Phylogenomic Analysis of a 55.1-kb 19-Gene Dataset Resolves a Monophyletic Fusarium that Includes the Fusarium solani Species Complex

Scientific communication is facilitated by a data-driven, scientifically sound taxonomy that considers the end-user's needs and established successful practice. In 2013, the Fusarium community voiced near unanimous support for a concept of Fusarium that represented a clade comprising all agriculturally and clinically important Fusarium species, including the F. solani species complex (FSSC). Subsequently, this concept was challenged in 2015 by one research group who proposed dividing the genus Fusarium into seven genera, including the FSSC described as members of the genus Neocosmospora, with subsequent justification in 2018 based on claims that the 2013 concept of Fusarium is polyphyletic. Here, we test this claim and provide a phylogeny based on exonic nucleotide sequences of 19 orthologous protein-coding genes that strongly support the monophyly of Fusarium including the FSSC. We reassert the practical and scientific argument in support of a genus Fusarium that includes the FSSC and several other basal lineages, consistent with the longstanding use of this name among plant pathologists, medical mycologists, quarantine officials, regulatory agencies, students, and researchers with a stake in its taxonomy. In recognition of this monophyly, 40 species described as genus Neocosmospora were recombined in genus Fusarium, and nine others were renamed Fusarium. Here the global Fusarium community voices strong support for the inclusion of the FSSC in Fusarium, as it remains the best scientific, nomenclatural, and practical taxonomic option available.

Structure of the Ambrosia Beetle (Coleoptera: Curculionidae) Mycangia Revealed Through Micro-Computed Tomography

Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae and Platypodinae) rely on a symbiosis with fungi for their nutrition. Symbiotic fungi are preserved and transported in specialized storage structures called mycangia. Although pivotal in the symbiosis, mycangia have been notoriously difficult to study, given their minute size and membranous structure. We compared the application of novel visualization methods for the study of mycangia, namely micro-computed tomography (micro-CT) and laser ablation tomography (LATscan) with traditional paraffin sectioning. Micro-CT scanning has shown the greatest promise in new organ discovery, while sectioning remains the only method with sufficient resolution for cellular visualization. All three common types of mycangia (oral, mesonotal, and pronotal) were successfully visualized and presented for different species of ambrosia beetles: Ambrosiodmus minor (Stebbing) 1909, Euplatypus compositus (Say) 1823, Premnobius cavipennis Eichhoff 1878, Scolytoplatypus raja Blandford 1893, Xylosandrus crassiusculus (Motschulsky) 1866 and X. amputatus (Blandford) 1894. A reconstruction of the mycangium and the surrounding musculature in X. amputatus is also presented. The advantages of micro-CT compared to the previously commonly used microtome sectioning include the easy visualization and recording of three-dimensional structures, their position in reference to other internal structures, the ability to distinguish natural aberrations from technical artifacts, and the unprecedented visualizations of the anatomic context of mycangia enabled by the integrated software.

Fusarium oligoseptatum sp. nov., a mycosymbiont of the ambrosia beetle Euwallacea validus in the Eastern U.S. and typification of F. ambrosium

Fusarium oligoseptatum sp. nov. was isolated from the invasive Asian ambrosia beetle Euwallacea validis (Coleoptera, Scolytinae, Xyleborini) and from the galleries that females had constructed in dying Ailanthus altissima (tree-of-heaven) symptomatic for Verticillium wilt in south-central Pennsylvania, USA. This ambrosia fungus was cultivated by Euwallacea validis as the primary source of nutrition together with a second symbiont, Raffaelea subfusca . Female beetles transport their fungal symbionts within and from their natal galleries in paired pre-oral mycangia. Fusarium oligoseptatum was distinguished phenotypically from the 11 other known members of the Ambrosia Fusarium Clade (AFC) by uniquely producing mostly 1–2 septate clavate sporodochial conidia that were swollen apically. Phylogenetic analysis of multilocus DNA sequence data resolved F. oligoseptatum as a genealogically exclusive species-level lineage but evolutionary relationships with other members of the AFC were unresolved. Published studies have shown that F. oligoseptatum can be identified via phylogenetic analysis of multilocus DNA sequence data or a PCR multiplex assay employing species-specific oligonucleotide primers. In addition, to provide nomenclatural stability, an epitype was prepared from an authentic strain of F. ambrosium that was originally isolated from a gallery constructed in Chinese tea (Camellia sinensis ) by E. fornicatus in India, together with its lectotypification based on a published illustration.

Two new Geosmithia species in G. pallida species complex from bark beetles in eastern USA

Species of Geosmithia are cosmopolitan but understudied fungi, and most are associated with phloem-feeding bark beetles on various woody hosts. We surveyed 207 bark and ambrosia beetles from 37 species in the eastern USA for associated fungi. The community is dominated by species in the G. pallida species complex (GPSC) and included several Geosmithia isolates that appear to be new to science. The new Geosmithia isolates exhibited the characteristic brownish-colored colonies typical for the G. pallida species complex and were phylogenetically resolved as two genealogically exclusive lineages based on a concatenated multilocus data set based on the internal transcribed spacers (ITS) of the nuc rDNA (ITS1-5.8S-ITS2 = ITS), and the translation elongation factor 1-α (TEF1-α), β-tubulin (TUB2), and RNA polymerase II second largest subunit (RPB2) genes. Two new Geosmithia species, G. brunnea and G. proliferans, are proposed, and their morphological traits and phylogenetic placements are presented.

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.

Two novel Fusarium species that cause canker disease of prickly ash (Zanthoxylum bungeanum) in northern China form a novel clade with Fusarium torreyae

Canker disease of prickly ash (Zanthoxylum bungeanum) has caused a decline in the production of this economically important spice in northern China in the past 25 y. To identify the etiological agent, 38 fungal isolates were recovered from symptomatic tissues from trees in five provinces in China. These isolates were identified by conducting BLASTN queries of NCBI GenBank and phylogenetic analyses of DNA sequence data from the nuclear ribosomal internal transcribed spacer region (ITS rDNA), a portion of the translation elongation factor 1-α (TEF1) gene, and genes encoding RNA polymerase II largest (RPB1) and second largest (RPB2) subunits. Results of these analyses suggested that 30/38 isolates belonged to two novel fusaria most closely related to the Florida torreya (Torreya taxifolia Arn.) pathogen, Fusarium torreyae in Florida and Georgia. These three canker-inducing tree pathogens form a novel clade within Fusarium here designated the F. torreyae species complex (FTOSC). BLASTN queries of GenBank also revealed that 5/38 isolates recovered from cankers represented an undescribed phylogenetic species within the F. solani species complex (FSSC) designated FSSC 6. Stem inoculations of three fusaria on Z. bungeanum resulted in consistent canker symptoms from which these three fusaria were recovered. The two novel fusaria, however, induced significantly larger lesions than FSSC 6. Herein, the two novel prickly ash pathogens are formally described as F. zanthoxyli and F. continuum.

New Fungus-Insect Symbiosis: Culturing, Molecular, and Histological Methods Determine Saprophytic Polyporales Mutualists of Ambrosiodmus Ambrosia Beetles

Ambrosia symbiosis is an obligate, farming-like mutualism between wood-boring beetles and fungi. It evolved at least 11 times and includes many notorious invasive pests. All ambrosia beetles studied to date cultivate ascomycotan fungi: early colonizers of recently killed trees with poor wood digestion. Beetles in the widespread genus Ambrosiodmus, however, colonize decayed wood. We characterized the mycosymbionts of three Ambrosiodmus species using quantitative culturing, high-throughput metabarcoding, and histology. We determined the fungi to be within the Polyporales, closely related to Flavodon flavus. Culture-independent sequencing of Ambrosiodmus minor mycangia revealed a single operational taxonomic unit identical to the sequences from the cultured Flavodon. Histological sectioning confirmed that Ambrosiodmus possessed preoral mycangia containing dimitic hyphae similar to cultured F. cf. flavus. The Ambrosiodmus-Flavodon symbiosis is unique in several aspects: it is the first reported association between an ambrosia beetle and a basidiomycotan fungus; the mycosymbiont grows as hyphae in the mycangia, not as budding pseudo-mycelium; and the mycosymbiont is a white-rot saprophyte rather than an early colonizer: a previously undocumented wood borer niche. Few fungi are capable of turning rotten wood into complete animal nutrition. Several thousand beetle-fungus symbioses remain unstudied and promise unknown and unexpected mycological diversity and enzymatic innovations.

Expanded Host Range Testing for Verticillium nonalfalfae: Potential Biocontrol Agent Against the Invasive Ailanthus altissima

The naturally occurring Verticillium nonalfalfae has been proposed as a biocontrol agent against the highly invasive Ailanthus altissima in the eastern United States. We tested 71 nontarget woody species for susceptibility to the potential biocontrol agent. In the field, only devil's walkingstick (17% incidence) and striped maple (3%) acquired infections through natural spread from infected A. altissima (100%). Staghorn sumac (16% incidence) also exhibited wilt in close proximity to diseased Ailanthus, although V. nonalfalfae was never recovered. Stem inoculations, which are highly artificial in that they bypass root defenses and flood the xylem with millions of conidia, induced varying levels of wilt and mortality in 10 nontarget species from which V. nonalfalfae was reisolated, although recovery and crown rebuilding occurred following initial wilt in several species including sassafras and northern catalpa. Thirty-seven of the 71 inoculated species exhibited vascular discoloration, although 23 of these species exhibited no outward symptoms (wilt, dieback) for up to 6 years postinoculation. However, V. nonalfalfae was reisolated from three of the 23 species, indicating a tolerant host response. Our results suggest that V. nonalfalfae is generally host-adapted to A. altissima with 78 of 78 A. altissima seed sources from 26 states and Canada showing susceptibility, and offers support for adoption and dissemination of V. nonalfalfae to combat the highly invasive A. altissima.

Discordant phylogenies suggest repeated host shifts in the Fusarium-Euwallacea ambrosia beetle mutualism

The mutualism between xyleborine beetles in the genus Euwallacea (Coleoptera: Curculionidae: Scolytinae) and members of the Ambrosia Fusarium Clade (AFC) represents one of 11 known evolutionary origins of fungiculture by ambrosia beetles. Female Euwallacea beetles transport fusarial symbionts in paired mandibular mycangia from their natal gallery to woody hosts where they are cultivated in galleries as a source of food. Native to Asia, several exotic Euwallacea species were introduced into the United States and Israel within the past two decades and they now threaten urban landscapes, forests and avocado production. To assess species limits and to date the evolutionary diversification of the mutualists, we reconstructed the evolutionary histories of key representatives of the Fusarium and Euwallacea clades using maximum parsimony and maximum likelihood methods. Twelve species-level lineages, termed AF 1-12, were identified within the monophyletic AFC and seven among the Fusarium-farming Euwallacea. Bayesian diversification-time estimates placed the origin of the Euwallacea-Fusarium mutualism near the Oligocene-Miocene boundary ∼19-24 Mya. Most Euwallacea spp. appear to be associated with one species of Fusarium, but two species farmed two closely related fusaria. Euwallacea sp. #2 in Miami-Dade County, Florida cultivated Fusarium spp. AF-6 and AF-8 on avocado, and Euwallacea sp. #4 farmed Fusarium ambrosium AF-1 and Fusarium sp. AF-11 on Chinese tea in Sri Lanka. Cophylogenetic analyses indicated that the Euwallacea and Fusarium phylogenies were largely incongruent, apparently due to the beetles switching fusarial symbionts (i.e., host shifts) at least five times during the evolution of this mutualism. Three cospeciation events between Euwallacea and their AFC symbionts were detected, but randomization tests failed to reject the null hypothesis that the putative parallel cladogenesis is a stochastic pattern. Lastly, two collections of Euwallacea sp. #2 from Miami-Dade County, Florida shared an identical cytochrome oxidase subunit 1 (CO1) allele with Euwallacea validus, suggesting introgressive hybridization between these species and/or pseudogenous nature of this marker. Results of the present study highlight the importance of understanding the potential for and frequency of host-switching between Euwallacea and members of the AFC, and that these shifts may bring together more aggressive and virulent combinations of these invasive mutualists.

First Report of Seedling Blight of Eastern Poison Ivy (Toxicodendron radicans) by Colletotrichum fioriniae in Virginia

Colletotrichum fioriniae is a member of the large cosmopolitan C. acutatum species complex (2). Known agricultural hosts of C. acutatum include apple, European blueberry, grape, olive, papaya, and strawberry (2). In contrast, the life history of C. fioriniae ranges from an epizootic of certain scale insect populations to an endophyte of plants (3,4). The present study extends the phytopathology of C. fioriniae to include poison ivy seedlings. Poison ivy (Toxicodendron radicans) drupes were collected from solitary lianas in Roanoke and Montgomery counties, Virginia. These drupes were subjected to experiments aimed at producing sterile seedlings (1); however, there was extensive blighting and wilting in the germinated seedlings. Associated with the drupes and seedlings was a fungus with white to pale olivaceous grey mycelium with orange blister-like conidiomata and sclerotial masses enclosing the drupe mesocarp as well as conidiomata emerging from blighted, necrotic leaves. Condiomata were plated onto acidified potato dextrose agar (APDA) and oatmeal agar (OA). This consistently yielded colonies identical to those described from diseased tissues and were putatively identified as C. acutatum based on the presence of acervuli containing hyaline, smooth-walled, aseptate conidia with acute ends, the absence of setae, and formation of red pigments in culture (2). Conidial dimensions of four isolates most closely aligned with reported measurements for C. fioriniae (4): mean length ± SD × width ± SD = 15.1 ± 1.7 × 4.9 ± 0.3 μm, L/W ratio = 3.04 on OA. Fungal DNA was isolated and used as template in PCR reactions using oligonucleotide primer pairs corresponding to the internal transcribed spacer (ITS) region, and a portion of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes. The resulting PCR fragments were sequenced and used as queries in BLASTN searches of the GenBank NR database. All of the amplified ITS DNA sequences (497 bp KF944356 and KF944357) were identical to Glomerella/Colletotrichum fioriniae (JN121190 and KF278459). Similarly, the amplified (672 bp) GAPDH sequences (KF944354 and KF944355) were 99.6% similar over the 254 bp overlapping with C. fioriniae (JQ948622). Pathogenicity of two randomly chosen C. fioriniae isolates, TR-123 and TR-126, was confirmed by placing 4.75 mm diam. inoculated agar plugs from 8-day-old fungal cultures or a sterile plug (negative control) at the base of an axenic young seedling ~1.5 to 6.5 cm in height with at least one set of true leaves (1). Each treatment was replicated five times. Acute wilt and blighting of leaves and production of orange acervuli on cotyledons disease symptoms developed by 3 weeks post inoculation (WPI). By 7 WPI all but one of the Colletotrichum-inoculated plants were dead, whereas all of the control plants were healthy with significantly lower area under the disease progress curve values. Colletotrichum was consistently re-isolated, and confirmed morphologically and molecularly, from six of seven diseased seedlings, whereas two of two randomly chosen control seedlings remained asymptomatic and did not yield Colletotrichum. In summary, C. fioriniae may represent a natural biocontrol agent against poison ivy and scale insect herbivores thereof. References: (1) E. Benhase and J. Jelesko. HortScience 48:1, 2013. (2) U. Damm et al. Stud. Mycol. 73:37, 2012. (3) J. Marcelino et al. J. Insect Sci. 9:25, 2009. (4) R. Shivas et al. Fungal Divers. 39:111.

Comparative pathogenicity, biocontrol efficacy, and multilocus sequence typing of Verticillium nonalfalfae from the invasive Ailanthus altissima and other hosts

Verticillium wilt, caused by Verticillium nonalfalfae, is currently killing tens of thousands of highly invasive Ailanthus altissima trees within the forests in Pennsylvania, Ohio, and Virginia and is being considered as a biological control agent of Ailanthus. However, little is known about the pathogenicity and virulence of V. nonalfalfae isolates from other hosts on Ailanthus, or the genetic diversity among V. nonalfalfae from confirmed Ailanthus wilt epicenters and from locations and hosts not associated with Ailanthus wilt. Here, we compared the pathogenicity and virulence of several V. nonalfalfae and V. alfalfae isolates, evaluated the efficacy of the virulent V. nonalfalfae isolate VnAa140 as a biocontrol agent of Ailanthus in Pennsylvania, and performed multilocus sequence typing of V. nonalfalfae and V. alfalfae. Inoculations of seven V. nonalfalfae and V. alfalfae isolates from six plant hosts on healthy Ailanthus seedlings revealed that V. nonalfalfae isolates from hosts other than Ailanthus were not pathogenic on Ailanthus. In the field, 100 canopy Ailanthus trees were inoculated across 12 stands with VnAa140 from 2006 to 2009. By 2011, natural spread of the fungus had resulted in the mortality of >14,000 additional canopy Ailanthus trees, 10,000 to 15,000 Ailanthus sprouts, and nearly complete eradication of Ailanthus from several smaller inoculated stands, with the exception of a few scattered vegetative sprouts that persisted in the understory for several years before succumbing. All V. nonalfalfae isolates associated with the lethal wilt of Ailanthus, along with 18 additional isolates from 10 hosts, shared the same multilocus sequence type (MLST), MLST 1, whereas three V. nonalfalfae isolates from kiwifruit shared a second sequence type, MLST 2. All V. alfalfae isolates included in the study shared the same MLST and included the first example of V. alfalfae infecting a non-lucerne host. Our results indicate that V. nonalfalfae is host adapted and highly efficacious against Ailanthus and, thus, is a strong candidate for use as a biocontrol agent.

First Report of Verticillium Wilt Caused by Verticillium nonalfalfae on Tree-of-Heaven (Ailanthus altissima) in Ohio

Verticillium wilt of the highly invasive tree-of-heaven [Ailanthus altissima (Mill.) Swingle], caused by Verticillium nonalfalfae Interbitzin et al. (1), formerly classified as V. albo-atrum Reinke and Berthold, has been reported in the United States from two states: Pennsylvania (2) and Virginia (3). Infected A. altissima in both states exhibited similar symptoms of wilt, premature defoliation, terminal dieback, yellow vascular discoloration, and mortality. In June 2012, the second author observed dead and dying A. altissima trees in southern Ohio (Pike County) that exhibited symptoms similar to those on diseased A. altissima trees in Pennsylvania and Virginia. Samples were collected from stems of three symptomatic A. altissima trees and sent to Penn State for morphological and molecular identification. Immediately upon arrival, samples were surface-disinfected and plated onto plum extract agar (PEA), a semi-selective medium for Verticillium spp., amended with neomycin and streptomycin (2). The samples yielded six isolates, two from each of the three symptomatic trees, all of which were putatively identified as V. nonalfalfae based on the presence of verticillate conidiophores and formation of melanized hyphae. DNA was extracted from three isolates and molecular analyses performed using known primers (1) coding for elongation factor 1-alpha (EF), glyceraldehyde-3-phosphate dehydrogenase (GPD), and tryptophan synthase (TS). A BLAST search generated sequences that revealed 100% similarity to V. nonalfalfae for all three protein coding genes among the three Ohio isolates and reference sequences from Ailanthus, including isolates VnAaPA140 (GenBank Accession Nos. KC307764, KC307766, and KC307768) and VnAaVA2 (KC307758, KC307759, and KC307760), as well as isolate PD592 from potato (JN188227, JN188163, and JN188035), thereby confirming taxonomic placement of the Ohio Ailanthus isolates among those recovered from Ailanthus in Pennsylvania and Virginia. Aligned sequences from one representative isolate, VnAaOH1, were deposited into GenBank as accessions KC307761 (EF), KC307762 (GPD), and KC307763 (TS). In August 2012, the pathogenicity of all six isolates was confirmed by root-dipping 10 healthy 3-week-old A. altissima seedlings (seeds collected in University Park, PA) into conidial suspensions of 1 × 10⁷ cfu/ml, wherein all inoculated seedlings wilted and died within 4 and 9 weeks, respectively. V. nonalfalfae was reisolated from all inoculated seedlings; control seedlings inoculated with distilled water remained asymptomatic. Ohio is the third state from which V. nonalfalfae has been reported to be pathogenic on A. altissima. If V. nonalfalfae proves to be widespread, it may represent a natural biocontrol for the invasive A. altissima. Also, since USDA APHIS evaluates and regulates new potential biocontrol agents on a state-by-state basis, it is important to document each state in which V. nonalfalfae is killing A. altissima, so that in-state inoculum can be used for biocontrol efforts, simplifying the regulatory process. References: (1) P. Inderbitzin et al. 2011 PLoS ONE, 6, e28341, 2011. (2) M. J. Schall and D. D. Davis. Plant Dis. 93:747, 2009. (3) A. L. Snyder et al. Plant Dis. 96:837, 2013.

First Report of Verticillium Wilt of Ailanthus altissima in Virginia Caused by Verticillium nonalfalfae

Ailanthus altissima (Mill.) Swingle, commonly known as tree-of-heaven, is an invasive tree species that has spread throughout the United States since its introduction in 1784 (2). During a survey in July 2009, approximately 1,100 A. altissima trees were observed at two locations in western Virginia (a roadside in Montgomery Co. and a wooded area adjacent to a railroad in Bedford Co.) exhibiting foliar wilt symptoms, defoliation, yellowish vascular discoloration, or death at an incidence of ~77%. Similar symptoms on A. altissima were reported in Roanoke, VA in the early 1930s and after 2005 in Pennsylvania, attributed to a Verticillium sp. (1,2). To identify the causal agent, discolored xylem tissue samples were excised from 10 symptomatic A. altissima trees at both locations, soaked in 1% NaOCl for 2 min, rinsed with sterilized distilled water for 5 min, and placed onto plum extract agar. Cultures were incubated in the dark at 22°C for 7 to 14 days. The resultant colonies (three to four per location) were subcultured and identified putatively as a Verticillium sp. closely related to Verticillium albo-atrum Reinke and Berthold (3), based on melanized, thick-walled, resting mycelia and phialides arranged in verticillate whorls that amassed round, oval-shaped conidia (5.1 ± 1.2 μm × 2.8 ± 0.4 μm, n = 100). Molecular identification of two fungal isolates (one per location) was determined by amplification of the protein coding genes elongation factor 1-alpha (EF), glyceraldehyde-3-phosphate dehydrogenase (GPD), and tryptophan synthase (TS), using PCR primers developed recently for Verticillium (3). A BLAST search on the edited contigs revealed 100% sequence similarity for all three protein coding genes among the two isolates and reference sequences of isolates PD592 (GenBank Accessions JN188227, JN188163, and JN188035 for EF, GPD, and TS, respectively) and VnAaPA140 (KC307764, KC307766, and KC307768 for EF, GPD, and TS, respectively) of the newly-proposed species, V. nonalfalfae (formerly V. albo-atrum). Aligned sequences from one representative isolate, VnAaVA2 (Bedford Co.), were deposited into GenBank as KC307758 (EF), KC307759 (GPD), and KC307760 (TS). To confirm pathogenicity to A. altissima, the two molecularly characterized isolates (one per location) were inoculated into 18 10-week old A. altissima stems that were grown in an environmental chamber at 24°C, 60% RH, and a 12-h photoperiod from seeds collected in Blacksburg, VA. A conidial suspension of each isolate was injected into each stem (0.1 ml of 1 × 10⁸ CFU/ml/stem). All 36 seedlings inoculated with the proposed V. nonalfalfae isolates developed wilting of leaflets within 2 weeks post-inoculation (WPI), defoliation of leaflets by 6 WPI, and were dead by 9 WPI. Eighteen control seedlings were inoculated similarly with distilled water, and remained asymptomatic. Fungi resembling the proposed species V. nonalfalfae were reisolated from all inoculated stems except the control plants, and the species confirmed morphologically as described above. V. nonalfalfae is a recently proposed species that can infect a variety of plant species (3). To our knowledge, this is the first report of this proposed species on A. altissima in Virginia. New state reports of this pathogen on A. altissima are important for regulatory issues associated with using this pathogen as a potential biological control agent. References: (1) G. F. Gravatt and R. B. Clapper. Plant Dis. Rep. 16:96, 1932. (2) M. J. Schall and D. D. Davis. Plant Dis. 93:747, 2009. (3) P. Inderbitzin et al. PLoS ONE, 6, e28341, 2011.

An inordinate fondness for Fusarium: phylogenetic diversity of fusaria cultivated by ambrosia beetles in the genus Euwallacea on avocado and other plant hosts

Ambrosia beetle fungiculture represents one of the most ecologically and evolutionarily successful symbioses, as evidenced by the 11 independent origins and 3500 species of ambrosia beetles. Here we document the evolution of a clade within Fusarium associated with ambrosia beetles in the genus Euwallacea (Coleoptera: Scolytinae). Ambrosia Fusarium Clade (AFC) symbionts are unusual in that some are plant pathogens that cause significant damage in naïve natural and cultivated ecosystems, and currently threaten avocado production in the United States, Israel and Australia. Most AFC fusaria produce unusual clavate macroconidia that serve as a putative food source for their insect mutualists. AFC symbionts were abundant in the heads of four Euwallacea spp., which suggests that they are transported within and from the natal gallery in mandibular mycangia. In a four-locus phylogenetic analysis, the AFC was resolved in a strongly supported monophyletic group within the previously described Clade 3 of the Fusarium solani species complex (FSSC). Divergence-time estimates place the origin of the AFC in the early Miocene ∼21.2 Mya, which coincides with the hypothesized adaptive radiation of the Xyleborini. Two strongly supported clades within the AFC (Clades A and B) were identified that include nine species lineages associated with ambrosia beetles, eight with Euwallacea spp. and one reportedly with Xyleborus ferrugineus, and two lineages with no known beetle association. More derived lineages within the AFC showed fixation of the clavate (club-shaped) macroconidial trait, while basal lineages showed a mix of clavate and more typical fusiform macroconidia. AFC lineages consisted mostly of genetically identical individuals associated with specific insect hosts in defined geographic locations, with at least three interspecific hybridization events inferred based on discordant placement in individual gene genealogies and detection of recombinant loci. Overall, these data are consistent with a strong evolutionary trend toward obligate symbiosis coupled with secondary contact and interspecific hybridization.