Showing papers in "Forest Pathology in 2016"

Widespread Phytophthora infestations in European nurseries put forest, semi-natural and horticultural ecosystems at high risk of Phytophthora diseases

Abstract: An analysis of incidence of Phytophthora spp. in 732 European nurseries producing forest transplants, larger specimen trees, landscape plants and ornamentals, plus 2525 areas in which trees and shrubs were planted, is presented based on work conducted by 37 research groups in 23 European countries between 1972 and 2013. Forty-nine Phytophthora taxa were recorded in 670 nurseries (91.5%); within these nurseries, 1614 of 1992 nursery stands (81.0%) were infested, although most affected plants appeared healthy. In forest and landscape plantings, 56 Phytophthora taxa were recovered from 1667 of 2525 tested sites (66.0%). Affected plants frequently showed symptoms such as crown thinning, chlorosis and dieback caused by extensive fine root losses and/or collar rot. Many well-known highly damaging host-Phytophthora combinations were frequently detected but 297 and 407 new Phytophthora-host associations were also observed in nurseries and plantings, respectively. On average, 1.3 Phytophthora species/taxa per infested nursery stand and planting site were isolated. At least 47 of the 68 Phytophthora species/taxa detected in nurseries and plantings were exotic species several of which are considered well established in both nurseries and plantings in Europe. Seven known Phytophthora species/taxa were found for the first time in Europe, while 10 taxa had not been previously recorded from nurseries or plantings; in addition, 5 taxa were first detections on woody plant species. Seven Phytophthora taxa were previously unknown to science. The reasons for these failures of plant biosecurity in Europe, implications for forest and semi-natural ecosystems and possible ways to improve biosecurity are discussed.

Global geographic distribution and host range of Dothistroma species: a comprehensive review

Abstract: Summary Dothistroma needle blight (DNB) is one of the most important diseases of pine. Although its notoriety stems from Southern Hemisphere epidemics in Pinus radiata plantations, the disease has increased in prevalence and severity in areas of the Northern Hemisphere, including Europe, during the last two decades. This increase has largely been attributed to expanded planting of susceptible hosts, anthropogenic dispersal of the causative pathogens and changes in climate conducive to disease development. The last comprehensive review of DNB was published in 2004, with updates on geographic distribution and host species in 2009. Importantly, the recognition that two species, Dothistroma septosporum and D. pini, cause DNB emerged only relatively recently in 2004. These two species are morphologically very similar, and DNA-based techniques are needed to distinguish between them. Consequently, many records of host species affected or geographic location of DNB prior to 2004 are inconclusive or even misleading. The objectives of this review were (i) to provide a new database in which detailed records of DNB from 62 countries are collated; (ii) to chart the current global distribution of D. septosporum and D. pini; (iii) to list all known host species and to consider their susceptibility globally; (iv) to collate the published results of provenance trials; and (v) to consider the effects of site factors on disease incidence and severity. The review shows that DNB occurs in 76 countries, with D. septosporum confirmed to occur in 44 and D. pini in 13. There are now 109 documented Pinaceae host taxa for Dothistroma species, spanning six genera (Abies, Cedrus, Larix, Picea, Pinus and Pseudotsuga), with Pinus being the dominant host genus, accounting for 95 host taxa. The relative susceptibilities of these hosts to Dothistroma species are reported, providing a resource to inform species choice in forest planting. Country records show that most DNB outbreaks in Europe occur on Pinus nigra and its subspecies. It is anticipated that the collaborative work described in this review will both underpin a broader global research strategy to manage DNB in the future and provide a model for the study of other forest pathogens.

Dothistroma needle blight, weather and possible climatic triggers for the disease's recent emergence.

Abstract: Summary Dothistroma needle blight (DNB), caused by the two fungi Dothistroma septosporum and D. pini, is a major disease of pines with a worldwide distribution. Increases in the incidence and severity of disease in areas where the disease has long been established and notable range expansions have both recently been observed. The aim of this review was to assess the relationship between DNB, weather factors and climate to better understand possible underlying causes of this recent intensification in disease. A substantial body of literature shows that the life cycles of the fungi are closely related to weather factors such as precipitation and temperature. Given the rapid response of DNB to favourable weather conditions, it seems plausible that changes in disease behaviour could be due to changes in climate. The recurrent El Nino-Southern oscillation (ENSO) phenomenon influences patterns of temperature and precipitation in many regions of the world, often resulting in warmer and wetter conditions than normal. We found that since the 1950s, four of the past five strong El Nino events appear to have coincided with reports of increased DNB activity on an intercontinental scale. The lack of long-term standardized data records limits our ability to fully interpret this relationship, but the projected future climatic conditions in the Northern Hemisphere appear to be increasingly favourable for the disease. Still, other areas of the world may become less favourable, and further research is required to be able to accurately predict DNB outbreaks and their impact on pine forests in the future.

A worldwide perspective on the management and control of Dothistroma needle blight

Abstract: This study was partially supported by the EU COST Action FP1102 DIAROD (Determining Invasiveness and Risk of Dothistroma, http:// www.cost.eu/COST_Actions/fps/FP1102)

Temporal evolution of collar lesions associated with ash dieback and the occurrence of Armillaria in Belgian forests

Abstract: Summary Ash dieback, caused by the fungus Hymenoscyphus fraxineus, has been observed in Europe for several years. In Belgium, the disease was first reported in 2010. Besides crown defoliation and dieback, collar lesions have sometimes been reported. To evaluate the prevalence and the progression of collar lesions and crown defoliation in ash dieback-affected stands of various ages, a survey was conducted in 2013 and 2014 on 268 ash trees (Fraxinus excelsior) originating from 17 Walloon forest stands. The results showed that the proportion of trees with collar lesions greatly increased between June 2013 and September 2014 and that there appeared to be no significant link between a tree's diameter-at-breast height (DBH) and collar lesion occurrence. The mean percentage of defoliation increased in each forest stand across time, with observations conducted in September 2013 and 2014 showing a positive correlation with the mean percentage of trees with collar lesions. Molecular tests were carried out on 103 additional trees originating from 12 of the 17 stands to evaluate the occurrence of H. fraxineus and Armillaria spp. at the collar level. Most of the trees (98%) were infected by H. fraxineus. In contrast, only 41% of the samples were infected with Armillaria spp., most commonly A. gallica and A. cepistipes. This study discusses the role of Armillaria spp. and the rapid increase in the number of trees with collar lesions within the context of the evolution of ash dieback in Europe.

Neotypification of Dothistroma septosporum and epitypification of D. pini, causal agents of Dothistroma needle blight of pine

Abstract: Summary Dothistroma needle blight (DNB) is one of the most devastating needle diseases on Pinus spp. worldwide. Ever since the description of the causal agent of the disease in Europe in 1911 as Cytosporina septospora, and independently in the USA in 1941 as Dothistroma pini, there has been considerable taxonomic discordance regarding the name of the pathogen used in literature. This was compounded both by the proposal of different varieties of the pathogen based on differences in spore size and the application of dual nomenclature where three names, Scirrhia pini, Eruptio pini and Mycosphaerella pini, were used to describe the sexual morph of the fungus. More recent studies using sequence-based methods revealed that DNB can be caused by either one of two distinct species, that is D. septosporum and D. pini. These important species have not been adequately typified, and this perpetuates lack of stability for their names. In this study, these names are fixed to reference sequences linked to living cultures representing type specimens. To achieve this goal, we designate an epitype for D. pini and a neotype for D. septosporum. The known polymorphism in the ITS region, the barcoding gene for these fungi, is characterized and a complete taxonomic history is provided for the genus Dothistroma.

Powdery mildew disease of rubber tree

Abstract: Summary Powdery mildew disease of rubber trees affects young rubber leaves, buds, inflorescences and other immature tissues reducing rubber latex yields by up to 45%. The disease is present in all rubber-growing regions, with a high incidence rate in subtropical environments. The causal agent of powdery mildew disease of rubber trees was first described as Oidium heveae, but later research on the morphological characteristics suggests that O. heveae was in the past confused with Erysiphe quercicola. However, the most appropriate classification is still under debate between the genera Golovinomyces or Podosphaera. Molecular and phylogenetic analyses have established some relationships between rubber powdery mildew fungus and other powdery mildew species, but the generic sexual state of rubber powdery mildew fungus has not yet been established. Rubber powdery mildew conidia are wind-spread spores that are produced in great numbers when growth conditions of the disease are favourable. The optimum conditions for conidial germination are 97–100% relative humidity and temperatures between 25 and 28°C. While some newly bred rubber clones have shown resistance to the disease, it can also be controlled with a number of fungicides and biological control agents. It is clear from recent knowledge about climate–fungus relationships that changes in weather strongly influence disease incidence and severity. The aim of this review is to highlight the classification conflicts, main causes and influencing factors behind the disease spreading, as well as draw attention to the impact of weather changes on the outbreaks of the disease. The information in this review will be helpful to adopt better control measures of the powdery mildew disease of rubber, especially in higher humidity areas, thereby minimizing the loss of rubber yields due to this disease.

Endohyphal bacteria from fungal endophytes of the Mediterranean cypress (Cupressus sempervirens) exhibit in vitro bioactivity

Abstract: Summary Endohyphal organisms of endophytic fungi can induce, or promote, beneficial effects of their respective host fungi to the host plant that harbours them. The Cupressaceae plant family (Coniferales) hosts highly bioactive endophytic fungi. Here, we show that a fraction of such endophytic fungi harbours bioactive endohyphal bacteria with a non-obligatory symbiotic lifestyle. Indeed, 5 of 16 (31.25%) endophytic fungi of Cupressus sempervirens harboured endofungal bacterial strains of Bacillaceae (G+, Bacilli) and Sphingomonadaceae (G−, α-Proteobacteria), that is Bacillus pumilus (from the fungi Leptosphaeria CSE211 and Pyrenochaeta CSE134), Bacillus subtilis (from the fungi Leptosphaeria CSE212 and Ascorhizoctonia CSE148) and Sphingomonas paucimobilis (from the fungus Ascorhizoctonia CSE195). Notably, each endophytic fungal species contained only one endofungal bacterial species that was stably maintained in symbiosis over several rounds of subculturing. Moreover, we investigated whether cypress endofungal bacteria (CEB) could benefit their host fungus competing with other fungi and bacteria or the host plant against the invading microorganisms. In vitro assays indicated that CEB possessed antagonistic activity against cypress endophytic and pathogenic microbiome. Also, CEB metabolites and volatile compounds (VOCs) exhibited antifungal and antibacterial activity against the target microbiome. Bioactivity of CEB was less than that of the endophytic microbiome of Cupressaceae, on which we reported earlier. In conclusion, our work is the first to document endohyphal bacteria of fungal endophytes of C. sempervirens and the bioactivity of such endohyphal symbionts. These findings implicate a complicated interrelationship among host plant, endophytic microbiome and endofungal bacteria, which might be of high importance for evolutionary, as well as environmental and agricultural studies. Eventually, endohyphal bacteria may be introduced as a novel source for lead molecule discovery.

A review of Pinaceae resistance mechanisms against needle and shoot pathogens with a focus on the Dothistroma–Pinus interaction

Abstract: Dothistroma needle blight (DNB), caused by Dothistroma septosporum and Dothistroma pini, is a highly damaging disease of pine. DNB was originally considered a problem on exotic Pinus radiata plantations in the Southern Hemisphere and on both exotic and native pines in parts of North America in the 1960s. Since the mid-1990s, however, DNB has increased in importance in various parts of the world, including Europe. On susceptible species, DNB causes premature needle drop, a loss of yield and, in some circumstances, mortality. In some areas, DNB is controlled by the application of copper-based fungicides and silvicultural techniques, such as thinning and pruning. In New Zealand, there has also been a long history of selection of more resistant P. radiata for use in breeding programmes. A richer understanding of the resistance mechanisms involved in the Dothistroma–Pinus interaction will play a critical role in helping the development of sustainable integrated DNB management strategies. This review therefore summarizes current knowledge of defence mechanisms involved in the defence of Pinaceae against needle and shoot pathogens and identifies research gaps. Collaborative research efforts from countries directly or indirectly affected by DNB are rapidly generating new knowledge to address these gaps.

Identification and characterization of fungi associated with internal wood lesions and decline disease of willow and poplar trees in Iran

Abstract: Summary During the study of fungal trunk pathogens associated with urban trees decline in Shiraz (Iran), a serious decline of willow and poplar trees was observed. Therefore, an investigation was conducted on these trees in some areas of this city during spring and summer 2012 and 2013, to determine the main fungal trunk pathogens associated with these ornamental plants. Plant materials were collected from trees exhibiting disease symptoms such as yellowing, shoot canker, shoot dieback, defoliation and internal wood necrosis and decayed wood. Fungal isolations were made from discoloured or decayed wood tissue onto 2% malt extract agar (MEA) amended with streptomycin sulphate. Nine species, Fomes fomentarius, Diplodia seriata, Lasiodiplodia theobromae, Dothiorella sarmentorum, Neoscytalidium hyalinum, Diatrype whitmanensis, Phaeoacremonium rubrigenum, P. aleophilum and P. parasiticum, were identified based on morphology and DNA sequence comparisons. Pathogenicity tests were performed on detached shoots of willow and poplar trees under greenhouse conditions. Lasiodiplodia theobromae caused the longest lesions on willow. On poplar shoots, the longest lesions were caused by P. parasiticum. Diplodia seriata produced the smallest lesions on both woody hosts. First reports from willow wood include P. parasiticum, P. rubrigenum, D. whitmanensis, L. theobromae, D. seriata and N. hyalinum, while new reports from poplar wood include P. parasiticum and Do. sarmentorum. Based on our knowledge, this is also the first report of D. whitmanensis in Iran.

Individual resistance of Fraxinus angustifolia clones to ash dieback.

Abstract: Summary The presumed resistance of individual ash trees to ash dieback caused by invasive pathogen Hymenoscyphus fraxineus is an important issue for the maintenance of ash in European forests. All known studies regarding the resistance of ash trees to ash dieback were conducted in plantations and stands of F. excelsior; however, no such data exist for F. angustifolia. Crown damage assessments were performed over four consecutive years between 2009 and 2012 at a F. angustifolia clonal plantation in Hrascica, Slovenia. Inoculation of H. fraxineus into the branches of the most and least damaged clones of F. angustifolia and leaf phenology assessments was performed to verify the presence of defence mechanisms that limit fungal growth or promote disease escape. Additionally, root collars of selected clones were inspected for fungal infections. The crown damage assessments showed considerable differences among F. angustifolia clones, indicating genetic variability in susceptibility to ash dieback. Crown dieback progressed significantly over the 4-year time period; the mean crown damage of individual clones in 2012 varied between 16.7% and 83.8%. Significant differences among F. angustifolia clones were found in the inoculation trials and leaf phenology assessments. However, defence mechanisms such as early leaf flushing, early leaf shedding and the ability to inhibit pathogen growth in host tissues were not confirmed. High frequency of Armillaria spp. and H. fraxineus root collar infection demonstrated the need for whole tree inspection to determine causal agent of damages on individual ash trees. Armillaria spp. may be highly associated with ash decline epidemiology.

Fungal root endophytes of Quercus robur subjected to flooding

Abstract: Summary In August 2011, fungal endophytes were isolated from fine (0.1–0.5 cm diameter) and structural (0.6–2.0 cm) roots from eighteen Q. robur trees at six sites in a Q. robur-dominated forest displaying symptoms of oak decline. Five sites were subjected to periodic flooding for 3 months in 1997 and 1 month in 2010. Fungal colonization was detected in 94% of 1296 root fragments examined. Fungi representing 126 taxa from Zygomycota (four species), Ascomycota (117 species) and Basidiomycota (five species) were isolated using culture-based methods and identified by morphotyping and sequencing of the ITS 1 and 2 rDNA. The most frequent eudominants (with colonization frequencies ≥10%) were Aspergillus spp., Cosmospora sp., Ilyonectria radicicola, Pezicula radicicola, Pyrenochaeta cava and six species of Trichoderma. Species composition did not vary greatly between sites, but only 3% of species occurred in all sites. Number of species was higher in roots subjected to floods. Eudominants and dominants present only on flooded sites included Aspergillus spp., Chaetomium globosum, Cosmospora sp., I. radicicola, Sporothrix inflata, Trichoderma harzianum, T. pubescens and T. virens. Structural roots were usually colonized by a higher number of species than fine roots. The majority of species detected belong to Class 2 NC-endophytes. Pezicula radicicola and Phialocephala fortinii belong to Class 4 NC-endophytes.

The distribution of Dothistroma septosporum and its mating types in Poland

Abstract: Summary Dothistroma needle blight (DNB), one of the most dangerous foliar diseases of pines, is the cause of much economic loss in pine plantations worldwide. The threat to pine-dominated Polish forestry from this disease is therefore very large. However, the impact of DNB has not been high mainly due to the planting of P. sylvestris, a less susceptible native species. Until now, DNB was recorded in Poland only on highly susceptible exotic P. nigra. The current situation concerning the disease in Poland is described in this article. This disease, caused by Dothistroma septosporum, was first recorded in a single location (Domiarki) in southern Poland in 1990. This study reports the occurrence of D. septosporum in 37 new locations, demonstrating that the disease has now spread across the whole country. Pinus nigra remains the predominant host species in Poland. However, three new hosts for this fungus are reported, that is P. sylvestris, P. mugo and P. ponderosa. The ratio of D. septosporum mating types varies significantly between sites, ranging from an equal proportion of each mating type to single mating type populations. For the oldest known Polish population of D. septosporum, the mating type ratio has shifted towards equilibrium over time.

Biological control of Dothistroma needle blight on pine with Aneurinibacillus migulanus

Abstract: Summary The ability of two strains of the antibiotic-producing bacillus Aneurinibacillus migulanus to control Dothistroma septosporum infection of pine was tested in artificial inoculation experiments on 2-year-old Pinus contorta plants. Disease severity (% needles with conidiomata) on control plants was 5.8 ± 1.7%, compared with 6.2 ± 2.0% on plants treated with A. migulanus NCTC 7096. In contrast, treatment with A. migulanus Nagano reduced Dothistroma needle blight (DNB) severity to 1.1 ± 0.4%. The conidial density and percentage germination of D. septosporum on needles were also greatly reduced on seedlings treated with A. migulanus Nagano compared with the A. migulanus NCTC 7096 and control treatments. The results suggest that A. migulanus Nagano has potential as a biological control agent for use against DNB in forest nurseries.

Visualizing the early infection of Agathis australis by Phytophthora agathidicida, using microscopy and fluorescent in situ hybridization

Abstract: Summary Phytophthora agathidicida (PTA) causes a root rot and collar rot of New Zealand kauri (Agathis australis). This study developed techniques to visualize early infection of kauri by PTA in deliberately inoculated seedlings. Conventional light microscopy was carried out on cleared and stained roots using trypan blue to observe PTA structures. Additionally, scanning electron microscopy (SEM) was used to study the PTA root structures at a higher resolution. A fluorescent in situ hybridization assay (FISH) was developed using a PTA-specific probe to label PTA structures in planta. Infection progression in roots of 2-year-old kauri inoculated with PTA at 5, 10, 16 and 20 days post-inoculation (d.p.i.) was compared using these three approaches. Light microscopy identified no Phytophthora-like structures in the control treatments. In PTA-inoculated plants, lignitubers were produced 5 d.p.i. in cortical cells. Infection was localized after 5 days, but as the infection progressed (up to 20 d.p.i.), the ‘degree’ of root infection increased, as did the number of replicates in which structures were observed. SEM provided higher resolution images; again, no PTA structures were observed in the negative control material examined. The slide-based FISH-specificity assay successfully hybridized with PTA hyphae. Fluorescence was observed using 330–380 nm excitation and an emission filter at 420 nm (DAPI), with PTA nuclei fluorescing a bright greenish-yellow. Cross-reactivity was not observed when the assay was applied to six other non-target Phytophthora species. Successful hybridization reactions occurred between the primer and PTA structures in planta. Applying this FISH assay has allowed clear differentiation of the intracellular and intercellular structures of PTA. The technique can be applied to longer term studies or analysis of ex situ inoculation studies aiming to elucidate differential host-responses to the pathogen. Additionally, the technique could be applied to study the interactions with other fungal endophytes (e.g. mycorrhizal fungi), which could be assessed for biocontrol potential as part of the integrated management of the disease.

Disease development of Dothistroma needle blight in seedlings of Pinus sylvestris and Pinus contorta under Nordic conditions

Abstract: Dothistroma needle blight (DNB), caused by Dothistroma septosporum, was observed for the first time in the Nordic countries during the 21st century, and the dynamics of the disease under Nordic conditions are still poorly explored. In this study, we followed the development of DNB on seedlings of Pinus sylvestris and Pinus contorta, planted at two forest sites in central Sweden. PCR with species-specific primers was used to detect infections of D. septosporum in needle samples collected over a two-year period. The seedlings were also examined for typical red bands and fruit bodies (conidiomata). One-year-old needles that were present on the seedlings at the time of planting became infected during the first summer. The first conidiomata appeared on P. sylvestris in autumn the same year and on P. contorta in spring the following year. The first infections of the current-year needles of both host species occurred in summer, as they were starting to elongate, and the following spring the first conidiomata appeared. On one of the sites, many seedlings carried latent infections without any symptom development. At some time points, infections of D. septosporum were detected in more than 50% of the seedlings, but red bands and conidiomata were only observed on a small number of the seedlings throughout the study period. No clear difference was observed in the susceptibility of infection between the two host species; nonetheless, at the same site, the mortality of P. sylvestris was higher than that of P. contorta, and this is likely primarily due to other stresses and the presence of another needle pathogen, Lophodermium seditiosum.

Physiological and biochemical differences among Ulmus minor genotypes showing a gradient of resistance to Dutch elm disease

Abstract: Summary Dutch elm disease (DED) spread across Europe and North America in the 20th century killing most natural elm populations. Today, breeding programmes aim at identifying, propagating and studying elm clones resistant to DED. Here, we have compared the physiology and biochemistry of six genotypes of Ulmus minor of variable DED resistance. Leaf gas exchange, water potential, stem hydraulic conductivity and biochemical status were studied in 5-year-old trees of AB-AM2.4, M-DV2.3, M-DV2 × M-CC1.5 and M-DV1 and 6-year-old trees of VA-AP38 and BU-FL7 before and after inoculation with Ophiostoma novo-ulmi. Leaf water potential and net photosynthesis rates declined, while the percentage loss of hydraulic conductivity (PLC) increased after the inoculation in susceptible trees. By the 21st day, leaf predawn and midday water potential, stomatal conductance to water vapour and net photosynthesis rates were lower, and PLC was higher in trees of susceptible (S) genotypes inoculated with the pathogen than in control trees inoculated with water, whereas no significant treatment effect was observed on these variables in the resistant (R) genotypes. Fourier transform infrared spectroscopy analyses revealed a different biochemical profile for branches of R and S clones. R clones showed higher absorption peaks that could be assigned to phenolic compounds, saturated hydrocarbons, cellulose and hemicellulose than S clones. The differences were more marked at the end of the experiment than at the beginning, suggesting that R and S clones responded differently to the inevitable wounding from inoculation and repeated sampling over the experimental course. We hypothesize that a weak activation of the defence system in response to experimental wounding can contribute to the susceptibility of some genotypes to O. novo-ulmi. In turn, the decline in shoot hydraulic conductivity and leaf carbon uptake caused by the infection further exacerbates tree susceptibility to the fungus.

Genetic variability of Alder yellows phytoplasma in Alnus glutinosa in its natural Spreewald habitat

Abstract: Summary The genus ‘Candidatus Phytoplasma’ comprises wall-less bacteria colonizing the phloem of plants and insect tissues. Phytoplasmas are associated with diseases in over 1000 plant species worldwide, including many important crops as well as forest trees. Alder yellows (AldY) phytoplasma, which frequently infects Alnus spp., is closely related to the economically important phytoplasma causing Flavescence doree (FD) in grapevines. In a natural habitat (Spreewald, Brandenburg, Germany), 57 Alnus glutinosa (black alder) trees were examined for phytoplasma infection in summer 2013. No phytoplasma typical infection-associated symptoms such as yellowing and decline were observable in this natural swamp-alder area. Amplification followed by a restriction fragment length polymorphism, and a sequence analysis of the 16S rDNA, allowed for the detection of AldY phytoplasmas in all examined trees and their assignment to the taxonomic group 16SrV-C. Additional analyses of the non-ribosomal marker gene methionine aminopeptidase (map) revealed diverse strains as well as mixed infections with closely related AldY strains, and the strains were assigned to phylogenetic clusters closely related to German Palatinate grapevine yellows, AldY or FD strains. The results confirmed that AldY phytoplasmas infection in A. glutinosa is prevalent. The results also indicate a presence of an established phytoplasma population in chronically infected black alder.

Screening of Corymbia and Eucalyptus species for resistance to Calonectria pteridis leaf blight

Abstract: Summary Calonectria leaf blight (CLB), caused by Calonectria pteridis, is a major foliar disease of eucalypt plantations in warm and high rainfall regions in Brazil. The use of resistant genotypes is the best method for disease control in the field, so identification of sources of resistance is strategic for the long-term genetic breeding programmes of eucalypt. In this study, resistance of 13 species of Eucalyptus and 3 species of Corymbia to CLB was evaluated by spray inoculation of a spore suspension (1 × 104 conidia ml−1) of the pathogen, under controlled conditions. Eucalyptus brassiana, E. saligna, E. scias and E. agglomerata were the most resistant, while E. robusta, E. urophylla, E. camaldulensis, E. longirostrata and C. toreliana were moderately resistant and E. cloeziana, E. pellita, E. tereticornis, E. pilularis, C. maculata, E. grandis, E. dunnii and C. citriodora were the most susceptible. The broad inter and intraspecific variability of the species tested demonstrates the potential for introgression of resistance genes into valuable genotypes as a strategy for the breeding programmes and commercial plantation of eucalypt.

Interactions between callus cultures of Pinus sylvestris and pine fungi with different trophic properties

Abstract: Summary Fungal virulence may be studied using tissues cultures of host plants in dual cultures in vitro, enabling analyses of interactions with undifferentiated cells of their host plants. Three genotypes of Pinus sylvestris callus, initiated by somatic embryogenesis, were used for establishing dual cultures with fungi pathogenic, endophytic or saprotrophic on pine needles or shoots. Fungal growth towards the plant callus tissue differed, depending on the life strategy of the fungus. The pathogen Gremmeniella abietina proved the slowest colonizer of callus whereas the saprotrophic Phacidium lacerum was the fastest. Gremmeniella abietina partially overgrew the callus, causing extensive necrosis and death within 10 days after inoculation. Anthostomella formosa, an endophyte of pines, did not cause evident symptoms of callus degradation: after 10 days of dual culture, the callus cells remained greenish and at least 50% of cells were alive. In dual cultures Ph. lacerum, callus remained alive until the end of the experiment, maintaining a white-creamy colour with a loose cell structure. Electrophoresis of protein extracts from the callus showed the presence of additional bands of 25–35 kDa only in host tissues challenged with the pathogen G. abietina, possibly indicating the production of pathogenesis-related proteins. This work has shown that pine callus does not respond equally to challenge with different fungal isolates. In general, one-third of the isolates of each fungus examined showed greater virulence compared to other isolates.

Diversity and bioactivity of bacterial endophyte community of Cupressaceae

Abstract: Summary The plant family Cupressaceae (Coniferales) harbours diverse endophytic fungi with antifungal, antibacterial and antiproliferative activities. Here, endophytic association of a broad bacterial community with the healthy foliar tissues of Cupressus arizonica, Cupressus sempervirens, Juniperus communis and Thuja orientalis (Cupressaceae) is shown. We isolated over 69 endophytic bacterial strains of Proteobacteria, Bacilli and Actinobacteria from Cupressaceae. The initial screening for antifungal activity against Pyricularia oryzae identified eleven superior bacterial strains which were identified as Brevundimonas diminuta CAE24 (G−, Caulobacteraceae, Alphaproteobacteria); Stenotrophomonas maltophilia CAE23, CSE4, CSE12, CSE42, CSE49 and CSE62 (G−, Xanthomonadaceae, Gammaproteobacteria); Bacillus pumilus CSE66 and Bacillus subtilis POE26 (G+, Bacillaceae, Bacilli); and Microbacterium resistens CSE19 (G+, Microbacteriaceae, Actinobacteria). The dominant isolated bacterial species was S. maltophilia. This species represented 63.6% of the superior strains which was ubiquitous and also non-host specific. In addition, the superior bacterial strains produced bioactive secondary metabolites and volatile compounds (VOCs) with antifungal activity against the fungal pathogens of Cupressaceae, that is Diplodia seriata, Phaeobotryon cupressi and Spencermartinsia viticola. The antagonistic activity of the endophytic bacteria on the target fungi was also confirmed in vitro. To our knowledge, this is the first to document such an endophytic bacterial community in Cupressaceae and its bioactivity. These findings may find application in organic agroforestry for plant disease biocontrol and in biopharmacy for lead molecule discovery.

Infection of Cedrus species by Dothistroma septosporum

Abstract: Summary Dothistroma septosporum, primarily a pathogen of Pinus foliage, was found on Cedrus atlantica var. glauca needles in the Cruikshank Botanic Garden in Aberdeen, Scotland. The susceptibility of three Cedrus species, Cedrus atlantica var. glauca, C. deodara and C. libani subsp. libani, was investigated by artificial inoculation. Dothistroma septosporum infection of all three Cedrus species was demonstrated, although disease severity was low, with less than 7% of needles developing acervuli after 10 weeks.

Screening brassicaceous plants as biofumigants for management of Phytophthora cinnamomi oak disease

Abstract: Summary Brassicaceous plants rich in glucosinolates have been used as biofumigants for the management of soilborne pathogens. Efficacy of Brassica plant tissue has mainly been attributed to toxic isothiocyanates released upon the hydrolysis of glucosinolates. Management of Phytophthora cinnamomi, the causal agent of oak root rot in rangeland ecosystems using biofumigation, is promising, but requires further validation. The biofumigation activity of 14 brassicaceous plants was evaluated under experimental conditions. All evaluated plants rich in sinigrin suppressed (100%) the mycelial growth of P. cinnamomi, while plants rich in aromatic or other aliphatic glucosinolates had little or no suppressive effect. Simulating soil amendment in field conditions, the effects on natural soil artificially infested with P. cinnamomi chlamydospores were examined with Brassica juncea, Eruca vesicaria and Lepidium sativum, three species with different glucosinolate profiles. Only B. juncea decreased the viability of chlamydospores significantly in comparison with untreated soil only 1 day after biofumigation, whereas E. vesicaria needed 8 days to reach significance and L. sativum had no effect at all. Despite the decreases in soil inoculum, biofumigation with B. juncea did not prevent the root infections in a highly susceptible host (Lupinus luteus). However, biofumigation with plants rich in sinigrin, such as B. juncea, decreased P. cinnamomi soil inoculum under the experimental minimum threshold for oak disease expression. Although biofumigation should be considered as an effective measure to be incorporated in integrated control of the oak disease, biofumigation by itself would not be effective enough for the substantial suppression of P. cinnamomi inoculum.

Action of fosetyl‐al and metalaxyl against Phytophthora austrocedri

Abstract: Fil: Silva, Patricia Valeria. Centro de Investigacion y Extension Forestal Andino Patagonico; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

Canker disease of willow and poplar caused by Cryptosphaeria pullmanensis recorded in China

Abstract: Summary A new canker disease of Salix alba and Populus alba has been observed in Xinjiang, China. Black circular spots on dead branches and stems are the symptoms of the disease. Sixty-seven isolates recovered from Salix matsudana, S. alba and Populus alba were identified as Cryptosphaeria pullmanensis based on morphological features and multigene phylogeny. Pathogenicity tests were performed on S. alba and P. alba stems using the C. pullmanensis isolates. Cankers on and Cryptosphaeria pullmanensis of C. pullmanensis from the stems fulfilled Koch's postulates and confirmed C. pullmanensis as the causal agent of the canker disease. C. pullmanensis is characterized by its yellow stromatic tissue surrounded by a black conceptacle with regularly arranged multiple locules sharing common walls and hyaline, allantoid, aseptate conidia (mean size 7.42 × 1.72 μm). This is the first report of C. pullmanensis causing Cryptosphaeria canker in China, and S. alba and P. alba are new host records for C. pullmanensis.

Characterization of Cylindrocarpon-like species associated with litter in the old-growth beech forests of Central Europe

Abstract: Summary Cylindrocarpon-like fungi are globally distributed plant pathogens and have a wide range of host species However, very little is known about the species that live in the topsoil of forests and their potential role in reducing the natural regeneration of tree species, particularly of forest trees that produce abundant fruit only once every few years To enhance our understanding of the species that inhabit the topsoil, we studied the diversity and pathogenicity of Cylindrocarpon-like fungi inhabiting the litter in old-growth mixed-beech forests in the Carpathians (Poland) and in the Alps (Austria), and in a managed beech stand in the Krakowsko-Czestochowska Highland (Poland) The fungi inhabiting the beech litter were investigated using beechnuts and pine seedlings as bait Isolates were identified based on morphology and DNA sequencing The pathogenicity of the most common species was investigated by inoculating beech germinants A wide range of Cylindrocarpon-like fungi were associated with the beech litter: 718 cultures representing 12 species were isolated Five taxa were identified down to species level: namely Ilyonectria crassa, I pseudodestructans, I rufa, Neonectria candida and N obtusispora, and seven species were identified to genus level (Neonectria or Ilyonectria species) Ilyonectria destructans, which is considered to be the sexual morph of ‘Cylindrocarpon destructans’, was not found There were qualitative and quantitative differences between the different forest sites in terms of Neonectria and Ilyonectria species composition in beech litter The isolation frequency and species richness of Cylindrocarpon-like fungi were greatest in beech litter taken from old-growth mixed-beech forests Neonectria and Ilyonectria species were capable of killing beech germinants, suggesting that they may play a negative role in natural beech regeneration

Analyses of the ash dieback pathogen, Hymenoscyphus fraxineus, suggest role of tree species diversity on colonization and population structure differentiation

Abstract: Summary Microsatellite markers were used to investigate the population structure of the Ash Dieback pathogen, Hymenoscyphus fraxineus, across a tree species diversity gradient containing common ash, Fraxinus excelsior, in the Hainich National Park in central Germany. Population differentiation was determined at a local spatial scale that may be driven by tree species mixtures.

Differences in susceptibility to ash dieback in Czech provenances of Fraxinus excelsior

Abstract: Summary The impact of ash dieback caused by Hymenoscyphus fraxineus on 17 provenances of Fraxinus excelsior and one provenance of Fraxinus angustifolia was studied in an extensive field trial established in the Czech Republic prior to the H. fraxineus invasion in 1999. A difference in the level of resistance to ash dieback between the species was found: F. angustifolia was significantly less affected by the disease than F. excelsior. Moreover, particular provenances of F. excelsior showed important differences in the level of resistance to H. fraxineus. A relationship between the impact of ash dieback and altitude was also discovered – the provenances from altitudes above 600 m a.s.l. were less affected by the pathogen than were the provenances from lower areas. No difference in the impact of the disease among provenances of F. excelsior from different ecotopes (ravine, calcareous ravine and alluvial) was found. Substantial among-tree variability in resistance to H. fraxineus was observed throughout the trial – promising genotypes (with crown defoliation up to 5%) were identified in all 18 tested provenances. In regard to this finding, it appears that the main source of resistance to the pathogen is probably at the individual genotype level in the trial. A secondary but massive attack by Hylesinus fraxini was identified in the trees that had been greatly damaged by ash dieback, and the beetle caused their health to deteriorate significantly. A significant negative effect of the presence of collar necroses caused by H. fraxineus and browse damage was also identified.

Inter- and intraspecific variation in susceptibility to dothistroma needle blight in Britain. How susceptible are Pinus sylvestris and Pinus contorta?

Abstract: Summary Dothistroma needle blight (DNB), caused by Dothistroma septosporum, is a serious disease in British pine plantations. Natural infection (NI) and artificial inoculation (AI) experiments were conducted to evaluate the susceptibility of Pinus sylvestris and Pinus contorta to DNB, relative to Pinus mugo, Pinus muricata, Pinus nigra ssp. laricio, Pinus nigra ssp. nigra and Pinus ponderosa. A range of P. sylvestris and P. contorta provenances were included in experiments to simultaneously investigate intraspecific variation within these host species. In NI experiments, 20–30 12-month-old seedlings of each species/provenance were planted adjacent to infected mature trees at two Scottish sites. In the AI experiment, eighteen 16-month-old seedlings of each species/provenance were inoculated with a D. septosporum conidial suspension and maintained under optimum conditions for D. septosporum infection and development. In the NI experiments, the most DNB-susceptible species were P. muricata and P. ponderosa, while the least susceptible species were P. contorta and P. sylvestris. Pinus nigra spp. nigra and P. nigra spp. laricio had intermediate DNB susceptibility. In the AI experiment, there was no evidence for interspecific variation in DNB susceptibility. Intraspecific variation in DNB susceptibility within P. sylvestris was seen in the NI experiment, but not the AI experiment. Intraspecific variation in DNB susceptibility within P. contorta was not observed in either experiment. In a further AI experiment with 24-month-old P. sylvestris and P. contorta seedlings, the virulence of three Scottish D. septosporum isolates (haplotypes) was examined. There was no significant interaction between isolate and relative susceptibility of pine species/provenances. Furthermore, no between-isolate variation in virulence was observed.