Next Article in Journal
Enhanced Emission of Monoterpene 3-Carene in Pinus densiflora Infected by Pine Wood Nematode and Characterization of 3-Carene Synthase
Previous Article in Journal
Radial Variation of Wood Anatomical Properties Determines the Demarcation of Juvenile-Mature Wood in Schima superba
Previous Article in Special Issue
Phylogenetic Position of Geosmithia spp. (Hypocreales) Living in Juniperus spp. Forests (Cupressaceae) with Bark Beetles of Phloeosinus spp. (Scolytinae) from the Northeast of Mexico
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Forests
Volume 12
Issue 4
10.3390/f12040513
forests-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Raffaelea quercina sp. nov. Associated with Cork Oak (Quercus suber L.) Decline in Portugal

by
Maria L. Inácio
1,*,
José Marcelino
2,
Arlindo Lima
3,4,
Edmundo Sousa
1 and
Filomena Nóbrega
1
1
Instituto Nacional de Investigação Agrária e Veterinária, Quinta do Marquês, 2780-159 Oeiras, Portugal
2
Entomology and Nematology Department, University of Florida, 1881 Natural Area Dr., Gainesville, FL 32608, USA
3
LEAF—Linking Environment Agriculture and Food, Instituto Superior de Agronomia (ISA), University of Lisbon, Tapada da Ajuda, 1349-017 Lisboa, Portugal
4
LPVVA—Laboratório de Patologia Vegetal “Veríssimo de Almeida”, Instituto Superior de Agronomia (ISA), University of Lisbon, Tapada da Ajuda, 1349-017 Lisboa, Portugal
*
Author to whom correspondence should be addressed.
Forests 2021, 12(4), 513; https://doi.org/10.3390/f12040513
Submission received: 25 February 2021 / Revised: 14 April 2021 / Accepted: 14 April 2021 / Published: 20 April 2021
(This article belongs to the Special Issue Insects as Vectors of Forest Diseases)
Browse Figures
Review Reports Versions Notes

Abstract

:
Research Highlights: Raffaelea quercina sp. nov. is an ophiostomatoid fungus isolated from the ambrosia beetle Platypus cylindrus. The species occurs in symptomatic Portuguese cork oak trees, (Quercus suber L.), exhibiting vegetative decline. Background and Objectives: Quercus suber L. is a species restricted to the Mediterranean basin, of special economic importance as it constitutes the crucial raw material for the cork production industry, in particular for Portugal, the world’s leading producer. Over the last three decades a progressive and alarming decline of cork oak trees has been observed across its distribution area, including Portugal. The ambrosia beetle Platypus cylindrus, commonly known as the oak pinhole borer, establishes symbiotic relationships with fungi from which it depends for survival and for oak colonization. Some of these fungi are ophiostomatoid species of the Raffaelea genus, known as ambrosia fungi associated with ambrosia beetles. Some Raffaelea species exhibit phytopathogenic activity causing wilting and/or death of trees. The objective of the present study is to identify the association between P. cylindrus and Raffaelea species in Portuguese cork oak stands showing symptoms of disease and decline. Materials and Methods: A total of 300 adult insects were collected as they emerged from cork oak logs, sampled from symptomatic trees. Axenic isolates of Raffaelea species were obtained from the beetles and their galleries in the trunks and identified based on morphological features and molecular analysis of the SSU and LSU rDNA regions. Results: Two Raffaelea species were identified, i.e., R. montetyi and a novel Raffaelea species closely related to R. canadensis. The novel species is morphologically and genetically characterized in this study, and erected as Raffaelea quercina M.L. Inácio, E. Sousa & F. Nóbrega, sp. nov. Raffaelea quercina constitutes a new phytopathogenic fungal species associated with P. cylindrus and cork oak trees exhibiting symptoms of vegetative decline. Conclusions: Raffaelea species appear to have a significant role in cork oak decline. Future research on the association between P. cylindrus and Raffaelea species, encompassing the trans-European and North African wide-range of cork oak stands, would further clarify the relationships between ambrosia beetles, associated fungi and cork oak decline, contributing to a better understanding of the phenomena and for strategies aiming to halt the continuous decline of the unique cork oak stands enclosed in the Mediterranean basin.

1. Introduction

The cork oak (Quercus suber L.) is an oak species native to the Mediterranean zones of southwest Europe and northwest Africa. In Portugal, cork oak landscapes (montados) cover approximately 720 thousand ha [1], providing a vital source of income, especially due to the ability to produce cork, a raw material widely used for wine bottle stoppers. Montados are listed under the EU Habitats Directive and are key protected habitats part of the Natura 2000 network and considered a EUNIS habitat type.
Since the 1890s, a cork oak decline has been reported in southwestern Portugal [2]. The occurrence of the decline was assumed as a complex phenomenon caused by the interaction of multiple biotic and abiotic factors [3], such as climatic variations (drought and frost), excessive harvesting and pruning, and attacks of insect pests and pathogens [4,5,6,7]. Coinciding with the gradual decline of cork oak stands increasing attacks by the wood borer Platypus cylindrus Fab. were reported [8,9,10]. The adults dig galleries in the wood of the host plants (Q. suber) while inoculating fungal ectosymbionts whose mycelium is fed on by both adults and larvae (Figure 1).
In literature, more than 300 species of fungi are reported on cork oak, of which at least 100 are pathogenic [11,12,13,14,15,16,17,18,19]. Despite the numerous investigations carried out so far, it is difficult at first to assess which fungi could be phytopathogenic and thus responsible for participating in cork oak decline. However, several Raffaelea species were noticed provoking tree mortality and should be taking into consideration. Raffaelea (Arx & Hennebert 1965) is a genus of primarily asexual fungi including more than 20 species in Ophiostomatales [20,21] although more recently a species was found to have a sexual stage [22]. Some species in the genus, such as the causal agents of oak wilt in Japan (R. quercivora) [23] and Korea (R. quercus-mogolicae) [24], and laurel wilt in the USA (R. lauricola) [25] are important tree-killing pathogens.
The genus Raffaelea (Ophiostomatales) belongs to the ophiostomatoid fungi communities generally living in symbiosis with wood-boring bark beetles and their host’s species. The symbiotic Raffaelea species exhibit frequent associations with the ambrosia beetle Platypus cylindrus, living in specialized structures called mycangia, particularly of female adults (Figure 2). Platypus cylindrus act as a vector for the dispersal of phytopathogenic fungi and this symbiotic behavior has been contributing for increasing the cork oak decline.
Species of Raffaelea are difficult to distinguish as they lack clearly defining morphological features, so identification can be based on rDNA sequences [26,27], in particular on the nuclear large subunit ribosomal DNA (LSU rDNA) [20].
The aim of this work was to ascertain the transportation and inoculation of Raffaelea species by P. cylindrus and to discuss their role in cork oak decline. During our research, adult insects emerged from symptomatic cork oak trees were collected and Raffaelea-like cultures were isolated, both from the insects and the galleries, and their identity determined based on morphological characters and DNA phylogenetic inference.

2. Materials and Methods

2.1. Beetle Collection and Fungal Isolation

From May 2005–2007, independent surveys were undertaken in two declining cork oak regions of Portugal, Ribatejo and Alentejo provinces. From cork oak trees severely infested by P. cylindrus and based on visible symptoms of decline, a total of 12 logs with ca. 30 cm diameter and 0.5 m length were collected, one from each tree. In the INIAV laboratories, three hundred adult P. cylindrus, 158 females and 142 males, emerged and were gathered live in fine mesh nets attached to a silicone joint on logs. Each beetle was dissected aseptically with iris scissors to obtain their mycangia, aiming to determine the fungal presence within these morphological structures. At the same time, pieces of wood containing fragments of the respective gallery were collected. All biological material was surface sterilized for 1 min in 1% sodium hypochlorite and then rinsed in sterile dH2O and plated in malt extract agar (10 g MEA, Difco™, Franklin Lakes, NJ, USA, 15 g agar) amended with 500 mg/L cycloheximide and 500 mg/L streptomycin. Plates were incubated at room temperature in the dark for 1–2 weeks depending on fungal growth. Colonies of different size, color and mycelial pattern (concentric rings, yeasty growth, hyaline margins, etc.) were considered putative species.
Axenic cultures of each fungal strain were obtained (PC acronyms) and voucher specimens of each mycelial phenotype were deposited in the culture collection of INIAV Institute (Micoteca da Estação Agronómica Nacional (MEAN). In addition, mycelial plugs of at least three isolates of each putative fungal species were placed in the voucher specimen collection at Iowa State University (C acronyms) for storage and subsequent DNA extraction and sequencing (Table 1).

2.2. Fungal Morphology

Colony morphology was observed after 10 days of cultivation on 1.5% MEA medium at 25 °C in the dark. Colonized agar plugs (5 mm diam) were excised from actively growing 1 wk old cultures of three different isolates of each putative species. These discs were transferred to the centers of fresh dishes containing 20 mL 1.5% MEA. Growth rates were determined at temperatures ranging from 5–35 °C, at five-degree intervals, three and ten days after inoculation, in the dark. Colony diameter of six replicates cultures were calculated by averaging the twelve measurements. Mycelial colors were described using the terminology from Saccardo [28]. Tolerance to cycloheximide was assessed by measuring fungal growth on MEA amended with 100, 500 and 1.000 ppm cycloheximide after autoclaving. For fungal morphological characterization 3–5-day-old slide cultures [29] mounted in lactophenol were examined with light microscopy with differential interference contrast microscopy (BX-41 with DP11, Olympus, Center Valley, PA, USA). Fifty measurements were obtained for each taxonomically informative structure. For scanning electron microscopy (SEM), small wood blocks (5 × 2 × 5 mm) bearing fungal structures were fixed [30,31]. After fixation, samples were critical point dried, sputter coated twice with gold palladium (98:2) and examined using a JEOL 35 scanning electron microscope (JEOL, Peabody, MA, USA).

2.3. DNA Extraction, Amplification and Sequencing

Fourteen axenic fungal strains representing all the putative fungi species retrieved from P. cylindrus were selected for molecular analyses. Genomic DNA was extracted from mycelium plugs scraped with a sterile scalpel from the surface of individual cultures using the extraction kit Puregene® DNA Purification (Gentra Systems Inc., Minneapolis, MN, USA) following the manufacturer’s instructions. Cultures of Raffaelea montetyi Morelet from Centraalbureau voor Schimmelcultures (strain CBS 451.94) and R. quercivora Kubono & Shin (isolates MAFF919 and MAFF921) from Mie University, Dep. Forest Pathology and Mycology, Japan, were used as reference material.
Polymerase Chain Reactions (PCR) were performed using PCR primer pairs NS1, NS3, NS4 and NS6 [32] for generating amplicons of the small subunit region of the ribosomal RNA gene (SSU rDNA) and the primers NL1 and NL4 [27] and LROR and LR5 to amplify the D1/D2 region of the large subunit region (LSU rDNA). All PCR reactions were performed in a 50 µL reaction containing 50–100 ng DNA template, 0.2 units of Taq Dream DNA polymerase (MBI Fermentas, Vilnius, Lithuania), 1× reaction buffer, 0.2 mM dNTPs, 4% (v/v) DMSO and 0.4 µM of each primer. PCR reactions were performed in a Biometra TGradient thermo cycler (Biometra, Göttingen, Germany) and the thermal cycling parameters included an initial denaturation at 95 °C for 5 min, 35 cycles at 94 °C for 1 min, annealing at 50 °C for SSU and 40 cycles at 55 °C for the LSU, and primer elongation at 72 °C for 1.5 min. PCR products were purified with QIAquick PCR Purification kit (Qiagen Inc., Valencia, CA, USA) following the manufacturer’s instructions and sequenced in both directions at STABVida Sequencing Laboratory, Caparica (Portugal) on an ABI PRISM 3730xl DNA analyser (Applied Biosystems, Foster City, CA USA) using the same primers as those used for the amplification reaction for the SSU region and the primers LROR and LR3 for the LSU region [20]. Chromatograms were edited and consensus sequences were generated with Sequencher™ (Gene Codes Corp., Ann Arbor, MI, USA). Sequences were analyzed with all closely related sequences obtained from GenBank using BLAST (i.e., Maximum Identity of database segments against the subject sequence above 97%) and previously reported sequences [20,26,27,31]. Sequences were aligned individually with the Clustal W [33] and retrieved with Jalview software [34]. When necessary, subsequent manual adjustments were made. Sequences generated in this study were deposited in GenBank (accession numbers are included in Table 1). Primers were excluded from published sequences and sequence alignments.

2.4. Phylogenetic Analysis

Additional sequences using the BLAST algorithm on the National Center for Biotechnology Information (NCBI, https://blast.ncbi.nlm.nih.gov/ accessed on 29 June 2020) database were selected and incorporated in the analyses (Table 1). Phylogenetic analysis was conducted separately for the two rDNA regions (nSSU and nLSU) and the outgroup sequences were selected based on their genetic distance to Ophiostomatales used in the phylogenetic analyses [27,35,36]. Phylogenetic relationships were performed using MEGA X [37] and the Maximum Likelihood (ML) method based on the Kimura 2-parameter model. The robustness of ML tree was inferred using 1.000 bootstrap replicates.

3. Results

3.1. Fungal Isolation and Identification

Fungal isolations were performed directly from adult P. cylindrus emerged from symptomatic cork oaks, and from pieces of their galleries. From these beetles, 249 (83%) yielded a least one species of Ophiostomatales and only 4% yielded more than one species. It was possible to retrieve at least one species from each tree. A total of 270 individual ophiostomatalean isolates were obtained which, utilizing cultural features, microscopic characteristics and growth rate, were grouped according to colony morphologies. Among other fungi, a total of 14 Raffaelea-like colonies were selected for further studies.

3.2. Phylogenetic Analyses

Molecular identification of the 14 isolates based on SSU and LSU rDNA sequences confirmed that obtained sequences were species of Raffaelea (i.e., Raffaelea sp. and R. montetyi). The two species isolated were distinguished from each other by analysis of sequences and Maximum Likelihood (ML) phylogenetic analyses (Figure 3 and Figure 4). A total of 1.568 base pairs were sequenced and the ML analysis revealed that one of the species represent a new species of Raffaelea belonging to the Raffaelea sensu stricto De Beer & Wingfield (2013) and described here as R. quercina sp. nov.

3.3. Morphology and Taxonomy

Raffaelea quercina M.L. Inácio, E. Sousa & F. Nóbrega, sp. nov. (Figure 5).
(1)
MycoBank: 838901
(2)
Holotype: LISE 96317
(3)
Etymology: Named after the host genus from which it was isolated, Quercus
(4)
Host/Distribution: On galleries of Quercus suber in Portugal = on mycangia of Playpus cylindrus
Description: Colonies effuse, yeast-like, with aerial brownish green floccose mycelium in the center, attaining a diam of 45–46 mm after 10 days on MEA, at 25 °C. Colony color from cream (27) to fuliginous (11) (Figure 5A). Hyphae hyaline and septate repeatedly branched and interlocked, hyphal ends sometimes developing into torulose swellings. Conidiophores unbranched, hyaline, solitary or clustered together to form hyaline sporodoquia. Conidiogenous cells without conspicuous scars from conidial dehiscence. Conidia blastosporic (sprout cells), unicellular and hyaline, usually solitary but sometimes in monilioid chains after germination in situ, smooth-walled, triangular to ovoid or fusiform, (6.7-)7.7-8.4(-10.9) × (2.5-)3.2-3.6(-5.0) µm.
Material examined: PORTUGAL, Chamusca (Santarém), in galleries of the insect Platypus cylindrus on declining Quercus suber, Maria L. Inácio, July 2005 (LISE 96,317 holotype; ex-type culture PC05.042 = MEAN 1292 = C2513 = CBS 147555); PORTUGAL, Chamusca (Santarém) in the mycangia of Platypus cylindrus emerged from Quercus suber, Maria L. Inácio, July 2005 (living culture, PC05.041 = MEAN 1291 = C2516); PORTUGAL, Chamusca (Santarém) in the mycangia of Platypus cylindrus emerged from Quercus suber, Maria L. Inácio, May 2005 (living culture, PC05.007 = MEAN 1290 = C2516 = CBS 147554).
Notes: Raffaelea quercina is morphologically similar to R. canadensis but colonies never wrinkled at the centre and with no cracks in agar under the wrinkled area; odour of ripened bananas never present as in R. canadensis cultures; R. canadensis spores usually globose (5-)6.5-8.0(-13) µm while triangular to ovoid or fusiform in R. quercina (6.7-)7.7-8.4(-10.9) × (2.5-)3.2-3.6(-5.0) µm. They are clearly separated in the phylograms of both SSU and LSU rDNA regions (see Figure 3 and Figure 4).
The new Portuguese Raffaelea species presents a stable position in the inferred phylogenetic relationships. The species is clearly separated in the phylogram based on SSU and LSU sequence data, R. quercina isolates formed a separate clade with strong support values on the analyses performed.

4. Discussion

In this research, Raffaelea quercina is described as a new species of the genus Raffaelea, isolated from the ambrosia beetle Platypus cylindrus and its galleries on symptomatic cork oak trees in Portugal in 2005 and in the following years during entomological surveys (data not shown).
The known association between Raffaelea species and P. cylindrus implies that R. quercina was probably transmitted to the trees by the insects. Based on the morphology and molecular phylogenetic analyses of SSU and LSU sequence data, this taxon proved to be distinct from other species from the genus.
Raffaelea montetyi was the predominant Raffaelea species isolated from P. cylindrus in Portugal [4], consistent with the results already described [26,38]. Isolations from adults yielded R. montetyi in about 45% of the asexual cycloheximide-tolerant symbionts, being R. quercina less frequent (33 individual isolates corresponding to 12.2% of the isolates). In contrast to the slow growth of most of ambrosia fungi, R. montetyi grows rapidly being able to colonize the galleries system much faster than the other symbionts. Taking into consideration previous studies on P. cylindrus mycoflora [12,39,40,41] where R. montetyi was not identified, its presence on the symbiosis appears to constitute an ecological adaptation aiming faster and efficient host colonization. Raffaelea montetyi had previously been isolated from P. cylindrus [38] but confirmation of its implication with declining oaks was not assessed until the work of Inácio et al. [4].
Portuguese Raffaelea near R. canadensis isolates retrieved from P. cylindrus and its galleries in cork oak were identical to the holotype R. canadensis, both morphologically and genetically, with modest differences. Pairwise p distances between Portuguese and holotype strains available in GenBank showed nucleotide differences of ca. 2% (5 bp) for the more discriminate nuclear rDNA LSU regions. This far, R. canadensis had been solely identified in association Gnathotrichus sulcatus Lec. (as A. sulcati) in Psedotsuga menziesii (Douglas fir) [42]. However, a recent association of an unidentified Raffaelea species similar to R. canadensis (1.9% bp divergence for the LSU region, EU177458) was also reported from another ambrosia beetle, Xyleborus glabratus Eichh. in Persea borbonia (redbay) hosts [43]. Based on the comprehensive molecular and morphological data from our study we believe the new associations recently found with the ambrosia beetles P. cylindrus may consist of unreported Raffaelea closely related to R. canadensis with a selective preference for associations with a specific insect species. Raffaelea quercina is therefore newly described both in associations with P. cylindrus and with cork oak declining trees.
It has generally been accepted that one or few fungal species are associated with a particular ambrosia beetle species [42,44] but recent studies pointed out that the symbionts of ambrosia beetles are more diverse [45,46,47], more promiscuous [48] and more competitive than previously assumed and Raffaelea species may compete among each other for entrance to and growth within the mycangium [20,43]. Species of Raffaelea have been related with mass mortality of oak trees in Japan [23,27] and laurel wilt of redbay in the USA [49]. Portuguese Raffaelea isolates have a proven pathogenicity against cork oak seedlings and therefore could have a significant role in cork oak decline, in particular R. montetyi [4]. Raffaelea quercina was shown to cause wilting on the inoculated seedlings but with a low level of aggressiveness, as obtained for other Raffaelea species [50,51]. A comprehensive morphological and phytopathological assessment, coupled with a robust phylogenetic analysis, of the complex of fungi associated with P. cylindrus populations across a trans-European and north African wide-range number of cork oak stands could further clarify the relationships of ambrosia beetles and their associated fungi with cork oak decay and contribute to halt the spread of the decline in the unique cork oak landscapes enclosed in the Mediterranean basin.

5. Conclusions

A novel fungal species, Raffaelea quercina was described. Our previous works demonstrated that R. quercina is a pathogenic fungus towards Q. suber seedlings as R. montetyi, hence probably contributing to cork oak decline and to the establishment of its associated ambrosia insect, Platypus cylindrus.
Cork oak forests represent a very specific, delicately balanced ecosystem which only persists in the Mediterranean basin. It is therefore of major concern that over the last three decades an alarming decline of trees has increased across its distribution area, namely in the representative Portuguese cork oak stands. Being cork oak decline a multifactorial process, several causes have been pointed out as contributors to tree mortality and loss of vigour, namely biotic factors. Platypus cylindrus emerged as a determinant factor in the decline of stands and its population outbreaks in the last decades have caused heavy economic damages since cork loses its quality and ultimately trees death overcomes. The symptoms and signs exhibited by cork oaks attacked by P. cylindrus, including the presence of numerous entry holes and profuse sawdust emerging from these holes, do not reveal the real dimension of the attack intensity within the trunk. Only cutting the attacked tree and following the insect tunnels, is possible to ascertain the extent of the galleries into the sapwood. The galleries system often becomes quite complex. Coupled with this extensive boring activity, the inoculation of ambrosia fungi is part of the insect strategy to establish its offspring in the host trees.
In terms of role in oak decline, the combined action of P. cylindrus massive attacks and extensive boring with the inoculation of ambrosia fungi, leads to an increase of tree mortality enhanced in these past three decades through these new associations with more aggressive and wilt causing fungi. Understanding the ecology and population dynamics of P. cylindrus-associated fungi is important for the surveillance and management of the beetle-fungal complex, and could improve prediction and modeling. The ambrosia beetles and their associated fungi constitute a small part of a much larger food web, the complexities of which we have barely start to understand. There are indeed many unanswered questions about the extraordinary complexity between these wood-inhabiting beetles, the assembly of fungi which they transmit, and the tree which supports the whole community. We believe the research described herein is a contribution to clarify focal aspects of the pathology of cork oak decline, aiming to preserve the economic and cultural heritage of the unique cork oak stands and landscapes present in the Mediterranean.

Author Contributions

Conceptualization, M.L.I. and E.S.; methodology, M.L.I., E.S. and F.N.; software, F.N. and J.M.; validation, M.L.I., J.M., A.L., E.S. and F.N.; formal analysis, M.L.I., J.M., A.L., E.S. and F.N.; resources, M.L.I., E.S. and F.N.; data curation, M.L.I. and F.N.; writing—original draft preparation, M.L.I. and F.N.; writing—review and editing, M.L.I., J.M., A.L., E.S. and F.N.; visualization, M.L.I., J.M., A.L., E.S. and F.N.; supervision, E.S. and A.L.; project administration, M.L.I.; funding acquisition, M.L.I., E.S. and F.N. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported in part by a grant from the Fundação para a Ciência e a Tecnologia (FCT) BD/26033/2005 and by Instituto Nacional de Investigação Agrária, I.P.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are openly available in [GenBank].

Acknowledgments

The authors would like to thank Marina Cardoso for the technical assistance and Joana Henriques for the valuable contribution in some parts of the practical work, for the enthusiasm and passion for the ambrosia fungi shared with us for some years. We are also grateful to Thomas Harrington of Iowa State University (USA) and Wilhelm de Beer and. Michael Wingfield of FABI, University of Pretoria (South Africa) for teaching us so many important things about Raffaelea fungi, and for receiving our precious strains.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. ICNF. 6° Inventário Florestal Nacional (IFN6), 22 pp, Versão 1.0 2019. Instituto da Conservação da Natureza e das Florestas. Available online: http://www2.icnf.pt/portal/florestas/ifn/ifn6 (accessed on 6 December 2020).
  2. Cabral, M.T.; Ferreira, M.C.; Moreira, T.; Carvalho, E.C.; Diniz, A.C. Diagnóstico das causas da anormal mortalidade dos sobreiros a Sul do Tejo. Sci. Gerund. 1992, 18, 205–214. [Google Scholar]
  3. Cabral, M.T.; Lopes, F.; Sardinha, R.M. Determinação das causas da morte do sobreiro nos concelhos de Santiago do Cacém, Grândola e Sines. Silva Lusit. 1993, 1, 7–24. [Google Scholar]
  4. Inácio, M.L.; Henriques, J.; Lima, A.; Sousa, E.B. Ophiostomatoid fungi associated with cork oak mortality in Portugal. Iobc/Wprs Bull. 2012, 76, 89–92. [Google Scholar]
  5. Linaldeddu, B.T.; Sirca, C.; Spano, D.; Franceschini, A. Variation of endophytic cork oak-associated fungal communities in relation to plant health and water stress. For. Pathol. 2011, 41, 193–201. [Google Scholar] [CrossRef] [Green Version]
  6. Kim, H.N.; Jin, H.Y.; Kwak, M.J.; Khaine, I.; You, H.N.; Lee, T.Y.; Ahn, T.H.; Woo, S.Y. Why does Quercus suber species decline in Mediterranean areas? J. Asia Pac. Biodivers. 2017, 10, 337–341. [Google Scholar] [CrossRef]
  7. Ragazzi, A.; Vagniluca, S.; Moricca, S. European expansion of oak decline: Involved microorganisms and methodological approaches. Phytopathol. Mediterr. 1995, 34, 207–226. [Google Scholar]
  8. Ferreira, M.C.; Ferreira, G.W. Platypus cylindrus F. (Coleóptera: Platipodidae) Plaga de Quercus suber. Boletin. Sanid. Veg. Plagas 1989, 4, 301–305. [Google Scholar]
  9. Sousa, E.M.; Débouzie, D.; Pereira, H. Le rôle de l’insecte Platypus cylindrus F. (Coleoptera, Platypodidae) dans le processus de dépérissement des peuplements de chêne-liège au Portugal. IOBC WPRS Bull. 1995, 18, 24–37. [Google Scholar]
  10. Cabral, M.T.; Ferreira, M.C. Pragas dos Montados; Estação Florestal Nacional: Lisboa, Portugal, 1999; p. 94. [Google Scholar]
  11. Félix, C.; Pinto, G.; Amaral, J.; Fernandes, I.; Alves, A.; Esteves, A.C. Strain-related pathogenicity in Diplodia corticola. For. Pathol. 2017, 47, e12366. [Google Scholar] [CrossRef]
  12. Sousa, E.; Tomaz, I.L.; Moniz, F.A.; Basto, S. La répartition spatiale des champignons associés à Platypus cylindrus Fab. (Coleoptera: Platypodidae). Phytopathol. Mediterr. 1997, 36, 145–153. [Google Scholar]
  13. Santos, M.N.; Machado, M.H.; Bragança, M.H.; Ramos, H.; Sousa, E.; Tomaz, I. Mycoflora associated with cork oak (Quercus suber L.) in Portugal. IOBC WPRS Bull. 1999, 22, 25–28. [Google Scholar]
  14. Luque, J.; Parladé, J.; Pera, J. Pathogenicity of fungi isolated from Quercus suber in Catalonia NE Spain). For. Pathol. 2000, 30, 247–263. [Google Scholar] [CrossRef]
  15. Moreira, C. Distribution of Phytophthora cinnamomi in cork oak stands in Portugal. IOBC WPRS Bull. 2002, 25, 41–48. [Google Scholar]
  16. Franceschini, A.; Linaldeddu, B.T.; Marras, F. Occurrence and distribution of fungal endophytes in declining cork oak forests in Sardinia (Italy). IOBC WPRS Bull. 2005, 28, 67–74. [Google Scholar]
  17. Luque, J.; Pera, J.; Parladé, J. Evaluation of fungicides for the control of Botryosphaeria corticola on cork oak in Catalania (NE Spain). For. Pathol. 2008, 38, 147–155. [Google Scholar] [CrossRef]
  18. Linaldeddu, B.T.; Sirca, C.; Spano, D.; Franceschini, A. Physiological responses of cork oak and holm oak to infection by fungal pathogens involved in oak decline. For. Pathol. 2009, 39, 232–238. [Google Scholar] [CrossRef]
  19. Linaldeddu, B.T.; Scanu, B.; Maddau, L.; Franceschini, A.; Belbahri, L. Diplodia corticola and Phytophthora cinnamomi: The main pathogens involved in oak decline on Caprera Island (Italy). For. Pathol. 2014, 44, 191–200. [Google Scholar] [CrossRef]
  20. Harrington, T.C.; Aghayeva, D.N.; Fraedrich, S.W. New combinations in Raffaelea, Ambrosiella, and Hyalorhinocladiella, and four new species from the redbay ambrosia beetle, Xyleborus glabratus. Mycotaxon 2010, 111, 337–361. [Google Scholar] [CrossRef] [Green Version]
  21. De Beer, Z.W.; Wingfield, B.D.; Wingfield, M. The Ophiostoma piceae complex in the Southern Hemisphere: A phylogenetic study. Mycol. Res. 2003, 107, 469–476. [Google Scholar] [CrossRef] [PubMed]
  22. Musvuugwa, T.; de Beer, Z.W.; Duong, T.A.; Dreyer, L.L.; Oberlander, K.C.; Roets, F. New species of Ophiostomatales from Scolytinae and Platypodinae beetles in the Cape Floristic Region, including the discovery of the sexual state of Raffaelea. Antonie Van Leeuwenhoek J. Microbiol. 2015, 108, 933–950. [Google Scholar] [CrossRef] [PubMed]
  23. Kubono, T.; Ito, S. Raffaelea quercivora sp. nov. associated with mass mortality of Japanese oak, and the ambrosia beetle (Platypus quercivorus). Mycoscience 2002, 43, 255–260. [Google Scholar] [CrossRef]
  24. Kim, K.H.; Choi, Y.J.; Seo, S.T.; Shin, H.D. Raffaelea quercus-mongolicae sp. nov. associated with Platypus koryoensis on oak in Korea. Mycotaxon 2009, 110, 189–197. [Google Scholar] [CrossRef]
  25. Harrington, T.C.; Fraedrich, S.W.; Aghayeva, D.N. Raffaelea lauricola, a new ambrosia beetle symbiont and pathogen on the Lauraceae. Mycotaxon 2008, 104, 399–404. [Google Scholar]
  26. Gebhardt, H.; Begerow, D.; Oberwinkler, F. Identification of the ambrosia fungus of Xyleborus monographus and X. dryographus (Coleoptera: Curculionidae, Scolytinae). Mycol. Prog. 2004, 3, 95–102. [Google Scholar] [CrossRef]
  27. Matsuda, Y.; Kimura, K.; Ito, S. Genetic characterization of Raffaelea quercivora isolates collected from areas of oak wilt in Japan. Mycoscience 2010, 51, 310–316. [Google Scholar] [CrossRef]
  28. Saccardo, P.A. Chromotaxia seu Nomenclator Colorum Polyglottus Adclitis Speciminibus Coloratis ad Botanicorum et Zoologorum; Patavii, Italy, 1891; p. 22. [Google Scholar]
  29. Riddell, R.W. Permanent stained mycological preparations obtained by slide culture. Mycologia 1950, 42, 265–270. [Google Scholar] [CrossRef]
  30. Lee, S.; Kim, J.-J.; Fung, S.; Breuil, C. A PCR-RFLP marker distinguishing Ophiostoma clavigerum from morphologically similar Leptographium species associated with bark beetles. Can. J. Bot. 2003, 81, 1104–1112. [Google Scholar] [CrossRef]
  31. Massoumi Alamouti, S.; Tsui, C.M.; Breuil, C. Multigene phylogeny of filamentous ambrosia fungi associated with ambrosia and bark beetles. Mycol. Res. 2009, 113, 822–835. [Google Scholar] [CrossRef]
  32. White, T.J.; Bruns, T.; Lee, S.; Taylor, J. Amplification and direct sequencing of fungal ribosomal RNA genes for phylogenetics. In PCR Protocols: A Guide to Methods and Applications; Innis, M.A., Gelfand, D.H., Sninsky, J.J., White, T.J., Eds.; Academic Press: San Diego, CA, USA, 1990; pp. 315–322. [Google Scholar]
  33. Chenna, R.; Sugawara, H.; Koike, T.; Lopez, R.; Gibson, T.J.; Higgins, D.G.; Thompson, J.D. Multiple sequence alignment with the Clustal series of programs. Nucleic Acid Res. 2003, 31, 3497–3500. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  34. Clamp, M.; Cuff, J.; Searle, S.M.; Barton, G.J. The Jalview java alignment editor. Bioinformatics 2004, 20, 426–427. [Google Scholar] [CrossRef] [Green Version]
  35. Gebhardt, H.; Oberwinkler, F. Conidial development in selected ambrosial species of the genus Raffaelea. Antonie Van Leeuwenhoek 2005, 88, 61–66. [Google Scholar] [CrossRef] [PubMed]
  36. Luo, A.R.; Zhang, Y.Z.; Qiao, H.J.; Shi, W.F.; Murphy, R.W.; Zhu, C.-D. Outgroup selection in tree reconstruction: A case of the family Halictidae (Hymenoptera: Apoidea). Acta Entomol. Sin. 2010, 53, 192–201. [Google Scholar]
  37. Kumar, S.; Stecher, G.; Li, M.; Knyaz, C.; Tamura, K. MEGA X: Molecular Evolutionary Genetics Analysis across computing platforms. Mol. Biol. Evol. 2018, 35, 1547–1549. [Google Scholar] [CrossRef] [PubMed]
  38. Morelet, M. Une espèce nouvelle de Raffaelea, isolée de Platypus cylindrus, coléoptère xylomycetophage des chênes. Ann. De La Société Des. Sci. Nat. De Toulon Et Du Var. 1998, 50, 185–193. [Google Scholar]
  39. Sousa, E.M. Contribution à l’étude de la biologie de populations de Platypus cylindrus (Coleóptera: Platypodidae) dans des peuplements de chênes liège au Portugal. In Thèse de Doctorat; Université de Lyon: Lyon, France, 1996; p. 153. [Google Scholar]
  40. Baker, J.M. Ambrosia beetle and their fungi, with particular reference to Platypus cylindrus Fab. Symp. Soc. Gen. Microbiol. 1963, 13, 323–354. [Google Scholar]
  41. Von Arx, J.A.; Hennebert, G.L. Deux champignons ambrosia. Mycopathol. Et. Mycol. Appl. 1965, 25, 309–315. [Google Scholar] [CrossRef]
  42. Funk, A. Fungal symbionts of the ambrosia beetle Gnathotrichus sulcatus. Can. J. Bot. 1970, 48, 1445–1448. [Google Scholar] [CrossRef]
  43. Harrington, T.C.; Yun, H.Y.; Lu, S.; Goto, H.; Aghayeva, D.; Fraedrich, S. Isolations from the redbay ambrosia beetle, Xyleborus glabratus, confirm that the laurel wilt pathogen, Raffaelea lauricola, originated in Asia. Mycologia 2011, 103, 1028–1036. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  44. Batra, L.R. Ecology of ambrosia fungi and their dissemination by beetles. Trans. Kans. Acad. Sci. 1963, 66, 213–236. [Google Scholar] [CrossRef]
  45. Simmons, D.R.; de Beer, Z.W.; Huang, Y.-T.; Bateman, C.; Campbell, A.S.; Dreaden, T.J.; Li, Y.; Ploetz, R.C.; Black, A.; Li, H.-F.; et al. New Raffaelea species (Ophiostomatales) from the USA and Taiwan associated with ambrosia beetles and plant hosts. IMA Fungus 2016, 7, 265–273. [Google Scholar] [CrossRef] [Green Version]
  46. Vanderpool, D.; Bracewell, R.R.; McCutcheon, J.P. Know your farmer: Ancient origins and multiple independent domestications of ambrosia beetle fungal cultivars. Mol. Ecol. 2017, 27, 2077–2094. [Google Scholar] [CrossRef] [PubMed]
  47. Mayers, C.G.; Harrington, T.C.; Mcnewa, D.L.; Roeperb, R.A.; Biedermann, P.; Masuyad, H.; Bateman, C.C. Four mycangium types and four genera of ambrosia fungi suggest a complex history of fungus farming in the ambrosia beetle tribe Xyloterini. Mycologia 2020, 112, 1104–1137. [Google Scholar] [CrossRef] [PubMed]
  48. Li, Y.; Huang, Y.T.; Kasson, M.T.; Macias, A.M.; Skelton, J.; Carlson, P.S.; Yin, M.; Hulcr, J. Specific and promiscuous ophiostomatalean fungi associated with Platypodinae ambrosia beetles in the southeastern United States. Fungal Ecol. 2018, 35, 42–50. [Google Scholar] [CrossRef]
  49. Fraedrich, S.W.; Harrington, T.C.; Rabaglia, R.J.; Ulyshen, M.D.; Mayfield, A.E.; Hanula, J.L.; Eickwort, J.M.; Miller, D.R. A fungal symbiont of the redbay ambrosia beetle causes a lethal wilt in redbay and other Lauraceae in the southeastern United States. Plant Dis. 2008, 92, 215–224. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  50. Eskalen, A.; McDonald, V. First Report of Raffaelea canadensis Causing Laurel Wilt Disease Symptoms on Avocado in California. Plant Dis. 2011, 95, 1189. [Google Scholar] [CrossRef] [PubMed]
  51. Procter, M.; Nel, W.J.; Marincowitz, S.; Crous, P.W.; Wingfield, M.J. A new species of Raffaelea from beetle-infested Leucaena leucocephala. Fungal Syst. Evol. 2020, 6, 305–314. [Google Scholar] [CrossRef] [PubMed]
Forests 12 00513 g001 550
Figure 1. Symptoms on Quercus suber after the attack of Platypus cylindrus; white arrowed, sign of the presence of P. cylindrus on the trunk: orange sawdust coming out of the entry holes. Internal lesions caused by P. cylindrus in the trunk of Q. suber trees: (a) wood staining accompanying the galleries system (b) detail of a gallery section with surrounding wood staining brown (c) bore holes in cork oak heartwood in cross-section (black arrow).
Figure 1. Symptoms on Quercus suber after the attack of Platypus cylindrus; white arrowed, sign of the presence of P. cylindrus on the trunk: orange sawdust coming out of the entry holes. Internal lesions caused by P. cylindrus in the trunk of Q. suber trees: (a) wood staining accompanying the galleries system (b) detail of a gallery section with surrounding wood staining brown (c) bore holes in cork oak heartwood in cross-section (black arrow).
Forests 12 00513 g001
Forests 12 00513 g002 550
Figure 2. Mycangia of Platypus cylindrus: (a) female mycangia, (b) micrograph of female mycangia, (c,d) micrographs of male mycangia, (d) detail of integumentary pits filled with tightly packed spores of ambrosia fungi, (e) dying insect covered by the ambrosial mycelium coming out of the mycangia.
Figure 2. Mycangia of Platypus cylindrus: (a) female mycangia, (b) micrograph of female mycangia, (c,d) micrographs of male mycangia, (d) detail of integumentary pits filled with tightly packed spores of ambrosia fungi, (e) dying insect covered by the ambrosial mycelium coming out of the mycangia.
Forests 12 00513 g002
Forests 12 00513 g003 550
Figure 3. Phylogenetic relationships of Raffaelea isolates collected from Platypus cylindrus emerged from cork oak logs based on the sequence alignment of the partial sequence (1.028 bp) of the SSU region or the rDNA. The phylogram was generated by ML analyses with 1.000 bootstrap replications. Bootstrap values are indicated at the nodes. The analysis involved 31 nucleotide sequences. There were a total of 1.022 positions in the final dataset. Evolutionary analyses were conducted in MEGA X [37].
Figure 3. Phylogenetic relationships of Raffaelea isolates collected from Platypus cylindrus emerged from cork oak logs based on the sequence alignment of the partial sequence (1.028 bp) of the SSU region or the rDNA. The phylogram was generated by ML analyses with 1.000 bootstrap replications. Bootstrap values are indicated at the nodes. The analysis involved 31 nucleotide sequences. There were a total of 1.022 positions in the final dataset. Evolutionary analyses were conducted in MEGA X [37].
Forests 12 00513 g003
Forests 12 00513 g004 550
Figure 4. Phylogenetic relationships of Raffaelea isolates collected from Platypus cylindrus and its galleries on cork oak logs based on the sequence alignment of the partial sequence of the LSU region or the rDNA. The phylogram was generated by ML analyses with 1.000 bootstrap replications. Bootstrap values are indicated at the nodes. The analysis involved 34 nucleotide sequences. There were a total of 540 positions in the final dataset. Evolutionary analyses were conducted in MEGA X [37].
Figure 4. Phylogenetic relationships of Raffaelea isolates collected from Platypus cylindrus and its galleries on cork oak logs based on the sequence alignment of the partial sequence of the LSU region or the rDNA. The phylogram was generated by ML analyses with 1.000 bootstrap replications. Bootstrap values are indicated at the nodes. The analysis involved 34 nucleotide sequences. There were a total of 540 positions in the final dataset. Evolutionary analyses were conducted in MEGA X [37].
Forests 12 00513 g004
Forests 12 00513 g005 550
Figure 5. Culture, conidiophores and conidia of Raffaelea quercina sp. nov. (isolate PC05.042 = MEAN 1292) (A) Colony morphology after 2 weeks on malt extract agar in a 90 mm diameter plate. (B) Scanning electron micrograph showing ovoid conidia (bar = 1 μm) (C,D). Light micrographs of conidia and conidiogenous cells without conspicuous scars from conidial dehiscence (bar = 10 μm).
Figure 5. Culture, conidiophores and conidia of Raffaelea quercina sp. nov. (isolate PC05.042 = MEAN 1292) (A) Colony morphology after 2 weeks on malt extract agar in a 90 mm diameter plate. (B) Scanning electron micrograph showing ovoid conidia (bar = 1 μm) (C,D). Light micrographs of conidia and conidiogenous cells without conspicuous scars from conidial dehiscence (bar = 10 μm).
Forests 12 00513 g005
Table
Table 1. Details of Raffaelea isolates obtained in this study (bold) and of strains representing species of Raffaelea retrieved from GenBank and used in phylogenetic analyses.
Table 1. Details of Raffaelea isolates obtained in this study (bold) and of strains representing species of Raffaelea retrieved from GenBank and used in phylogenetic analyses.
SpeciesCollection No. aCountryHost/SourceGenBank Accession Nrs. b
SSU sDNALSU rDNA
R. quercina quercina sp. nov.MEAN 1290 = PC05.007 = C2512 = CBS 147554Portugal (Santarém)Platypus cylindrusJF909509JF909537
R. quercina quercina sp. nov.MEAN 1291 = PC05.041 = C2516Portugal (Santarém)P. cylindrusJF909510JF909538
R. quercina quercina sp. nov.MEAN 1292 = PC05.042 = C2513 = CBS 147555Portugal (Santarém)Quercus suber, P. cylindrusJF909511JF909539
R. albimanensC2223 = CBS 271.70S. AfricaP. externedentatusEU170269
R. albimanensCBS271.70S. Africa EU984296
R. ambrosiaeC2225 = CBS 185.64UKP. cylindrusEU170278EU984297
R. amasaeTUB F4290GermanyAmasa aff. glaberAY858661
R. arxiiC2218 = CBS 273.70South AfricaXyleborus torquatusEU170279EU984298
R. brunneaC2229 = CBS378.68USAMonarthrum sp.EU170280EU177457
R. canadensisC2233 = CBS 168.66CanadaP. wilsonniEU170270EU177458
R. canadensisCBS 168.66CanadaP. wilsonniAY858665
A. sulcatiC592 = CBS 805.70CanadaGnathotrichus sulcatusEU170281
R. ellipticosporaC2346USAX. glabratus EU177444
R. fuscaC2254USAX. glabratus EU177447
R. gnathotrichiC2219 = CBS 379.68USAG. retususEU170282EU177460
R. lauricolaC2203USAX. glabratusEU123076EU123077
R. lauricolaC2339 = CBS 121567USAX. glabratus EU177440
R. montetyiPC06.001, C2506Portugal (Alentejo)P. cylindrusJF909512JF909540
R. montetyiPC07.003, C2505Portugal (Alentejo)Quercus suber, P. cylindrusJF909513JF909541
R. montetyiPC06.038, C2504Portugal (Alentejo)P. cylindrusJF909514JF909542
R. montetyiPC06.039, C2514Portugal (Alentejo)Quercus suber, P. cylindrusJF909515JF909543
SpeciesCollection No. aCountryHost/SourceGenBank accession nrs. b
SSU sDNALSU rDNA
C2220 = CBS451.94Portugal (Alentejo)P. cylindrus-EU177461
CBS451.94PortugalP. cylindrus EU984301
C2221 = CBS463.94FranceP. cylindrusEU170283
TUB F4264GermanyX. dryographusAY497522
R. quercivoraPC10.919, MAFF919JapanP. quercivorusJF909517JF909547
PC10.921, MAFF921JapanP. quercivorusJF909516JF909546
JCM 15683JapanP. quercivorus AB552937
MAFF410918JapanQ. crispula/P. quercivorusAB496428AB496454
R. santoroiCBS 399.67ArgentinaM. mutatusEU984261EU984302
R. subalbaC2368USAX. glabratus EU177441
R. subfuscaC2253USAX. glabratusEU170268
R. sulcatiC2234 = CBS806.70CanadaG. sulcatusEU170271EU177462
R. sulphureaC593 = CBS380.68USAX. saxeseniEU170272EU177463
R. tritirachiumC2222 = CBS 726.69USAM. maliEU170273EU984303
Raffaelea sp.C1941USAunknownEU170274
Raffaelea sp.C2224 = CBS326.70S. AfricaP. externedentatus EU177467
R. amasaeCBS 116694TaiwanA. concitatusAY858660
R. brunneaCBS378.68unknownMonarthrum sp. AY858654
R. lauricolaC2204USAX. glabratusEU170266
R. subfuscaC2335 = CBS121571USAX. glabratus EU177450
aPC—fungal strains obtained from Platypus cylindrus and its galleries on Quercus suber, MEAN culture collection of INIAV Institute, Oeiras, Portugal; C, Iowa State University, Dept. of Plant Pathology, USA; CBS, Culture collection of the Westerdijk Fungal Biodiversity Institute, the Netherlands; MAFF, Mie University, Dep. Forest Pathology and Mycology, Japan. b Accession numbers of sequences newly produced (bold). SSU rDNA: small subunit region of of the ribosomal RNA gene; LSU rDNA: large subunit region of of the ribosomal RNA gene.
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Inácio, M.L.; Marcelino, J.; Lima, A.; Sousa, E.; Nóbrega, F. Raffaelea quercina sp. nov. Associated with Cork Oak (Quercus suber L.) Decline in Portugal. Forests 2021, 12, 513. https://doi.org/10.3390/f12040513

AMA Style

Inácio ML, Marcelino J, Lima A, Sousa E, Nóbrega F. Raffaelea quercina sp. nov. Associated with Cork Oak (Quercus suber L.) Decline in Portugal. Forests. 2021; 12(4):513. https://doi.org/10.3390/f12040513

Chicago/Turabian Style

Inácio, Maria L., José Marcelino, Arlindo Lima, Edmundo Sousa, and Filomena Nóbrega. 2021. "Raffaelea quercina sp. nov. Associated with Cork Oak (Quercus suber L.) Decline in Portugal" Forests 12, no. 4: 513. https://doi.org/10.3390/f12040513

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop