A Robust Disease Scoring Method to Screen Eucalyptus for Resistance Against the Aggressive Leaf Pathogen Teratosphaeria destructans

Shoot and leaf blight caused by Teratosphaeria destructans is one of the most devastating foliar diseases on Eucalyptus. Therefore, breeding for resistance to this disease is considered urgent. Differences in susceptibility to T. destructans have been observed in the field but a robust inoculation protocol has, until recently, been unavailable and a disease scoring method for precise phenotyping has not been established. A first objective of this study was to determine the optimal conidial concentration for T. destructans inoculations on a susceptible Eucalyptus host. This concentration was then used to determine differences in susceptibility of six genotypes of Eucalyptus grandis × E. urophylla to the pathogen by assessing the percentage of infected stomata using electron microscopy and the percentage of leaf area covered by lesions (PLACL) using image processing. In addition, we developed a disease susceptibility index (SI) of six categories ranging from highly resistant (SI = 0) to highly susceptible (SI = 1.5 to 2). The more resistant genotypes were moderately resistant, with an SI value of 0.49 to 0.54 and a PLACL of 6.5 to 9%. In contrast, the more susceptible genotype scored an SI of 1.52 and PLACL of 48%. Host susceptibility was also assessed relative to the sporulation of the pathogen. This showed that the percentage of sporulation was not significantly correlated with host resistance. Overall, the results provide the basis for rigorous screening and selection of resistant genotypes to the disease caused by T. destructans using artificial inoculation.

Citizen science can enhance strategies to detect and manage invasive forest pests and pathogens

Incorporating a citizen science approach into biological invasion management strategies can enhance biosecurity. Many citizen science projects exist to strengthen the management of forest pest and pathogen invasions within both pre- and post-border scenarios. Besides the value of citizen science initiatives for early detection and monitoring, they also contribute widely to raising awareness, informing decisions about eradication and containment efforts to minimize pest and pathogen spread, and even finding resistant plant material for restoration of landscapes degraded by disease. Overall, many projects actively engage citizens in the different stages of forest pest and pathogen invasions, but it is unclear how they work together across all stages of the entire biological invasion process to enhance biosecurity. Here we provide examples of citizen science projects for each stage of the biological invasion process, discuss options for developing a citizen science program to enhance biosecurity, and suggest approaches for integrating citizen science into biosecurity measures to help safeguard forest resources in the future.

Comparison of the Infection Biology of Teratosphaeria destructans and Teratosphaeria epicoccoides on Eucalyptus

Leaf blight caused by Teratosphaeria destructans is one of the most important diseases of Eucalyptus planted in the subtropics and tropics. In contrast, the better-known T. epicoccoides, though also a primary pathogen of Eucalyptus, causes less damage to trees in these areas. Although T. destructans is an aggressive pathogen, nothing is known about its infection biology. In this study, the conditions for infection and disease development caused by T. destructans and T. epicoccoides were evaluated and compared on a Eucalyptus grandis × E. urophylla hybrid clone. The optimal temperature for germination ranged from 25 to 30°C for T. destructans and 15 to 20°C for T. epicoccoides. The germination of these pathogens was favored under conditions of light and high levels of RH. Penetration by T. destructans and T. epicoccoides occurred via stomata, and the hyphae colonized the intercellular spaces of infected leaves. Symptoms were clearly visible 3 weeks after inoculation by both pathogens, and reproductive structures started to develop in substomatal cavities at 4 weeks after inoculation. The results of this study will facilitate the establishment of rapid screening trials based on artificial inoculations aimed at reducing the impact of disease caused by T. destructans.

Calonectria in the age of genes and genomes: Towards understanding an important but relatively unknown group of pathogens

The genus Calonectria includes many aggressive plant pathogens causing diseases on various agricultural crops as well as forestry and ornamental tree species. Some species have been accidentally introduced into new environments via international trade of putatively asymptomatic plant germplasm or contaminated soil, resulting in significant economic losses. This review provides an overview of the taxonomy, population biology, and pathology of Calonectria species, specifically emerging from contemporary studies that have relied on DNA-based technologies. The growing importance of genomics in future research is highlighted. A life cycle is proposed for Calonectria species, aimed at improving our ability to manage diseases caused by these pathogens.

Phytophthora podocarpi sp. nov. from Diseased Needles and Shoots of Podocarpus in New Zealand

Foliage samples from Podocarpus totara with severe needle browning and needle loss in the lower part of the crown were observed in 2011 in the Gisborne region of New Zealand. A Phytophthora genus-specific test applied directly to the needles gave a strong positive result, and subsequent isolations yielded colonies of a slow-growing oomycete. Morphological examination in vitro revealed a Phytophthora species. Preliminary comparisons of the rDNA (ITS), and ras-related protein (Ypt) gene regions with international DNA sequence revealed low sequence similarity to species from the downy mildew genus Peronospora, as well as clade 3 Phytophthora species. Other studies have also demonstrated the close relationship with Peronospora. The species was given the interim designation Phytophthora taxon tōtara pending further examination. Here, we formally describe Phytophthora podocarpi sp. Nov. and its associated disease, tōtara needle blight.

New and Emerging Insect Pest and Disease Threats to Forest Plantations in Vietnam

The planted forest area in Vietnam increased from 3.0 to 4.4 million hectares in the period 2010–2020, but the loss of productivity from pests and diseases continues to be a problem. During this period, frequent and systematic plantation forest health surveys were conducted on 12 native and 4 exotic genera of trees as well as bamboo across eight forest geographic regions of Vietnam. Damage caused by insects and pathogens was quantified in the field and laboratory in Hanoi. The threats of greatest concern were from folivores (Antheraea frithi, Arthroschista hilaralis, Atteva fabriciella, Hieroglyphus tonkinensis, Lycaria westermanni,Krananda semihyalina, and Moduza procris), wood borers (Batocera lineolata, Euwallacea fornicatus, Tapinolachnus lacordairei, Xyleborus perforans, and Xystrocera festiva), sap-sucking insects (Aulacaspis tubercularis and Helopeltis theivora) and pathogens (Ceratocystis manginecans, Fusarium solani, and Phytophthora acaciivora). The number of new and emerging pests and pathogens increased over time from 2 in 2011 to 17 in 2020, as the damage became more widespread. To manage these pests and diseases, it is necessary to further invest in the selection and breeding of resistant genotypes, improve nursery hygiene and silvicultural operations, and adopt integrated pest management schemes. Consideration should be given to developing forest health monitoring protocols for forest reserves and other special-purpose forests.

Population Diversity and Genetic Structure Reveal Patterns of Host Association and Anthropogenic Impact for the Globally Important Fungal Tree Pathogen Ceratocystis manginecans

Species in the Ceratocystis manginecans complex are important fungal pathogens of plantation trees globally. The most important hosts include species of Eucalyptus, Acacia, Mangifera, and Punica. Despite their relevance and widespread occurrence, little is known regarding their population genetics and how this might relate to their host associations or geographic regions in which they occur. A global collection of 491 isolates representing the C. manginecans complex, from four different plant hosts and nine countries, were genotyped using microsatellite markers. Population genetic analyses using numerous tools were conducted to interrogate how their genetic diversity and structure might be affected by host or areas of occurrence. Results of genetic diversity studies showed that when grouping isolates into populations based on their host associations, the population on Eucalyptus was most diverse, and it also has a broad global distribution. When considering countries of origin as a basis for defining populations, the gene and genotypic diversity were highest in populations from China, Indonesia, and Brazil. In contrast, populations from Oman and Pakistan collected from Mangifera had the lowest genetic diversity and were clonal. Molecular variance, population differentiation, and network and structure analyses showed that the genetic structure of isolates in the C. manginecans complex is influenced by both host association as well as geographical isolation. Furthermore, the results reflected the movement of genotypes between plant hosts and geographic regions that have implications regarding the broad global distribution of this pathogen.

Phylogeography of the wide-host range panglobal plant pathogen Phytophthora cinnamomi

Various hypotheses have been proposed regarding the origin of the plant pathogen Phytophthora cinnamomi. P. cinnamomi is a devastating, highly invasive soilborne pathogen associated with epidemics of agricultural, horticultural and forest plantations and native ecosystems worldwide. We conducted a phylogeographic analysis of populations of this pathogen sampled in Asia, Australia, Europe, southern and northern Africa, South America, and North America. Based on genotyping-by-sequencing, we observed the highest genotypic diversity in Taiwan and Vietnam, followed by Australia and South Africa. Mating type ratios were in equal proportions in Asia as expected for a sexual population. Simulations based on the index of association suggest a partially sexual, semi-clonal mode of reproduction for the Taiwanese and Vietnamese populations while populations outside of Asia are clonal. Ancestral area reconstruction provides new evidence supporting Taiwan as the ancestral area, given our sample, indicating that this region might be near or at the centre of origin for this pathogen as speculated previously. The Australian and South African populations appear to be a secondary centre of diversity following migration from Taiwan or Vietnam. Our work also identified two panglobal, clonal lineages PcG1-A2 and PcG2-A2 of A2 mating type found on all continents. Further surveys of natural forests across Southeast Asia are needed to definitively locate the actual centre of origin of this important plant pathogen.

Global Genetic Diversity and Mating Type Distribution of Calonectria pauciramosa: An Important Wide-Host-Range Plant Pathogen

The fungal pathogen, Calonectria pauciramosa, has caused serious diseases of many important plants worldwide. Understanding the genetic diversity and mating type distribution of this pathogen provides an essential step toward the development of disease control measures. In this study, we designed 15 polymorphic microsatellite markers by using genome sequences of two Ca. pauciramosa isolates having opposite mating type and from different countries. These markers were used to determine the genetic diversity of 145 isolates representing 13 different hosts (12 plant hosts residing in 12 genera, and soil) from 10 countries. In addition, mating type genes were amplified to investigate the reproduction mode of the pathogens in these populations by using mating type primers designed for Calonectria spp. Results revealed that a single dominant genotype, isolated from 11 plant genera residing in eight families, was present in seven countries across five continents. Only mating type MAT1-1 or MAT1-2 was amplified in each of the isolates, confirming that Ca. pauciramosa is heterothallic. Both mating types were detected in isolates from Eucalyptus in South Africa and Uruguay. The MAT1-2 phenotype was widely distributed in isolates from 12 different hosts (11 plant hosts and soil) collected in 10 countries. Overall, the results suggest that there has been substantial global movement of Ca. pauciramosa and that this has shaped its current population structure.

IMA genome - F14 : Draft genome sequences of Penicillium roqueforti, Fusarium sororula, Chrysoporthe puriensis, and Chalaropsis populi

Draft genomes of Penicillium roqueforti, Fusarium sororula, Chalaropsis populi, and Chrysoporthe puriensis are presented. Penicillium roqueforti is a model fungus for genetics, physiological and metabolic studies, as well as for biotechnological applications. Fusarium sororula and Chrysoporthe puriensis are important tree pathogens, and Chalaropsis populi is a soil-borne root-pathogen. The genome sequences presented here thus contribute towards a better understanding of both the pathogenicity and biotechnological potential of these species.

Cryphonectria carpinicola sp. nov. Associated with hornbeam decline in Europe

Since the early 2000s, reports on declining hornbeam trees (Carpinus betulus) are spreading in Europe. Two fungi are involved in the decline phenomenon: One is Anthostoma decipiens, but the other etiological agent has not been identified yet. We examined the morphology, phylogenetic position, and pathogenicity of yellow fungal isolates obtained from hornbeam trees from Austria, Georgia and Switzerland, and compared data with disease reports from northern Italy documented since the early 2000s. Results demonstrate distinctive morphology and monophyletic status of Cryphonectria carpinicola sp. nov. as etiological agent of the European hornbeam decline. Interestingly, the genus Cryphonectria splits into two major clades. One includes Cry. carpinicola together with Cry. radicalis, Cry. decipiens and Cry. naterciae from Europe, while the other comprises species known from Asia-suggesting that the genus Cryphonectria has developed at two evolutionary centres, one in Europe and Asia Minor, the other in East Asia. Pathogenicity studies confirm that Car. betulus is a major host species of Cry. carpinicola. This clearly distinguished Cry. carpinicola from other Cryphonectria species, which mainly occur on Castanea and Quercus.

Tree health in South Africa: Retrospect and prospect

South Africa is a country with very limited natural forest cover. Consequently, the timber and fibre needs of the country cannot be provided for from indigenous forest. It is largely for this reason that South Africa initially developed a highly productive plantation forest industry, which today makes a substantial contribution to the local economy. These plantations are based on non-native species of Eucalyptus, Pinus and Australian Acacia. In the early years of establishment, South African plantations were relatively free of pest and pathogen problems. But, over time, an increasing number of insects, fungi and bacteria have emerged as serious threats to the sustainability of the forestry industry. Numerous native pests and pathogens, especially insects, have adapted to these introduced tree species to cause damage or disease. The problem is compounded by the accidental introduction of non-native pests and pathogens, and this has been at a rapidly increasing rate over the past three decades. Some of these introduced pests and pathogens also threaten the fitness and even the survival of many indigenous South African tree species. Fortunately, South Africa has developed an impressive knowledge base and range of integrated management options to deal with these problems. This development was first driven by government programmes, and in more recent years by public–private partnerships between industry, universities and government. It is clear from the pattern of emergence of pests and pathogens in recent years that South Africa will deal with an increasing number of these problems and a continuously changing tree health environment. This requires robust investment in both quarantine and mitigation mechanisms to protect the country’s biodiversity as well as to ensure the sustainability of its wood and fibre industries.

Harmonising the fields of invasion science and forest pathology

Invasive alien species are widely recognised as significant drivers of global environmental change, with far reaching ecological and socio-economic impacts. The trend of continuous increases in first records, with no apparent sign of saturation, is consistent across all taxonomic groups. However, taxonomic biases exist in the extent to which invasion processes have been studied. Invasive forest pathogens have caused, and they continue to result in dramatic damage to natural forests and woody ecosystems, yet their impacts are substantially underrepresented in the invasion science literature. Conversely, most studies of forest pathogens have been undertaken in the absence of a connection to the frameworks developed and used to study biological invasions. We believe this is, in part, a consequence of the mechanistic approach of the discipline of forest pathology; one that has been inherited from the broader discipline of plant pathology. Rather than investigating the origins of, and the processes driving the arrival of invasive microorganisms, the focus of pathologists is generally to investigate specific interactions between hosts and pathogens, with an emphasis on controlling the resulting disease problems. In contrast, central to the field of invasion science, which finds its roots in ecology, is the development and testing of general concepts and frameworks. The lack of knowledge of microbial biodiversity and ecology, speciation and geographic origin present challenges in understanding invasive forest pathogens under existing frameworks, and there is a need to address this shortfall. Advances in molecular technologies such as gene and genome sequencing and metagenomics studies have increased the “visibility” of microorganisms. We consider whether these technologies are being adequately applied to address the gaps between forest pathology and invasion science. We also interrogate the extent to which the two fields stand to gain by becoming more closely linked.

IMA Genome - F13: Draft genome sequences of Ambrosiella cleistominuta, Cercospora brassicicola, C. citrullina, Physcia stellaris, and Teratosphaeria pseudoeucalypti

Draft genomes of the fungal species Ambrosiella cleistominuta, Cercospora brassicicola, C. citrullina, Physcia stellaris, and Teratosphaeria pseudoeucalypti are presented. Physcia stellaris is an important lichen forming fungus and Ambrosiella cleistominuta is an ambrosia beetle symbiont. Cercospora brassicicola and C. citrullina are agriculturally relevant plant pathogens that cause leaf-spots in brassicaceous vegetables and cucurbits respectively. Teratosphaeria pseudoeucalypti causes severe leaf blight and defoliation of Eucalyptus trees. These genomes provide a valuable resource for understanding the molecular processes in these economically important fungi.

Disease in Invasive Plant Populations

Non-native invasive plants can establish in natural areas, where they can be ecologically damaging and costly to manage. Like cultivated plants, invasive plants can experience a relatively disease-free period upon introduction and accumulate pathogens over time. Diseases of invasive plant populations are infrequently studied compared to diseases of agriculture, forestry, and even native plant populations. We evaluated similarities and differences in the processes that are likely to affect pathogen accumulation and disease in invasive plants compared to cultivated plants, which are the dominant focus of the field of plant pathology. Invasive plants experience more genetic, biotic, and abiotic variation across space and over time than cultivated plants, which is expected to stabilize the ecological and evolutionary dynamics of interactions with pathogens and possibly weaken the efficacy of infectious disease in their control. Although disease is expected to be context dependent, the widespread distribution of invasive plants makes them important pathogen reservoirs. Research on invasive plant diseases can both protect crops and help manage invasive plant populations.

Pathologists and entomologists must join forces against forest pest and pathogen invasions

The world’s forests have never been more threatened by invasions of exotic pests and pathogens, whose causes and impacts are reinforced by global change. However, forest entomologists and pathologists have, for too long, worked independently, used different concepts and proposed specific management methods without recognising parallels and synergies between their respective fields. Instead, we advocate increased collaboration between these two scientific communities to improve the long-term health of forests.

Our arguments are that the pathways of entry of exotic pests and pathogens are often the same and that insects and fungi often coexist in the same affected trees. Innovative methods for preventing invasions, early detection and identification of non-native species, modelling of their impact and spread and prevention of damage by increasing the resistance of ecosystems can be shared for the management of both pests and diseases.

We, therefore, make recommendations to foster this convergence, proposing in particular the development of interdisciplinary research programmes, the development of generic tools or methods for pest and pathogen management and capacity building for the education and training of students, managers, decision-makers and citizens concerned with forest health.

Pine Pitch Canker (PPC): Pathways of Pathogen Spread and Preventive Measures

Fusarium circinatum (Nirenberg and O’ Donnell) is the causal agent of pine pitch canker (PPC) disease, one of the most devastating forest diseases worldwide. Long-distance spread occurs mainly through the movement of infected seeds whereas at regional level, the movement of seedlings, substrates, or containers may play an important role in fungal dispersal. Invasion of nurseries takes place via infected seeds and further spread can occur by planting contaminated seedlings, especially due to the possibility of infected plants remaining symptomless. Once established, F. circinatum spreads by rain, wind, and insects. The natural spread of the pathogen is limited due to the short dispersal distances of the spores and the fairly short flight distances of disseminating insects. In this review, we summarize the currently known dispersal pathways of the pathogen, discussing both natural and human-assisted processes. With the purpose of understanding how to best intervene in the disease’s development in nurseries and forests, we outline the epidemiology of the pathogen describing the key factors influencing its spread. Preventive measures to control the spread of F. circinatum locally and globally are described with special emphasis on the challenges in implementing them.

Interacting Effects of Global Change on Forest Pest and Pathogen Dynamics

Pathogens and insect pests are important drivers of tree mortality and forest dynamics, but global change has rapidly altered or intensified their impacts. Predictive understanding of changing disease and outbreak occurrence has been limited by two factors: ( a) tree mortality and morbidity are emergent phenomena determined by interactions between plant hosts, biotic agents (insects or pathogens), and the environment; and ( b) disparate global change drivers co-occur, obscuring net impacts on each of these components. To expand our understanding of changing forest diseases, declines, and outbreaks, we adopt a framework that identifies and organizes observed impacts of diverse global change drivers on the primary mechanisms underlying agent virulence and host susceptibility. We then discuss insights from ecological theory that may advance prediction of forest epidemics and outbreaks. This approach highlights key drivers of changing pest and pathogen dynamics, which may inform forest management aimed at mitigating accelerating rates of tree mortality globally.

Botryosphaeriaceae associated with Acacia heterophylla (La Réunion) and Acacia koa (Hawaii)

Acacia koa and A. heterophylla are commonly occurring native trees on the Hawaiian Islands and La Réunion, respectively. A recent phylogenetic study suggested that A. heterophylla renders A. koa paraphyletic, and that the former likely arose from the Hawaiian Islands around 1.4 million years ago. An intriguing question is whether their microbiota is similar, although they occur naturally in two very distant geographical locations. In this study, we compared the fungi in the Botryosphaeriaceae isolated from natural populations of A. koa and A. heterophylla. These fungi were chosen because they commonly occur on woody plants and some are important pathogens. They are also known to have been moved globally on asymptomatic plant materials. Isolates were identified based on comparisons of DNA sequence data for the rDNA-ITS, TEF1-α and β-tubulin loci. Ten Botryosphaeriaceae species were identified, of which four species were specific to A. koa from the Hawaiian Islands and five to A. heterophylla in La Réunion. Only one species, Neofusicoccumparvum, which is known to have a wide global distribution, was common to both hosts. The overall results of this study suggest that although A. koa and A.heterophylla share a recent evolutionary history, they have established independent microbiota, at least in terms of the Botryosphaeriaceae.

Foliar pathogens of eucalypts

Species of eucalypts are commonly cultivated for solid wood and pulp products. The expansion of commercially managed eucalypt plantations has chiefly been driven by their rapid growth and suitability for propagation across a very wide variety of sites and climatic conditions. Infection of foliar fungal pathogens of eucalypts is resulting in increasingly negative impacts on commercial forest industries globally. To assist in evaluating this threat, the present study provides a global perspective on foliar pathogens of eucalypts. We treat 110 different genera including species associated with foliar disease symptoms of these hosts. The vast majority of these fungi have been grown in axenic culture, and subjected to DNA sequence analysis, resolving their phylogeny. During the course of this study several new genera and species were encountered, and these are described. New genera include: Lembosiniella (L. eucalyptorum on E. dunnii, Australia), Neosonderhenia (N. eucalypti on E. costata, Australia), Neothyriopsis (N. sphaerospora on E. camaldulensis, South Africa), Neotrichosphaeria (N. eucalypticola on E. deglupta, Australia), Nothotrimmatostroma (N. bifarium on E. dalrympleana, Australia), Nowamyces (incl. Nowamycetaceae fam. nov., N. globulus on E. globulus, Australia), and Walkaminomyces (W. medusae on E. alba, Australia). New species include (all from Australia): Disculoides fraxinoides on E. fraxinoides, Elsinoe piperitae on E. piperita, Fusculina regnans on E. regnans, Marthamyces johnstonii on E. dunnii, Neofusicoccum corticosae on E. corticosa, Neotrimmatostroma dalrympleanae on E. dalrympleana, Nowamyces piperitae on E. piperita, Phaeothyriolum dunnii on E. dunnii, Pseudophloeospora eucalyptigena on E. obliqua, Pseudophloeospora jollyi on Eucalyptus sp., Quambalaria tasmaniae on Eucalyptus sp., Q. rugosae on E. rugosa, Sonderhenia radiata on E. radiata, Teratosphaeria pseudonubilosa on E. globulus and Thyrinula dunnii on E. dunnii. A new name is also proposed for Heteroconium eucalypti as Thyrinula uruguayensis on E. dunnii, Uruguay. Although many of these genera and species are commonly associated with disease problems, several appear to be opportunists developing on stressed or dying tissues. For the majority of these fungi, pathogenicity remains to be determined. This represents an important goal for forest pathologists and biologists in the future. Consequently, this study will promote renewed interest in foliar pathogens of eucalypts, leading to investigations that will provide an improved understanding of the biology of these fungi.

The value of sentinel plants for risk assessment and surveillance to support biosecurity

Effective surveillance for early detection of invasive alien species in natural ecosystems, or on valued plants found in modified areas, could prevent potentially devastating and costly impacts (whether environmental, economic or cultural) of new invasions on the invaded country. Surveillance technologies are often constrained by a range of factors. Determining which species present a significant risk before they reach the border is an effective strategy to minimize the possibility of invasion and/or the impact of invasion. Surveillance of sentinel plants provides an important tool to strengthen biosecurity programs assisting with i) detecting and identifying insect pests, nematodes and plant diseases that could potentially invade uncolonized countries, and ii) developing pest risk analysis profiles to eliminate or mitigate the risk of arrival. This review examines some of the challenges and opportunities provided by sentinel plant research and discusses the factors that could affect the success of their use for biosecurity risk assessment and surveillance in the New Zealand context.

Molecular analyses identify hybridization-mediated nuclear evolution in newly discovered fungal hybrids

Hybridization may be a major driver in the evolution of plant pathogens. In a high elevation Alpine larch stand in Montana, a novel hybrid fungal pathogen of trees originating from the mating of Heterobasidion irregulare with H. occidentale has been recently discovered. In this study, sequence analyses of one mitochondrial and four nuclear loci from 11 Heterobasidion genotypes collected in the same Alpine larch stand indicated that hybridization has increased allelic diversity by generating novel polymorphisms unreported in either parental species. Sequence data and ploidy analysis through flow cytometry confirmed that heterokaryotic (n + n) genotypes were not first-generation hybrids, but were the result of multiple backcrosses, indicating hybrids are fertile. Additionally, all admixed genotypes possessed the H. occidentale mitochondrion, indicating that the hybrid progeny may have been backcrossing mostly with H. occidentale. Based on reticulate phylogenetic network analysis by PhyloNet, Bayesian assignment, and ordination tests, alleles can be defined as H. irregulare-like or H. occidentale-like. H. irregulare-like alleles are clearly distinct from all known H. irregulare alleles and are derived from the admixing of both Heterobasidion species. Instead, all but one H. occidentale alleles found in hybrids, although novel, were not clearly distinct from alleles found in the parental H. occidentale population. This discovery demonstrates that Alpine larch can be a universal host favouring the interspecific hybridization between H. irregulare and H. occidentale and the hybridization-mediated evolution of a nucleus, derived from H. irregulare parental species but clearly distinct from it.

Ten new species of Calonectria from Indonesia and Vietnam

Vietnam and Indonesia have rapidly growing and extensive plantation forestry programs, especially of Acacia spp. and Eucalyptus spp. As these plantations expand, the threat from pests and diseases also increases. Calonectria species are among those pathogens causing diseases of trees in plantations and nurseries in these countries. Extensive surveys were conducted across plantations and nurseries of Vietnam and parts of Indonesia, where a large number of Calonectria isolates were retrieved from diseased leaves and soils associated with symptomatic trees. The aim of this study was to identify and resolve the phylogenetic relationships among these isolates using DNA sequence comparisons of four gene regions as well as morphological characters. From a collection of 165 isolates, the study revealed five known and 10 undescribed species. The relatively high diversity of Calonectria species found in this study supports the view that many more species in this genus remain to be discovered in other areas of Southeast Asia.

Teratosphaeria stem canker of Eucalyptus: two pathogens, one devastating disease

BACKGROUND

Teratosphaeria gauchensis and T. zuluensis are closely related fungi that cause Teratosphaeria (previously Coniothyrium) stem canker disease on Eucalyptus species propagated in plantations for commercial purposes. This disease is present in many countries in which Eucalyptus trees are planted, and continues to spread with the international trade of infected plant germplasm.

TAXONOMY

Fungi, Ascomycota, Pezizomycotina, Dothideomycetes, Dothideomycetidae, Capnodiales, Teratosphaeriaceae, Teratosphaeria.

IDENTIFICATION

The causal agents form dark masses of pycnidia that are visible on the surface of distinct stem cankers that typically form on young green stem tissues. Accurate diagnosis of the causal agents requires DNA sequence data.

HOST RANGE

Nine species of Eucalyptus are known to be affected. Of these, E. grandis and its hybrids, which include some of the most important planting stock globally, appear to be particularly vulnerable.

DISEASE SYMPTOMS

Small necrotic lesions develop on young green stem tissue. These lesions coalesce to form large cankers that exude gum. Epicormic shoots develop below the girdling canker and, in severe cases, trees die.

USEFUL WEBSITES

Mycobank, https://www.mycobank.org; Publications of the Forestry and Agricultural Biotechnology Institute (FABI), https://www.fabinet.up.ac.za/index.php/journals.

Phylogeny and Pathogenicity of Celoporthe Species from Plantation Eucalyptus in Southern China

The family of Cryphonectriaceae (Diaporthales) includes many important tree pathogens, such as those that cause severe cankers on Eucalyptus trees. Recently, stem canker and cracked bark were observed on 8-year-old Eucalyptus grandis × E. urophylla trees in a plantation in southern China. Fruiting structures typical of Cryphonectriaceae fungi were observed on the surface of the diseased tissues. In this study, the isolated fungi were identified based on DNA sequence analyses and morphological characteristics, and their pathogenicity was tested on three Eucalyptus clones. DNA sequence comparisons of the internal transcribed spacer (ITS) regions (including the intervening 5.8S nrRNA gene), two regions of β-tubulin (BT2/BT1), and partial translation elongation factor1-α (TEF-1α), indicated that these isolates represent Celoporthe syzygii and one previously undescribed species. The undescribed species was also morphologically distinct from the other species of Celoporthe. The new species was described and named C. cerciana sp. nov. The results of this study based on the ITS, BT2/BT1, and TEF-1α sequences indicated that more than one haplotype was isolated from the same Eucalyptus tree. The findings of a previous study, whereby C. eucalypti was isolated from the same plantation as that of this study, revealed the high species diversity of Celoporthe within a single plantation, which is associated with a single Eucalyptus sp. in southern China. The results further suggested that hybridization may occur between C. syzygii and C. eucalypti. In addition to the Eucalyptus trees, C. syzygii was also isolated from native Melastoma candidum in the same Eucalyptus plantation. The inoculation results showed that these fungi isolated from E. grandis × E. urophylla and M. candidum are pathogenic to all three tested E. grandis hybrid clones. Significant differences in tolerance were observed between the tested Eucalyptus clones, suggesting that disease-tolerant Eucalyptus genotypes can be selected for disease management.

Nine draft genome sequences of Claviceps purpurea s.lat., including C. arundinis, C. humidiphila, and C. cf. spartinae, pseudomolecules for the pitch canker pathogen Fusarium circinatum, draft genome of Davidsoniella eucalypti, Grosmannia galeiformis, Quambalaria eucalypti, and Teratosphaeria destructans

This genome announcement includes draft genomes from Claviceps purpurea s.lat., including C. arundinis, C. humidiphila and C. cf. spartinae. The draft genomes of Davidsoniella eucalypti, Quambalaria eucalypti and Teratosphaeria destructans, all three important eucalyptus pathogens, are presented. The insect associate Grosmannia galeiformis is also described. The pine pathogen genome of Fusarium circinatum has been assembled into pseudomolecules, based on additional sequence data and by harnessing the known synteny within the Fusarium fujikuroi species complex. This new assembly of the F. circinatum genome provides 12 pseudomolecules that correspond to the haploid chromosome number of F. circinatum. These are comparable to other chromosomal assemblies within the FFSC and will enable more robust genomic comparisons within this species complex.

Planting exotic relatives has increased the threat posed by Dothistroma septosporum to the Caledonian pine populations of Scotland

To manage emerging forest diseases and prevent their occurrence in the future, it is essential to determine the origin(s) of the pathogens involved and identify the management practices that have ultimately caused disease problems. One such practice is the widespread planting of exotic tree species within the range of related native taxa. This can lead to emerging forest disease both by facilitating introduction of exotic pathogens and by providing susceptible hosts on which epidemics of native pathogens can develop. We used microsatellite markers to determine the origins of the pathogen Dothistroma septosporum responsible for the current outbreak of Dothistroma needle blight (DNB) on native Caledonian Scots pine (Pinus sylvestris) populations in Scotland and evaluated the role played by widespread planting of two exotic pine species in the development of the disease outbreak. We distinguished three races of D. septosporum in Scotland, one of low genetic diversity associated with introduced lodgepole pine (Pinus contorta), one of high diversity probably derived from the DNB epidemic on introduced Corsican pine (Pinus nigra subsp. laricio) in England and a third of intermediate diversity apparently endemic on Caledonian Scots pine. These races differed for both growth rate and exudate production in culture. Planting of exotic pine stands in the UK appears to have facilitated the introduction of two exotic races of D. septosporum into Scotland which now pose a threat to native Caledonian pines both directly and through potential hybridization and introgression with the endemic race. Our results indicate that both removal of exotic species from the vicinity of Caledonian pine populations and restriction of movement of planting material are required to minimize the impact of the current DNB outbreak. They also demonstrate that planting exotic species that are related to native species reduces rather than enhances the resilience of forests to pathogens.

Looking for relationships between the populations of Dothistroma septosporum in northern Europe and Asia

Dothistroma septosporum, a notorious pine needle pathogen with an unknown historical geographic origin and poorly known distribution pathways, is nowadays found almost in all areas inhabited by pines (Pinus spp.). The main aim of this study was to determine the relationship between North European and East Asian populations. In total, 238 Eurasian D. septosporum isolates from 11 countries, including 211 isolates from northern Europe, 16 isolates from Russian Far East and 11 isolates from Bhutan were analysed using 11 species-specific microsatellite and mating type markers. The most diverse populations were found in northern Europe, including the Baltic countries, Finland and European Russia. Notably, D. septosporum has not caused heavy damage to P. sylvestris in northern Europe, which may suggest a long co-existence of the host and the pathogen. No indication was obtained that the Russian Far East or Bhutan could be the indigenous area of D. septosporum, as the genetic diversity of the fungus there was low and evidence suggests gene flow from northern Europe to Russian Far East. On the western coast of Norway, a unique genetic pattern was observed, which differed from haplotypes dominating other Fennoscandian populations. As an agent of dothistroma needle blight, only D. septosporum was documented in northern Europe and Asia, while D. pini was found in Ukraine and Serbia.