Endophyte Symbiosis Research Articles

Enhancing cold tolerance in tobacco through endophytic symbiosis with Piriformospora indica.

Tobacco, a warm-season crop originating from the Americas, is highly susceptible to cold stress. The utilization of symbiotic fungi as a means to bolster crops' resilience against abiotic stresses has been proven to be a potent strategy. In this study, we investigated the effect of endophytic fungus Piriformospora indica on the cold resistance of tobacco. When exposed to cold stress, the colonization of P.indica in tobacco roots effectively stimulates the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX). This, in turn, reduces the accumulation of reactive oxygen species (ROS), thereby mitigating oxidative damage. Additionally, P. indica elevates the levels of osmolytes, such as soluble sugars, proline, and soluble proteins, thus facilitating the restoration of osmotic balance. Under cold stress conditions, P. indica also induces the expression of cold-responsive genes. Furthermore, this fungus not only enhances photosynthesis in tobacco by stimulating the synthesis of photosynthetic pigments, strengthening Rubisco activity, and elevating PSII efficiency, but also fortifies tobacco's nitrogen assimilation by inducing the expression of nitrate transporter gene and activating enzymes related to nitrogen assimilation. Consequently, this synergistic optimization of nitrogen and carbon assimilation provides a solid material and energetic foundation for tobacco plants to withstand cold stress. Our study demonstrates that a mycorrhizal association between P. indica and tobacco seedlings provides multifaceted protection to tobacco plants against low-temperature stress and offers a valuable insight into how P. indica enhances the cold tolerance of tobacco.

Reduced seed viability in exchange for transgenerational plant protection: Does the defensive mutualism concept pass the fitness test?

Epichloë endophytes are vertically transmitted via grass seeds and chemically defend their hosts against herbivory. Endophyte-conferred plant defence via alkaloid biosynthesis may occur independently of costs for host plant growth. However, fitness consequences of endophyte-conferred defence and transgenerational effects on herbivore resistance of progeny plants, are rarely studied. The aim of this study was to test whether severe defoliation in mother plants affects their seed production, seed germination rate, and the endophyte-conferred resistance of progeny plants. In a field study, we tested the effects of defoliation and endophyte symbiosis (Epichloë uncinata) on host plant (Festuca pratensis) performance, loline alkaloid concentrations in leaves and seeds, seed biomass and seed germination rates. In a subsequent greenhouse study, we challenged the progeny of the plants from the field study to aphid herbivory and tested whether defoliation of mother plants affects endophyte-conferred resistance against aphids in progeny plants. Defoliation of the mother plants resulted in a reduction of alkaloid concentrations in leaves and elevated the alkaloid concentrations in seeds when compared with non-defoliated endophyte-symbiotic plants. Viability and germination rate of seeds of defoliated endophyte-symbiotic plants were significantly lower compared to those of non-defoliated endophyte-symbiotic plants and endophyte-free (defoliated and non-defoliated) plants. During six weeks growth, seedlings of defoliated endophyte-symbiotic mother plants had elevated alkaloid concentrations, which negatively correlated with aphid performance. Endophyte-conferred investment in higher alkaloid levels in seeds -elicited by defoliation- provided herbivore protection in progenies during the first weeks of plant establishment. Better protection of seeds via high alkaloid concentrations negatively correlated with seed germination indicating trade-off between protection and viability.

Predicting Field Effectiveness of Endophytic Bacillus subtilis Inoculants for Common Bean Using Morphometric and Biochemical Markers.

According to four field experiments, after the inoculation of Phaseolus vulgaris L. cultivar Ufimskaya with the commercial strain Bacillus subtilis 26D and the promising strain B. subtilis 10-4, it was found that inoculation with B. subtilis 10-4 improved seed productivity (SP) by 31-41% per plant, but only in dry years. In contrast, all 4 years of inoculation with B. subtilis 26D were ineffective or neutral. It was intended to determine the growing and biochemical characteristics of inoculated 7-day-old plants, which correlate with the field SP of bacterial preparations. The SP of inoculated plants (average of 4 years) correlated with root length (0.83), MDA content (-0.98), and catalase (CAT) activity in roots (-0.96) of week-old seedlings. High correlation coefficients between the H2O2 content in the roots and SP (0.89 and 0.77), as well as between the H2O2 content in shoots and SP (0.98 and 0.56), were observed only in two dry years, when the influence of bacteria was detected. These physiological indicators were identified as potential markers for predicting the effectiveness of the endophytic symbiosis between bean plants and B. subtilis strains. The findings may be used to develop effective microbial-based, eco-friendly technologies for bean production.

Dark septate endophyte Anteaglonium sp. T010 promotes biomass accumulation in poplar by regulating sucrose metabolism and hormones.

Plant biomass is a highly promising renewable feedstock for the production of biofuels, chemicals and materials. Enhancing the content of plant biomass through endophyte symbiosis can effectively reduce economic and technological barriers in industrial production. In this study, we found that symbiosis with the dark septate endophyte (DSE) Anteaglonium sp. T010 significantly promoted the growth of poplar trees and increased plant biomass, including cellulose, lignin and starch. To further investigate whether plant biomass was related to sucrose metabolism, we analyzed the levels of relevant sugars and enzyme activities. During the symbiosis of Anteaglonium sp. T010, sucrose, fructose and glucose levels in the stem of poplar decreased, while the content of intermediates such as glucose-6-phosphate (G6P), fructose-6-phosphate (F6P) and UDP-glucose (UDPG), and the activity of enzymes related to sucrose metabolism, including sucrose synthase (SUSY), cell wall invertase (CWINV), fructokinase (FRK) and hexokinase, increased. In addition, the contents of glucose, fructose, starch, and their intermediates G6P, F6P and UDPG, as well as the enzyme activities of SUSY, CWINV, neutral invertase and FRK in roots were increased, which ultimately led to the increase of root biomass. Besides that, during the symbiotic process of Anteaglonium sp. T010, there were significant changes in the expression levels of root-related hormones, which may promote changes in sucrose metabolism and consequently increase the plant biomass. Therefore, this study suggested that DSE fungi can increase the plant biomass synthesis capacity by regulating the carbohydrate allocation and sink strength in poplar.

Interactions between Epichloë endophyte and the plant microbiome impact nitrogen responses in host Achnatherum inebrians plants.

The clavicipitaceous fungus Epichloë gansuensis forms symbiotic associations with drunken horse grass (Achnatherum inebrians), providing biotic and abiotic stress protection to its host. However, it is unclear how E. gansuensis affects the assembly of host plant-associated bacterial communities after ammonium nitrogen (NH4+-N) treatment. We examined the shoot- and root-associated bacterial microbiota and root metabolites of A. inebrians when infected (I) or uninfected (F) with E. gansuensis endophyte. The results showed more pronounced NH4+-N-induced microbial and metabolic changes in the endophyte-infected plants compared to the endophyte-free plants. E. gansuensis significantly altered bacterial community composition and β-diversity in shoots and roots and increased bacterial α-diversity under NH4+-N treatment. The relative abundance of 117 and 157 root metabolites significantly changed with E. gansuensis infection under water and NH4+-N treatment compared to endophyte-free plants. Root bacterial community composition was significantly related to the abundance of the top 30 metabolites [variable importance in the projection (VIP) > 2 and VIP > 3] contributing to differences between I and F plants, especially alkaloids. The correlation network between root microbiome and metabolites was complex. Microorganisms in the Proteobacteria and Firmicutes phyla were significantly associated with the R00693 metabolic reaction of cysteine and methionine metabolism. Co-metabolism network analysis revealed common metabolites between host plants and microorganisms.IMPORTANCEOur results suggest that the effect of endophyte infection is sensitive to nitrogen availability. Endophyte symbiosis altered the composition of shoot and root bacterial communities, increasing bacterial diversity. There was also a change in the class and relative abundance of metabolites. We found a complex co-occurrence network between root microorganisms and metabolites, with some metabolites shared between the host plant and its microbiome. The precise ecological function of the metabolites produced in response to endophyte infection remains unknown. However, some of these compounds may facilitate plant-microbe symbiosis by increasing the uptake of beneficial soil bacteria into plant tissues. Overall, these findings advance our understanding of the interactions between the microbiome, metabolome, and endophyte symbiosis in grasses. The results provide critical insight into the mechanisms by which the plant microbiome responds to nutrient stress in the presence of fungal endophytes.

A seed-borne endophyte mediates plant drought responses and intergenerational effects on seed characteristics

Global warming is expected to increase drought severity in diverse environments, impacting plant performance. Plants acclimate to drought by mechanisms like stomatal closure and osmotic adjustment. Maternally inherited symbiotic microorganisms with capacity to regulate these mechanisms have the potential to influence intergenerational plant drought responses. We studied how a seedborne endophyte affects maternal drought effects on seed germination water requirements and specialized metabolites. Isotopic analysis of seed cellulose indicated that drought led to improved water use efficiency (WUE; higher δ13C) in endophyte-free mother plants, seemingly without affecting stomatal conductance (non-significant δ18O change). Alternatively, endophyte-symbiotic plants did not exhibit a change in WUE but apparently an increase in stomatal conductance (significant δ18O decrease). Regardless of the symbiosis, drought reduced seed production but not seed size. Endophyte symbiosis improved the seed concentration of mannitol and sorbitol, but this increment was higher under drought. Maternal plant responses to drought did not increase seed germination under reduced water potential but induced dormancy in seeds from endophyte-free but not endophyte-symbiotic plants. Our findings suggest that although differential accumulation of metabolites in seeds results from how endophyte-symbiotic plants perceive and respond to drought, this response may not form part of a mechanism that would enhance seed performance of progeny under drought.

Root endophyte-mediated alteration in plant H2O2 homeostasis regulates symbiosis outcome and reshapes the rhizosphere microbiota.

Endophytic symbioses between plants and fungi are a dominant feature of many terrestrial ecosystems, yet little is known about the signaling that defines these symbiotic associations. Hydrogen peroxide (H2O2) is recognized as a key signal mediating the plant adaptive response to both biotic and abiotic stresses. However, the role of H2O2 in plant-fungal symbiosis remains elusive. Using a combination of physiological analysis, plant and fungal deletion mutants, and comparative transcriptomics, we reported that various environmental conditions differentially affect the interaction between Arabidopsis and the root endophyte Phomopsis liquidambaris, and link this process to alterations in H2O2 levels and H2O2 fluxes across root tips. We found that enhanced H2O2 efflux leading to a moderate increase in H2O2 levels at the plant-fungal interface is required for maintaining plant-fungal symbiosis. Disturbance of plant H2O2 homeostasis compromises the symbiotic ability of plant roots. Moreover, the fungus-regulated H2O2 dynamics modulate the rhizosphere microbiome by selectively enriching for the phylum Cyanobacteria, with strong antioxidant defenses. Our results demonstrated that the regulation of H2O2 dynamics at the plant-fungal interface affects the symbiotic outcome in response to external conditions and highlight the importance of the root endophyte in reshaping the rhizosphere microbiota.

Symbiosis with endophyte leads to greater C accumulation in grassland soils

Epichloë coenophiala forms aboveground symbiotic relationships with tall fescue (Festuca arundinacea) and provides the host with better fitness. This study investigated the effects of endophyte symbiosis on carbon mineralization in soil. Two soils were amended with endophyte-infected (E+) or endophyte-free (E−) residues of two tall fescue genotypes. At the end of the experiment, CO2 evolution rates were monitored to quantify the mineralized carbon. The indices of carbon mineralization were significantly greater (LSD, P < 0.05) in the E−compared to E+ plant residue treated soils. Cellulose, hemicellulose, lignin contents, C:N and lignin:N ratios were significantly greater (LSD, P < 0.05) in soils with the E+ residues than in those with E− residues. Additionally, the E+ plant residues consistently contained significantly less N (LSD, P < 0.05). Overall, it is concluded that grass-endophyte symbiosis results in the production of less biodegradable plant residues, in turn reducing the residue biodegradability and promoting greater C accumulation in the soils.

The “Trojan horse” strategy: Seed fungal endophyte symbiosis helps to explain the invasion success of the grass, Poa annua, in Maritime Antarctica

AbstractAimPoa annua L. (annual bluegrass) is presently the sole invasive vascular plant species to have successfully established in Maritime Antarctica, where it poses a significant conservation threat to native plant species. However, the reasons for its success in the region have yet to be established. Here, we determined whether the invasiveness of P. annua, and its competitiveness with the native Antarctic hairgrass Deschampsia antarctica, is influenced by symbioses formed with seed fungal endophytes, and whether plants derived from seeds from four global regions differ in their performance.LocationsFour regions (Maritime Antarctica, sub‐Antarctica, South America and Europe).MethodsEndophyte frequency was measured in P. annua seeds collected from the four regions. The germination, survival, biomass accumulation, flowering and competitiveness with D. antarctica of P. annua plants grown from endophyte‐uncolonised and uncolonised seeds was determined in the laboratory. The effects of endophytes on P. annua seed germination and survival and seedling osmoprotection were also assessed in the Maritime Antarctic natural environment using locally‐sourced seeds.ResultsEndophytes were at least twice as frequent in seeds from Maritime Antarctica than in those from other regions. A higher proportion of endophyte‐colonized seeds germinated and survived than did uncolonised seeds, but only when they originated from Maritime Antarctica. Seed endophytes increased the competitiveness of P. annua with D. antarctica, but only for plants grown from Maritime Antarctic seeds. In the field, endophyte‐colonized seeds from Maritime Antarctica germinated and survived more frequently than uncolonised seeds, and osmoprotection was higher in seedlings grown from colonized seed.Main ConclusionsThe findings indicate beneficial effects of seed endophytes on invasion‐related traits of P. annua, such as survival, germination success and flowering. Together with vegetative and reproductive traits facilitating the colonization process, the seed‐fungal endophyte symbiosis can be invoked as an important factor explaining the invasiveness of P. annua in Maritime Antarctica.

Effect of Seed Priming with Endophytic Bacillus subtilis on Some Physio-Biochemical Parameters of Two Wheat Varieties Exposed to Drought after Selective Herbicide Application.

Wheat plants are frequently exposed to combined herbicide and drought stress (HDS) which induces complex responses negatively, affects productivity, and is becoming more exacerbated with current climate change. In this work, we studied the influence of seed priming with endophytic bacteria Bacillus subtilis (strains 104 and 26D) on growth and tolerance of two wheat (Triticum aestivum L.) varieties (E70-drought tolerant; SY-drought susceptible) exposed to soil drought after application of selective herbicide Sekator® Turbo in pot experiments under controlled conditions; 17-day-old plants sprayed with herbicide and after 3 days were subjected to soil drought by stopping irrigating the plants for 7 days with subsequent resumption of normal irrigation (recovery). Additionally, the growth of tested strains (104, 26D) in the presence of different concentrations of herbicide Sekator® Turbo and drought (PEG-6000) were evaluated. It was established that both strains are herbicide and drought tolerant and capable to improve seed germination and early seedlings' growth under different herbicide and drought stress degrees. The results of pot experiments showed that HDS exposure declined growth (plant length, biomass), photosynthetic pigments (chlorophyll a and b), leaf area, and increased lipid peroxidation (LPO) and proline accumulation in plants, demonstrating higher damaging effects for SY variety. Strains 104 and 26D mitigated (in different levels) such negative impacts of HDS on growth of both varieties by increasing length of roots and shoots, biomass, photosynthetic pigments (chlorophyll a and b), and leaf area, reducing stress-caused LPO (i.e., malondialdehyde), and regulating proline biosynthesis, as well as contributing to a faster recovery of growth, photosynthetic pigments, and redox-status of plants in post-stress period in comparison with non-primed plants. These ultimately manifested in forming a better grain yield of both varieties primed with 104, 26D, and exposed to HDS. Thus, both strains 104 and 26D (which are herbicide and drought tolerant) may be used as seed priming agents to improve wheat HDS tolerance and grain yield; however, strain 104 more effectively protected plants of E70, while strain 26D-plants of SY. Further research should be focused on understanding the mechanisms that determine the strain and variety-specificity of endophytic symbiosis and the role of bacteria in the modulation of physiological states of primed plants under stress conditions, including HDS.

Comparative Transcriptomics Profiling of Perennial Ryegrass Infected with Wild Type or a ΔvelA Epichloë festucae Mutant Reveals Host Processes Underlying Mutualistic versus Antagonistic Interactions

Epichloë species form bioprotective endophytic symbioses with many cool-season grasses, including agriculturally important forage grasses. Despite its importance, relatively little is known about the molecular details of the interaction and the regulatory genes involved. VelA is a key global regulator in fungal secondary metabolism and development. In previous studies, we showed the requirement of velA for E. festucae to form a mutualistic interaction with Lolium perenne. We showed that VelA regulates the expression of genes encoding proteins involved in membrane transport, fungal cell wall biosynthesis, host cell wall degradation, and secondary metabolism, along with several small-secreted proteins in Epichloë festucae. Here, by a comparative transcriptomics analysis on perennial ryegrass seedlings and mature plants, which are endophyte free or infected with wild type (mutualistic interaction) or mutant ΔvelA E. festucae (antagonistic or incompatible interaction), regulatory effects of the endophytic interaction on perennial ryegrass development was studied. We show that ΔvelA mutant associations influence the expression of genes involved in primary metabolism, secondary metabolism, and response to biotic and abiotic stresses compared with wild type associations, providing an insight into processes defining mutualistic versus antagonistic interactions.

Endophyte symbiosis: evolutionary development, and impacts of plant agriculture

Endophyte symbiosis: evolutionary development, and impacts of plant agriculture

Root biomass and cumulative yield increase with mowing height in Festuca pratensis irrespective of Epichloë symbiosis

Increasing agricultural soil carbon sequestration without compromising the productivity of the land is a key challenge in global climate change mitigation. The carbon mitigation potential of grass-based agriculture is particularly high because grasslands represent 70% of the world’s agricultural area. The root systems of grasses transfer large amounts of carbon to below-ground storage, and the carbon allocation to the roots is dependent on the grasses’ photosynthesizing shoot biomass. In a common-garden experiment, Festuca pratensis was used as a model species to study how mowing and weed control practices of perennial cool-season fodder grasses affect total yield and root biomass. Additionally, grass-associated Epichloë endophytes and soil residual glyphosate were tested for their effect on the total yield and root biomass alone or in interaction with mowing. The results demonstrate that elevating the cutting height increases both cumulative yield and root biomass in F. pratensis. Endophyte symbiosis increased the total yield, while glyphosate-based herbicide residues in the soil decreased the root biomass, which indicates a reduction of soil bound carbon sequestration. The findings demonstrate that carbon sequestration and yield quantities on farmed grasslands may significantly be improved by optimizing strategies for the use of plant protection products and adjustment of mowing intensity.

Evaluation of colonization and mutualistic endophytic symbiosis of Escherichia coli with tomato and Bermuda grass seedlings.

Escherichia coli is generally considered a bacterium associated with animal microbiomes. However, we present evidence that E. coli may also mutualistically colonize roots of plant species, even to the extent that it may become endophytic in plants. In this study we used GFP tagged E. coli to observe its colonization and effects on tomato (Solanum lycopersicum) and Bermuda grass (Cynodon dactylon) seedling development and growth. Inoculation with the bacterium significantly improved root development of both seedlings tested. Treatment also increased the photosynthetic pigments in Bermuda grass seedlings. However, effects on shoot length in both seedlings were not significant. This bacterium was found to produce indole acetic acid (IAA) up to 8.68 ± 0.43 µg ml−1 in the broth medium amended with tryptophan. Effects on seedling root growth could, in part, be explained by IAA production. Bacteria successfully colonized the root surfaces and interiors of both seedlings. Tagged bacteria expressing the GFP were observed in the vascular tissues of Bermuda grass seedling roots. Seedlings with bacteria showed greater survival and were healthier than seedlings without bacteria, indicating that E. coli set up a successful mutualistic symbiosis with seedlings. E. coli is not commonly considered to be a plant endophyte but is more generally considered to be a crop contaminant. In this study we show that E. coli may also be an endophyte in plant tissues.

Host-Species Variation and Environment Influence Endophyte Symbiosis and Mycotoxin Levels in Chinese Oxytropis Species.

Oxytropis plants are widely distributed in the grasslands in northern China. Some Oxytropis species have been reported to contain the mycotoxin swainsonine, an alkaloid which causes poisoning in livestock, referred to as locoism. Previous studies showed that endophytic fungi (Alternaria oxytropis) symbiotically associate with these Oxytropis species to produce swainsonine. However, the influence of variation within the Oxytropis genus on the fixation or loss of symbiosis and toxicity is poorly understood, as is the influence of environmental factors. Here we used a collection of 17 common Oxytropis species sampled in northern China to assess genetic diversity using genotyping by sequencing which was compared with the levels of the endophyte and swainsonine. Results showed that nine Oxytropis species have detectable A. oxytropis colonisation, and seven Oxytropis species contain sufficient swainsonine to be considered poisonous, whereas the rest may be non-toxic. Species variation rather than the genetic lineage was associated with the fixation or loss of endophyte and swainsonine production, which appears to have resulted from genetic drift. Genotype × Environment (G × E) effects were also found to influence endophyte and swainsonine levels amongst species of the Oxytropis genus. Our study will provide a better understanding about the evolutionary basis of A. oxytropis symbiosis and swainsonine biosynthesis in locoweeds.

Mixed Nanocomposite Fertilizers Influencing Endophytic Symbiosis and Nutritional and Antioxidant Properties of Oryza sativa as a Sustainable Alternative for Commercial Fertilizers.

This study investigated the comparative effects of mixed nanocomposite (MNC) fertilizers as an alternative to commercial fertilizers (CFs) on endophytic symbiosis and nutritional properties of rice grains. We synthesized MNC fertilizers with different concentrations and characterized them by using scanning electron microscopy and Fourier transform infrared spectroscopy. The CF was applied as per the method followed by local farmers; however, for MNC fertilizers both foliar and soil applications were done. Comparative analysis of growth and development, rice–endophyte symbiosis, and nutritional properties of rice grains was conducted. The panicles per hill, length of panicles, grain per panicles, 1000-grain weight, and dry matter of rice plants treated with MNC fertilizers were found to be not statistically (p > 0.05) different compared to those of CF. However, growth parameters were significantly (p < 0.05) higher in MNC fertilizer-treated crops than in CF-treated crops. Several predominant endophytes such as Penicillium spp., Aspergillus fumigatus, Rhizopus spp., and Fusarium spp. that could have significant effects on the enhancement of growth and nutritional properties of rice grains were identified in rice plants treated with MNC fertilizers at different concentrations. Contrarily, stem-associated Cercospora spp. was found in the CF-treated field and fission yeast was observed in the blank-treated field. In addition, the contents of proteins, fibers, carbohydrates, energy-yielding components, vitamin A, and minerals were significantly increased in rice plants treated with MNC fertilizers. Thus, we would like to conclude that MNC fertilizers could be one of the most potential alternatives to CFs for achieving better rice–endophyte symbiosis as well as nutritional improvements in rice grains for sustainable production.

Effect of Coexistence of Bacterial and Fungal Isolates with Cotton’s “Aleppo 118” Variety in Improving Cotton Growth and Enhancing Cotton’s Resistance to the Whitefly Bemisia tabaci (Genn.) by Using Different Inoculation Methods

In this study, four methods of inoculation were used to assess coexistence of microorganisms with cotton plant: seeds coating (chemical shaved / unshaved), aerial spraying, irrigation and their effects on germination, endophytic symbiosis, growth parameters, density of whitefly’s population density. For this purpose a number of bacterial and fungal isolates were tested (3 isolates of Trichoderma harzianum (Twood, T.L.C, T950), 2 isolates of Beauveria bassiana (GHA, K), 2 isolates of Bacillus subtilis (B.s, B.bacteria), one isolate of Lecanicillium lecanii (B), and one isolate of Aspergillus sp. (Asp)). Propagation of these isolates were conducted. Fungal isolates were propagated on burgol (cracked wheat), whereas bacterial isolates were propagated in Petri dishes contained NA medium, then suspension concentration was adjusted to 1x108 cell/ml for bacterial isolates and 1x106 conidia/ml for fungal isolates. Seeds of each treatment were planted in pots with 3 replicates per treatment, in addition to a control treatment. The results obtained showed that there was no significant difference between control and each of other treatments in germination rate, whereas highest coexistent rates were recorded for GHA, K, B, Asp isolates in all plant parts. Also, there were significant differences in roots length, foliage height, dry and fresh weight between Twood, B.bacteria, GHA, T950,Asp, B.S. treatments and control treatment. Inoculation with the isolates T.L.C, K, GHA, T950, Asp, B.bacteria produced low densities of whitefly’s nymphs per leaf. Finally, shaved and unshaved seeds coating and soil irrigation methods produced low densities of whitefly’s nymphs compared with the spraying treatment and all inoculation methods used had significant differences with control treatment. Microorganisms used improved cotton growth and decreased whitefly population density. This approach can be used as a component in integrated pest management programs for cotton. Keywords: Beneficial microorganisms, growth parameters, resistance, cotton, whitefly

Improvement of salt tolerance in Stevia rebaudiana by co-application of endophytic fungi and exogenous spermidine

Stevia (Stevia rebaudiana Bertoni) is an important and salt-sensitive medicinal plant used as a natural sweetener in food products. In this work, we used a pot experiment to investigate the role of microbial inoculation and exogenous polyamine spermidine (Spd) in conferring salt stress tolerance in stevia by analyzing plant growth, chlorophyll (Chl) content, Chl a fluorescence, antioxidant defense system and steviol glycosides. The inoculated plants with Piriformospora indica (Pi), Tricuderma virens (Trich) or Pi+Trich were grown in optimum conditions. At the late of vegetative stage (BBCH growth stage 47), plants sprayed with different concentrations of Spd (0, 0.75, and 1.5 mM) and then were exposed to salinity stress by irrigation with saline treatments (mix of Caspian Sea and distilled water; 0, 6, and 12 dS m−1). The results revealed that salt stress increased hydrogen peroxide (H2O2) and lipid peroxidation (Malondialdehyde: MDA), and consequently plant growth characteristics and maximum photochemical quantum yield of PSII (Fv/Fm) as well as Chl content decreased, but antioxidant enzymes activity including superoxide (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) increased in the plants. Exposure to moderate salinity increased stevioside (Stv) and rebaudioside A (Reb A) content, while these compounds were decreased in the presence of severe salinity. The endophytic symbiosis and foliar spray of Spd (especially in Pi+Trich and Spd 0.75 mM) mitigated salt stress by significant increases in antioxidant enzymes activity and a decrease in H2O2 content and lipid peroxidation. Inoculation with Pi, Trich, and especially Pi+Trich increased the Chl content, Fv/Fm, shoot dry weight, and Stv and Reb A content at all salinity levels. Consequently, combined inoculation of Pi and Trich and foliar application of Spd can be a good approach to improve tolerance, growth and steviol glycosides production of stevia in salt stress conditions.

Effect of Epichloë fungal endophyte symbiosis on tall fescue to cope with flooding-derived oxygen-limited conditions depends on the host genotype

Effect of Epichloë fungal endophyte symbiosis on tall fescue to cope with flooding-derived oxygen-limited conditions depends on the host genotype

Rethinking of the Roles of Endophyte Symbiosis and Mycotoxin in Oxytropis Plants.

Plants in the Oxytropis genus can live with the endophytic fungi Alternaria sect. Undifilum. Swainsonine, the mycotoxin produced by the endophyte render the host plant toxic and this has been detrimental to grazing livestock in both China and U.S.A. Despite previous efforts, many questions remain to be solved, such as the transmission mode and life cycle of host–endophyte symbiont, the biosynthesis pathway of swainsonine, and in particular the ecological role and evolution of such symbiosis. In this review, we compile the literature to synthesize ideas on the diversity of the symbiosis and propagation of the endophyte. We further compare the previous work from both Alternaria sect. Undifilum and other swainsonine producing fungi to orchestrate a more comprehensive biosynthesis pathway of swainsonine. We also connect swainsonine biosynthesis pathway with that of its precursor, lysine, and link this to a potential role in modulating plant stress response. Based on this we hypothesize that this host–endophyte co-evolution originated from the needs for host plant to adapt for stress. Validation of this hypothesis will depend on future research on endophytic symbiosis in Oxytropis and help in better understanding the roles of plant–endophyte symbiosis in non-Poaceae species.