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

Plant Disease ◽  
2008 ◽  
Vol 92 (6) ◽  
pp. 976-976 ◽  
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.

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

Plant Disease ◽  
2009 ◽  
Vol 93 (2) ◽  
pp. 198-198 ◽  
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.

scholarly journals Quantification of Propagules of the Laurel Wilt Fungus and Other Mycangial Fungi from the Redbay Ambrosia Beetle, Xyleborus glabratus

2010 ◽  
Vol 100 (10) ◽  
pp. 1118-1123 ◽  
Author(s):  
T. C. Harrington ◽  
S. W. Fraedrich
Keyword(s):  
South Carolina ◽  
Southeastern United States ◽  
Ambrosia Beetle ◽  
Fungal Symbiont ◽  
Laurel Wilt ◽  
Xyleborus Glabratus ◽  
Raffaelea Lauricola ◽  
Redbay Ambrosia Beetle ◽  
Yeast Phase ◽  
Isolated Species

The laurel wilt pathogen, Raffaelea lauricola, is a fungal symbiont of the redbay ambrosia beetle, Xyleborus glabratus, which is native to Asia and was believed to have brought R. lauricola with it to the southeastern United States. Individual X. glabratus beetles from six populations in South Carolina and Georgia were individually macerated in glass tissue grinders and serially diluted to quantify the CFU of fungal symbionts. Six species of Raffaelea were isolated, with up to four species from an individual adult beetle. The Raffaelea spp. were apparently within the protected, paired, mandibular mycangia because they were as numerous in heads as in whole beetles, and surface-sterilized heads or whole bodies yielded as many or more CFU as did nonsterilized heads or whole beetles. R. lauricola was isolated from 40 of the 41 beetles sampled, and it was isolated in the highest numbers, up to 30,000 CFU/beetle. Depending on the population sampled, R. subalba or R. ellipticospora was the next most frequently isolated species. R. arxii, R. fusca, and R. subfusca were only occasionally isolated. The laurel wilt pathogen apparently grows in a yeast phase within the mycangia in competition with other Raffaelea spp.

scholarly journals California Laurel Is Susceptible to Laurel Wilt Caused by Raffaelea lauricola

Plant Disease ◽  
2008 ◽  
Vol 92 (10) ◽  
pp. 1469-1469 ◽  
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.

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

Plant Disease ◽  
2011 ◽  
Vol 95 (11) ◽  
pp. 1479-1479 ◽  
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.

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

Plant Disease ◽  
2011 ◽  
Vol 95 (12) ◽  
pp. 1589-1589 ◽  
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.

Isolations from the redbay ambrosia beetle, Xyleborus glabratus, confirm that the laurel wilt pathogen, Raffaelea lauricola, originated in Asia

Mycologia ◽  
2011 ◽  
Vol 103 (5) ◽  
pp. 1028-1036 ◽  
Author(s):  
Thomas C. Harrington ◽  
Hye Young Yun ◽  
Sheng-Shan Lu ◽  
Hideaki Goto ◽  
Dilzara N. Aghayeva ◽  
...  
Keyword(s):  
Ambrosia Beetle ◽  
Laurel Wilt ◽  
Xyleborus Glabratus ◽  
Raffaelea Lauricola ◽  
Redbay Ambrosia Beetle

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

Plant Disease ◽  
2011 ◽  
Vol 95 (12) ◽  
pp. 1588-1588 ◽  
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.

Evaluation of repellents for the redbay ambrosia beetle,Xyleborus glabratus, vector of the laurel wilt pathogen

2017 ◽  
Vol 141 (8) ◽  
pp. 653-664 ◽  
Author(s):  
M. A. Hughes ◽  
X. Martini ◽  
E. Kuhns ◽  
J. Colee ◽  
A. Mafra-Neto ◽  
...  
Keyword(s):  
Ambrosia Beetle ◽  
Laurel Wilt ◽  
Xyleborus Glabratus ◽  
Redbay Ambrosia Beetle

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

Plant Disease ◽  
2011 ◽  
Vol 95 (9) ◽  
pp. 1189-1189 ◽  
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.

Sign in / Sign up

Export Citation Format

Share Document