Special Issue "Emerging Pathogens in Forest Ecosystems"

A special issue of Forests (ISSN 1999-4907). This special issue belongs to the section "Forest Ecology and Management".

Deadline for manuscript submissions: closed (20 July 2020).

Special Issue Editors

Dr. Benedetto T. Linaldeddu
E-Mail Website
Guest Editor
Dipartimento Territorio e Sistemi Agro-Forestali (TESAF), University of Padova, viale dell’Università 16, I-35020 Legnaro, Italy
Interests: forest pathology; molecular ecology; fungal endophytes; invasive Phytophthora species; diversity, biology, pathogenicity and taxonomy of Botryosphaeriaceae species
Special Issues, Collections and Topics in MDPI journals
Dr. Simone Prospero
E-Mail Website
Guest Editor
Swiss Federal Institute for Forest, Snow and Landscape Research WSL
Interests: forest pathology; invasive and emerging fungal pathogens; population biology; population genetics; biocontrol; chestnut blight; Phytophthora species

Special Issue Information

Dear Colleagues,

Invasive plant pathogenic oomycetes and fungi are increasingly threatening forests and natural ecosystems worldwide. The ecological impact of disease outbreaks resulting from new host–pathogen associations, host shifts, or emergence of more virulent genotypes in the pathogen population has also been exacerbated by environmental changes and human activities. At the same time, global trade and environmental changes are important drivers for the introduction and spread of invasive pathogens. Therefore, there is an urgent need to expand knowledge about the pathway of biological invasions, the effects of invasive pathogens on forest biodiversity, and the strategies for minimizing the impact of invasive pathogens in new environments and/or on new hosts. For this Special Issue, we welcome studies providing new insights into the patterns and processes of biological invasions in forest ecosystems. Original studies on new management strategies to control invasive plant pathogens are also welcome.

Dr. Benedetto T. Linaldeddu
Dr. Simone Prospero
Guest Editors

Manuscript Submission Information

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Keywords

  • New forest diseases
  • Invasive plant pathogens
  • Host shifts
  • Biosafety
  • Forest management

Published Papers (9 papers)

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Research

Article
Phytophthora mediterranea sp. nov., a New Species Closely Related to Phytophthora cinnamomi from Nursery Plants of Myrtus communis in Italy
Forests 2021, 12(6), 682; https://doi.org/10.3390/f12060682 - 27 May 2021
Cited by 1 | Viewed by 1674
Abstract
Monitoring surveys of Phytophthora related diseases in four forest nurseries in Italy revealed the occurrence of fourteen Phytophthora species to be associated with collar and root rot on fourteen plants typical of Mediterranean and alpine regions. In addition, a multilocus phylogeny analysis based [...] Read more.
Monitoring surveys of Phytophthora related diseases in four forest nurseries in Italy revealed the occurrence of fourteen Phytophthora species to be associated with collar and root rot on fourteen plants typical of Mediterranean and alpine regions. In addition, a multilocus phylogeny analysis based on nuclear ITS and ß-tubulin and mitochondrial cox1 sequences, as well as micromorphological features, supported the description of a new species belonging to the phylogenetic clade 7c, Phytophthora mediterranea sp. nov. Phytophthora mediterranea was shown to be associated with collar and root rot symptoms on myrtle seedlings. Phylogenetically, P. mediterranea is closely related to P. cinnamomi but the two species differ in 87 nucleotides in the three studied DNA regions. Morphologically P. mediterranea can be easily distinguished from P. cinnamomi on the basis of its smaller sporangia, colony growth pattern and higher optimum and maximum temperature values. Data from the pathogenicity test showed that P. mediterranea has the potential to threaten the native Mediterranean maquis vegetation. Finally, the discovery of P. cinnamomi in alpine nurseries, confirms the progressive expansion of this species towards cold environments, probably driven by climate change. Full article
(This article belongs to the Special Issue Emerging Pathogens in Forest Ecosystems)
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Article
Diversity and Pathogenicity of Phytophthora Species Associated with Declining Alder Trees in Italy and Description of Phytophthora alpina sp. nov
Forests 2020, 11(8), 848; https://doi.org/10.3390/f11080848 - 05 Aug 2020
Cited by 5 | Viewed by 1277
Abstract
Extensive decline and mortality events of alder trees have recently been observed in several riparian ecosystems in Italy. Since there is little information about the aetiology of this disease and given the high ecological relevance of riparian ecosystems, an in-depth study was conducted [...] Read more.
Extensive decline and mortality events of alder trees have recently been observed in several riparian ecosystems in Italy. Since there is little information about the aetiology of this disease and given the high ecological relevance of riparian ecosystems, an in-depth study was conducted in three sites spanning from the Mediterranean to Alpine regions. From spring 2019 to spring 2020, 261 samples of bleeding cankers, rhizosphere soil and leaves used as baits along waterways were collected and used for Phytophthora isolation. Based on morphology, colony appearance and DNA sequence data, 10 species belonging to 6 clades were identified. These included P. plurivora (84 isolates), P. pseudocryptogea (50), P. hydropathica (18), P. gonapodyides (14), P. bilorbang (13), P. pseudosyringae (12), P. lacustris (11), P. acerina (7), P. cactorum (1) and one isolate of the hybrid Phytophthora ×serendipita. In addition, two new Phytophthora species, one of which is described here as Phytophthora alpina sp. nov., were isolated. The pathogenicity of P. alpina and other species obtained from samples collected in the green alder stand was assessed on 3-year-old seedlings. All species proved to be pathogenic on green alder causing symptoms congruent with field observations. Results obtained have allowed us to expand knowledge about alder decline aetiology. The diversity of pathogenicity of Phytophthora species associated with symptomatic alder trees suggested that no single agent is responsible for the disease, but that it is the result of multiple infections of different Phytophthora species, variable in assemblages among sites. Full article
(This article belongs to the Special Issue Emerging Pathogens in Forest Ecosystems)
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Article
Pestalotiopsis pini sp. nov., an Emerging Pathogen on Stone Pine (Pinus pinea L.)
Forests 2020, 11(8), 805; https://doi.org/10.3390/f11080805 - 25 Jul 2020
Cited by 3 | Viewed by 1563
Abstract
Research Highlights: Pestalotiopsis pini sp. nov. is an emerging pathogen on stone pine, Pinus pinea L., in Portugal. Background and Objectives: Stone pine is one of the most important forest tree species in Portugal and in the whole Mediterranean basin. Pestalotiopsis [...] Read more.
Research Highlights: Pestalotiopsis pini sp. nov. is an emerging pathogen on stone pine, Pinus pinea L., in Portugal. Background and Objectives: Stone pine is one of the most important forest tree species in Portugal and in the whole Mediterranean basin. Pestalotiopsis species are common endophytes, saprobes or pathogens in a variety of hosts and environments. The objective of the present study was to identify the Pestalotiopsis species associated with the symptomatic stone pine trees. Materials and Methods: Samples of stone pine trees showing shoot blight and stem necrosis were obtained from stone pine orchards and urban areas in Portugal, and the isolated Pestalotiopsis species were identified based on morphology and combined ITS, TEF and TUB DNA sequence data. Artificial inoculations on one-year-old stone pine seedlings were performed with the two species most frequently found in association with shoot blight disease. Results: Five Pestalotiopsis spp. were isolated. A taxonomic novelty, Pestalotiopsis pini is described, representing a new pathogen for stone pine. Conclusions: Pestalotiopsis species may represent a threat to the health of pine forests in the Mediterranean basin. Future research should be done in order to increase our knowledge about the potential impact of pestalotioid species in stone pine, in order to develop management strategies against these pathogens. Full article
(This article belongs to the Special Issue Emerging Pathogens in Forest Ecosystems)
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Article
Dieback of Euonymus alatus (Celastraceae) Caused by Cytospora haidianensis sp. nov. in China
Forests 2020, 11(5), 524; https://doi.org/10.3390/f11050524 - 07 May 2020
Cited by 3 | Viewed by 843
Abstract
Euonymus alatus (Celastraceae) is widely cultivated in China for its economic value and landscape benefits. Euonymus alatus dieback occurs due to members of Cytospora and has become one of the most severe diseases affecting its cultivation in China. In this study, we examined [...] Read more.
Euonymus alatus (Celastraceae) is widely cultivated in China for its economic value and landscape benefits. Euonymus alatus dieback occurs due to members of Cytospora and has become one of the most severe diseases affecting its cultivation in China. In this study, we examined the causal agent of bough dieback on campuses of University Road, Beijing, China. Among the strains, three were morphologically consistent with Cytospora, showing hyaline and allantoid conidia. Based on phylogenetic analyses of the concatenated actin (ACT), internal transcribed spacer (ITS), RNA polymerase II second largest subunit (RPB2), translation elongation factor 1-alpha (TEF1-α) and beta-tubulin (TUB2) gene sequences, along with morphological and physiological features, we propose C. haidianensis as a novel species. It was confirmed as a causal agent of dieback of E. alatus by pathogenicity tests. Mycelial growth of Cytospora haidianensis occurred at pH values ranging from 3.0 to 11.0, with optimum growth at 8.3, and at temperatures from 5 to 35 °C, with optimum growth at 19.8 °C. We also tested the growth of C. haidianensis in the presence of six carbon sources. Sucrose, maltose and glucose were highly efficient and xylose was the least. The ability of C. haidianensis to grow at 19.8 °C may help to explain its occurrence causing dieback of E. alatus in Beijing during the autumn season. Full article
(This article belongs to the Special Issue Emerging Pathogens in Forest Ecosystems)
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Article
Eutypella parasitica and Other Frequently Isolated Fungi in Wood of Dead Branches of Young Sycamore Maple (Acer pseudoplatanus) in Slovenia
Forests 2020, 11(4), 467; https://doi.org/10.3390/f11040467 - 20 Apr 2020
Cited by 4 | Viewed by 1807
Abstract
Eutypella parasitica R.W. Davidson and R.C. Lorenz is the causative agent of Eutypella canker of maple, a destructive disease of maples in Europe and North America. The fungus E. parasitica infects the trunk through a branch stub or bark wound. Because the fungal [...] Read more.
Eutypella parasitica R.W. Davidson and R.C. Lorenz is the causative agent of Eutypella canker of maple, a destructive disease of maples in Europe and North America. The fungus E. parasitica infects the trunk through a branch stub or bark wound. Because the fungal community may have an impact on infection and colonization by E. parasitica, the composition of fungi colonizing wood of dead branches of sycamore maple (Acer pseudoplatanus L.) was investigated in five sampling sites in Slovenia. Forty samples from each sampling site were collected between the November 2017 and March 2018 period. Isolations were made from the wood in the outer part of dead branches and from discoloured wood in the trunk that originated from a dead branch. Pure cultures were divided into morphotypes, and one representative culture per morphotype was selected for further molecular identification. From a total of 2700 cultured subsamples, 1744 fungal cultures were obtained, which were grouped into 212 morphotypes. The investigated samples were colonized by a broad spectrum of fungi. The most frequently isolated species were Eutypa maura (Fr.) Sacc., Eutypa sp. Tul. and C. Tul., Fusarium avenaceum (Fr.) Sacc., Neocucurbitaria acerina Wanas., Camporesi, E.B.G. Jones and K.D. Hyde and E. parasitica. In this study, we distinguished species diversity and the fungal community. There were no significant differences in the diversity of fungal species between the five sampling sites, and branch thickness did not prove to be a statistically significant factor in fungal species diversity. Nevertheless, relatively low Jaccard similarity index values suggested possible differences in the fungal communities from different sampling sites. This was confirmed by an analysis of similarities, which showed that the isolated fungal community distinctly differed between the five sampling sites and between the different isolation sources. Eutypella parasitica was isolated from all five investigated sampling sites, although Eutypella cankers were observed in only three sampling sites, indicating the possibility of asymptomatic infection. Full article
(This article belongs to the Special Issue Emerging Pathogens in Forest Ecosystems)
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Article
An Emerging Pathogen from Rotted Chestnut in China: Gnomoniopsis daii sp. nov.
Forests 2019, 10(11), 1016; https://doi.org/10.3390/f10111016 - 13 Nov 2019
Cited by 9 | Viewed by 1051
Abstract
Nut quality is fundamental to the economic viability of the Chinese sweet chestnut industry, but fruit rot disease significantly reduces this quality. In this study, we investigated chestnut rot in Anhui and Hubei provinces in China. Typical brown rot symptoms were observed, affecting [...] Read more.
Nut quality is fundamental to the economic viability of the Chinese sweet chestnut industry, but fruit rot disease significantly reduces this quality. In this study, we investigated chestnut rot in Anhui and Hubei provinces in China. Typical brown rot symptoms were observed, affecting nuts from different plantations. Isolates were obtained from symptomatic tissues of rotted fruits that were identified based on morphological comparison and phylogenetic analyses of partial internal transcribed spacer (ITS), and tef1 and tub2 gene sequences. The inoculation results showed that the tested fungal species is pathogenic to chestnut fruits. Hence, a new and severe pathogen that causes Chinese sweet chestnut brown rot, Gnomoniopsis daii sp. nov., is introduced herein. Full article
(This article belongs to the Special Issue Emerging Pathogens in Forest Ecosystems)
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Article
Pseudodidymella fagi in Slovenia: First Report and Expansion of Host Range
Forests 2019, 10(9), 718; https://doi.org/10.3390/f10090718 - 21 Aug 2019
Cited by 1 | Viewed by 2060
Abstract
The fungus Pseudodidymella fagi is spreading in Europe and causing leaf blotch of European beech, Fagus sylvatica. Between 2008 and 2017, outbreaks of P. fagi were observed on European beech in Switzerland, Germany (also on F. orientalis), Austria, and Slovakia. In [...] Read more.
The fungus Pseudodidymella fagi is spreading in Europe and causing leaf blotch of European beech, Fagus sylvatica. Between 2008 and 2017, outbreaks of P. fagi were observed on European beech in Switzerland, Germany (also on F. orientalis), Austria, and Slovakia. In Slovenia, leaf blotch symptoms were first observed on F. sylvatica in 2018. P. fagi was identified as the causal agent of the observed symptoms in Slovenia by morphological examinations together with sequencing of the internal transcribed spacer (ITS) region of the rDNA. This study links the fungus to the expansion of the known distribution of the disease to Slovenia, and based on in vitro pathogenicity trials, also to a new potential host, Quercus petraea. The pathogenicity tests confirmed F. sylvatica and F. orientalis as hosts for P. fagi, but not Castanea sativa, where pathogenicity to F. orientalis was proved for first time in vitro. Although Koch’s postulates could not be proven for C. sativa, it seems to be partially susceptible in vitro because some of the inoculation points developed lesions. Additionally, damage to Carpinus betulus related to P. fagi near heavily infected beech trees was observed in vivo but was not tested in laboratory trials. Based on the results and our observations in the field, it is likely that P. fagi has a wider host range than previously thought and that we might be witnessing host switching. Full article
(This article belongs to the Special Issue Emerging Pathogens in Forest Ecosystems)
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Article
Forest Decline Triggered by Phloem Parasitism-Related Biotic Factors in Aleppo Pine (Pinus halepensis)
Forests 2019, 10(8), 608; https://doi.org/10.3390/f10080608 - 24 Jul 2019
Cited by 6 | Viewed by 1310
Abstract
Climate models predict increasing mean temperatures and reduced precipitation for Mediterranean ecosystems already subjected to major hydrological fluctuations. Forest decline phenomena relate extreme droughts or heat waves with other organisms, e.g., insects or microorganisms acting as pests, but their role needs to be [...] Read more.
Climate models predict increasing mean temperatures and reduced precipitation for Mediterranean ecosystems already subjected to major hydrological fluctuations. Forest decline phenomena relate extreme droughts or heat waves with other organisms, e.g., insects or microorganisms acting as pests, but their role needs to be elucidated. A biotic factor responsible for forest diseases is Candidatus Phytoplasma pini which is a phloem-parasitism that negatively affects Spanish pine forests in drought-prone areas. In several healthy and declining Aleppo pine stands, we monitored pine infection by PCR (Polimerase Chain Reation), determined the tree phloem tissue terpene composition, carbohydrate content, measured several relevant morpho-physiological variables and examined trees affected by bark beetles. PCR confirmed C. P. pini infection was widespread in all stands, regardless of to the presence of symptomatically affected trees. However, visible symptomatic decline only occurred in trees living under more stressful conditions. The terpene composition of pines in declining stands differed from those in healthy ones, and could be related with bark beetle attacks when pines were previously weakened by the phytoplasma disease. Our results indicate that biotic factors, such as C. P. pini, affecting phloem tissue may be triggering factors for drought-mediated forest decline and suggest that phloem diseases can play a key role in forest declining processes during extreme drought. Full article
(This article belongs to the Special Issue Emerging Pathogens in Forest Ecosystems)
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Article
Plant Pathogenic Fungi Associated with Coraebus florentinus (Coleoptera: Buprestidae) Attacks in Declining Oak Forests
Forests 2019, 10(6), 488; https://doi.org/10.3390/f10060488 - 06 Jun 2019
Cited by 8 | Viewed by 2067
Abstract
The black-banded oak borer, Coraebus florentinus, is an emerging pest of oak trees in the western Mediterranean region. Larvae of the insect are xylophagous and progressively excavate an annular gallery that interrupts sap flow, resulting in the death of the attacked branches. [...] Read more.
The black-banded oak borer, Coraebus florentinus, is an emerging pest of oak trees in the western Mediterranean region. Larvae of the insect are xylophagous and progressively excavate an annular gallery that interrupts sap flow, resulting in the death of the attacked branches. Until now, limited information has been available regarding the ecological interactions between C. florentinus and the main plant pathogenic fungi involved in the etiology of oak decline. Knowledge of these interactions is important in understanding their impact in natural ecosystems and developing appropriate management strategies. Therefore, in this study, we characterized the fungal communities occurring in the exoskeleton of adults and larvae of C. florentinus and associated with the necrotic wood tissues surrounding the branch galleries of declining oak trees. A total of 29 fungal species were identified based on DNA sequence data and morphological features, of which 14 were from symptomatic woody tissues, six from insect exoskeleton, and nine from both insects and symptomatic wood tissues. The most frequent fungal species, Cryphonectria naterciae (15.9% of isolates), Dothiorella iberica (11.3%), and Diplodia corticola (9.9%), were isolated from both insect and gallery systems. All three species are well-known oak pathogens and are reported here, for the first time, to be associated with C. florentinus. At the same time, 89.6% of the fungal taxa were isolated from one or two sites, highlighting the site-dependence of fungal community assemblages. Full article
(This article belongs to the Special Issue Emerging Pathogens in Forest Ecosystems)
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