Fungal Root Research Articles

Crop Cycle and Tillage Role in the Outbreak of Late Wilt Disease of Maize Caused by Magnaporthiopsis maydis.

The destructive maize late wilt disease (LWD) has heavy economic implications in highly infected areas such as Israel, Egypt, and Spain. The disease outbreaks occur near the harvest, leading to total yield loss in severe cases. Crop rotation has long been known as an effective means to reduce plant diseases. Indeed, agricultural soil conservation practices that can promote beneficial soil and root fungi have become increasingly important. Such methods may have a bioprotective effect against Magnaporthiopsis maydis, the LWD causal agent. In this two-year study, we tested the role of crop rotation of maize with either wheat or clover and the influence of minimum tillage in restricting LWD. In the first experiment, wheat and clover were grown in pots with LWD infected soil in a greenhouse over a full winter growth period. These cultivations were harvested in the spring, and each pot’s group was split into two subgroups that underwent different land processing practices. The pots were sown with LWD-sensitive maize cultivar and tested over a whole growth period against control soils without crop rotation or soil with commercial mycorrhizal preparation. The maize crop rotation with wheat without tillage achieved prominent higher growth indices than the control and the clover crop cycle. Statistically significant improvement was measured in the non-tillage wheat soil pots in sprout height 22 days after sowing, in the healthy plants at the season’s end (day 77), and in shoot and cob wet weight (compared to the control). This growth promotion was accompanied by a 5.8-fold decrease in pathogen DNA in the plant stems. The tillage in the wheat-maize growth sequence resulted in similar results with improved shoot wet-weight throughout the season. In contrast, when maize was grown after clover, the tillage reduced this parameter. The addition of commercial mycorrhizal preparation to the soil resulted in higher growth measures than the control but was less efficient than the wheat crop cycle. These results were supported by a subsequent similar experiment that relied on soil taken from commercial wheat or clover fields. Here too, the wheat-maize growth cycle (without permanent effect for the tillage) achieved the best results and improved the plants’ growth parameters and immunity against LWD and lowered pathogen levels. In conclusion, the results of this study suggest that wheat and perhaps other crops yet to be inspected, together with the adjusted tillage system, may provide plants with better defense against the LWD pathogen.

Herbivory and Soil Water Availability Induce Changes in Arbuscular Mycorrhizal Fungal Abundance and Composition.

We tested the prediction that abundance and composition of arbuscular mycorrhizal fungi (AMF) in Ipomopsis aggregata roots and soils are influenced by ungulate herbivory and drought conditions by examining the effects in a field setting over two years. We used a multi-metric approach to quantify AMF root colonization, AMF reproduction, and AMF community composition in roots and soils. We incorporated complimentary community characterization assays by morphologically identifying spores from trap cultures and the use of terminal restriction fragment length polymorphism (T-RFLP) fingerprinting. Herbivory caused a twofold increase in spore production, an increase in AMF taxa diversity in roots, and a shift in AMF species composition in rhizosphere soils. The impact of herbivory was dependent on water availability, which differed in the two contrasting years. This study demonstrates that both soil water availability and herbivory shape arbuscular mycorrhizal fungi communities. The changes to mycorrhizal communities may help in understanding mycorrhizal function in changing climates.

A novel plant-fungal association reveals fundamental sRNA and gene expression reprogramming at the onset of symbiosis

Abstract Background Beneficial associations between plants and microbes are widespread in nature and have been studied extensively in the microbial-dominant environment of the rhizosphere. Such associations are highly advantageous for the organisms involved, benefiting soil microbes by providing them access to plant metabolites, while plant growth and development are enhanced through the promotion of nutrient uptake and/or protection against (a)biotic stresses. While the establishment and maintenance of mutualistic associations have been shown to require genetic and epigenetic reprogramming, as well as an exchange of effector molecules between microbes and plants, whether short RNAs are able to effect such changes is currently unknown. Here, we established an interaction between the model grass species Brachypodium distachyon (Bd, Pooideae) and the beneficial fungal root endophyte Serendipita indica (Si, syn. Piriformospora indica, Sebacinales) to elucidate RNA interference-based regulatory changes in gene expression and small (s)RNA profiles that occurred during establishment of a Sebacinalean symbiosis. Results Colonization of Bd roots with Si resulted in higher grain yield, confirming the mutualistic character of this interaction. Resequencing of the Si genome using the Oxford Nanopore technique, followed by de novo assembly yielded in 57 contigs and 9441 predicted genes, including putative members of several families involved in sRNA production. Transcriptome analysis at an early stage of the mutualistic interaction identified 2963 differentially expressed genes (DEG) in Si and 317 in Bd line 21-3. The fungal DEGs were largely associated with carbohydrate metabolism, cell wall degradation, and nutrient uptake, while plant DEGs indicated modulation of (a)biotic stress responses and defense pathways. Additionally, 10% of the upregulated fungal DEGs encode candidate protein effectors, including six DELD proteins typical for Sebacinales. Analysis of the global changes in the sRNA profiles of both associated organisms revealed several putative endogenous plant sRNAs expressed during colonization belonging to known micro (mi)RNA families involved in growth and developmental regulation. Among Bd- and Si-generated sRNAs with putative functions in the interacting organism, we identified transcripts for proteins involved in circadian clock and flowering regulation as well as immunity as potential targets of fungal sRNAs, reflecting the beneficial activity of Si. Conclusions We detected beneficial effects of Si colonization on Bd growth and development, and established a novel plant-mutualist interaction model between these organisms. Together, the changes in gene expression and identification of interaction-induced sRNAs in both organisms support sRNA-based regulation of defense responses and plant development in Bd, as well as nutrient acquisition and cell growth in Si. Our data suggests that a Sebacinalean symbiosis involves reciprocal sRNA targeting of genes during the interaction.

The effectiveness of the Fungus Beauveria bassiana in reducing the infection of okra plant Abelmosechus eseulentus with fungal root diseases.

This study was conducted in the laboratories of the College of Agriculture - University of Basra in the years 2020 and 2021, in which the fungus B.bassiana was used. To combat the root fungus that infects okra, the results showed the isolation of many pathogenic fungi, and these fungi showed a significant difference in the effect on seed germination and seedling fall. The entomopathogenic fungus B.bassiana has a high ability to colonize roots and promote plant growth, such as plant height, fresh weight, and plant dry weight. The results of field surveys of four areas in Basra governorate showed, namely Shatt Al-Arab, Abu Al-Khasib, Al-Qurnah and Al-Madina. The highest incidence and severity of okra root rot disease was in Al-Madinah region, where the infection rate was 37% and the infection intensity was 67.33%, followed by Abu Al-Khasib district, where the infection rate was 24% and the infection severity was 52.89%. This disease is caused by the fungi Rhizoctonia solani, Fusarium solani and Macrophomina phaseolina. Pathogenicity test results showed that F. solani gave the highest mortality rate for seedlings, followed by R. solani and M.phaseolina efficiently inhibiting the growth of pathogenic fungi. In the greenhouse experiment test, the experiment showed that the highest length of the vegetative group was in the biological treatment of fungi,Corresponding author: E-mail (abdu1988875@yahoo.com) Al-Muthanna University All rights reserved

Strong host-specific selection and over-dominance characterize arbuscular mycorrhizal fungal root colonizers of coastal sand dune plants of the Mediterranean region.

Sand dunes of the Mediterranean region constitute drought-stressed, low-fertility ecosystems. Arbuscular mycorrhizal fungi (AMF) are regarded as key components of their biota, that contribute to plant host adaptation and fitness. However, AMF community assembly rules in the roots of the psammophilous plants of coastal sand dunes have not been investigated. We studied the root colonizing AMF communities of four characteristic native plants of eastern Mediterranean coastal foredunes, in nine locations in Greece. Host-specificity (plant identity) was the major driver of AMF community assembly in the plant roots, while geographical distance between locations was not related to differences in the AMF communities. Additionally, colonizer AMF communities were characterized by over-dominance of a single operational taxanomic unit (OTUs), which was remarkably host-specific among locations. Wider dissimilarity in AMF communities was observed in small and disturbed (SD) sites compared to large and undisturbed (LU) sites, a trait that may be attributed to relaxed environmental filtering and facilitated AMF dispersal/immigration in SD sites from surrounding habitats. Overall, our results indicate that the assembly of root-colonizing AMF communities in the eastern Mediterranean sand dunes is characterized by strong biotic filtering (host identity), suggesting that co-adaptation processes may be more pronounced than previously proposed, under extreme environmental conditions.

DECOLORISATION OF BATIK WASTE WATER BY Marasmiellus palmivorus USING MODIFIED FIXED BED REACTOR

Batik waste water is dominated by textile dyes that are recalcitrant, hydrophobic, and molecular complexes. Azo, Nitroso, Azine, and Thiazolesare are among synthetic dyes used in batik industry. One of the well known white root fungus species that is able to degrade such dyes is Marasmiellus palmivorus. It has the ability to produce various enzymes such as manganese peroxidase, lignin peroxidase and laccase. Laccase (EC 1.10.3.2) catalyzes wide variety of aromatic hydrogen oxidation by reduction of oxygen and water. This research was conducted using two types of azo dye coloring agents, namely Levafix blue E-RA gran and Telon Red. This study was performed using optimized age of Solid State Fermentation (SSF), which was then inserted into a modified fixed bed reactor for 4 hours. Reduction of the color was observed every 15 minutes and the substrate used for growth of fungus was sawdust. The experiments demonstrated that crude enzyme of Marasmiellus- SSF had activity of 97.8 U/L using ABTS reagent at 22-day of age bag log incubation. The total protein content, which was measured using the Bradford reagent, peaked at 154 mg/L on the 10th day. Such results indicated the great potential of utilizing Marasmiellus-SSF in modified fixed bad reactor to treat batik waste water.

Spatial changes of arbuscular mycorrhizal fungi in peach and their correlation with soil properties.

Arbuscular mycorrhizal (AM) fungi have beneficial effects on host plants, but their growth is influenced by various factors. This study was carried out to analyze the variation of AM fungi in soils and roots of peach (Prunus persica L. var. Golden Honey 3, a yellow-flesh variety) trees in different soil layers (0–40 cm) and their correlation with soil properties. The peach tree could be colonized by indigenous AM fungi (2.2–8.7 spores/g soil and 1.63–3.57 cm hyphal length/g soil), achieving 79.50–93.55% of root AM fungal colonization degree. The mycorrhizal growth, root sugars, soil three glomalins, NH4+-N, NO3−-N, available P and K, and soil organic matter (SOM) had spatial heterogeneity. Soil spores, but not soil hyphae contributed to soil glomalin, and soil glomalin also contributed to SOM. There was a significant correlation of soil hyphae with spore density, soil NO3−-N, and SOM. Root mycorrhiza was positively correlated with spore density, NH4+-N, NO3−-N, and easily extractable glomalin-related soil protein. Notably, spore density positively correlated with NO3−-N, available K, SOM, and root fructose and glucose, while negatively correlated with available P and root sucrose. These findings concluded that mycorrhiza of peach showed spatial distribution, and soil properties mainly affected/altered based on the soil spore density.

Legacy effects of pre-crop plant functional group on fungal root symbionts of barley.

Arbuscular mycorrhizal (AM) fungi, a group of widespread fungal symbionts of crops, could be important in driving crop yield across crop rotations through plant-soil feedbacks (PSF). However, whether preceding crops have a legacy effect on the AM fungi of the subsequent crop is poorly known. We set up an outdoor mesocosm crop rotation experiment that consisted of a first phase growing either one of four pre-crops establishing AM and/or rhizobial symbiosis or not (spring barley, faba bean, lupine, canola), followed by an AM crop, winter barley. After the pre-crop harvest, carbon-rich organic substrates were applied to test whether it attenuated, accentuated or modified the effect of pre-crops. The pre-crop mycorrhizal status, but not its rhizobial status, affected the richness and composition of AM fungi, and this difference, in particular community composition, persisted and increased in the roots of winter barley. The effect of a pre-crop was driven by its single symbiotic group, not its mixed symbiotic group and/or by a crop-species-specific effect. This demonstrates that the pre-crop symbiotic group has lasting legacy effects on the AM fungal communities and may steer the AM fungal community succession across rotation phases. This effect was accentuated by sawdust amendment, but not wheat straw. Based on the previous observation of decreased crop yield after AM pre-crops, our findings suggest negative PSF at the level of the plant symbiotic group driven by a legacy effect of crop rotation history on AM fungal communities, and that a focus on crop symbiotic group offers additional understanding of PSF.

Efficacy of application time of Penicillium sp. suspension on White Root Fungus (Rigidoporus lignosus) in Nutmeg (Myristica fragrans)

Cultivation of nutmeg (Myristica fragrans) is running into several problems, one of these is caused by white root fungus (Rigidoporus lignosus) which causes losses to nutmeg farmers. This fungus is known to be controlled by biological control using microorganisms such as Penicillium sp. This research was conducted to determine the efficacy of application time of Penicillium sp. crude extract against white root fungus (Rigidoporus lignosus) in nutmeg plants. The design used in this study was a non-factorial completely randomized design with the main factor being the application time of Penicilllium sp. crude extract with 4 treatments. Each treatment on 7 replicates. Control without suspension application Penicillium sp. (PK0), Application of Penicillium sp. 7 days before inoculation of Rigidoporus lignosus (PK1), Application of suspension of Penicillium sp. concurrently with Rigidoporus lignosus (PK2) inoculation, Application of suspension of Penicillium sp. 7 days after Rigidoporus lignosus (PK3) inoculation. Total are 28 experimental units. In this case, the test plants used are 11 months old nutmeg. The research parameters consisted of the incubation period, disease incidence and attack intensity. The results showed that the treatment at one-time application of the suspension of Penicillium sp. Significantly affect the intensity of attacks and the incidence of infectious disease pathogens Rigidoporus lignosus. Application time for Penicillium sp. 7 days before the suspension of Rigidoporus lignosus is the best offer in the attack of Rigidoporus lignosus disease.

Land‐use history alters the diversity, community composition and interaction networks of ectomycorrhizal fungi in beech forests

Abstract Forests have expanded across Europe over the last centuries as a consequence of farmland (agricultural and pasture) abandonment. Agricultural practices usually increase soil fertility and reduce the diversity and abundance of ectomycorrhizal (ECM) fungi, essential mutualists of many woody species in temperate and Mediterranean forests. The recovery of this biotic interaction after the cessation of human activities is, thus, crucial for the re‐establishment of functional forest ecosystems. Here we addressed the legacies of past land use and the recovery of the mutualism between ECM fungi and Fagus sylvatica trees in recent beech forests (<50 years) in Northeast Spain. Soil and root samples were collected in six long‐established and eight recent beech forests to analyse soil abiotic properties and the ECM fungi associated with beech roots (Illumina DNA metabarcoding of ECM tips). Up to 609 amplicon sequence variants (ASVs) of ECM fungi were identified, with 220 ASVs found in both forest types. Recent forests had a significantly lower soil organic matter and phosphorus content, which had a significant effect on the community structure of ECM fungi in beech roots. Moreover, beech trees in recent forests interacted with less fungal taxa but had a higher relative abundance of Ascomycota. Tarzetta spp. (Ascomycota, Pezizales) and Lactarius blennius (Basidiomycota, Russulales) emerge as the particular taxa associated with recent and long‐established forests respectively. More specialized mutualistic networks with a lower species normalized degree were found in recent forests, which might result in a lower quality and resilience of the ECM mutualism. Synthesis. Land‐use history modulated the mycorrhizal symbiosis in regenerating beech forests through changes in soil organic matter and nitrogen, which were the main drivers of the differences in fungal community composition and functional types associated with beech trees in recent forests.

Comparative roles of three adhesin genes (adh1-3) in insect-pathogenic lifecycle of Beauveria bassiana.

Adherence of conidia to insect integument is crucial for initiation of fungal infection through cuticular penetration and was previously reported to rely upon the Metarhizium-type adhesin Mad1 rather than Mad2, another adhesin crucial for conidial adherence of Metarhizium anisopliae to plant root surface. Mad1 and Mad2 have since been considered to function in fungal insect pathogenesis and plant root colonization respectively. Here, three adhesins were characterized in Beauveria bassiana, including Adh1/Mad1, Adh2/Mad2, and Adh3 known as filamentous hemagglutinin/adhesin and virulence factor in animal-pathogenic bacteria. Among those, only Adh2 was found to play a substantial role in sustaining the fungal virulence and some phenotypes associated with biological control potential. Disruption of adh2 resulted in decreased conidial adherence to insect wing cuticle, attenuated virulence via normal cuticle infection or cuticle-bypassing infection (injection), reduced blastospore production in an insect hemolymph-mimicking broth, largely reduced conidiation capacity, impaired conidial quality indicative of lowered viability, hydrophobicity, and UV resistance, but no growth defects on rich and scant media under normal or stressful culture conditions. The main phenotypic changes correlated well with repressed expression of developmental activator genes required for aerial conidiation and submerged blastospore production and of key hydrophobin genes essential for hydrophobin synthesis and assembly into rodlet bundles of conidial coat crucial for conidial adherence. In contrast, either adh1 or adh3 disruption caused insignificant changes in all phenotypes examined. These findings offer novel insight into a significance of Adh2, but a dispensability of Adh1 or Adh3, for insect-pathogenic lifecycle of B. bassiana. KEY POINTS: • Three adhesins (Adh1-3) of Beauvera bassiana are functionally characterized. • Adh2 plays a role in sustaining virulence and lifecycle-related cellular events. • Either Adh1 or Adh3 is dispensable for insect-pathogenic lifecycle of B. bassiana.

Pioneer plant species and fungal root endophytes in metal-polluted tailings deposited near human populations and agricultural areas in Northern Mexico

As a consequence of industrial mining activity, high volumes of tailings are scattered around Mexico. Frequently, tailings contain heavy metals (HM) which entail threats against all organisms. The aim of this research was to identify plants and root fungal endophytes in polymetallic polluted tailings with the potential to be used in strategies of bioremediation. Four deposits of mine wastes, situated in a semi-arid region near urban and semi-urban populations, and agricultural areas, were studied. The physical and chemical characteristics of substrates, accumulation of HM in plant tissues, root colonization between arbuscular mycorrizal (AMF) and dark septate endophyte (DSE) fungi, and the identification of DSE fungi isolated from the roots of two plant species were studied. Substrates from all four sites exhibited extreme conditions: high levels in sand; low water retention; poor levels in available phosphorus and nitrogen content; and potentially toxic levels of lead (Pb), cadmium (Cd), and zinc (Zn). The native plants Lupinus campestris, Tagetes lunulata, and Cerdia congestiflora, as well as the exotic Cortaderia selloana and Asphodelus fistulosus, demonstrated a relevant potential role in the phytostabilization and/or phytoextraction of Pb, Cd, and Zn, according to the accumulation of metal in roots and translocation to shoots. Roots of eleven analyzed plant species were differentially co-colonized between AMF and DSE fungi; the presence of arbuscules and microsclerotia suggested an active physiological interaction. Fourteen DSE fungi were isolated from the inner area of roots of T. lunulata and Pennisetum villosum; molecular identification revealed the predominance of Alternaria and other Pleosporales. The use of native DSE fungi could reinforce the establishment of plants for biological reclamation of mine waste in semi-arid climate. Efforts are needed in order to accelerate a vegetation practice of mine wastes under study, which can reduce, in turn, their potential ecotoxicological impact on organisms, human populations, and agricultural areas.

Effects of Rhizophagus intraradices on Plant Growth and the Composition of Microbial Communities in the Roots of Continuous Cropping Soybean at Maturity

Soybean is the major food and oil crop in the world. However, soybean continuous cropping can significantly reduce soybean yield. In this study, the effects of Rhizophagus intraradices on soybean growth and the composition of microbial communities in soybean roots under different continuous cropping regimes were investigated at maturity. The results showed that the mycorrhizal colonization rate was affected by R. intraradices and soybean continuous cropping. The mycorrhizal colonization rate was the highest in the inoculated soybean plants under 1 year of continuous cropping. Inoculation of R. intraradices significantly increased soybean plant growth. The greatest biomass parameters were obtained from the soybean plants inoculated with R. intraradices under 0 years of continuous cropping. Bacterial diversity was decreased by soybean continuous cropping, while the opposite result occurred for fungal diversity. Moreover, inoculation of R. intraradices could increase and decrease the diversity of bacteria and fungi in soybean roots, respectively. It also indicated that R. intraradices and soybean continuous cropping had significant effects on the composition of microbial communities in soybean roots. Proteobacteria and Ascomycota were the most dominant bacterial and fungal phylum in all samples, respectively. It would contribute to developing a biocontrol strategy to alleviate the soybean continuous cropping obstacles.

Soil properties and climate affect arbuscular mycorrhizal fungi and soil microbial communities in Mediterranean rainfed cereal cropping systems

Soil microorganisms are generally considered sensitive indicators of soil health and fertility. Understanding the role of environmental factors in driving soil microorganisms’ distributions is vital for sustainable crop production, particularly in vulnerable agricultural systems. This study aims to investigate the effect of environmental factors on the variation of soil microbial biomass and arbuscular mycorrhizal (AM) fungi in Mediterranean rainfed cereal systems. To do so, plant roots and soil were sampled from three cereal crops: Avena sativa L., Hordeum vulgare L. and Triticum turgidum L. growing in 24 rainfed sites from three different bioclimatic zones (sub-humid, superior semi-arid and middle semi-arid) in northern Tunisia. Soil microbial phospholipid fatty acids (PLFA) fingerprints, percentage of root length colonized by AM fungi as well as AM fungal spore density were then assessed. The redundancy analysis (RDA) revealed that soil organic matter (SOM), temperature, altitude and soil sand content accounted for 22.7 % of the variation of the microbial PLFA profiles used to estimate both soil microbial biomass and their distribution across different microbial groups. These environmental factors were the most important drivers affecting bacterial PLFAs. However, no significant relationships were observed between fungal PLFAs and environmental factors. Mycorrhizal colonization differed significantly among the different host species and regions. The RDA results indicated that environmental factors, in particular mean annual precipitation (MAP), pH, available phosphorus (P) and carbon/ nitrogen ratio (C/N) explained 44.8 % of AM fungal root colonization and spore number variation. Mycorrhizal colonization was positively correlated with pH but negatively with P, C/N and MAP. Concerning AM fungal spore number, it was positively linked to P and MAP. In contrast, it was inversely related to soil pH. Highlighting the main edaphic and climatic factors disturbing soil microorganisms, especially AM fungi, helps to better understand how environmental change will influence soil microbial communities in Mediterranean rainfed cereal systems.

Divergence of a genomic island leads to the evolution of melanization in a halophyte root fungus

Understanding how organisms adapt to extreme living conditions is central to evolutionary biology. Dark septate endophytes (DSEs) constitute an important component of the root mycobiome and they are often able to alleviate host abiotic stresses. Here, we investigated the molecular mechanisms underlying the beneficial association between the DSE Laburnicola rhizohalophila and its host, the native halophyte Suaeda salsa, using population genomics. Based on genome-wide Fst (pairwise fixation index) and Vst analyses, which compared the variance in allele frequencies of single-nucleotide polymorphisms (SNPs) and copy number variants (CNVs), respectively, we found a high level of genetic differentiation between two populations. CNV patterns revealed population-specific expansions and contractions. Interestingly, we identified a ~20 kbp genomic island of high divergence with a strong sign of positive selection. This region contains a melanin-biosynthetic polyketide synthase gene cluster linked to six additional genes likely involved in biosynthesis, membrane trafficking, regulation, and localization of melanin. Differences in growth yield and melanin biosynthesis between the two populations grown under 2% NaCl stress suggested that this genomic island contributes to the observed differences in melanin accumulation. Our findings provide a better understanding of the genetic and evolutionary mechanisms underlying the adaptation to saline conditions of the L. rhizohalophila–S. salsa symbiosis.

Pseudomonas Strains Induce Transcriptional and Morphological Changes and Reduce Root Colonization of Verticillium spp.

Phytopathogenic Verticillia cause Verticillium wilt on numerous economically important crops. Plant infection begins at the roots, where the fungus is confronted with rhizosphere inhabiting bacteria. The effects of different fluorescent pseudomonads, including some known biocontrol agents of other plant pathogens, on fungal growth of the haploid Verticillium dahliae and/or the amphidiploid Verticillium longisporum were compared on pectin-rich medium, in microfluidic interaction channels, allowing visualization of single hyphae, or on Arabidopsis thaliana roots. We found that the potential for formation of bacterial lipopeptide syringomycin resulted in stronger growth reduction effects on saprophytic Aspergillus nidulans compared to Verticillium spp. A more detailed analyses on bacterial-fungal co-cultivation in narrow interaction channels of microfluidic devices revealed that the strongest inhibitory potential was found for Pseudomonas protegens CHA0, with its inhibitory potential depending on the presence of the GacS/GacA system controlling several bacterial metabolites. Hyphal tip polarity was altered when V. longisporum was confronted with pseudomonads in narrow interaction channels, resulting in a curly morphology instead of straight hyphal tip growth. These results support the hypothesis that the fungus attempts to evade the bacterial confrontation. Alterations due to co-cultivation with bacteria could not only be observed in fungal morphology but also in fungal transcriptome. P. protegens CHA0 alters transcriptional profiles of V. longisporum during 2 h liquid media co-cultivation in pectin-rich medium. Genes required for degradation of and growth on the carbon source pectin were down-regulated, whereas transcripts involved in redox processes were up-regulated. Thus, the secondary metabolite mediated effect of Pseudomonas isolates on Verticillium species results in a complex transcriptional response, leading to decreased growth with precautions for self-protection combined with the initiation of a change in fungal growth direction. This interplay of bacterial effects on the pathogen can be beneficial to protect plants from infection, as shown with A. thaliana root experiments. Treatment of the roots with bacteria prior to infection with V. dahliae resulted in a significant reduction of fungal root colonization. Taken together we demonstrate how pseudomonads interfere with the growth of Verticillium spp. and show that these bacteria could serve in plant protection.

Endophytic fungi in blueberry cultivars, in three production areas of Argentina

Blueberries develop a shallow and fibrous root system, with sparse root hairs, normally colonized by mycorrhizal fungi. The presence of endophytic fungi in blueberry roots has been studied mainly in the area of origin of each species. The aims of the present study were to determine the occurrence of endophytic fungi in the roots of southern highbush blueberry (SHB) cultivars, in the three most important blueberry production areas of Argentina, and identify them. Soil samples with blueberry rootlets were obtained and endophytic fungi were isolated from them. Some of them by classical taxonomy identification, and, when this was not possible, PCR amplified material were sequenced (Macrogen laboratory), DNA fragments were analyzed with the Basic Local Alignment Search Tool (BLAST) and identified, through GenBank. Blueberry roots were found to be colonized by a large number of fungal genera, which varied greatly among locations and cultivars. Some of the endophytic fungi identified have pathogenic function, others are only plant hosts, and some of them have mycorrhizal function as is the case of genus Oidiodendron where we found O. maius and O. echinulatum. We may conclude that SHB is associated with local ericoid fungi, some of which are mycorrhizal and some dark septate endophytes, which, in most cases, do not match with those found in production regions of their native area, but same of them are important to promote blueberry growth.

Biological control of Fusarium wilt caused by Fusarium equiseti in Vicia faba with broad spectrum antifungal plant-associated Bacillus spp.

Fusarium wilt caused by root infections by Fusarium equiseti is a serious disease of Vicia faba that causes significant economic losses in bean. Among management strategies, biological control is a sustainable alternative to chemical control, and Bacillus species emerge as suitable candidates. Bacillus strains have been developed in recent years as biocontrol agents of several plant diseases, mainly for fungal root disease control. In this study, 24 strains of Bacillus spp. were selected among 455 isolates obtained from V. faba plants for their antifungal activity against a broad-spectrum of phytopathogenic fungi belonging to Fusarium, Alternaria, Penicillium, Botrytis, and Rutstroemia genera. Particularly, the strains which inhibited growth of F. equiseti were identified as B. cereus, B. mojavensis, B. velezensis, B. subtilis and B. amyloliquefaciens by sequencing rpoB gene. The strains were further characterized for the presence of cyclolipopeptides (cLP) genes (fenD, bmyB, spaS, dfnM, ituA, mycA, srfAA), genes encoding plant-induced resistance factors (ysnE, yxvQ, β-Glu), and for the production of lipopeptides (iturins, fengycins, surfactins), indoleacetic acid, siderophores, hydrocyanic acid, extracellular enzymes (amylase, protease, pectinase, cellulase) and phosphate solubilization. Hierarchical and correspondence analysis showed the clustering of Bacillus strains into three different groups, where the strains with the highest antifungal activity are correlated to the presence of different biosynthetic genes and production of broad spectra of metabolites. They include strains of B. amyloliquefaciens, B. velezensis, B. subtilis and B. mojavensis. Furthermore, these strains showed high levels of Fusarium wilt reduction in V. faba under greenhouse conditions, as well as they have shown plant promoting activity.

Fungi associated with aeroponic roots in caves and mines of New Brunswick

We provide the first analysis of the fungi associated with a very special habitat, the aeroponic roots found in caves and mines in New Brunswick, Canada. Fungal diversity was assessed by Illumina sequencing using three complementary primer sets targeting ribosomal RNA genes, and roots were identified using the non-coding trnH - psbA spacer. Early colonizing ectomycorrhizal fungi such as Agaricales, Helotiales, Pezizales, and Thelephorales were predominant. Saprotrophs, endophytes and plant pathogens were also present, but Glomeromycota (arbuscular mycorrhizal fungi) were not detected. Fungal root communities were generally most similar within sites. Fungal diversity was inversely correlated with winter dark zone temperatures and distance from the entrance. By using a combination of three primer sets, we detected more fungal taxa than with any one primer set. This study adds to the understanding of these subterranean ecosystems and suggests that future studies investigate factors limiting the presence of late-stage ectomycorrhizal fungi and Glomeromycota. • We provide a first analysis of fungi associated with aeroponic roots in caves and mines. • We detected ectomycorrhizal fungi, endophytes, saprotrophs and plant pathogens. • Late-stage ectomycorrhizal fungi and arbuscular mycorrhizal fungi were not found. • Similarity of fungal communities was related more to site than host or proximity. • Combining three NGS primer sets detected more fungi than any single primer set.

Specific and conserved patterns of microbiota-structuring by maize benzoxazinoids in the field

BackgroundPlants influence their root and rhizosphere microbial communities through the secretion of root exudates. However, how specific classes of root exudate compounds impact the assembly of root-associated microbiotas is not well understood, especially not under realistic field conditions. Maize roots secrete benzoxazinoids (BXs), a class of indole-derived defense compounds, and thereby impact the assembly of their microbiota. Here, we investigated the broader impacts of BX exudation on root and rhizosphere microbiotas of adult maize plants grown under natural conditions at different field locations in Europe and the USA. We examined the microbiotas of BX-producing and multiple BX-defective lines in two genetic backgrounds across three soils with different properties.ResultsOur analysis showed that BX secretion affected the community composition of the rhizosphere and root microbiota, with the most pronounced effects observed for root fungi. The impact of BX exudation was at least as strong as the genetic background, suggesting that BX exudation is a key trait by which maize structures its associated microbiota. BX-producing plants were not consistently enriching microbial lineages across the three field experiments. However, BX exudation consistently depleted Flavobacteriaceae and Comamonadaceae and enriched various potential plant pathogenic fungi in the roots across the different environments.ConclusionsThese findings reveal that BXs have a selective impact on root and rhizosphere microbiota composition across different conditions. Taken together, this study identifies the BX pathway as an interesting breeding target to manipulate plant-microbiome interactions.4atbM_n1-Xmh1rBaQ1rPHqVideo