ambrosia Beetle

Laurel wilt is a vascular disease of redbay (Persea borbonia (L.) Spreng.) and other plants in the family Lauraceae in the southeastern United States. It is caused by a fungus (Raffaelea sp.) that is vectored by a non-native insect of Asian origin, the redbay ambrosia beetle (Xyleborus glabratus Eichhoff) (1). Since the initial detection of the redbay ambrosia beetle near Savannah, GA in 2002, laurel wilt has caused widespread mortality of redbay in Georgia, South Carolina, and Florida (1). In September 2007, an avocado (Persea americana Mill.) tree planted approximately 10 years earlier in a residential neighborhood in Jacksonville, FL was discovered to be infected with laurel wilt. The crown was in various stages of decline, including upper branches that were dead and leafless, those with wilted and drooping foliage, and those with healthy foliage. Removal of bark from wilted branch sections revealed black-to-brown streaks of discoloration in the sapwood and a few ambrosia beetle holes from which the discoloration extended into the adjacent wood. A Raffaelea sp. was isolated from discolored wood samples by surface sterilizing wood chips by submersion in a 5% sodium hypochlorite solution for 30 s and plating them on cycloheximide streptomycin malt agar (2). Small subunit (18S) sequences from the rDNA were amplified by PCR and sequenced with primers NS1 and NS4 (3). BLASTn searches revealed homology to Raffaelea sp. C2203 (GenBank Accession No. EU123076, 100% similarity, e-value of 0.0, and a total score of 1,886), which is known to be the causal agent of laurel wilt (1). The small-subunit rDNA sequence for this isolate has been deposited into GenBank and has been assigned accession No. EU257806. Pathogenicity of the laurel wilt pathogen on Persea spp. in growth chamber trials has been previously demonstrated (1). Laurel wilt is of concern to the commercial avocado industry and is a potential threat to the Lauraceae elsewhere in the Americas. References: (1) S. W. Fraedrich et al. Plant Dis. 92:215, 2008. (2) T. C. Harrington. Mycologia 73:1123, 1981. (3) T. J. White et al. Page 315 in: PCR Protocols, a Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, CA, 1990.

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First Report of Laurel Wilt Caused by Raffaelea lauricola on Sassafras in Mississippi

Plant Disease ◽

10.1094/pdis-05-11-0446 ◽

2011 ◽

Vol 95 (11) ◽

pp. 1479-1479 ◽

Cited By ~ 10

Author(s):

J. J. Riggins ◽

S. W. Fraedrich ◽

T. C. Harrington

Keyword(s):

United States ◽

South Carolina ◽

The United States ◽

Ambrosia Beetle ◽

Malt Extract ◽

Laurel Wilt ◽

First Report ◽

Raffaelea Lauricola ◽

Redbay Ambrosia Beetle ◽

Soil Interface

Laurel wilt is caused by the fungus Raffaelea lauricola T.C. Harrin., Aghayeva & Fraedrich and is lethal to redbay (Persea borbonia (L.) Spreng.), sassafras (Sassafras albidum (Nutt.) Nees), and other species in the Lauraceae (1). The fungus is carried by the redbay ambrosia beetle (Xyleborus glabratus Eichh.), which is native to Asia. After being discovered in Georgia in 2002 (1), X. glabratus and R. lauricola have spread rapidly, causing extensive redbay mortality in South Carolina, Georgia, Florida, and Mississippi (1,4). The disease has also been confirmed on sassafras in Florida, South Carolina (1), and Georgia. Questions remain as to whether laurel wilt will continue to spread on sassafras, which often occurs as scattered trees in the eastern United States. In June 2010, a homeowner reported that a sassafras tree north of Van Cleave, MS (30.668°N, 88.686°W) had begun wilting in late May. This landscape tree had three 10-m high stems (~20 cm in diameter at breast height). Dark staining in the xylem was observed around the entire circumference of all three stems and nearly all leaves were bronze colored and wilted. No ambrosia beetle tunnels were observed in the stems. No other symptomatic Lauraceae were encountered in the wooded area within 300 m. The nearest known location with laurel wilt on redbay was ~15 km away (4). A Lindgren funnel trap baited with manuka oil (2) was placed at the site in June and monitored biweekly until November, but no X. glabratus adults were captured. Chips from discolored xylem of the sassafras were surface sterilized, plated on cycloheximide-streptomycin malt agar, and R. lauricola was readily isolated (1). Identity of the fungus (isolate C2792 in collection of T. Harrington) was confirmed by using partial sequences of the 28S rDNA (3). The sassafras sequence was identical to that of all known sequences of R. lauricola in the United States, including GenBank No. EU123076 (the holotype isolate from redbay). To confirm pathogenicity, isolate C2792 was grown on malt extract agar and three redbay (average: 141 cm high and 12 mm in diameter at soil interface) and three sassafras (average: 170 cm high and 17 mm in diameter at soil interface) potted plants were wound inoculated with 0.2 ml of a spore suspension (4.9 × 106 conidia/ml) (1). Three control plants of each species were inoculated with sterile deionized water. After 8 weeks in a growth chamber at 26°C, all inoculated redbay and sassafras plants exhibited xylem discoloration above and below the inoculation point, two of the redbay and two of the sassafras had died, and the other plant of each species exhibited partial wilt (the main terminal or one or more branches). All control plants were asymptomatic. R. lauricola was reisolated from all inoculated symptomatic plants but not from controls. To our knowledge, this is the first report of laurel wilt on sassafras in Mississippi. Both redbay (4) and sassafras appear to be highly susceptible to the disease as it moves westward. Sassafras is less attractive than redbay to X. glabratus and it was thought that this might contribute to slowing the spread of laurel wilt once outside the range of redbay (2). Nonetheless, our observations confirm that sassafras can be infected where laurel wilt on redbay is not in the immediate vicinity. References: (1) S. W. Fraedrich et al. Plant Dis. 92:215, 2008. (2) J. L. Hanula et al. J. Econ. Entomol. 101:1276, 2008. (3) T. C. Harrington et al. Mycotaxon 111:337, 2010. (4) J. J. Riggins et al. Plant Dis. 94:634, 2010.

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