Root Symbionts Research Articles

Feeding specialization shapes the bottom‐up effect of arbuscular mycorrhizal fungi across a plant–aphid–parasitoid system

Societal Impact StatementArbuscular mycorrhizal fungi (AMF) impact the relationships between plants, aphids (insects that feed on plant phloem), and their natural enemies (insects that prey on or parasitize aphids). The presence of AMF influences the growth and population of different aphid species and affects the development of aphid‐killing wasps and their attraction to plants. This research has been conducted also considering the insects' feeding strategy and their feeding specialization. This study provides novel perspectives on how these fungi shape interactions in the natural world, offering potential insights for the development of sustainable pest management strategies in agriculture.Summary Arbuscular mycorrhizal fungi (AMF) are major root symbionts regulating plant physiology. Their presence affects the performance of aboveground insect herbivores in relation to their feeding strategy and their feeding specialization. For example, the effect of the arbuscular mycorrhizal (AM) symbiosis on chewing insects, positive for specialists and negative for generalists, has been previously demonstrated. Conversely, the impact of AMF on phloem‐suckers with relatively different levels of specialization remains unexplored. We tested the influence of the AM Funneliformis mosseae on the fitness of the specialist aphid Acyrthosiphon pisum and the generalist aphid Myzus persicae on Vicia faba plants. Further, we investigated the effects of AMF on the higher trophic level, the aphid parasitoids Aphidius ervi (specialist) and Aphidius colemani (generalist), by evaluating plant attractiveness and parasitoid fitness. To support the results of behavioral and biological bioassays we characterized the photosynthetic parameters, the volatilome and the transcriptome of tested plants. Mycorrhizal plants proved unsuitable for the generalist M. persicae but enhanced the fitness of the specialist A. pisum. The AM symbiosis had no effects on the behavioral response of A. colemani and enhanced the attraction and fitness of A. ervi. Volatilome and transcriptome profiling corroborated the results of bioassay highlighting a bottom‐up effect of the AMF across a plant–aphid–parasitoid system.

Nitrogen-fixing bacteria boost floral attractiveness in a tropical legume species during nutrient limitation.

Legumes establish mutualistic interactions with pollinators and nitrogen (N)-fixing bacteria that are critical for plant reproduction and ecosystem functioning. However, we know little about how N-fixing bacteria and soil nutrient availability affect plant attractiveness to pollinators. In a two-factorial greenhouse experiment to assess the impact of N-fixing bacteria and soil types on floral traits and attractiveness to pollinators in Chamaecrista latistipula (Fabaceae), plants were inoculated with N-fixing bacteria (NF+) or not (NF-) and grown in N-rich organic soil (+N organic soil) or N-poor sand soil (-N sand soil). We counted buds and flowers and measured plant size during the experiment. We also measured leaf, petal, and anther reflectance with a spectrophotometer and analyzed reflectance curves. Using the bee hexagon model, we estimated chromatic contrasts, a crucial visual cues for attracting bees that are nearby and more distant. NF+ plants in -N sand soil had a high floral display and color contrasts. On the other hand, NF- plants and/or plants in +N organic soil had severely reduced floral display and color contrasts, decreasing floral attractiveness to bee pollinators. Our findings indicate that the N-fixing bacteria positively impact pollination, particularly when nutrients are limited. This study provides insights into the dynamics of plant-pollinator interactions and underscores the significant influence of root symbionts on key floral traits within tropical ecosystems. These results contribute to understanding the mechanisms governing mutualisms and their consequences for plant fitness and ecological dynamics.

The role of the plant microbiome for forestry, agriculture and urban greenspace in times of environmental change.

This Lilliput article provides a literature overview on ecological effects of the plant microbiome with a focus on practical application in forestry, agriculture and urban greenspace under the spectre of climate change. After an overview of the mostly bacterial microbiome of the model plant Arabidopsis thaliana, worldwide data from forests reveal ecological differentiation with respect to major guilds of predominantly fungal plant root symbionts. The plant-microbiome association forms a new holobiont, an integrated unit for ecological adaptation and evolutionary selection. Researchers explored the impact of the microbiome on the capacity of plants to adapt to changing climate conditions. They investigated the impact of the microbiome in reforestation programs, after wildfire, drought, salination and pollution events in forestry, grasslands and agriculture. With increasing temperatures plant populations migrate to higher latitudes and higher altitudes. Ecological studies compared the dispersal capacity of plant seeds with that of soil microbes and the response of soil and root microbes to experimental heating of soils. These studies described a succession of microbiome associations and the kinetics of a release of stored soil carbon into the atmosphere enhancing global warming. Scientists explored the impact of synthetic microbial communities (SynComs) on rice productivity or tea quality; of whole soil addition in grassland restoration; or single fungal inoculation in maize fields. Meta-analyses of fungal inoculation showed overall a positive effect, but also a wide variation in effect sizes. Climate change will be particularly prominent in urban areas ("urban heat islands") where more than half of the world population is living. Urban landscape architecture will thus have an important impact on human health and studies started to explore the contribution of the microbiome from urban greenspace to ecosystem services.

Optimizing chickpea growth: Unveiling the interplay of arbuscular mycorrhizal fungi and rhizobium for sustainable agriculture

AbstractArbuscular mycorrhizal fungi (AMF) are beneficial root symbionts that form mutual partnerships with approximately 90% of plants. They provide water, nutrients, and protection from stresses while receiving photosynthetic products from the host plants. These fungi are essential components of the soil ecosystem, and their absence or decline can negatively impact ecosystem efficiency. In chickpea cultivation, the interaction between AMF and rhizobium is vital for soil processes and plant productivity. Alongside other beneficial microorganisms in the rhizosphere, they enhance the acquisition of essential nutrients like nitrogen (N) and phosphorus (P), promoting chickpea growth and development. These interactions are particularly crucial in low‐input, eco‐friendly agricultural systems that rely on biological processes to sustain soil quality and productivity without heavy use of agrochemicals. The combination of root nodules' N‐fixation and AMF synergism also improves plant P nutrition and stimulates the proliferation of phosphate‐solubilizing fungi. However, genetic diversity among native strains and their genes/enzymes can influence the interactions between AMF and rhizobium. To achieve sustainable chickpea production, it is crucial to gain a deeper understanding of these interactions, allowing optimized combinations of microorganisms to be used as effective soil inoculants for promoting plant growth and fitness. This review aims to provide insights into the mechanistic interactions of AMF and rhizobium, their impact on rhizosphere soil health, and the role of environmental factors in regulating chickpea productivity and sustainability.

Interactions between foredune morphologies and vegetation: Exploring the occurrence of arbuscular mycorrhizal fungi

Vegetation is a key trait for understanding the foredune morphologies. However, the rhizosphere in coastal dunes imposes high levels of water and nutrient stress on plants. In these conditions, arbuscular mycorrhizal fungi (AMF) are prominent root symbionts that play a crucial role in improving to abiotic stress and promoting plant growth. On the south coast of the state of São Paulo, foredunes were studied for their floristic composition, relative frequency of AMF and grain size of rhizosphere. Foredune was classified regarding the morphology as terrace, ridge I, and ridge II. The terrace has a low height (<0.5 m) and is composed of native species canopies low (<0.2 m) and high (0.5–1.5 m) characterized by AMF colonization close to 60%. In contrast, ridge I showed wavy crests that were about 1 m high and ∼30 m wide, with a predominance of plant species with low canopy and 68% AMF colonization. The morphology ridge II reaches the greatest height (3 m), to the detriment of a smaller width (up to 15 m) and the plants present high canopy (>0.5 m) with close to 75% AMF. The increase of the relative frequency AMF from the terrace to ridges I and II may indicate that the increase of sand accumulation with continuous burial of roots is rather positive to plant growth. Yet, varied canopy heights of the plants species control the verticalization and horizontalization of the foredune. Low-canopy species, gradually slow down wind flow, causing spatialized deposition and widening. Conversely, species with highest canopies swiftly reduce wind flow due to the density of their aerial portion (leaves), resulting in deposition just below their structure fostering foredune vertical growth.

Spores of arbuscular mycorrhizal fungi host surprisingly diverse communities of endobacteria.

Arbuscular mycorrhizal fungi (AMF) are ubiquitous plant root symbionts, which can house two endobacteria: Ca. Moeniiplasma glomeromycotorum (CaMg) and Ca. Glomeribacter gigasporarum (CaGg). However, little is known about their distribution and population structure in natural AMF populations and whether AMF can harbour other endobacteria. We isolated AMF from two environments and conducted detailed analyses of endobacterial communities associated with surface-sterilised AMF spores. Consistent with the previous reports, we found that CaMg were extremely abundant (80%) and CaGg were extremely rare (2%) in both environments. Unexpectedly, we discovered an additional and previously unknown level of bacterial diversity within AMF spores, which extended beyond the known endosymbionts, with bacteria belonging to 10 other phyla detected across our spore data set. Detailed analysis revealed that: CaGg were not limited in distribution to the Gigasporaceaefamily of AMF, as previously thought; CaMg population structure was driven by AMF host genotype; and a significant inverse correlation existed between the diversity of CaMg and diversity of all other endobacteria. Based on these data, we generate novel testable hypotheses regarding the function of CaMg in AMF biology by proposing that they might act as conditional mutualists of AMF.

Root symbionts modify biomass of white clover (Trifolium repens) through changes in radiation interception and radiation-use efficiency

Context Root symbionts affect forage production by influencing host plant growth, but their specific effects on canopy intercepted photosynthetically active radiation (IPAR) and its conversion to plant biomass have not been investigated. Aims We evaluated the extent to which changes in plant biomass resulting from arbuscular mycorrhizal fungi (AMF) and rhizobia can be explained by alterations in IPAR and aboveground and total radiation-use efficiency (RUE: the ratio between shoot or total biomass and IPAR). Methods Under controlled greenhouse conditions, we evaluated single and dual inoculation effects of AMF and rhizobia on the forage legume white clover (Trifolium repens L.). Experimental units comprised canopies created in trays (50 cm by 34 cm by 13 cm deep). Key results On average, AMF inoculation increased IPAR by 43%, owing to greater leaf area and density, and decreased total RUE by 30%. Aboveground RUE was lower in AMF-inoculated plants without rhizobial inoculation, despite their higher leaf phosphorus status and greenness during the vegetative and reproductive stages, respectively. Rhizobial inoculation reduced the negative effect of AMF inoculation on aboveground RUE. Conclusions Both AMF and rhizobia alter white clover structure and function at canopy level. These variations may not be detected if the analysis considers only the impact of root symbionts on plant biomass. Implications These findings offer valuable insights into the intricate interactions between root symbionts and canopy-level processes, providing a basis for further research at agricultural scale.

Plant choice between arbuscular mycorrhizal fungal species results in increased plant P acquisition.

Arbuscular mycorrhizal fungi (AMF) are plant root symbionts that provide phosphorus (P) to plants in exchange for photosynthetically fixed carbon (C). Previous research has shown that plants-given a choice among AMF species-may preferentially allocate C to AMF species that provide more P. However, these investigations rested on a limited set of plant and AMF species, and it therefore remains unclear how general this phenomenon is. Here, we combined 4 plant and 6 AMF species in 24 distinct plant-AMF species compositions in split-root microcosms, manipulating the species identity of AMF in either side of the root system. Using 14C and 32P/33P radioisotope tracers, we tracked the transfer of C and P between plants and AMF, respectively. We found that when plants had a choice of AMF species, AMF species which transferred more P acquired more C. Evidence for preferential C allocation to more beneficial AMF species within individual plant roots was equivocal. However, AMF species which transferred more P to plants did so at lower C-to-P ratios, highlighting the importance both of absolute and relative costs of P acquisition from AMF. When plants had a choice of AMF species, their shoots contained a larger total amount of P at higher concentrations. Our results thus highlight the benefits of plant C choice among AMF for plant P acquisition.

Pervasive associations between dark septate endophytic fungi with tree root and soil microbiomes across Europe

Trees interact with a multitude of microbes through their roots and root symbionts such as mycorrhizal fungi and root endophytes. Here, we explore the role of fungal root symbionts as predictors of the soil and root-associated microbiomes of widespread broad-leaved trees across a European latitudinal gradient. Our results suggest that, alongside factors such as climate, soil, and vegetation properties, root colonization by ectomycorrhizal, arbuscular mycorrhizal, and dark septate endophytic fungi also shapes tree-associated microbiomes. Notably, the structure of root and soil microbiomes across our sites is more strongly and consistently associated with dark septate endophyte colonization than with mycorrhizal colonization and many abiotic factors. Root colonization by dark septate endophytes also has a consistent negative association with the relative abundance and diversity of nutrient cycling genes. Our study not only indicates that root-symbiotic interactions are an important factor structuring soil communities and functions in forest ecosystems, but also that the hitherto less studied dark septate endophytes are likely to be central players in these interactions.

Utilization of Metarhizium as an insect biocontrol agent and a plant bioinoculant with special reference to Brazil.

Brazil has a long history of using biological control and has the largest program in sugarcane agriculture to which a biocontrol program has been applied. This achievement is at least partly due to the utilization of the entomopathogenic fungus Metarhizium. This well-known fungal genus exhibits pathogenicity against a broad range of arthropod hosts and has been used globally as a biocontrol agent. This fungus is also a root symbiont, and in this capacity, it is a plant growth promoter. However, this feature (i.e., as a plant symbiont) has yet to be fully explored and implemented in Brazil, although the number of reports demonstrating Metarhizium's utility as a plant bioinoculant is increasing. The Brazilian bioproduct industry targets agricultural pests, and is limited to two Metarhizium species represented by four fungal isolates as active ingredients. Entomopathogenic fungi have also been successful in controlling arthropods of public health concern, as shown in their control of mosquitoes, which are vectors of diseases. The isolation of new indigenous Metarhizium isolates from a variety of substrates such as soil, insects, and plants shows the wide genetic diversity within this fungal genus. In this review, we emphasize the significance of Metarhizium spp. for the biological control of insects in Brazil. We also suggest that the experience and success of biological control with fungi in Brazil is an important resource for developing integrated pest management and sustainable strategies for pest control worldwide. Moreover, the future implementation prospects of species of Metarhizium being used as bioinoculants and possible new advances in the utility of this fungus are discussed.

Cover crop identity determines root fungal community and arbuscular mycorrhiza colonization in following main crops

AbstractCover crops (CC) can promote nutrient retention and recycling for main crops yet may also promote soilborne pathogens or suppress beneficial root symbionts such as arbuscular mycorrhizal fungi (AMF). We investigated how root fungal communities of main crop are affected by preceding CC monocultures and mixtures and by main crop identity. We expected that AMF abundance and diversity in main crops are promoted by AM‐host CC, and suppressed by non‐AM‐host CC, and that mixtures of CC species can promote beneficial and suppress pathogenic root fungi. Our full‐factorial field experiment comprised crop rotation in sand soil with different CC treatments (monocultures of radish [AM non‐host], ryegrass, clover, vetch [AM hosts], mixtures of radish + vetch, ryegrass + clover and fallow) and two main crops (oat and endive). At peak crop growth, we investigated the root fungal communities in the main crops using microscopy and high throughput sequencing (Illumina MiSeq). Cover crop identity was of prime importance and CC legacy overruled main crop identity in determining root fungal communities in main crops. Compared with fallow, CC with ryegrass increased AMF colonization and richness in both main crops and of non‐AMF in oat. Legacies of ryegrass, ryegrass + clover and vetch resulted in distinct root fungal communities in the main crops, while the legacy of CC with radish were similar to the legacy of fallow. Root fungal community in crops after clover had highest abundance of representative fungal pathogens in contrast with the other CC treatments that resulted in fungal communities where pathogens were scarce. Oppositely to expected, CC mixtures did not enhance fungal symbionts or suppressed pathogens. Overall, fungal communities in roots of the main crops in our field experiment were determined by the preceding CC species in monoculture, rather than by the CC AMF preference or functional group. This research highlights that the choice of CC determines the root fungal community in main crop which may influence crop quality.

Production of Arbuscular Mycorrhizal Spores by Providing Nasa Liquid Organic Fertilizer (LOF)

Arbuscular mycorrhizal fungi (AMF) are root symbionts that are in symbiosis with the majority of plants and are generally found in terrestrial ecosystems. The propagation of AMF is influenced by many factors, including fertilization. This study aims to determine the increase in arbuscular mycorrhizal spore production by administering Nasa LOF. The research was conducted at the Plastic House of the Indonesian Mycorrhizal Association, Southeast Sulawesi Branch and the Laboratory of the Forestry Department, Faculty of Forestry and Environmental Sciences, UHO in January - April 2023 using a factorial Completely Randomized Design (CRD) with two factors, namely the first factor, the type of AMF including Glomus coronatum and Glomus claroideum and the second factor is Nasa LOF control, 2.5 ml/1000 ml water, 5 ml/1000 ml water. The results showed that the combination treatment of Glomus claroideum and administration of 5 ml Nasa LOF increased the number of spores in the 3rd month and spores after drying. Nasa LOF 5 ml is relatively applied for the production of Glomus claroideum.

Arbuscular mycorrhizal fungi heterokaryons have two nuclear populations with distinct roles in host-plant interactions.

Arbuscular mycorrhizal fungi (AMF) are prominent root symbionts that can carry thousands of nuclei deriving from two parental strains in a large syncytium. These co-existing genomes can also vary in abundance with changing environmental conditions. Here we assemble the nuclear genomes of all four publicly available AMF heterokaryons using PacBio high-fidelity and Hi-C sequencing. We find that the two co-existing genomes of these strains are phylogenetically related but differ in structure, content and epigenetics. We confirm that AMF heterokaryon genomes vary in relative abundance across conditions and show this can lead to nucleus-specific differences in expression during interactions with plants. Population analyses also reveal signatures of genetic exchange indicative of past events of sexual reproduction in these strains. This work uncovers the origin and contribution of two nuclear genomes in AMF heterokaryons and opens avenues for the improvement and environmental application of these strains.

The effect of peat soil and sandy soil on the growth of Eleutherine palmifolia and arbuscular mycorrhizal diversity

Abstract. Atikah TA, Purwanti EW. 2023. The effect of peat soil and sandy soil on the growth of Eleutherine palmifolia and arbuscular mycorrhizal diversity. Biodiversitas 24: 4373-4381. Arbuscular mycorrhizae as root symbionts is capable of inducing plant growth on marginal lands. It has the potential to be used as fertilizer or soil enhancer. Mycorrhizae are commonly found in peat soils endemic to the island of Borneo. Peat soil contains a lot of organic matter needed by mycorrhizae. The development of plant roots also influences the process of mycorrhizal colonization. Apart from functioning as fertilizer, mycorrhizae is associated with Dayak shallot (Eleutherine palmifolia Merr.; syn.: Sisyrinchium palmifolium L.) roots can also overcome fusarium wilt disease. This study aimed to explore the potential of peat soil to support the growth of E. palmifolia 's and to identify mycorrhizal colonization associated with the plant. Two soil types were used for planting E. palmifolia: peat and sand. Parameters observed were plant height, number of leaves, morphospecies and each population of arbuscular mycorrhizae. The plant growth data were tabulated and analyzed with an analysis of variance, and the population of arbuscular mycorrhizae was analyzed for the level of similarity in the structure of species. The results showed that peat soil promoted the growth of E. palmifolia better than sandy soil. The similarity value of mycorrhizal species structure was 28.7%. It means that the structure of mycorrhizal species on peat were differed that on sand media. Mycorrhizae successfully explored from sandy soil were 10 morpho-species with a population of 1.441 spores, while mycorrhizae from peat soil contained 6 morphospecies with a population of 462 spores.

Diversity of Endomycorrhizal Fungi in Argan Forest Stands: Implications for the Success of Reforestation Programs

Over the last few decades, argan trees (Argania spinosa L.) skeels have faced harsh ecological conditions and anthropogenic pressure, leading to a dramatic decline in surface and density of cultivation. Nowadays, most techniques used to regenerate argan trees have failed. Arbuscular mycorrhizal fungi (AMF) are root symbionts that increase plant resistance to biotic and abiotic stresses during transplantation. The exploration of these symbiotic fungi from different soils of argan stands is the starting point for the selection and production of high-performance organisms adapted to the reforestation sites. The objective of this study is to investigate the composition of the AMF community associated with the argan tree rhizosphere. Forty adult argan trees were sampled in eight forest sites representative of the distribution and genetic diversity of argan forest stands. Five sub-samples of rhizospheric soil were taken around each tree. Our results revealed the presence of different AMF structures (i.e., hyphae, vesicles/and arbuscules) in root samples. Based on morphological characterization, six genera of AMF spores were identified with a dominance of the genera Septoglomus (34%). In addition, soil organic matter and phosphorus concentrations showed a highly significant correlation with AMF spore density. The chi-square test showed a highly significant dependence of the distribution of genera on the site conditions of forest stands. These AMF could be tested and used during the inoculation of argan seedlings in forest nurseries for the success of restoration and reforestation programs, as well as for the development and sustainable improvement of this agroforestry system.

A symbiotic footprint in the plant root microbiome

BackgroundA major aim in plant microbiome research is determining the drivers of plant-associated microbial communities. While soil characteristics and host plant identity present key drivers of root microbiome composition, it is still unresolved whether the presence or absence of important plant root symbionts also determines overall microbiome composition. Arbuscular mycorrhizal fungi (AMF) and N-fixing rhizobia bacteria are widespread, beneficial root symbionts that significantly enhance plant nutrition, plant health, and root structure. Thus, we hypothesized that symbiont types define the root microbiome structure.ResultsWe grew 17 plant species from five families differing in their symbiotic associations (no symbioses, AMF only, rhizobia only, or AMF and rhizobia) in a greenhouse and used bacterial and fungal amplicon sequencing to characterize their root microbiomes. Although plant phylogeny and species identity were the most important factors determining root microbiome composition, we discovered that the type of symbioses also presented a significant driver of diversity and community composition. We found consistent responses of bacterial phyla, including members of the Acidobacteria, Chlamydiae, Firmicutes, and Verrucomicrobia, to the presence or absence of AMF and rhizobia and identified communities of OTUs specifically enriched in the different symbiotic groups. A total of 80, 75 and 57 bacterial OTUs were specific for plant species without symbiosis, plant species forming associations with AMF or plant species associating with both AMF and rhizobia, respectively. Similarly, 9, 14 and 4 fungal OTUs were specific for these plant symbiont groups. Importantly, these generic symbiosis footprints in microbial community composition were also apparent in absence of the primary symbionts.ConclusionOur results reveal that symbiotic associations of the host plant leaves an imprint on the wider root microbiome – which we term the symbiotype. These findings suggest the existence of a fundamental assembly principle of root microbiomes, dependent on the symbiotic associations of the host plant.

The transportome of the endophyte Serendipita indica in free life and symbiosis with Arabidopsis and its expression in moderate salinity.

Serendipita indica is an endophytic root symbiont fungus that enhances the growth of various plants under different stress conditions, including salinity. Here, the functional characterization of two fungal Na+/H+ antiporters, SiNHA1 and SiNHX1 has been carried out to study their putative role in saline tolerance. Although their gene expression does not respond specifically to saline conditions, they could contribute, together with the previously characterized Na+ efflux systems SiENA1 and SiENA5, to relieve Na+ from the S. indica cytosol under this stressed condition. In parallel, an in-silico study has been carried out to define its complete transportome. To further investigate the repertoire of transporters expressed in free-living cells of S. indica and during plant infection under saline conditions, a comprehensive RNA-seq approach was taken. Interestingly, SiENA5 was the only gene significantly induced under free-living conditions in response to moderate salinity at all the tested time points, revealing that it is one of the main salt-responsive genes of S. indica. In addition, the symbiosis with Arabidopsis thaliana also induced SiENA5 gene expression, but significant changes were only detected after long periods of infection, indicating that the association with the plant somehow buffers and protects the fungus against the external stress. Moreover, the significant and strongest induction of the homologous gene SiENA1 occurred during symbiosis, regardless the exposure to salinity. The obtained results suggest a novel and relevant role of these two proteins during the establishment and maintenance of fungus-plant interaction.

Invasion‐mediated mutualism disruption is evident across heterogeneous environmental conditions and varying invasion intensities

The impact of a biological invasion on native communities is expected to be uneven across invaded landscapes due to differences in local abiotic conditions, invader abundance, and traits and composition of the native community. One way to improve predictive ability about the impact of an invasive species given variable conditions is to exploit known mechanisms driving invasive species' success. Invasive plants frequently exhibit allelopathic traits, which can be directly toxic to plants or indirectly impact them via disruption of root symbionts, including mycorrhizal fungi. The indirect mechanism – mutualism disruption – is predicted to impact plants that rely on mycorrhizas but not affect non‐mycorrhizal plant species. To assess whether invader‐driven mutualism disruption explains observed changes in native plant communities, we analyzed long‐term (1998–2018) plant cover data from forest plots across the state of Illinois. We evaluated native plant communities experiencing a range of abundance of invasive allelopathic garlic mustard Alliaria petiolata and varying environmental conditions. Consistent with the mutualism disruption hypothesis, we showed that as garlic mustard abundance increased over time in 0.25 m2 sampling quadrats, the abundance of mycorrhizal plant species decreased, but non‐mycorrhizal plant species did not. Over space and time, garlic mustard abundance predicted plant abundances and diversity at the quadrat level, but this relationship was not present at a larger scale when quadrats were aggregated within sites. Garlic mustard's impact on the plant community was highly localized, yet it was as important as abiotic variables for predicting local plant diversity. We showed that garlic mustard abundance was a key predictor of patterns of plant diversity across invasion intensity and environmental heterogeneity in a way that is consistent with mutualism disruption. Our work indicates that the mutualism disruption hypothesis can provide generalizable predictions of the impacts of allelopathic invasive plants that are evident at a broad spatial scale.

Application of Trichoderma sp. and PGPR for preventing downy mildew incidence on sweet corn

Downy mildew is a disease caused by the fungus Peronosclerospora maydis. Application of biological agents to control downy mildew is a kind of environmentally friendly control method, that widely promoted recently. Trichoderma sp. and plant growth promoter rhizobacteria (PGPR) are root symbionts, which can induce plant resistance against disease infection. This study aimed to determine the effective application of Trichoderma sp. combined with various concentrations of rhizobacteria to control downy mildew. This study used a completely randomized design (CRD) method with 6 treatments and 5 replications. The treatment was the concentration of rhizobacteria consisting of P0 (control) = without treatment, P1= 15 mL L-1. P2 = 30 mL L-1. P3 = 45 mL L-1. P4 = 60 mL L-1 and P5 (positive control) = seed treatment with 5 g kg-1 dimetomorf fungicide. Each rhizobacteria suspension was mixed with Trichoderma sp. solution as much as 15 mL L-1. The parameters observed consisted of plant height (cm), number of leaves, disease incidence (%), and disease severity (%). The results showed that the combination of Trichoderma sp. and rhizobacteria of 60 mL L-1 was able to inhibit the incidence of the disease up to 66.53% and the severity of the disease up to 89.84%.&#x0D; Keywords: bacteria, concentration, downy mildew, sweet corn, Trichoderma sp.

Beech Leaf Disease Severity Affects Ectomycorrhizal Colonization and Fungal Taxa Composition.

Beech leaf disease (BLD) is an emerging forest infestation affecting beech trees (Fagus spp.) in the midwestern and northeastern United States and southeastern Canada. BLD is attributed to the newly recognized nematode Litylenchus crenatae subsp. mccannii. First described in Lake County, Ohio, BLD leads to the disfigurement of leaves, canopy loss, and eventual tree mortality. Canopy loss limits photosynthetic capacity, likely impacting tree allocation to belowground carbon storage. Ectomycorrhizal fungi are root symbionts, which rely on the photosynthesis of autotrophs for nutrition and growth. Because BLD limits tree photosynthetic capacity, ECM fungi may receive less carbohydrates when associating with severely affected trees compared with trees without BLD symptoms. We sampled root fragments from cultivated F. grandifolia sourced from two provenances (Michigan and Maine) at two timepoints (fall 2020 and spring 2021) to test whether BLD symptom severity alters colonization by ectomycorrhizal fungi and fungal community composition. The studied trees are part of a long-term beech bark disease resistance plantation at the Holden Arboretum. We sampled from replicates across three levels of BLD symptom severity and compared fungal colonization via visual scoring of ectomycorrhizal root tip abundance. Effects of BLD on fungal communities were determined through high-throughput sequencing. We found that ectomycorrhizal root tip abundance was significantly reduced on the roots of individuals of the poor canopy condition resulting from BLD, but only in the fall 2020 collection. We found significantly more ectomycorrhizal root tips from root fragments collected in fall 2020 than in spring 2021, suggesting a seasonal effect. Community composition of ectomycorrhizal fungi was not impacted by tree condition but did vary between provenances. We found significant species level responses of ectomycorrhizal fungi between levels of both provenance and tree condition. Of the taxa analyzed, two zOTUs had significantly lower abundance in high-symptomatology trees compared with low-symptomatology trees. These results provide the first indication of a belowground effect of BLD on ectomycorrhizal fungi and contribute further evidence to the role of these root symbionts in studies of tree disease and forest pathology.