Development of Multilocus PCR Assays for Raffaelea lauricola, Causal Agent of Laurel Wilt Disease

Flexibility in the ambrosia symbiosis of Xyleborus bispinatus

Introduction

Ambrosia beetles maintain strict associations with specific lineages of fungi. However, anthropogenic introductions of ambrosia beetles into new ecosystems can result in the lateral transfer of their symbionts to other ambrosia beetles. The ability of a Florida endemic ambrosia beetle, Xyleborus bispinatus, to feed and establish persistent associations with two of its known symbionts (Raffaelea subfusca and Raffaelea arxii) and two other fungi (Harringtonia lauricola and Fusarium sp. nov.), which are primary symbionts of invasive ambrosia beetles, was investigated.

Methods

The stability of these mutualisms and their effect on the beetle's fitness were monitored over five consecutive generations. Surface-disinfested pupae with non-developed mycangia were reared separately on one of the four fungal symbionts. Non-treated beetles (i.e., lab colony) with previously colonized mycangia were used as a control group.

Results

Xyleborus bispinatus could exchange its fungal symbionts, survive, and reproduce on different fungal diets, including known fungal associates and phylogenetically distant fungi, which are plant pathogens and primary symbionts of other invasive ambrosia beetles. These changes in fungal diets resulted in persistent mutualisms, and some symbionts even increased the beetle's reproduction. Females that developed on Fusarium sp. nov. had a significantly greater number of female offspring than non-treated beetles. Females that fed solely on Harringtonia or Raffaelea symbionts produced fewer female offspring.

Discussion

Even though some ambrosia beetles like X. bispinatus can partner with different ambrosia fungi, their symbiosis under natural conditions is modulated by their mycangium and possibly other environmental factors. However, exposure to symbionts of invasive beetles can result in stable partnerships with these fungi and affect the population dynamics of ambrosia beetles and their symbionts.

First Report of Laurel Wilt Caused by Harringtonia lauricola (previously Raffaelea lauricola) on Northern Spicebush in Kentucky and Tennessee

Laurel wilt (LW) is a vascular disease caused by the fungus Harringtonia lauricola (previously Raffaelea lauricola) and transmitted by its primary vector, the redbay ambrosia beetle (Xyleborus glabratus, RAB), both of which were first detected in the United States (US) in 2002, likely introduced from their native range in Asia (Fraedrich et al. 2008; Harrington et al. 2008). LW has since spread across the southeastern US causing the death of millions of native redbay, sassafras, silk bay, swamp bay and other native Lauraceae species (Hughes et al. 2017). Detection of LW on the deciduous understory shrub northern spicebush (Lindera benzoin) was previously reported in South Carolina (Fraedrich et al. 2016) and Louisiana (Olatinwo et al. 2021) and is hereby confirmed in Kentucky and Tennessee. Spicebush plants displaying typical LW symptoms were observed in September 2020 on a property spanning the KY/TN border (Christian Co., KY and Montgomery Co., TN). Several dense stands of spicebush exhibited leaf wilt, early fall leaf coloration, dead leaves on branches, and black streaks of discolored xylem. LW was already confirmed on sassafras in the area (Loyd et al. 2020), and there were abundant dead sassafras nearby. Ambrosia beetle boring dust was observed and callow female RABs emerged from containerized bolts of spicebush collected from the site, indicating that the vector used spicebush as a brood host. Samples of spicebush sapwood tissue collected from two symptomatic plants were plated onto CSMA (cycloheximide-streptomycin malt extract agar) medium. The cultures were grown at room temperature in ambient light, and a fungus was recovered and further transferred onto MEA (malt extract agar) and PDA (potato dextrose agar) media. The morphology of the two fungal isolates, referred to as LW415 and LW416, matched the typical white mucoid growth and ovoid conidia of H. lauricola (Harrington et al. 2008). DNA was extracted from conidia harvested from two-week-old MEA cultures using a modified method of Dreaden et al. (2014). The identity of the fungus was confirmed by performing PCR with the H. lauricola-specific microsatellite primer sets IFW and CHK (Dreaden et al. 2014, Parra et al. 2020). A positive amplification product was obtained for LW415 and LW416 for both primer sets, validating their identification as H. lauricola. To confirm pathogenicity, four spicebush seedlings (mean height 22.5 cm; mean ground line diameter 3.3 mm) were inoculated: two with H. lauricola isolate LW415 grown on PDA for two weeks at room temperature in the dark, and two were mock-inoculated with sterile PDA as a control. A scalpel was used to nick the spicebush stem at a bud about 5 cm above groundline, and a 3 mm2 agar plug was placed in the wound and wrapped with parafilm. The spicebush seedlings were maintained in a growth chamber with an average temperature of 24°C and a 15 h photoperiod. Wilt symptoms were evident on inoculated seedlings after two weeks, while the control plants remained healthy. Four weeks post-inoculation, black staining of the vascular tissue was present in the symptomatic seedlings, and a fungus matching the morphology of H. lauricola was consistently recovered, while no fungus was isolated from the control plants. These results provide additional evidence that northern spicebush populations may be threatened by LW and could serve as a reservoir for the pathogen and vector (Gramling 2010). The spread of LW and RAB on spicebush may gain importance as preferred hosts (e.g., sassafras) are killed.

Everything Is Faster: How Do Land-Grant University-Based Plant Diagnostic Laboratories Keep Up with a Rapidly Changing World?

Plant diagnostic laboratories (PDLs) are at the heart of land-grant universities (LGUs) and their extension mission to connect citizens with research-based information. Although research and technological advances have led to many modern methods and technologies in plant pathology diagnostics, the pace of adopting those methods into services at PDLs has many complexities we aim to explore in this review. We seek to identify current challenges in plant disease diagnostics, as well as diagnosticians' and administrators'perceptions of PDLs' many roles. Surveys of diagnosticians and administrators were conducted to understand the current climate on these topics. We hope this article reaches researchers developing diagnostic methods with modern and new technologies to foster a better understanding of PDL diagnosticians' perspective on method implementation. Ultimately, increasing researchers' awareness of the factors influencing method adoption by PDLs encourages support, collaboration, and partnerships to advance plant diagnostics.

Rapid Detection of Raffaelea lauricola Directly from Host Plant and Beetle Vector Tissues Using Loop-Mediated Isothermal Amplification

Since its introduction in 2002, laurel wilt disease has devastated indigenous lauraceous species in the southeastern United States. The causal agent is a fungal pathogen, Raffaelea lauricola, which, after being introduced into the xylem of trees by its vector beetle, Xyleborus glabratus, results in a fatal vascular wilt. Rapid detection and accurate diagnosis of infections is paramount to the successful implementation of disease management strategies. Current management operations to prevent the spread of laurel wilt disease are largely delayed by time-consuming laboratory procedures to confirm the diagnosis. In order to greatly speed up the operations, we developed a loop-mediated isothermal amplification (LAMP) species-specific assay that targets the β-tubulin gene region of R. lauricola, and allows for the rapid detection of the pathogen directly from host plant and beetle tissues. The assay is capable of amplifying as little as 0.5 pg of fungal DNA and as few as 50 conidia. The assay is also capable of detecting R. lauricola directly from wood tissue of artificially inoculated redbay saplings as early as 10 and 12 days postinoculation, when testing high-quality and crude DNA extracts, respectively. Finally, crude DNA extracts of individual adult female X. glabratus beetles were assayed and the pathogen was detected from all specimens. This assay greatly reduces the time required to confirm a laurel wilt diagnosis and, because LAMP technology is well suited to provide point-of-care testing, it has the potential to expedite and facilitate implementation of management operations in response to disease outbreaks.

Genomic and transcriptomic insights into Raffaelea lauricola pathogenesis

BACKGROUND

Laurel wilt caused by Raffaelea lauricola is a lethal vascular disease of North American members of the Lauraceae plant family. This fungus and its primary ambrosia beetle vector Xyleborus glabratus originated from Asia; however, there is no report of laurel wilt causing widespread mortality on native Lauraceae trees in Asia. To gain insight into why R. lauricola is a tree-killing plant pathogen in North America, we generated and compared high quality draft genome assemblies of R. lauricola and its closely related non-pathogenic species R. aguacate.

RESULTS

Relative to R. aguacate, the R. lauricola genome uniquely encodes several small-secreted proteins that are associated with virulence in other pathogens and is enriched in secondary metabolite biosynthetic clusters, particularly polyketide synthase (PKS), non-ribosomal peptide synthetase (NRPS) and PKS-NRPS anchored gene clusters. The two species also exhibit significant differences in secreted proteins including CAZymes that are associated with polysaccharide binding including the chitin binding CBM50 (LysM) domain. Transcriptomic comparisons of inoculated redbay trees and in vitro-grown fungal cultures further revealed a number of secreted protein genes, secondary metabolite clusters and alternative sulfur uptake and assimilation pathways that are coordinately up-regulated during infection.

CONCLUSIONS

Through these comparative analyses we have identified potential adaptations of R. lauricola that may enable it to colonize and cause disease on susceptible hosts. How these adaptations have interacted with co-evolved hosts in Asia, where little to no disease occurs, and non-co-evolved hosts in North America, where lethal wilt occurs, requires additional functional analysis of genes and pathways.

Domestication-driven changes in plant traits associated with changes in the assembly of the rhizosphere microbiota in tetraploid wheat

Despite the large morphological and physiological changes that plants have undergone through domestication, little is known about their impact on their microbiome. Here we characterized rhizospheric bacterial and fungal communities as well as the abundance of N-cycling microbial guilds across thirty-nine accessions of tetraploid wheat, Triticum turgidum, from four domestication groups ranging from the wild subspecies to the semi dwarf elite cultivars. We identified several microbial phylotypes displaying significant variation in their relative abundance depending on the wheat domestication group with a stronger impact of domestication on fungi. The relative abundance of potential fungal plant pathogens belonging to the Sordariomycetes class decreased in domesticated compared to wild emmer while the opposite was found for members of the Glomeromycetes, which are obligate plant symbionts. The depletion of nitrifiers and of arbuscular mycorrhizal fungi in elite wheat cultivars compared to primitive domesticated forms suggests that the Green Revolution has decreased the coupling between plant and rhizosphere microbes that are potentially important for plant nutrient availability. Both plant diameter and fine root percentage exhibited the highest number of associations with microbial taxa, highlighting their putative role in shaping the rhizosphere microbiota during domestication. Aside from domestication, significant variation of bacterial and fungal community composition was found among accessions within each domestication group. In particular, the relative abundances of Ophiostomataceae and of Rhizobiales were strongly dependent on the host accession, with heritability estimates of ~ 27% and ~ 25%, indicating that there might be room for genetic improvement via introgression of ancestral plant rhizosphere-beneficial microbe associations.

Genetic Analyses of the Laurel Wilt Pathogen, Raffaelea lauricola, in Asia Provide Clues on the Source of the Clone that is Responsible for the Current USA Epidemic

Laurel wilt is caused by the fungus Raffaelea lauricola T.C. Harr., Fraedrich and Aghayeva, a nutritional symbiont of its vector the redbay ambrosia beetle, Xyleborus glabratus Eichhoff. Both are native to Asia but appeared in Georgia in the early 2000s. Laurel wilt has since spread to much of the southeastern United States killing >300 million host trees in the Lauraceae plant family. The aims of this research were to elucidate the genetic structure of populations of R. lauricola, to examine its reproductive strategy, and determine how often the pathogen had been introduced to the USA. A panel of 12 simple sequence repeat (SSR) markers identified 15 multilocus genotypes (MLGs) in a collection of 59 isolates from the USA (34 isolates), Myanmar (18), Taiwan (6) and Japan (1). Limited diversity in the USA isolates and the presence of one MAT idiotype (mating type locus) indicated that R. lauricola was probably introduced into the country a single time. MLG diversity was far greater in Asia than the USA. Only three closely related MLGs were detected in the USA, the most prevalent of which (30 of 34 isolates) was also found in Taiwan. Although more work is needed, the present results suggest that a Taiwanese origin is possible for the population of R. lauricola in the USA. Isolates of R. lauricola from Myanmar were distinct from those from Japan, Taiwan and the USA. Although both MAT idiotypes were present in Myanmar and Taiwan, only the population from Taiwan had the genetic structure of a sexually reproducing population.

Partnerships Between Ambrosia Beetles and Fungi: Lineage-Specific Promiscuity Among Vectors of the Laurel Wilt Pathogen, Raffaelea lauricola

Nutritional mutualisms that ambrosia beetles have with fungi are poorly understood. Although these interactions were initially thought to be specific associations with a primary symbiont, there is increasing evidence that some of these fungi are associated with, and move among, multiple beetle partners. We examined culturable fungi recovered from mycangia of ambrosia beetles associated with trees of Persea humilis (silk bay, one site) and P. americana (avocado, six commercial orchards) that were affected by laurel wilt, an invasive disease caused by a symbiont, Raffaelea lauricola, of an Asian ambrosia beetle, Xyleborus glabratus. Fungi were isolated from 20 adult females of X. glabratus from silk bay and 70 each of Xyleborus affinis, Xyleborus bispinatus, Xyleborus volvulus, Xyleborinus saxesenii, and Xylosandrus crassiusculus from avocado. With partial sequences of ribosomal (LSU and SSU) and nuclear (β-tubulin) genes, one to several operational taxonomic units (OTUs) of fungi were identified in assayed individuals. Distinct populations of fungi were recovered from each of the examined beetle species. Raffaelea lauricola was present in all beetles except X. saxesenii and X. crassiusculus, and Raffaelea spp. predominated in Xyleborus spp. Raffaelea arxii, R. subalba, and R. subfusca were present in more than a single species of Xyleborus, and R. arxii was the most abundant symbiont in both X. affinis and X. volvulus. Raffaelea aguacate was detected for the first time in an ambrosia beetle (X. bispinatus). Yeasts (Ascomycota, Saccharomycotina) were found consistently in the mycangia of the examined beetles, and distinct, putatively co-adapted populations of these fungi were associated with each beetle species. Greater understandings are needed for how mycangia in ambrosia beetles interact with fungi, including yeasts which play currently underresearched roles in these insects.

Identification of the Achilles heels of the laurel wilt pathogen and its beetle vector

Ambrosia beetles harbor fungal symbionts that serve as food sources for larvae and adults. These beetles lay their eggs along tunnels in xylem sapwood, which is the substrate for fungal growth. Symbiotic fungi of the genus Raffaelea found in invasive and indigenous ambrosia beetles include the highly virulent plant pathogen Raffaelea lauricola affecting members of the Lauraceae family. R. lauricola is responsible for the deaths of > 500 million trees since 2005. Infection by as few as 100 spores can kill a healthy tree within months. Our data show that R. lauricola is cold-adapted with optimal growth between 16 and 26 °C, with little to no growth at temperatures ≥ 30 °C. The fungus is halophilic and shows a dramatic decrease in growth at pH ≥ 6.8. Fungicide resistance profiling revealed sensitivity of R. lauricola to prochloraz, dichlorofluanid, most conazoles, dithiocarbamates, and zineb (zinc fungicide), whereas the related species Raffaelea arxii showed more limited fungicide sensitivity. Entomopathogenic fungi potentially useful for beetle control were generally highly resistant to most fungicides tested. Coupling pH decreased the concentration for 95% inhibition of fungal growth (IC₉₅) of the most potent R. lauricola fungicides by 3-4-fold. Use of avocado bark plug insect bioassays revealed that commercially available Beauveria bassiana can be used as a biological control agent capable of effectively killing the beetle vectors. These data provide simple and practical recommendations to specifically target R. lauricola while having minimal effects on other symbiotic and entomopathogenic fungi, the latter of which can be used to manage the beetle vectors.

Xyleborus bispinatus Reared on Artificial Media in the Presence or Absence of the Laurel Wilt Pathogen (Raffaelea lauricola)

Like other members of the tribe Xyleborini, Xyleborus bispinatus Eichhoff can cause economic damage in the Neotropics. X. bispinatus has been found to acquire the laurel wilt pathogen Raffaelea lauricola (T. C. Harr., Fraedrich & Aghayeva) when breeding in a host affected by the pathogen. Its role as a potential vector of R. lauricola is under investigation. The main objective of this study was to evaluate three artificial media, containing sawdust of avocado (Persea americana Mill.) and silkbay (Persea humilis Nash.), for rearing X. bispinatus under laboratory conditions. In addition, the media were inoculated with R. lauricola to evaluate its effect on the biology of X. bispinatus. There was a significant interaction between sawdust species and R. lauricola for all media. Two of the media supported the prolific reproduction of X. bispinatus, but the avocado-based medium was generally more effective than the silkbay-based medium, regardless whether or not it was inoculated with R. lauricola. R. lauricola had a neutral or positive effect on beetle reproduction. The pathogen was frequently recovered from beetle galleries, but only from a few individuals which were reared on inoculated media, and showed limited colonization of the beetle's mycangia. Two media with lower water content were most effective for rearing X. bispinatus.

Rearing Xyleborus volvulus (Coleoptera: Curculionidae) on Media Containing Sawdust from Avocado or Silkbay, With or Without Raffaelea lauricola (Ophiostomatales: Ophiostomataceae)

Like other ambrosia beetles, Xyleborus volvulus Fabricius (Coleoptera: Curculionidae) lives in a mutualistic symbiotic relationship with fungi that serve as food source. Until recently, X. volvulus was not considered a pest, and none of its symbionts were considered plant pathogens. However, recent reports of an association between X. volvulus and Raffaelea lauricola T.C. Harr., Fraedrich & Aghayeva (Ophiostomatales: Ophiostomataceae), the cause of the laurel wilt disease of avocado (Persea americana Mill. [Laurales: Lauraceae]), and its potential role as vector of the pathogen merit further investigation. The objective of this study was to evaluate three artificial media containing sawdust obtained from avocado or silkbay (Persea humilis Nash) for laboratory rearing of X. volvulus. The effect of R. lauricola in the media on the beetle's reproduction was also evaluated. Of the three media, the one with the lowest content of sawdust and intermediate water content provided the best conditions for rearing X. volvulus. Reproduction on this medium was not affected by the sawdust species or the presence of R. lauricola. On the other two media, there was a significant interaction between sawdust species and R. lauricola. The presence of R. lauricola generally had a negative effect on brood production. There was limited colonization of the mycangia of X. volvulus by R. lauricola on media inoculated with the pathogen. From galleries formed within the best medium, there was 50% recovery of R. lauricola, but recovery was much less from the other two media. Here, we report the best artificial substrate currently known for X. volvulus.

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

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.

PCR Multiplexes Discriminate Fusarium Symbionts of Invasive Euwallacea Ambrosia Beetles that Inflict Damage on Numerous Tree Species Throughout the United States

Asian Euwallacea ambrosia beetles vector Fusarium mutualists. The ambrosial fusaria are all members of the ambrosia Fusarium clade (AFC) within the Fusarium solani species complex (FSSC). Several Euwallacea-Fusarium mutualists have been introduced into nonnative regions and have caused varying degrees of damage to orchard, landscape, and forest trees. Knowledge of symbiont fidelity is limited by current identification methods, which typically requires analysis of DNA sequence data from beetles and the symbionts cultured from their oral mycangia. Here, polymerase chain reaction (PCR)-based diagnostic tools were developed to identify the six Fusarium symbionts of exotic Euwallacea spp. currently known within the United States. Whole-genome sequences were generated for representatives of six AFC species plus F. ambrosium and aligned to the annotated genome of F. euwallaceae. Taxon-specific primer-annealing sites were identified that rapidly distinguish the AFC species currently within the United States. PCR specificity, reliability, and sensitivity were validated using a panel of 72 Fusarium isolates, including 47 reference cultures. Culture-independent multiplex assays accurately identified two AFC fusaria using DNA isolated from heads of their respective beetle partners. The PCR assays were used to show that Euwallacea validus is exclusively associated with AF-4 throughout its sampled range within eastern North America. The rapid assay supports federal and state agency efforts to monitor spread of these invasive pests and mitigate further introductions.

Evaluation of a Multilocus Indel DNA Region for the Detection of the Wheat Tan Spot Pathogen Pyrenophora tritici-repentis

Tan spot or yellow (leaf) spot disease of wheat (Triticum spp.) is caused by Pyrenophora tritici-repentis, a necrotrophic fungal pathogen that is widespread throughout the main wheat-growing regions in the world. This disease is currently the single most economically important crop disease in Australia. In this study, a real-time quantitative polymerase chain reaction (qPCR) assay was developed as a diagnostic tool to detect the pathogen on wheat foliar tissue. A multicopy locus (PtrMulti) present in the P. tritici-repentis genome was assessed for its suitability as a qPCR probe. The primer pair PtrMulti_F/R that targets the region was evaluated with respect to species specificity and sensitivity. A PtrMulti SYBR qPCR assay was developed and proved to be suitable for the identification and relative quantification of P. tritici-repentis with a detection limit of DNA levels at <0.1 pg. Variation of the PtrMulti copy number between the geographical representatives of P. tritici-repentis strains examined was minimal, with the range of 63 to 85 copies per genome. For naturally infected wheat field samples, the incidence of P. tritici-repentis DNA on leaves quantified by qPCR varied up to 1,000-fold difference in the concentration, with a higher incidence of DNA occurring on the lower canopy for most of the growth stages examined. At the early growth stages, qPCR assay was able to detect P. tritici-repentis DNA on the younger leaves in the absence of visible tan spot lesions. These results demonstrate the potential of PtrMulti probe to be used for early detection and rapid screening of tan spot disease on wheat plants.

Detection of laurel wilt disease in avocado using low altitude aerial imaging

Laurel wilt is a lethal disease of plants in the Lauraceae plant family, including avocado (Persea americana). This devastating disease has spread rapidly along the southeastern seaboard of the United States and has begun to affect commercial avocado production in Florida. The main objective of this study was to evaluate the potential to discriminate laurel wilt-affected avocado trees using aerial images taken with a modified camera during helicopter surveys at low-altitude in the commercial avocado production area. The ability to distinguish laurel wilt-affected trees from other factors that produce similar external symptoms was also studied. R_modGB digital values of healthy trees and laurel wilt-affected trees, as well as fruit stress and vines covering trees were used to calculate several vegetation indices (VIs), band ratios, and VI combinations. These indices were subjected to analysis of variance (ANOVA) and an M-statistic was performed in order to quantify the separability of those classes. Significant differences in spectral values among laurel wilt affected and healthy trees were observed in all vegetation indices calculated, although the best results were achieved with Excess Red (ExR), (Red–Green) and Combination 1 (COMB1) in all locations. B/G showed a very good potential for separate the other factors with symptoms similar to laurel wilt-affected trees, such as fruit stress and vines covering trees, from laurel wilt-affected trees. These consistent results prove the usefulness of using a modified camera (R_modGB) to discriminate laurel wilt-affected avocado trees from healthy trees, as well as from other factors that cause the same symptoms and suggest performing the classification in further research. According to our results, ExR and B/G should be utilized to develop an algorithm or decision rules to classify aerial images, since they showed the highest capacity to discriminate laurel wilt-affected trees. This methodology may allow the rapid detection of laurel wilt-affected trees using low altitude aerial images and be a valuable tool in mitigating this important threat to Florida avocado production.

Phylogeny of ambrosia beetle symbionts in the genus Raffaelea

The genus Raffaelea was established in 1965 when the type species, Raffaelea ambrosia, a symbiont of Platypus ambrosia beetles was described. Since then, many additional ambrosia beetle symbionts have been added to the genus, including the important tree pathogens Raffaelea quercivora, Raffaelea quercus-mongolicae, and Raffaelea lauricola, causal agents of Japanese and Korean oak wilt and laurel wilt, respectively. The discovery of new and the dispersal of described species of Raffaelea to new areas, where they can become invasive, presents challenges for diagnosticians as well as plant protection and quarantine efforts. In this paper, we present the first comprehensive multigene phylogenetic analysis of Raffaelea. As it is currently defined, the genus was found to not be monophyletic. On the basis of this work, Raffaelea sensu stricto is defined and the affinities of undescribed isolates are considered.