First Report of Laurel Wilt, Caused by Raffaelea lauricola, on Sassafras (Sassafras albidum) in Alabama

Laurel wilt, caused by Raffaelea lauricola, a fungal symbiont of the redbay ambrosia beetle, Xyleborus glabratus, is responsible for extensive mortality of native redbays (Persea borbonia and P. palustris) in the coastal plains of the southeastern United States (1). The wilt also affects the more widespread sassafras, Sassafras albidum, particularly in areas where diseased redbays are common and populations of X. glabratus are high. Because sassafras stems were thought to lack chemicals that are attractive to the beetle, and sassafras tends to be widely scattered in forests, it was believed that the advance of the laurel wilt epidemic front might slow once it reached the edge of the natural range of redbay, which is restricted to the coastal plains of the Gulf and Atlantic Coasts (2). In July and August of 2011, wilt-like symptoms (i.e., wilted and dead leaves, and streaks of black discoloration in the xylem) were observed on 1 to 10 sassafras trees (15 to 23 cm diameter; 6 to 9 m height) at each of three locations, which were approximately 6 km from one another in Marengo Co., Alabama. Samples of the discolored wood from five trees were plated on malt agar amended with cycloheximide and streptomycin (CSMA), and a fungus morphologically identical to R. lauricola was isolated from each tree (1). For confirmation, a portion of the large subunit (28S) of the rDNA region of three of the isolates was sequenced (3); in each case, the sequence matched exactly that of other isolates of R. lauricola (EU123077) from the United States. Symptomatic trees were found at all three sites when revisited in April 2012, and approximately 20 sassafras trees in various stages of wilt were observed at one location, where only one diseased tree had been noted in 2011. Bolts were cut from the main stem of a symptomatic tree, and eggs, larvae, and adults of X. glabratus were commonly found in tunnels, and R. lauricola was isolated from the discolored xylem. Three container-grown sassafras saplings (mean height 193 cm, mean diameter 2.1 cm at groundline) were inoculated as previously described (1) with conidia (~600,000) from an isolate of R. lauricola. Three additional sassafras saplings were inoculated with sterile, deionized water, and all plants were placed in a growth chamber at 25°C with a 15-h photoperiod. Inoculated plants began to exhibit wilt symptoms within 14 days, and at 30 days all inoculated plants were dead and xylem discoloration was observed. Control plants appeared healthy and did not exhibit xylem discoloration. Pieces of sapwood from 15 cm above the inoculation points were plated on CSMA, and R. lauricola was recovered from all wilted plants but not from control plants. This is the first record of laurel wilt in Alabama and is significant because the disease appears to be spreading on sassafras in an area where redbays have not been recorded (see http://www.floraofalabama.org ). The nearest previously documented case of laurel wilt is on redbay and sassafras in Jackson Co., Mississippi (4), approximately 160 km to the south. The exact source of the introduction of X. glabratus and R. lauricola into Marengo Co. is not known. The vector may have been transported into the area with storms, moved with infested firewood, or shipped with infested timber by companies that supply mills in the area. References: (1) S. Fraedrich et al. Plant Dis. 92:215, 2008. (2) J. Hanula et al. Econ. Ent. 101:1276, 2008. (3) T. Harrington et al. Mycotaxon 111:337, 2010. (4) J. Riggins et al. Plant Dis. 95:1479, 2011.

Download Full-text

Laurel Wilt: Current and Potential Impacts and Possibilities for Prevention and Management

Forests ◽

10.3390/f12020181 ◽

2021 ◽

Vol 12 (2) ◽

pp. 181

Author(s):

Rabiu O. Olatinwo ◽

Stephen W. Fraedrich ◽

Albert E. Mayfield

Keyword(s):

United States ◽

Tree Mortality ◽

The United States ◽

Persea Americana ◽

Laurel Wilt ◽

Important Species ◽

Invasive Insects ◽

Raffaelea Lauricola ◽

Redbay Ambrosia Beetle ◽

The Impact

In recent years, outbreaks of nonnative invasive insects and pathogens have caused significant levels of tree mortality and disturbance in various forest ecosystems throughout the United States. Laurel wilt, caused by the pathogen Raffaelea lauricola (T.C. Harr., Fraedrich and Aghayeva) and the primary vector, the redbay ambrosia beetle (Xyleborus glabratus Eichhoff), is a nonnative pest-disease complex first reported in the southeastern United States in 2002. Since then, it has spread across eleven southeastern states to date, killing hundreds of millions of trees in the plant family Lauraceae. Here, we examine the impacts of laurel wilt on selected vulnerable Lauraceae in the United States and discuss management methods for limiting geographic expansion and reducing impact. Although about 13 species belonging to the Lauraceae are indigenous to the United States, the highly susceptible members of the family to laurel wilt are the large tree species including redbay (Persea borbonia (L.) Spreng) and sassafras (Sassafras albidum (Nutt.) Nees), with a significant economic impact on the commercial production of avocado (Persea americana Mill.), an important species native to Central America grown in the United States. Preventing new introductions and mitigating the impact of previously introduced nonnative species are critically important to decelerate losses of forest habitat, genetic diversity, and overall ecosystem value.

Download Full-text

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.

Download Full-text

An Acaromyces Species Associated with Bark Beetles from Southern Pine Has Inhibitory Properties Against Raffaelea lauricola, the Causal Pathogen of Laurel Wilt Disease of Redbay

Plant Health Progress ◽

10.1094/php-06-19-0039-rs ◽

2019 ◽

Vol 20 (4) ◽

pp. 220-228 ◽

Cited By ~ 1

Author(s):

Rabiu Olatinwo ◽

Stephen Fraedrich

Keyword(s):

Secondary Metabolites ◽

Loblolly Pine ◽

Spore Germination ◽

Bark Beetles ◽

Dna Analysis ◽

The United States ◽

Malt Extract ◽

Laurel Wilt ◽

Raffaelea Lauricola ◽

Redbay Ambrosia Beetle

Laurel wilt is a destructive disease of redbay (Persea borbonia) and other species in the laurel family (Lauraceae). It is caused by Raffaelea lauricola, a fungal symbiont of the redbay ambrosia beetle, Xyleborus glabratus (Coleoptera: Curculionidae), cointroduced into the United States around 2002. During assessments of fungi associated with bark beetles from loblolly pine, an unknown fungus was isolated that appeared to have broad-spectrum antifungal activities. In this study, we identified the unknown fungus and determined the inhibitory effect of its secondary metabolites on R. lauricola. DNA analysis identified the fungus as Acaromyces ingoldii (GenBank accession no. EU770231). Secondary metabolites produced by the A. ingoldii completely inhibited R. lauricola mycelial growth on potato dextrose agar (PDA) plates preinoculated with A. ingoldii and reduced R. lauricola growth significantly on malt extract agar plates preinoculated with A. ingoldii. R. lauricola isolates inoculated on PDA plates 7 days after A. ingoldii were completely inhibited with no growth or spore germination. Direct evaluation of A. ingoldii crude extract on R. lauricola spores in a multi-well culture plate assay showed inhibition of spore germination at 10% and higher concentrations. Secondary metabolites from A. ingoldii could be potentially useful in managing the future spread of laurel wilt.

Download Full-text

First Report of Gulf Licaria, Licaria trianda, as a Suscept of Laurel Wilt

Plant Disease ◽

10.1094/pdis-01-13-0027-pdn ◽

2013 ◽

Vol 97 (9) ◽

pp. 1248-1248 ◽

Cited By ~ 12

Author(s):

R. C. Ploetz ◽

J. Konkol

Keyword(s):

United States ◽

Rare Plants ◽

South Florida ◽

Dade County ◽

Water Control ◽

Laurel Wilt ◽

Plant Family ◽

Centraalbureau Voor ◽

Raffaelea Lauricola ◽

Redbay Ambrosia Beetle

Gulf licaria, Licaria trianda (Sw.) Kosterm., is a federally endangered member of the Lauraceae plant family in Miami-Dade County, Florida. It was never common in the area, and urban development has extirpated it from most of its former range; as of 2001, fewer than 10 trees remained in a single, remnant habitat in the continental United States, Simpson Park (25°45′31″N, 80°11′46″W) (2). Laurel wilt, caused by the fungus Raffaelea lauricola T. C. Harr., Fraedrich & Aghayeva, has recently devastated members of the Lauraceae in the southeastern United States, most notably redbay, Persea borbonia (1). As R. lauricola and its vector, the redbay ambrosia beetle Xyleborus glabratus, have spread in the region, an increasing number of taxa in this plant family have been affected by this disease (1). In 2012, seedlings of gulf licaria and redbay were obtained from local nurseries; they were grown in 30 liter pots, 1.3 m tall, had stems 3 cm in diameter 20 cm above the soil line, and were maintained with standard watering and fertilization practices. In two pathogenicity experiments on July 6 and September 25, 2012, three plants each of gulf licaria and redbay were inoculated with an isolate of R. lauricola, RL4, as described in previous experiments (3), and two plants each were mock inoculated (water control). RL4 is deposited as CBS 127349 at the Centraalbureau voor Schimmelcultures (CBS Fungal Biodiversity Centre, Utrecht, The Netherlands), and a SSU rDNA sequence for it is deposited in GenBank under Accession No. HM446155. Beginning 2 weeks after inoculation, plants were rated on a weekly basis for the development of external symptoms, on a subjective 1 (no symptoms) to 10 (dead) scale (3). After 5 weeks, inoculated plants of redbay in each experiment (positive control) had died after first developing symptoms of wilt and necrotic foliage that are typical for this disease (1). In contrast, inoculated plants of gulf licaria developed severe symptoms by the time experiments were terminated 6 and 11 weeks after inoculation; chlorosis developed on some of the leaves of all plants and these eventually abscised (mean external severities of 7.3 and 6.5, respectively), but plants did not die. Brown to greyish discoloration of sapwood developed in all inoculated plants, and the pathogen was recovered from symptomatic sapwood on CSMA (3). No symptoms developed on mock inoculated plants and the pathogen was not recovered from them. It is concluded that gulf licaria is susceptible to laurel wilt, but that it is apparently less susceptible than redbay. Whether X. glabratus is attracted to, or will bore into, gulf licaria is not known, but will play a significant role in the extent to which this rare tree is affected by laurel wilt. References: (1) S. W. Fraedrich et al. Plant Dis. 92:215, 2008. (2) G. D. Gann et al. Rare Plants of South Florida: Their History, Conservation, and Restoration. Institute for Regional Conservation, Miami, 2002. (3) R. C. Ploetz et al. Plant Pathol. 61:801, 2012.

Download Full-text

Laurel Wilt, Caused by Raffaelea lauricola, is Confirmed in Miami-Dade County, Center of Florida's Commercial Avocado Production

Plant Disease ◽

10.1094/pdis-08-11-0633 ◽

2011 ◽

Vol 95 (12) ◽

pp. 1589-1589 ◽

Cited By ~ 21

Author(s):

R. C. Ploetz ◽

J. E. Peña ◽

J. A. Smith ◽

T. J. Dreaden ◽

J. H. Crane ◽

...

Keyword(s):

United States ◽

Pcr Primers ◽

The United States ◽

Small Subunit ◽

Rapid Identification ◽

Persea Americana ◽

Dade County ◽

Laurel Wilt ◽

Xyleborus Glabratus ◽

Raffaelea Lauricola

Laurel wilt, caused by Raffaelea lauricola, threatens native and nonnative species in the Lauraceae in the southeastern United States, including the important commercial crop, avocado, Persea americana (2,4). Although the pathogen's vector, Xyleborus glabratus, was detected in Miami-Dade County, FL in January 2010, laurel wilt had not been reported (4). In February 2011, symptoms of the disease were observed on native swampbay, P. palustris, in Miami-Dade County (25°72′N, 80°48′W). Externally, foliage was brown, necrotic, and did not abscise; internally, sapwood was streaked with dark gray-to-bluish discoloration; and, in dead trees, holes of natal galleries of the vector from which columns of frass were attached were evident. On a semiselective medium for R. lauricola, a fungus with the pathogen's phenotype was isolated from symptomatic sapwood. Colonies were slow growing, light cream in color, with dendritic, closely appressed mycelium and often a slimy surface. A representative strain of the fungus was further identified with PCR primers for diagnostic small subunit (SSU) rDNA (1) and its SSU sequence (100% match, GenBank Accession No. JN578863). In each of two experiments, plants of ‘Simmonds’ avocado, the most important cultivar in Florida, were inoculated with three strains of the fungus, as described previously (3). Symptoms of laurel wilt developed in all inoculated plants and the fungus was recovered from each. After aerial and further ground surveys, additional symptomatic swampbay trees, some of which had defoliated, were detected in the vicinity of the original site. Since swampbay defoliates only a year or more after symptoms develop (4), the 2010 detection of X. glabratus may have coincided with an undetected presence of the disease. As of July 2011, a 6-km-diameter disease focus was evident in the area, the southernmost edge of which is 5 km from the nearest commercial avocado orchard. In August 2011, a dooryard avocado tree immediately north of the above focus was affected by laurel wilt, and an SSU sequence confirmed the involvement of R. lauricola (GenBank Accession No. JN613280). The outbreak of laurel wilt in Miami-Dade County represents a 150 km southerly jump in the distribution of this disease in the United States ( http://www.fs.fed.us/r8/foresthealth/laurelwilt/dist_map.shtml ) and is the first time this disease has been found in close proximity to Florida's primary commercial avocado production area. Approximately 98% of the state's commercial avocados, worth nearly $54 million per year, are produced in Miami-Dade County. Since effective fungicidal and insecticidal measures have not been developed for large, fruit-bearing trees, mitigation efforts will focus on the rapid identification and destruction of infected trees (3,4). References: (1) T. J. Dreaden et al. Phytopathology 98:S48, 2008. (2) S. W. Fraedrich et al. Plant Dis. 92:215, 2008. (3) R. C. Ploetz et al. Plant Dis. 95:977, 2011. (4) R. C. Ploetz et al. Recovery Plan for Laurel Wilt of Avocado. National Plant Disease Recovery System, USDA, ARS, 2011.

Download Full-text

Redbay Survival Eleven Years after Infection with an Exotic Disease on St. Catherines Island, Georgia, USA

Environment and Natural Resources Research ◽

10.5539/enrr.v6n1p27 ◽

2015 ◽

Vol 6 (1) ◽

pp. 27 ◽

Cited By ~ 3

Author(s):

C. Ken Smith ◽

Elise Landreaux ◽

Hali Steinmann ◽

Deborah McGrath ◽

Christa Hayes ◽

...

Keyword(s):

United States ◽

Land Use ◽

Post Infection ◽

Vascular System ◽

The United States ◽

Ambrosia Beetle ◽

Old Field ◽

Laurel Wilt ◽

Raffaelea Lauricola ◽

Maritime Forest

Introduced to the United States in 2002, laurel wilt (Raffaelea lauricola) is a fungus that causes life threatening defensive responses in the vascular system of trees within the Lauraceae family, and it is introduced to the tree by the Asian ambrosia beetle (Xyleborus glabratus). Redbay (Persea borbonia) is the preferred host species within the US coastal plains and maritime forests, and it has experienced rapid mortality throughout its range in the southeastern United States since the introduction of the ambrosia beetle and associated fungus. In this study, we inventoried all dead and live redbay trees from replicated transects inside a maritime forest, a successional old-field forest (both located on the island’s Pleistocene core), and a Holocene hammock to examine the role of soils, prior land use and landscape position on redbay survival eleven years after the introduction of the exotic beetle and fungus on the island. Results indicated that the maritime forest had a significantly higher number of redbay trees prior to infection compared to the hammock or old-field sites. Eleven years post-infection, all three sites had similar densities of redbay trees and the surviving trees had similar diameter distributions among the three sites. Soils under the maritime forest had significantly higher phosphorous (P) and pH concentrations, and the Holocene hammock had a higher water table compared to the sites on the Pleistocene core. Almost all living trees at each site had signs of invertebrate herbivory and twig borer damage. Prior land use history and soils affected redbay densities before laurel wilt infection, but eleven years post-infection, all three site types had similar redbay densities, diameters, basal areas, and levels of herbivory and surviving trees did not demonstrate signs of photosynthetic stress.

Download Full-text

First Report of Laurel Wilt Disease Caused by Raffaelea lauricola on Spicebush in Louisiana

Plant Disease ◽

10.1094/pdis-11-20-2511-pdn ◽

2021 ◽

Author(s):

Rabiu Olatinwo ◽

Jaesoon Hwang ◽

Wood Johnson

Keyword(s):

United States ◽

Large Subunit ◽

Morphological Characteristics ◽

Wilt Disease ◽

Persea Americana ◽

Food Sources ◽

Laurel Wilt ◽

First Report ◽

Raffaelea Lauricola ◽

Laurel Wilt Disease

In the past two decades, laurel wilt disease has significantly affected members of the Lauraceae in the southeast United States, causing widespread mortality of native redbay (Persea borbonia (L.) Spreng), and incidence of infections in avocado (Persea americana Mill.), sassafras (Sassafras albidum L.) and swamp bay (Persea palustris [Raf.] Sarg.) (Fraedrich et al., 2008, 2015, Olatinwo, et al. 2019). Laurel wilt is a vascular disease caused by Raffaelea lauricola (T.C. Harr., Fraedrich & Aghayeva), a fungus vectored by a non-native ambrosia beetle Xyleborus glabratus Eichhoff (Fraedrich et al. 2008). In August 2020, we investigated the mortality of a spicebush shrub (Lindera benzoin L.) (3.8 cm diameter at root collar, two m height) located ca. 17 mi northeast of Colfax, Grant Parish, Louisiana (31.750263° N, -92.643694° W). Evaluation of the dead shrub revealed brown, persistent foliage, and black vascular discoloration of the sapwood, typical symptoms of laurel wilt (Fig. S1). Although, beetle holes were observed on the sapwood, no beetle was found in galleries at the time. In the laboratory, a fungus consistently isolated from surface-sterilized sapwood tissues plated on potato dextrose agar (PDA) was identified as R. lauricola based on the morphological characteristics of the isolate (i.e., mucoid growth, conidiophores, and oblong/ovoid shape conidia [Harrington et al. 2008]). The fungal isolate was denoted as SB1. The identity of the fungus was confirmed by positive PCR amplification of the large subunit ribosomal RNA gene region using species-specific primers; rab-lsu-rl_F: CCCTCGCGGCGTATTATAG and rab-lsu-rl_R: GCGGGGCTCCTACTCAAA (Olatinwo, unpublished). The sequence of the isolate SB1 (GenBank Accession no. MW207371) showed 100% homology to the R. lauricola strain CBS 127349 sequence (GenBank Accession no. MH877933). The pathogenicity of SB1 on spicebush was evaluated on four healthy shrubs (average: 1 m height and 40 mm in diameter) at the location from which the original detection was made. Stems of two spicebush shrubs were inoculated with SB1 agar plugs from a 14-day old culture on PDA, while plain PDA plugs were used on the remaining two shrubs as non-inoculated controls. Agar plugs were placed in 5 mm (0.2 in) diameter hole punched on the bark with cork-borer as described by Mayfield et al (2008). After six weeks, the R. lauricola inoculated shrubs were wilted with noticeable blackened tissue discoloration in the sapwood, while the control trees remained healthy (Fig. S2). Raffaelea lauricola was re-isolated from tissue of the two inoculated, symptomatic shrubs, but not from the control trees. The sequence of the re-isolated R. lauricola isolate, denoted as SB3 (GenBank Accession no. MW207372), showed 100% homology to the R. lauricola strain CBS 127349 and isolate SB1. This first documentation of laurel wilt on spicebush in Louisiana is significant because, spicebush berries, leaves, and twigs are food sources for forest animals, birds, and insects including whitetail deer and spicebush swallowtail (Papilio troilus L.). Since its first report on sassafras in 2014 (Fraedrich et al. 2015), laurel wilt has spread across Louisiana on sassafras and swamp bay (Olatinwo et al. 2019) and has been confirmed in14 parishes. This report shows the relentless nature of the disease, as the pathogen moves from one vulnerable host to the next, expanding into new locations and threatening forest ecosystems across the southern United States.

Download Full-text

Recovery Plan for Laurel Wilt of Avocado, Caused by Raffaelea lauricola

Plant Health Progress ◽

10.1094/php-12-16-0070-rp ◽

2017 ◽

Vol 18 (2) ◽

pp. 51-77 ◽

Cited By ~ 17

Author(s):

R. C. Ploetz ◽

M. A. Hughes ◽

P. E. Kendra ◽

S. W. Fraedrich ◽

D. Carrillo ◽

...

Keyword(s):

United States ◽

Crop Production ◽

Plant Disease ◽

Value Added ◽

The United States ◽

Persea Americana ◽

Laurel Wilt ◽

Recovery Plan ◽

Raffaelea Lauricola ◽

The Impact

Laurel wilt kills American members of the Lauraceae plant family, including avocado (Persea americana). The disease threatens commercial production in the United States and other countries, and currently impacts the avocado industry in Florida. As laurel wilt spreads, the National Germplasm Repository for avocado in Miami (USDA-ARS) and commercial and residential production in other states (e.g., California and Hawaii), U.S. protectorates (Puerto Rico), and other countries are at risk. In the United States, value-added production of avocado of more than $1.3 billion/year is threatened. This recovery plan was produced as part of the National Plant Disease Recovery System (NPDRS), called for in Homeland Security Presidential Directive Number 9 (HSPD-9) to insure that the tools, infrastructure, communication networks, and capacity required to mitigate the impact of high-consequence plant disease outbreaks are such that a reasonable level of crop production is maintained. It is intended to provide a brief primer on the disease, assess the status of critical recovery components, and identify disease management research, extension, and education needs.

Download Full-text

First Report of Laurel Wilt Caused by Raffaelea lauricola on Bay Laurel (Laurus nobilis) in the United States

Plant Disease ◽

10.1094/pdis-02-14-0194-pdn ◽

2014 ◽

Vol 98 (8) ◽

pp. 1159-1159 ◽

Cited By ~ 4

Author(s):

M. A. Hughes ◽

A. Black ◽

J. A. Smith

Keyword(s):

United States ◽

Fungal Growth ◽

The United States ◽

Ambrosia Beetle ◽

Growth Chamber ◽

Temperature Cycle ◽

Laurus Nobilis ◽

Laurel Wilt ◽

The Balkans ◽

Raffaelea Lauricola

Bay laurel (Laurus nobilis L.) is an economically important evergreen tree of the family Lauraceae. It is native to Asia Minor and the Balkans and was introduced into the United States for its ornamental and culinary uses (4). In September 2013, a 6-m-tall bay laurel in Gainesville, FL, attracted our attention because it had wilted leaves, discolored sapwood, and ambrosia beetle entrance holes, all symptoms of laurel wilt. In addition, the tree was growing close to an avocado that succumbed to the disease months earlier. In an effort to determine whether the laurel wilt pathogen (Raffaelea lauricola T.C. Harr., Fraedrich & Agaveya) was, indeed, involved in the decline of the tree of current interest, discolored sapwood was sectioned into 5-mm2 pieces, surface disinfested for 30 s in a 4% sodium hypochlorite solution, and plated onto CSMA media (1,2). Within 7 to 14 days, cream-colored, adpressed fungal growth typical of R. lauricola grew from the sapwood pieces (2). DNA was extracted from an isolate of a single conidium (PL1634) and a portion of the 18S rRNA gene was PCR-amplified with primers NS1/NS4, resulting in a 1,021-bp amplicon (GenBank Accession No. KF913344.1), with a BLASTn search revealing 100% homology to several R. lauricola isolates (3). To confirm pathogenicity, six bay laurel seedlings (0.5 m) and a silk bay (0.65 m) (Persea humilis, susceptible control) were wounded twice with a 0.5-mm-diameter drill bit. Then, 30 μl of a spore suspension of PL1634 (1.38 × 105 condia/plant) were introduced into the xylem by pipette and the wounds were wrapped in Parafilm (1). Negative controls consisted of a mock-inoculated (water) and non-inoculated bay laurel plus a mock-inoculated silk bay. Plants were placed in a growth chamber set to a 16/8 h (25/22°C) diurnal light/temperature cycle. After 60 days, all fungal-inoculated plants were completely wilted with dead leaves and subsequent necrosis of stems, while mock- and non-inoculated controls remained asymptomatic. Sapwood dissection revealed xylem discoloration similar to the original infected tree, and fungi morphologically similar to PL1634 were recovered from all inoculated plants upon isolation on CSMA media. Mock- and non-inoculated controls lacked vascular discoloration and fungal growth on media. In order to determine if the redbay ambrosia beetle, Xyleborus glabratus Eichoff (laurel wilt vector) could successfully reproduce in this host, symptomatic branches (7 cm in diameter) of L. nobilis with external evidence of ambrosia beetle attack (frass “toothpicks”) were placed in a plastic rearing box within a growth chamber (25°C). Within 4 weeks of incubation, dozens of immature and mature X. glabratus beetles emerged. This is the first record of Koch's postulates being completed for R. lauricola on L. nobilis and the ability of X. glabratus to infest and breed in its stems. This information may be of importance in the event of an introduction of X. glabratus and its fungal associate to Mediterranean areas where bay laurel is either growing wild or being cultivated as valuable commercial crop. 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., eds. PCR Protocols: A Guide to Methods and Applications. Academic Press. San Diego, CA, 1990. (4) A. O. Sari et al. New Forest 31:403, 2006.

Download Full-text

Genetic Variation in Native Populations of the Laurel Wilt Pathogen, Raffaelea lauricola, in Taiwan and Japan and the Introduced Population in the United States

Plant Disease ◽

10.1094/pdis-10-16-1517-re ◽

2017 ◽

Vol 101 (4) ◽

pp. 619-628 ◽

Cited By ~ 15

Author(s):

Caroline E. Wuest ◽

Thomas C. Harrington ◽

Stephen W. Fraedrich ◽

Hye-Young Yun ◽

Sheng-Shan Lu

Keyword(s):

United States ◽

Genetic Variation ◽

Mating Type ◽

Genetic Recombination ◽

Local Population ◽

The United States ◽

Extensive Study ◽

Laurel Wilt ◽

High Genetic Diversity ◽

Raffaelea Lauricola

Laurel wilt is a vascular wilt disease caused by Raffaelea lauricola, a mycangial symbiont of an ambrosia beetle, Xyleborus glabratus. The fungus and vector are native to Asia but were apparently introduced to the Savannah, GA, area 15 or more years ago. Laurel wilt has caused widespread mortality on redbay (Persea borbonia) and other members of the Lauraceae in the southeastern United States, and the pathogen and vector have spread as far as Texas. Although believed to be a single introduction, there has been no extensive study on genetic variation of R. lauricola populations that would suggest a genetic bottleneck in the United States. Ten isolates of R. lauricola from Japan, 55 from Taiwan, and 125 from the United States were analyzed with microsatellite and 28S rDNA markers, and with primers developed for two mating-type genes. The new primers identified isolates as either MAT1 or MAT2 mating types in roughly equal proportions in Taiwan and Japan, where there was also high genetic diversity within populations based on all the markers, suggesting that these populations may have cryptic sex. Aside from a local population near Savannah and a single isolate in Alabama that had unique microsatellite alleles, the U.S. population was genetically uniform and included only the MAT2 mating type, supporting the single introduction hypothesis. This study suggests the importance of preventing a second introduction of R. lauricola to the United States, which could introduce the opposite mating type and allow for genetic recombination.

Download Full-text