Nitrogen addition changed soil fungal community structure and increased the biomass of functional fungi in Korean pine plantations in temperate northeast China.

Nitrogen (N) deposition is a global environmental issue that can have significant impacts on the community structure and function in ecosystems. Fungi play a key role in soil biogeochemical cycles and their community structures are tightly linked to the health and productivity of forest ecosystems. Based on high-throughput sequencing and ergosterol extraction, we examined the changes in community structure, composition, and biomass of soil ectomycorrhizal (ECM) and saprophytic (SAP) fungi in 0-10 cm soil layer after 8 years of continuous N addition and their driving factors in a temperate Korean pine plantation in northeast China. Our results showed that N addition increased fungal community richness, with the highest richness and Chao1 index under the low N treatment (LN: 20 kg N ha-1 yr-1). Based on the FUN Guild database, we found that the relative abundance of ECM and SAP fungi increased first and then decreased with increasing N deposition concentration. The molecular ecological network analysis showed that the interaction between ECM and SAP fungi was enhanced by N addition, and the interaction was mainly positive in the ECM fungal network. N addition increased fungal biomass, and the total fungal biomass (TFB) was the highest under the MN treatment (6.05 ± 0.3 mg g-1). Overall, we concluded that N addition changed soil biochemical parameters, increased fungal activity, and enhanced functional fungal interactions in the Korean pine plantation over an 8-year simulated N addition. We need to consider the effects of complex soil conditions on soil fungi and emphasize the importance of regulating soil fungal community structure and biomass for managing forest ecosystems. These findings could deepen our understanding of the effects of increased N deposition on soil fungi in temperate forests in northern China, which can provide the theoretical basis for reducing the effects of increased N deposition on forest soil.

Effects of four bolete species on ectomycorrhizae formation and development in Pinus thunbergii and Quercus acutissima.

BACKGROUND: Bolete cultivation is economically and ecologically valuable. Ectomycorrhizae are advantageous for plant development and productivity. This study investigated how boletes affect the formation of Pinus thunbergii and Quercus acutissima ectomycorrhizae using greenhouse-based mycorrhizal experiments, inoculating P. thunbergii and Q. acutissima with four species of boletes (Suillus bovinus, Suillus luteus, Suillus grevillei, and Retiboletus sinensis). RESULTS: Three months after inoculation, morphological and molecular analyses identified S. bovinus, S. luteus, S. grevillei and R. sinensis ectomycorrhizae formation on the roots of both tree species. The mycorrhizal infection rate ranged from 40 to 55%. The host plant species determined the mycorrhiza morphology, which was independent of the bolete species. Differences in plant growth, photosynthesis, and endogenous hormone secretion primarily correlated with the host plant species. Infection with all four bolete species significantly promoted the host plants' growth and photosynthesis rates; indole-3-acetic acid, zeatin, and gibberellic acid secretion increased, and the abscisic acid level significantly decreased. Indole-3-acetic acid was also detected in the fermentation broths of all bolete species. CONCLUSIONS: Inoculation with bolete and subsequent mycorrhizae formation significantly altered the morphology and hormone content in the host seedlings, indicating growth promotion. These findings have practical implications for culturing pine and oak tree species.

Mixing of pine and arbuscular mycorrhizal tree species changed soil organic carbon storage by affecting soil microbial characteristics.

Pure and mixed pine forests are found all over the world. The mycorrhizal type affects soil microbial activity and carbon sequestration capacity in pure forests. However, the effects of mycorrhizal type on microbial characteristics and carbon sequestration capacity in pine mixed forests remain untested. Further, making it difficult to predict carbon storage of the conversion from pure pine forests to mixed forests at larger scales. Herein, a meta-analysis showed that the contents of soil microbial biomass, mineral-associated organic carbon, and soil organic carbon in pine mixed forests with introduced arbuscular mycorrhizal tree species (PMAM) increased by 26.41 %, 58.55 %, and 27.41 %, respectively, compared to pure pine forests, whereas those of pine mixed forests without arbuscular mycorrhizal tree species (PMEcM) remained unchanged. Furthermore, the effect size of microbial biomass, mineral-associated organic carbon and organic carbon contents in subsoil of PMAM are 56.48 %, 78.49 % and 43.05 %, respectively, which are higher than those in topsoil. The improvement of carbon sinks throughout the PMAM soil profile is positively correlated with increases in microbial biomass and mineral-associated organic carbon in subsoil, according to regression analysis and structural equation modelling. In summary, these results highlight that the positive effects of introducing arbuscular mycorrhizal tree species rather than ectomycorrhizal tree species into pure pine forests on soil microbial biomass and carbon sequestration. The positive link between microbial biomass, mineral-associated organic carbon, and soil organic carbon suggests an underlying mechanism for how soil microorganisms store carbon in pine mixed forests. Nevertheless, our findings also imply that the soil carbon pool of PMAM may be vulnerable under climate change. Based on the above findings, we propose that incorporating mycorrhizal type of tree species and soil thickness into mixed forests management and biodiversity conservation.

Terpenoids are involved in the expression of systemic-induced resistance in Austrian pine.

Terpenoids are defense metabolites that are induced upon infection or wounding. However, their role in systemic-induced resistance (SIR) is not known. Here, we explored the role of terpenoids in this phenomenon at a very early stage in the interaction between Austrian pine and the tip blight and canker pathogen Diplodia pinea. We induced Austrian pine saplings by either wounding or inoculating the lower stems with D. pinea. The seedlings were then challenged after 12 h, 72 h, or 10 days with D. pinea on the stem 15 cm above the induction. Lesion lengths and terpenoids were quantified at both induction and challenge locations. Key terpenoids were assayed for antifungal activity in in vitro bioassays. SIR increased with time and was correlated with the inducibility of several compounds. α-Pinene and a cluster of ß-pinene, limonene, benzaldehyde, dodecanol, and n-dodecyl acrylate were positively correlated with SIR and were fungistatic in vitro, while other compounds were negatively correlated with SIR and appeared to serve as a carbon source for D. pinea. This study shows that, overall, terpenoids are involved in SIR in this system, but their role is nuanced, depending on the type of induction and time of incubation. We hypothesize that some, such as α-pinene, could serve in SIR signaling.

Effects of root-colonizing fungi on pioneer Pinus thunbergii seedlings in primary successional volcanic mudflow on Kuchinoerabu Island, Japan.

Root-colonizing fungi, such as mycorrhizal fungi and dark septate endophyte fungi, are often found on pioneer plant species during early primary succession. However, little is known about which fungal species are responsible for the establishment of pioneer plants when these symbionts colonize simultaneously. We investigated the root-colonizing fungal communities of Pinus thunbergii that established prior to lichens, bryophytes, and short-lived herbaceous plants in a primary successional volcanic mudflow site on Kuchinoerabu Island, Japan. We collected a total of 54 current-year and 1- to 2-year-old seedlings. The colonization of root fungi was evaluated by direct observation of key structures (e.g., mantle, arbuscule, microsclerotia, and hyphae) and molecular analysis. Of the 34 current-year seedlings collected, only 12 individuals were colonized by ectomycorrhizal (ECM) fungi. By contrast, all 1- to 2-year-old seedlings were colonized by ECM fungi. Seedlings colonized by pine-specific ECM fungi, specifically Rhizopogon roseolus and Suillus granulatus, showed higher nitrogen and phosphorus contents in their needles compared to non-ECM seedlings. Arbuscular mycorrhizal fungi and dark septate endophyte fungi were found in only two and three individuals, respectively. The high density of mycophagous deer on Kuchinoerabu-jima may contribute to the favored dispersal of ECM fungi over other root-colonizing fungi. In conclusion, the seedling establishment of P. thunbergii at the volcanic mudflow may be largely supported by ECM fungi, with negligible effects of arbuscular mycorrhizal fungi and dark septate endophytes.

Distribution of Cronartium x flexili, an interspecific hybrid of two fungal tree rust pathogens, in subalpine forest ecosystems of western USA.

Interspecific hybridization plays a key role in the evolution of novel fungal pathogens, and when it occurs between native and invasive species, can lead to potentially serious consequences. In this study, we examined the temporal and spatial distribution of a recently detected hybrid (Cronartium x flexili) of two tree pathogens, invasive to North America Cronartium ribicola and native Cronartium comandrae. In total, 726 and 1452 aecia from 178 Pinus contorta ssp. latifolia and 357 Pinus flexilis trees were collected from 26 sites in four national forests in 2019-2021. Using morphological and molecular analyses, 71 aecia collected from 25 P. flexilis trees had intermediate morphology and contained heterozygous SNPs in two genomic regions. Population analyses revealed the presence of multiple hybrid genotypes randomly distributed among sites and years. No aecia from P. contorta ssp. latifolia were identified as hybrids suggesting unidirectional gene flow from native C. comandrae to invasive C. ribicola. Aeciospores from 2 hybrid aecia produced urediniospores on Ribes nigrum. Overall, these results suggest that, even though low in frequency, C. x flexili is persistent in the region and has pathogenic potential. Hybrid expansion into the large range of susceptible pines could have cascading impacts on forest health.

The essential role of arginine biosynthetic genes in lunate conidia formation, conidiation, mycelial growth, and virulence of nematophagous fungus, Esteya vermicola CBS115803.

BACKGROUND: The pinewood nematode (Bursaphelenchus xylophilus) causes severe damage to pine trees. The nematophagous fungus, Esteya vermicola, exhibits considerable promise in the biological control of Bursaphelenchus xylophilus due to its infectivity. Notably, the lunate conidia produced by E. vermicola can infect Bursaphelenchus xylophilus. In the study, we aim to investigate the genes involved in the formation of the lunate conidia of E. vermicola CBS115803. RESULTS: Esteya vermicola CBS115803 yielded 95% lunate conidia on the complete medium (CM) and 86% bacilloid conidia on the minimal medium (MM). Transcriptomic analysis of conidia from both media revealed a significant enrichment of differentially expressed genes in the pathway related to 'cellular amino acid biosynthesis and metabolism'. Functional assessment showed that the knockout of two arginine biosynthesis genes (EV232 and EV289) resulted in defects in conidia germination, mycelial growth, lunate conidia formation, and virulence of E. vermicola CBS115803 in Bursaphelenchus xylophilus. Remarkably, the addition of arginine to the MM improved mycelial growth, conidiation and lunate conidia formation in the mutants and notably increased conidia yield and the lunate conidia ratio in the wild-type E. vermicola CBS115803. CONCLUSION: This investigation confirms the essential role of two arginine biosynthesis genes in lunate conidia formation in E. vermicola CBS115803. The findings also suggest that the supplementation of arginine to the culture medium can enhance the lunate conidia yield. These insights contribute significantly to the application of E. vermicola CBS115803 in managing Bursaphelenchus xylophilus infections. © 2023 Society of Chemical Industry.

Durability of heat-treated Paulownia tomentosa and Pinus koraiensis woods in palm oil and air against brown- and white-rot fungi.

This study aimed to evaluate and compare the effects of oil- and air-heat treatments on the durability of Paulownia tomentosa and Pinus koraiensis woods against Fomitopsis palustris and Trametes versicolor. The wood samples were treated in palm oil and air at 180, 200, and 220 °C for 2 h. The weight loss, morphology, crystalline properties, and chemical compounds of untreated and heat-treated wood after fungal attack were investigated. The significant difference in weight loss between oil- and air-heat-treated samples was shown at 220 °C. Heat-treated wood exposed to white-rot fungus showed a lower weight loss than that exposed to brown-rot fungus. The cell components in the untreated- and heat-treated Paulownia tomentosa and Pinus koraiensis at 180 °C were severely damaged due to fungal exposure compared to those at 220 °C. A fungal effect on the relative crystallinity was observed in heat-treated wood at 180 °C, whereas the effect was not observed at 220 °C. Following brown-rot fungus exposure, untreated- and heat-treated wood at 180 °C showed a notable change in the Fourier transform infrared (FTIR) peaks of polysaccharides, whereas no noticeable change in lignin peaks was observed. Heat-treated wood at 220 °C showed no noticeable change in the FTIR spectra owing to brown-rot fungus exposure. Exposure to white-rot fungus did not noticeably change the FTIR spectra of untreated and heat-treated wood.

Dynamics of Microbial Community Structure, Function and Assembly Mechanism with Increasing Stand Age of Slash Pine (Pinus elliottii) Plantations in Houtian Sandy Area, South China.

Establishing slash pine plantations is the primary method for restoring sandification land in the Houtian area of South China. However, the microbial variation pattern with increasing stand age remains unclear. In this study, we investigated microbial community structure and function in bare sandy land and four stand age gradients, exploring ecological processes that determine their assembly. We did not observe a significant increase in the absolute abundance of bacteria or fungi with stand age. Bacterial communities were dominated by Chloroflexi, Actinobacteria, Proteobacteria, and Acidobacteria; the relative abundance of Chloroflexi significantly declined while Proteobacteria and Acidobacteria significantly increased with stand age. Fungal communities showed succession at the genus level, with Pisolithus most abundant in soils of younger stands (1- and 6-year-old). Turnover of fungal communities was primarily driven by stochastic processes; both deterministic and stochastic processes influenced the assembly of bacterial communities, with the relative importance of stochastic processes gradually increasing with stand age. Bacterial and fungal communities showed the strongest correlation with the diameter at breast height, followed by soil available phosphorus and water content. Notably, there was a significant increase in the relative abundance of functional groups involved in nitrogen fixation and uptake as stand age increased. Overall, this study highlights the important effects of slash pine stand age on microbial communities in sandy lands and suggests attention to the nitrogen and phosphorus requirements of slash pine plantations in the later stages of sandy management.

Green trees preservation: A sustainable source of valuable mushrooms for Ethiopian local communities.

In Ethiopia, Pinus radiata and Pinus patula are extensively cultivated. Both plantations frequently serve as habitats for edible fungi, providing economic and ecological importance. Our study aims were: (i) to investigate how plantation age and tree species influence the variety of edible fungi and sporocarps production; (ii) to determine edaphic factors contributing to variations in sporocarps composition; and (iii) to establish a relationship between the most influencing edaphic factors and the production of valuable edible mushrooms for both plantation types. Sporocarps were collected weekly from permanent plots (100 m2) established in 5-, 14-, and 28-year-old stands of both species in 2020. From each plot, composite soil samples were also collected to determine explanatory edaphic variables for sporocarps production and composition. A total of 24 edible species, comprising 21 saprophytic and three ectomycorrhizal ones were identified. Agaricus campestroides, Morchella sp., Suillus luteus, Lepista sordida, and Tylopilus niger were found in both plantations. Sporocarp yields showed significant variation, with the highest mean production in 28-year-old stands of both Pinus stands. Differences in sporocarps variety were also observed between the two plantations, influenced by factors such as pH, nitrogen, phosphorus, potassium, and cation exchange capacity. Bovista dermoxantha, Coprinellus domesticus, and A. campestroides made contributions to the variety. The linear regression models indicated that the abundance of specific fungi was significantly predicted by organic matter. This insight into the nutrient requirements of various fungal species can inform for a better plantation management to produce both wood and non-wood forest products. Additionally, higher sporocarps production in older stands suggests that retaining patches of mature trees after the final cut can enhance fungal habitat, promoting diversity and yield. Thus, implementing this approach could provide supplementary income opportunities from mushroom sales and enhance the economic outputs of plantations, while mature trees could serve as a source of fungal inoculum for new plantations.

Larger presence of ectomycorrhizae detected from pygmy pine ecotype in the fire-frequent pine barrens ecosystem.

Pine barrens ecosystem has acidic, sandy, and nutrient-poor soil and is prone to drought and fire. In the New Jersey Pine Barrens, the predominant pitch pine (Pinus rigida) consists of two ecotypes: the regular pitch pines with heights of 4.6-12 m, and the pygmy pines of low stature (1.2-1.8 m) in the New Jersey Pine Plains. Previous ecological studies suggested that the dwarf pines in the Pine Plains that are embedded within the Pine Barrens were an evolutionary adaptation to frequent fire. Pines are obligate ectomycorrhizal (EcM) mutualists, and their root mycobiota may contribute to stress protection and plant health. However, information on the mycobiota associated with plants in the pine barrens ecosystem is lacking. To have a holistic understanding of the evolution and adaptation in this stressed environment, we used both culture-independent metabarcoding and culture-based method to characterize the mycobiota from soil and root of the two ecotypes and to identify core mycobiota. We found that Agaricomycetes, Leotiomycetes, and Mucoromycotina are predominant fungi in the New Jersey Pine Barrens ecosystem, which is rich in root mutualistic fungi. We observed that the pygmy pine roots had significantly higher density of EcM tips than the regular pine roots. This was corroborated by our metabarcoding analysis, which showed that the pygmy pine trees had higher ratio of ectomycorrhiza-forming fungi than the regular-statured pines. We hypothesize that symbiotrophic EcM fungi associated with pygmy pines are capable of mitigating high fire stress in the Pine Plains.

Climate change-induced stress disrupts ectomycorrhizal interaction networks at the boreal-temperate ecotone.

The interaction networks formed by ectomycorrhizal fungi (EMF) and their tree hosts, which are important to both forest recruitment and ecosystem carbon and nutrient retention, may be particularly susceptible to climate change at the boreal-temperate forest ecotone where environmental conditions are changing rapidly. Here, we quantified the compositional and functional trait responses of EMF communities and their interaction networks with two boreal (Pinus banksiana and Betula papyrifera) and two temperate (Pinus strobus and Quercus macrocarpa) hosts to a factorial combination of experimentally elevated temperatures and reduced rainfall in a long-term open-air field experiment. The study was conducted at the B4WarmED (Boreal Forest Warming at an Ecotone in Danger) experiment in Minnesota, USA, where infrared lamps and buried heating cables elevate temperatures (ambient, +3.1 °C) and rain-out shelters reduce growing season precipitation (ambient, ~30% reduction). EMF communities were characterized and interaction networks inferred from metabarcoding of fungal-colonized root tips. Warming and rainfall reduction significantly altered EMF community composition, leading to an increase in the relative abundance of EMF with contact-short distance exploration types. These compositional changes, which likely limited the capacity for mycelial connections between trees, corresponded with shifts from highly redundant EMF interaction networks under ambient conditions to less redundant (more specialized) networks. Further, the observed changes in EMF communities and interaction networks were correlated with changes in soil moisture and host photosynthesis. Collectively, these results indicate that the projected changes in climate will likely lead to significant shifts in the traits, structure, and integrity of EMF communities as well as their interaction networks in forest ecosystems at the boreal-temperate ecotone.

Endofungal Bacterial Microbiota Promotes the Absorption of Chelated Inorganic Phosphorus by Host Pine through the Ectomycorrhizal System.

Ectomycorrhizal fungi play an irreplaceable role in phosphorus cycling. However, ectomycorrhizal fungi have a limited ability to dissolve chelated inorganic phosphorus, which is the main component of soil phosphorus. Endofungal bacteria in ectomycorrhizal fruiting bodies are always closely related to the ecological function of ectomycorrhizal fungi. In this study, we explore endofungal bacteria in the fruiting body of Tylopilus neofelleus and their function during the absorption of chelated inorganic phosphorus by host pine through the ectomycorrhizal system. The results showed that the endofungal bacterial microbiota in the fruiting body of T. neofelleus might be related to the dissolution of chelated inorganic phosphorus in soil. The soluble phosphorus content in the combined system of T. neofelleus and endofungal bacteria Bacillus sp. strain B5 was five times higher than the sum of T. neofelleus-only treatment and Bacillus sp. strain B5-only treatment in the dissolution experiment of chelated inorganic phosphorus. The results showed that T. neofelleus not only promoted the proliferation of Bacillus sp. strain B5 in the combined system but also improved the expression of genes related to organic acid metabolism, as assesed by transcriptomic analysis. Lactic acid content was five times higher in the combined system than the sum of T. neofelleus-only treatment and Bacillus sp. strain B5-only treatment. Two essential genes related to lactate metabolism of Bacillus sp. strain B5, gapA and pckA, were significantly upregulated. Finally, in a pot experiment, we verified that T. neofelleus and Bacillus sp. strain B5 could synergistically promote the absorption of chelated inorganic phosphorus by Pinus sylvestris in a ternary symbiotic system. IMPORTANCE Ectomycorrhizal fungi (ECMF) have a limited ability to dissolve chelated inorganic phosphorus, which is the main component of soil phosphorus. In the natural environment, the extraradical hyphae of ECMF alone may not satisfy the phosphorus demand of the plant ectomycorrhizal system. In this study, our results innovatively show that the ectomycorrhizal system might be a ternary symbiont in which ectomycorrhizal fungi might recruit endofungal bacteria that could synergistically promote the mineralization of chelated inorganic phosphorus, which ultimately promotes plant phosphorus absorption by the ectomycorrhizal system.

A Pine in Distress: How Infection by Different Pathogenic Fungi Affect Lodgepole Pine Chemical Defenses.

In North America, lodgepole pine is frequently subjected to attacks by various biotic agents that compromise its ability to defend against subsequent attacks by insect herbivores. We investigated whether infections of lodgepole pine by different pathogenic fungal species have varying effects on its defense chemistry. We selected two common pathogens, Atropellis canker, Atropellis piniphila, and western gall rust, Endocronartium harknessii, affecting mature lodgepole pine trees in western Canada. We also included three ophiostomatoid fungi Grosmannia clavigera, Ophiostoma montium, and Leptographium longiclavatum associated with the mountain pine beetle (Dendroctonus ponderosae), because they are commonly used to investigate induced defenses of host trees of bark beetles. We collected phloem samples from lodgepole pines infected with the rust or the canker and healthy lodgepole pines in the same stand. We also inoculated mature lodgepole pines with the three fungal symbionts and collected phloem samples 2 weeks later when the defense chemistry was at its highest level. Different fungal species differentially altered the terpene chemistry of lodgepole pine trees. E. harknessii and the fungal symbionts altered the terpene chemistry in a similar pattern while trees responded to the infection by the A. piniphila differently. Our study highlights the importance of considering specific biotic stress agents in tree susceptibility or resistance to the subsequent attacks by insect herbivores, such as mountain pine beetle.

A Reliable and Simple Method for the Production of Viable Pycnidiospores of the Pine Pathogen Diplodia sapinea and a Spore-Based Infection Assay on Scots Pine.

Diplodia sapinea is a globally distributed opportunistic fungal pathogen of conifers that causes severe production losses in forestry. The fungus frequently colonizes pine trees as an endophyte without causing visible symptoms but can become pathogenic when the host plant is weakened by stress, such as drought or heat. Forest damage might therefore further increase due to the effects of climate change. The future development of control strategies depends on a better understanding of the fungus' biology, which requires experimental methods for its investigation in the laboratory. An efficient, standardized protocol for the production and storage of highly viable pycnidiospores was developed, and a spore-based infection method was devised. We compared infection rates of dormant and actively growing, wounded, or nonwounded Scots pine seedlings inoculated with in vitro-produced spores and mycelium from agar-plugs. Spores were a much more efficient inoculum for causing disease symptoms on wounded plants than the conventional agar plug. The application of spores on nonwounded plants lead to high rates of asymptomatic infection, suggesting endophytic fungal development. These methods enable standardized spore infection and virulence assays and promote D. sapinea as a model organism for studying the switch from endophytic to pathogenic life styles of forest pathogens.

Beauveria bassiana exhibits strong virulence against Dendroctonus ponderosae in greenhouse and field experiments.

The mountain pine beetle (MPB) has infested over 16 million hectares of pine forests in western Canada, killing over 50% of mature lodgepole pine, Pinus contorta, in British Columbia alone. There are few tools available to manage irruptive bark beetle populations and to mitigate tree mortality. Beauveria bassiana is an entomopathogenic fungus that causes mortality to several bark beetle species. However, the potential for B. bassiana as a biocontrol agent against pine beetle populations is unknown. We selected three strains of B. bassiana from several culture collections and evaluated their conidial stability under cold storage, in planta (greenhouse, and pine bolts) and in natura (forest stand, pine bolts, and live pines) conditions. The stability assays showed that all fungal strains maintained a minimum effective conidial yield through the assay durations (3-12 weeks). In addition, we adapted a biphasic liquid-solid fermentation approach for the large-scale production of conidial biomass, yielding up to a 100-fold increase in production. In greenhouse virulence assays, the mean lethal time of MPBs was reduced to 3-4 days upon treatment with B. bassiana, where high B. bassiana-associated mycosis was also observed. Furthermore, the application of B. bassiana formulation substantially affected the gallery network of MPBs in bolts in the field, resulting in shorter larval galleries and significantly reduced offspring production. Indeed, high titer treatments reduced the mean larvae per gallery to virtually zero. Together these results demonstrate that B. bassiana may be a viable biocontrol tool to reduce mountain pine beetle populations in pine forests in western Canada. KEY POINTS: • Three B. bassiana strains identified to be stable at various test conditions. • Large-scale conidial biomass production using liquid-solid biphasic fermentation. • Reproductive success of D. ponderosae significantly reduced by B. bassiana formulation.

Light and scanning electron microscopy of aecia and aeciospores of Cronartium ribicola on Pinus koraiensis branch tissues.

Morphological characteristics of aecia and aeciospores of Cronartium ribicola on Pinus koraiensis branch tissues were investigated using light and field emission scanning electron microscopy (FESEM). Mature P. koraiensis trees in Jeongseon, Korea, showed yellowish aecia on stems and branches. Aecia and surrounding tissues were excised from the lesions and vapor-fixed for FESEM imaging, which revealed morphology including intact blister-shaped, flattened, and burst forms. Light microscopy revealed yellowish aeciospores having surface projections. Aeciospores were mostly ovoid and measured approximately 20 µm long. The FESEM showed irregularly shaped cracks on the aecia that had erupted through the bark of P. koraiensis. Some aeciospores had germinated, producing two germ tubes from a spore in a burst aecium. Aeciospores had both smooth and verrucose regions on the surface, and some had concave or convex regions. Aeciospore layers and underlying fungal matrices including aecial columns were obvious in the cross-sections of aecia. Approximately 1 µm-high wart-like surface projections could be resolved and comprised less than 10 angular platelets stacked in vertical rows. Remains of the primary spore wall were present between surface projections. These results provide insights into the morphology of the heteroecious rust fungus with the help of vapor fixation and high-resolution surface imaging.

Beyond the genomes of Fulvia fulva (syn. Cladosporium fulvum) and Dothistroma septosporum: New insights into how these fungal pathogens interact with their host plants.

Fulvia fulva and Dothistroma septosporum are closely related apoplastic pathogens with similar lifestyles but different hosts: F. fulva is a pathogen of tomato, whilst D. septosporum is a pathogen of pine trees. In 2012, the first genome sequences of these pathogens were published, with F. fulva and D. septosporum having highly fragmented and near-complete assemblies, respectively. Since then, significant advances have been made in unravelling their genome architectures. For instance, the genome of F. fulva has now been assembled into 14 chromosomes, 13 of which have synteny with the 14 chromosomes of D. septosporum, suggesting these pathogens are even more closely related than originally thought. Considerable advances have also been made in the identification and functional characterization of virulence factors (e.g., effector proteins and secondary metabolites) from these pathogens, thereby providing new insights into how they promote host colonization or activate plant defence responses. For example, it has now been established that effector proteins from both F. fulva and D. septosporum interact with cell-surface immune receptors and co-receptors to activate the plant immune system. Progress has also been made in understanding how F. fulva and D. septosporum have evolved with their host plants, whilst intensive research into pandemics of Dothistroma needle blight in the Northern Hemisphere has shed light on the origins, migration, and genetic diversity of the global D. septosporum population. In this review, we specifically summarize advances made in our understanding of the F. fulva-tomato and D. septosporum-pine pathosystems over the last 10 years.

Transcriptomic analysis of the fungus Graphilbum sp. in response to the pine wood nematode.

Graphilbum species are important blue stain fungi associated with pine trees and are widely distributed throughout Asia, Australia, and North Africa. Pine wood nematode (PWN) primarily feed on ophiostomatoid fungi such as Graphilbum sp. in wood, the population of PWNs was increased, and incomplete organelle structures were observed in Graphilbum sp. hyphal cells following exposure to PWNs. In this study, we showed that Rho and Ras were involved in the MAPK pathway, SNARE binding and small GTPase-mediated signal transduction, and their expression was upregulated in the treatment group. However, the expression of the Rab7 involved in MAPK and small GTPase-mediated signal pathway was downregulated in the treatment group. Thus, further research is needed to study the MAPK pathway and related Ras and Rho genes in Graphilbum sp. associated with the PWN population. Overall, transcriptomic analysis clarified the basic mechanisms of mycelial growth in Graphilbum sp. fungus used as a food source by PWNs.

Diplodia sapinea infection reprograms foliar traits of its pine (Pinus sylvestris L.) host to death.

Infection with the necrotrophic fungus Diplodia sapinea (Fr.) Fuckel is among the economically and ecologically most devastating diseases of conifers in the northern hemisphere and is accelerated by global climate change. This study aims to characterize the changes mediated by D. sapinea infection on its pine host (Pinus sylvestris L.) that lead to the death of its needles. For this purpose, we performed an indoor infection experiment and inoculated shoot tips of pine seedlings with virulent D. sapinea. The consequences for foliar traits, including the phytohormone profile, were characterized at both the metabolite and transcriptome level. Our results showed that D. sapinea infection strongly affected foliar levels of most phytohormones and impaired a multitude of other metabolic and structural foliar traits, such as reactive oxygen species scavenging. Transcriptome analysis revealed that these changes are partially mediated via modified gene expression by fungal exposure. Diplodia sapinea appears to overcome the defense reactions of its pine host by reprogramming gene expression and post-transcriptional controls that determine essential foliar metabolic traits such as the phytohormone profile, cell wall composition and antioxidative system.