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Declining Agonis flexuosa; (a) 'flagging', a symptom of crown dieback; (b) branch of A. flexuosa with the bark removed to reveal lesion.
Source publication
Recently, severe dieback symptoms have been observed in Agonis flexuosa, a tree native to the south-west of Western Australia. It was suspected that these symptoms were caused by an opportunistic
pathogen and a sampling strategy was designed to investigate the causal agent of the cankers in symptomatic trees and the
presence (or absence) of this pa...
Context in source publication
Context 1
... 2007, dieback symptoms were observed in WA peppermint in tuart forests south of Perth (Fig. 1). Lesions of dead tissue, extending up branches and leading to ringbarking, and crown dieback were observed. The reason for the decline was unknown, but the symptoms were typical of those caused by canker pathogens. This symptom is becoming more common (P. Barber, pers. comm.) and it is assumed that this is due either to an introduced ...
Citations
... The high adaptation of B. dothidea is proven by its broad geographical distribution (it is a cosmopolitan fungus) and its wide host range, continuously updated and expanding [24,26]. Hence, adverse environmental conditions like those caused by climate change can favor this fungus in attacking and infecting hosts previously uninfected, creating a greater impact and potential expansion in different parts of the world [15,[48][49][50][51][52][53][54][55][56][57][58]. D. fraxini has already been reported in studies on the etiology of diseases affecting Fraxinus [32]. ...
A severe dieback of flowering ash (Fraxinus ornus L.) has been observed in north-central Italy in the last decades. Symptoms include typical sunken, light-brown cankers on the stem and branches; vascular discoloration; tip and shoot dieback; and foliage necroses. The disease was more evident at the beginning of the growing season, and more severe on young regeneration. Six Botryosphaeriaceae species were consistently isolated from symptomatic plant tissues: Botryosphaeria dothidea, Diplodia fraxini, Diplodia subglobosa, Dothiorella iberica, Dothiorella omnivora and Neofusicoccum parvum. B. dothidea and D. fraxini expressed higher aggressiveness and showed a widespread incidence, being the species most frequently associated with cankers; the other four species were less virulent and more erratic, occurring mainly on succulent branch tips and foliage. Isolates were characterized using morphological and molecular approaches (colony/conidial phenotyping and rDNA-ITS genotyping). Phylogenetic analysis provided congruent phylogenies depicting the relationships of the six taxa with the most closely related conspecifics. Pathogenicity tests on 2-year-old seedlings confirmed the higher virulence of B. dothidea and D. fraxini. Extensive, multi-year field surveys at different sites supported the hypothesis that climatic vagaries, mainly heat, water and drought stresses, impaired tree health and vigor, facilitating infection and pervasive colonization by these Botryosphaeriaceae species. Environmental stressors are thus the key factor bringing the six fungal pathogens together in a multitrophic interaction with F. ornus in a novel, lethal fashion.
... Most ecosystems have also been affected by the introduction of species of the soil-borne water mold, Phytophthora (Shearer et al. 2007;Ritchie et al. 2021). Corresponding with these climate and disease changes, a wide variety of forest and woodland tree species have experienced episodes of tree die-off, crown decline and tree mortality (Hooper and Sivasithamparam 2005;Dakin et al. 2010;Matusick et al. 2012Matusick et al. , 2013Paap et al. 2017;Wentzel et al. 2018;Ritchie et al. 2021). Phytophthora cinnamomi, one of the most destructive plant pathogens worldwide Sena et al. 2018), remains the predominant pathogen threat to ecosystems in south-western Australia (Shearer et al. 2004(Shearer et al. , 2007, causing significant dieback. ...
Context Forest ecosystems experience compositional and structural changes as species’ environmental envelopes shift with climate change. Extreme climate events and pests/pathogens are driving these ecosystem changes. Determining which of the two potential drivers is causing a particular forest die-off can be challenging. In south-western Australia, widespread forest die-off in 2011 coincided with extremely hot and dry conditions. It occurred in a forest ecosystem that has historically experienced Phytophthora cinnamomi root disease (Phytophthora dieback). Aims To determine whether the causal agent of Phytophthora dieback, P. cinnamomi, was associated with forest die-off in the Northern Jarrah Forest. Methods A combination of direct (isolation of pathogen) and indirect (survey of susceptible indicator plant species) measurements were taken inside and outside patches of forest experiencing the die-off. Key results There was no consistent association between die-off patches and the presence of P. cinnamomi. P. cinnamomi was isolated from 3 of 33 control plots and 3 of 33 die-off plots. Although several plant species susceptible to P. cinnamomi were absent from die-off plots, the findings were inconsistent across species. This may be explained by plant tolerance to high temperatures and drought. Conclusions P. cinnamomi was not the proximate cause of the observed die-off in the Northern Jarrah Forest in 2011. Implications Novel disturbance caused by extreme climate events can mimic damage caused by certain pests/pathogens. More research is needed to determine the tolerances of plants to extreme temperature and drought conditions to disentangle abiotic and biotic drivers of tree die-off.
... B. dothidea is known to infect native and exotic tree species and can thus become a threat to commercial plantations and native ecosystems. Under climate change, B. dothidea and other stress-related pathogens could have a larger impact on eucalypts plantations, as it has been evidenced by the impact of Botryosphaeriaceae in plant populations with respect to climate conditions and stress (Dakin et al., 2010;Marsberg et al., 2017;Van Der Linde et al., 2012). High relative humidity benefits the conidial initiation, release, and germination of B. dothidea. ...
Species of Eucalyptus (Myrtaceae) are considered native to Australia, Tasmania, New Guinea, Timor, Philippines, and Indonesia,
but are planted worldwide, particularly in large-scale plantations. They form the basis of plantation forestry industries on multiple
continents where they provide a source of timber, fuel, energy, fiber, and industrial and medicinal oils. Currently, the land area for
planted eucalypts globally surpasses 20 million hectares, primarily for the production of pulp, energy, and timber, augmenting the
declining productivity of native forests. The worldwide eucalypt plantation and economy is, however, threatened by eucalypt
pathogens, most of which are often cryptic or latent species that escape detection methods and common quarantine measures. Among
the many threats to eucalypt plantations are Mycosphaerella leaf blotch or disease (MLD) caused by Mycosphaerella species,
Ceratocystis wilt caused mostly by Ceratocystis fimbriata, and Teratosphaeria stem canker caused by Teratosphaeria zuluensis and
T. gauchensis. A major threat for eucalypt plantations worldwide is Myrtle rust caused by Austropuccinia psidii. In this chapter, the
taxonomy, phylogeny, geographical distribution, host range and disease resistance, life cycle, and etiology of these pathogens are
discussed. Potential disease management strategies are also outlined.
... Hyperspectral imaging and other remote sensing tools could be considered [85]. Fungal population genetics studies can be used to assess if genotypes associated with disease differ from those in asymptomatic trees [86] or if new genotypes have been introduced to a region [87], well-planed hierarchical sampling can also determine if there is structure within populations [88]. Numerous population genetics studies have been undertaken considering invasive pathogens [15], but there are few examples with native pathogens. ...
Purpose of Review
Human-caused global change is fundamentally altering natural forest ecosystems. More trees are exhibiting a wide range of symptoms indicative of poor vigour, particularly stressed species at the edge of their native ranges and stands growing on marginal sites. This review will focus on complex tree diseases (declines) caused by native pathogens and the key environmental drivers that contribute to this phenomenon. These systems are frequently complex, with multiple drivers at work.
Recent Findings
Using four cases studies on different continents, we explored the direct and indirect environmental drivers underlying these decline syndromes. Although climate and weather events seem to be usually associated with forest decline, we found that environmental disturbance by either forest management or land-use changes is also a global predisposing factor of decline which deserves more attention. Changes in land use have directly benefited pathogens such as root rots in the Pyrenees (Spain) or indirectly by making the environment more conducive for canker and foliar diseases in Australia and the USA. Focus on land-use changes could improve understanding of current decline problems such as those affecting Araucaria in Chile.
Summary
The next century will almost certainly see an unprecedented rise in forest pathogen epidemics, requiring a proactive rather than reactive response. Diseases caused by native pathogens with complex aetiologies will become more common, and recognising, characterising and managing these epidemics are difficult because native pathogens are frequently already widespread, and eradication is not feasible. We need to start approaching these issues from a ‘whole ecosystem’ perspective, highlighting the many aspects and entanglements of forest declines and allowing us to respond with management options tailored to each scenario. The approach proposed here provides logical steps based on six questions to untangle the direct and indirect environmental drivers of tree declines.
... The occurrence of viral species showing similarity with Aspergillus mycoviruses, and their pattern of expression (higher in stems and roots, but also present in leaves) leads us to hypothesize that Aspergillus welwitschiae, a fungal species which causes the bole rot of sisal [70,71] is also part of the healthy microbiome of sisal, causing disease through imbalances in plant metabolism, rather than infecting vulnerable plants from spores in the environment. Such a pattern has been described in peppermint by Dakin et al. (2010) [72]. Nonetheless, it is also possible that this species is infecting the plant host, and not some associated fungal species, following the theories that mycoviruses originated from plant viruses [73] and that these mycoviruses can replicate in plant cells [74]. ...
... The occurrence of viral species showing similarity with Aspergillus mycoviruses, and their pattern of expression (higher in stems and roots, but also present in leaves) leads us to hypothesize that Aspergillus welwitschiae, a fungal species which causes the bole rot of sisal [70,71] is also part of the healthy microbiome of sisal, causing disease through imbalances in plant metabolism, rather than infecting vulnerable plants from spores in the environment. Such a pattern has been described in peppermint by Dakin et al. (2010) [72]. Nonetheless, it is also possible that this species is infecting the plant host, and not some associated fungal species, following the theories that mycoviruses originated from plant viruses [73] and that these mycoviruses can replicate in plant cells [74]. ...
Sisal is a common name for different plant varieties in the genus Agave (especially Agave sisalana) used for high-quality natural leaf fiber extraction. Despite the economic value of these plants, we still lack information about the diversity of viruses (virome) in non-tequilana species from the genus Agave. In this work, by associating RNA and DNA deep sequencing we were able to identify 25 putative viral species infecting A. sisalana, A. fourcroydes, and Agave hybrid 11648, including one strain of Cowpea Mild Mottle Virus (CPMMV) and 24 elements likely representing new viruses. Phylogenetic analysis indicated they belong to at least six viral families: Alphaflexiviridae, Betaflexiviridae, Botourmiaviridae, Closteroviridae, Partitiviridae, Virgaviridae, and three distinct unclassified groups. We observed higher viral taxa richness in roots when compared to leaves and stems. Furthermore, leaves and stems are very similar diversity-wise, with a lower number of taxa and dominance of a single viral species. Finally, approximately 50% of the identified viruses were found in all Agave organs investigated, which suggests that they likely produce a systemic infection. This is the first metatranscriptomics study focused on viral identification in species from the genus Agave. Despite having analyzed symptomless individuals, we identified several viruses supposedly infecting Agave species, including organ-specific and systemic species. Surprisingly, some of these putative viruses are probably infecting microorganisms composing the plant microbiota. Altogether, our results reinforce the importance of unbiased strategies for the identification and monitoring of viruses in plant species, including those with asymptomatic phenotypes.
... (Brooks and Ferrin, 1994;Swiecki and Bernhardt, 2003). They are also known to play a variety of functionally diverse roles, from asymptomatic endophytes (Fisher et al., 1993;Burgess et al., 2005;Taylor et al., 2005;Dakin et al., 2010) to obligate pathogens (Sakalidis et al., 2011;Phillips et al., 2013). Yet, while N. australe has been described around the world (Armengol et al., 2008;Amponsah et al., 2009;Espinoza et al., 2009), relatively few studies have been conducted on its specific interactions with host species, as it was only fairly recently described (Slippers et al., 2004;Phillips et al., 2013). ...
Premise:
Mortality events involving drought and pathogens in natural plant systems are on the rise due to global climate change. In Santa Barbara, California, United States, big berry manzanita (Arctostaphylos glauca) has experienced canopy dieback related to a multi-year drought and infection from fungal pathogens in the Botryosphaeriaceae family. A greenhouse experiment was conducted using Neofusicoccum australe to test the specific influences of drought and fungal infection on A. glauca.
Methods:
A full factorial design was used to compare four treatment groups (drought + inoculation; drought - inoculation; watering + inoculation; and control: watering - inoculation). Data were collected for 10 weeks on stress symptoms, changes in leaf fluorescence and photosynthesis, and mortality.
Results:
Results indicated significant effects of watering and inoculation treatments on net photosynthesis, dark-adapted fluorescence, and disease symptom severity (P < 0.05), and a strong correlation was found between physiological decline and visible stress (P < 0.0001). Mortality differed between treatments, with all groups except for the control experiencing mortality (43% mortality in drought - inoculation, 83% in watering - inoculation, and 100% in drought + inoculation). A Kaplan-Meier survival analysis showed drought + inoculation to have the least estimated survivorship compared to all other treatment groups.
Conclusions:
In addition to a possible synergistic interaction between drought and fungal infection in disease onset and mortality rates in A. glauca, these results indicate that young, non-drought-stressed plants are susceptible to mortality from N. australe infection, with important implications for the future of wildland shrub communities.
... Golzar & Burgess (2011) also reported that Diplodia species can cause canker and decline diseases in the species Norfolk Island pine in New Zealand and Australia. Araucaria heterophylla is currently among the exotic trees rapidly expanding in the recent years in Ethiopian cities like Addis Ababa and Adama at interior locations such as homes, apartments, offices, public buildings, shopping malls and urban streets, home gardens and parks; this makes them vulnerable to various stresses and susceptible to various infections (Zhonghua et al. 2001;W.A. Darge _______________________________________________________________________________________________________ Slippers et al. 2005;Dakin et al. 2010). The objective of this study was to identify fungal pathogen associated with Araucaria heterophylla disease observed on plantings in Addis Ababa (8°50'−9°05' N and 38° 39'−38° 55' E, in the altitude ranging from 2350 to 3300 m above sea level), and Adama (about 100 km South East of Addis Ababa with an average altitude of 1620 m above sea level). ...
... According to the studies by Dakin et al. (2010) and others, trees which are under environmental stress or with mechanical injuries can be vulnerable to attack by opportunistic fungal pathogens such as Diplodia resulting in stem canker, needle and shoot blight. Slippers et al. (2005) also showed that members of the Botryosphaeriaceae have been reported causing aggressive diseases on Araucaria cunninghamii and other conifer tree species. ...
Canker and needle blight of Araucaria heterophylla (Norfolk Island pine) trees were observed during the surveys conducted in Addis Ababa and Adama cities (Ethiopia) from November to December 2016. The main objective of this study was to investigate fungal pathogens that cause diseases on Araucaria heterophylla trees. Six localities with Araucaria heterophylla plantings were purposively surveyed for dis-ease symptoms. Samples from symptomatic parts of trees were collected, surface sterilized, cultured on PDA and morphologically identified for genus and species. A total of 36 isolates of fungi were identified from six localities. Based on macro- and microscopic morphological features of the colonies, the fungal isolates were found to be the genus Diplodia and species Lasiodiplodia theobromae (Pat.) Griffon & Maubl (syn. Botryodiplodia theobromae), the anamorph of Botryosphaeria rhodina (Berk. & M.A. Curtis) Arx. The pathogenicity test showed that the isolates of Lasiodiplodia theobromae, caused stem canker and nee-dle blight on Araucaria heterophylla. This finding is important in the study of management options for future prevention and control of diseases in the country.
... These have commonly also been linked to climate change events or cases of human disturbance. Notable examples are those for Agonis flexuosa in Western Australia (Dakin et al. 2010), O. carpinifolia in Slovenia and Italy (Piskur et al. 2011), Acacia species, Mangrove species (Avicennia marina, Bruguiera gymnorrhiza, Ceriops tagal, Lumnitzera racemosa, Rhizophora mucronata, and Xylocarpus granatum) and M. indica trees in Southern Africa (Jami et al. 2013;Slippers et al. 2014;Mehl et al. 2017;Osorio et al. 2017), Schizolobium parahyba in South America (Mehl et al. 2014), various ornamental trees across the Balkans (Zlatkovi c et al. 2016b), Anacardium occidentale in Brazil (Netto et al. 2017), Eriobotrya japonica in Italy (Giambra et al. 2016), amongst others. Whether this trend is increasing is not clear. ...
The Botryosphaeriales are amongst the most widespread, common and important fungal pathogens of woody plants. Many are also known to exist as endophytes in healthy plant tissues. This special issue highlights a number of key themes in the study of this group of fungi. In particular, there have been dramatic taxonomic changes in the decade since this order was first described; from one family to nine (including three in this special issue) and from 10 to 33 genera known from culture. It is also clear from many studies that neither morphology nor single locus sequence data are sufficient to define taxa. This problem is exacerbated by the increasing numbers of cryptic species being identified and for the first time as highlighted in this special issue, the recognition of hybrids. It is futile that management strategies, including quarantine, continue to rely on outdated taxonomic definitions and identification tools. This is especially true in light of growing evidence that many species continue to be moved globally as endophytes in plants and plant products. While the genomes of only 11 (mostly Botryosphaeriaceae) have been sequenced and released, these are already deeply changing our understanding of the group. Basic aspects of the biology such as the mode of sexual reproduction (which includes both homothallic and heterothallic species) are now being revealed. Likewise, the mechanisms that allow these fungi to infect their hosts, in some cases hundreds of host species, without eliciting a defence response are being revealed. A well defined natural classification and an extensive collection of tools to study the Botryosphaeriaceae now provide a springboard for a much deeper exploration of their biology, biogeography and host associations. This is both from the mycological and management perspectives.
... Consequently, the potential impact of the Botryosphaeriaceae in general, but specifically B. dothidea, which is a widespread pathogen already present as an endophyte in numerous plant communities in various parts of the world, might be exacerbated (Desprez-Loustau et al., 2006). Already, the impact of the pathogen in relation to climatic conditions and stress has been documented in plant communities in parts of southern Europe (Pi skur et al., 2011), Australia (Dakin et al., 2010), South Africa (Van Der Linde et al., 2011 and other countries (Brown and Hendrix, 1981;Ma et al., 2001a,b;Sturrock et al., 2011). ...
Taxonomy:
Botryosphaeria dothidea (Moug. ex Fr) Ces. & De Not, 1863. Kingdom Fungi, Phylum Ascomycota, Class Dothideomycetes, Order Botryosphaeriales, Family Botryosphaeriaceae, Genus Botryosphaeria, Species dothidea Host range: Confirmed on more than 24 host genera, including woody plants such as Acacia (=Vachellia), Eucalyptus, Vitis and Pistachio.
Disease symptoms:
Associated with twig, branch and stem cankers, tip and branch dieback, fruit rot, blue stain and plant death This article is protected by copyright. All rights reserved.
... Vegetative compatibility grouping (VCG) is a method traditionally used for evaluating population structure and genetic diversity of asexually reproducing fungi, which provides information on genetic diversity and the potential for genetic exchange in populations (Dakin et al., 2010;Baskarathevan et al., 2012a). Botryosphaeriaceae species are thought to reproduce asexually in the field (Phillips, 2002), with rare sexual reproduction (van Niekerk et al., 2006). ...
... Botryosphaeriaceae species are thought to reproduce asexually in the field (Phillips, 2002), with rare sexual reproduction (van Niekerk et al., 2006). Thus, surprisingly high genetic diversity has been observed in studies for these apparently asexual taxa (Dakin et al., 2010;Baskarathevan et al., 2012a;Bihon et al., 2012a). ...
... Amplified fragment length polymorphism (AFLP) Reyes-Franco et al., 2006;Piškur et al., 2010 Amplified ribosomal DNA restriction analysis (ARDRA) Machouart et al., 2004;Alves et al., 2005;Madrid et al., 2008 Diversity array technology (DarT) Kilian et al., 2005ISSR Zietkiewicz et al., 1994 microsatellite-primed PCR (MSP-PCR) Alves et al., 2007;Bahkali et al., 2012;Mahdizadeh et al., 2012 Randomly amplified polymorphic DNA (RAPD) Fuhlbohm, 1997;Su et al., 2001;Omar et al., 2007;Almeida et al., 2008 Restriction fragment length polymorphism (RFLP) Almeida et al., 2003;Purkayastha et al., 2006 Single nucleotide polymorphism (SNPs) Chen and Sullivan, 2003 Vegetative compatibility grouping (VCGs) Ma et al., 2001Ma et al., , 2003Ma et al., , 2004Dakin et al., 2010;Baskarathevan et al., 2012a Universal primed PCR (UP-PCR) Bulat et al., 1998;Abdollahzadeh et al., 2013 Genetic diversity of D. sapinea changes with different morphotypes, and taxonomy, biology and virulence also differ accordingly (Burgess et al., 2001). An endophytic population of D. sapinea showed greater genetic variation, compared to pathogenic populations obtained from dieback symptoms of P. patula after hail damage (Bihon et al., 2012a). ...
The family Botryosphaeriaceae is species rich and includes pathogens, saprobes and endophytes of economically important agricultural crops and plants. As pathogens, Botryosphaeriaceae species employ evolving defensive and counter-defensive strategies that enable them to infect their hosts. Molecular genetic results showed high genetic variability among Botryosphaeriaceae species, which could be a key determinant to their differing environmental roles on hosts and differences in their virulence. Improved technologies such as whole genome re-sequencing, integrated RNA-Seq, comparative and ab initio approaches for molecular genetics and mutation analysis have revealed possible virulence factors that might be involved in the pathogenicity of these fungi. Several genes involved in the pathogenicity processes of botryosphaeriaceous fungi have been identified and characterized. There are numerous reports on the involvement of phytotoxic metabolites in the pathogenic-ity of these taxa. Availability of whole genomes, genetic transformation and transcriptome analysis of some botryosphaeriaceous species have contributed towards identifying the biological functions of many genes in a fast and accurate way, enabling these fungi to be used as model organism for molecular research of plant opportunistic fungal pathogens in woody plants. The research on botryosphaeriaceous species will provide understanding of the infection mechanisms, and with designing control strategies against diseases caused by opportunistic fungal pathogens.
