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.

Raffaelea lauricola (laurel wilt).

2021 ◽  
Author(s):  
Stephen Fraedrich
Keyword(s):  
Solid Wood ◽  
Persea Americana ◽  
South Florida ◽  
Florida Current ◽  
Natural Ecosystems ◽  
Laurel Wilt ◽  
Southeastern Usa ◽  
Raffaelea Lauricola ◽  
Redbay Ambrosia Beetle ◽  
The Usa

Abstract Laurel wilt is responsible for the death of hundreds of millions of redbay (Persea borbonia sensu lato) trees throughout the southeastern USA, and the disease is also having significant effects on other species such as sassafras (Sassafras albidum) in natural ecosystems and avocado (Persea americana) in commercial production areas of south Florida. Laurel wilt is caused by the pathogen Raffaelea lauricola, a fungal symbiont of the redbay ambrosia beetle, Xyleborus glabratus. Thus far, the disease is confined to members of the Lauraceae that are native to the USA, or native to such places as the Caribbean, Central America and Europe and grown in the USA. The beetle and fungus are native to Asia and were likely introduced with untreated solid wood packing material at Port Wentworth, Georgia in the early 2000s. Since that time laurel wilt has spread rapidly in the coastal plains of the southeastern USA, spreading north into central North Carolina, as far west as Texas, and reaching the southernmost counties of Florida. Current models suggest that X. glabratus can tolerate temperature conditions that occur throughout much of the eastern USA, and so the disease threatens sassafras throughout much of this region. The disease poses a threat to lauraceous species indigenous to other areas of the Americas as well as Europe and Africa.

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 Raffaelea lauricola (Laurel wilt).

2021 ◽  
Author(s):  
Stephen Fraedrich
Keyword(s):  
Solid Wood ◽  
Persea Americana ◽  
South Florida ◽  
Florida Current ◽  
Natural Ecosystems ◽  
Laurel Wilt ◽  
Southeastern Usa ◽  
Raffaelea Lauricola ◽  
Redbay Ambrosia Beetle ◽  
The Usa

Abstract Laurel wilt is responsible for the death of hundreds of millions of redbay (Persea borbonia sensu lato) trees throughout the southeastern USA, and the disease is also having significant effects on other species such as sassafras (Sassafras albidum) in natural ecosystems and avocado (Persea americana) in commercial production areas of south Florida. Laurel wilt is caused by the pathogen Raffaelea lauricola, a fungal symbiont of the redbay ambrosia beetle, Xyleborus glabratus. Thus far, the disease is confined to members of the Lauraceae that are native to the USA, or native to such places as the Caribbean, Central America and Europe and grown in the USA. The beetle and fungus are native to Asia and were likely introduced with untreated solid wood packing material at Port Wentworth, Georgia in the early 2000s. Since that time laurel wilt has spread rapidly in the coastal plains of the southeastern USA, spreading north into central North Carolina, as far west as Texas, and reaching the southernmost counties of Florida. Current models suggest that X. glabratus can tolerate temperature conditions that occur throughout much of the eastern USA, and so the disease threatens sassafras throughout much of this region. The disease poses a threat to lauraceous species indigenous to other areas of the Americas as well as Europe and Africa.

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

Plant Disease ◽  
2009 ◽  
Vol 93 (10) ◽  
pp. 1079-1079 ◽  
Author(s):  
J. A. Smith ◽  
T. J. Dreaden ◽  
A. E. Mayfield ◽  
A. Boone ◽  
S. W. Fraedrich ◽  
...  
Keyword(s):  
South Carolina ◽  
Small Subunit ◽  
Wilt Disease ◽  
Laurel Wilt ◽  
Rdna Sequences ◽  
Raffaelea Lauricola ◽  
Laurel Wilt Disease ◽  
Redbay Ambrosia Beetle ◽  
Red Bay ◽  
Branch Dieback

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.

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

Forests ◽  
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.

scholarly journals 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

2019 ◽  
Vol 20 (4) ◽  
pp. 220-228 ◽  
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.

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 Variation in xylem characteristics of botanical races of Persea americana and their potential influence on susceptibility to the pathogen Raffaelea lauricola

2020 ◽  
Author(s):  
G. L. Beier ◽  
C. D. Lund ◽  
B. W. Held ◽  
R. C. Ploetz ◽  
J. L. Konkol ◽  
...  
Keyword(s):  
West Indian ◽  
Invasive Disease ◽  
Persea Americana ◽  
Vessel Density ◽  
Contributing Factors ◽  
The West ◽  
Laurel Wilt ◽  
Vessel Size ◽  
Raffaelea Lauricola ◽  
Specific Potential

Abstract Avocado (Persea americana), an important fruit crop, is under threat from an invasive disease, laurel wilt. The pathogen, Raffaelea lauricola, spreads rapidly in the xylem of infected trees and causes a lethal vascular wilt. A previous study showed that variation in susceptibility to the disease exists among different races of avocado, with the West Indian race being most susceptible. To help elucidate potential explanations for differences in susceptibility, xylem characteristics were examined for fourteen avocado cultivars from the Guatemalan, Mexican, and West Indian botanical races. Samples of each cultivar were assessed for vessel size, vessel density, vessel aggregation, and xylem-specific potential hydraulic conductivity. The West Indian race had significantly greater mean vessel diameters, mean maximum vessel diameters, and xylem-specific potential hydraulic conductivities than the Guatemalan and Mexican races (p < 0.05), which in turn did not differ for any of these variables (p > 0.05). There were no significant differences among the races for vessel aggregation or vessel density. Cultivars of the Mexican and Guatemalan races generally had smaller mean vessel diameters, mean maximum vessel diameters, and mean xylem-specific potential hydraulic conductivities than the West Indian race; however, there was considerable variation among cultivars of the Mexican race. Statistically significant differences in vessel grouping indices and vessel solitary fractions were evident among some cultivars but to lesser extents than were found for vessel size. This study indicates that larger vessel diameters and greater potential hydraulic conductivities exist in the West Indian, compared with the Guatemalan and Mexican races. We suggest that these attributes may be contributing factors in the greater susceptibility to laurel wilt that is evident in the West Indian race.

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.

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