Fungal Endophytes Promote Tomato Growth and Enhance Drought and Salt Tolerance

Fungal endophytes from saline-adapted shrubs induce salinity stress tolerance in tomato seedlings

To meet the food and feed demands of the growing population, global food production needs to double by 2050. Climate change-induced challenges to food crops, especially soil salinization, remain a major threat to food production. We hypothesize that endophytic fungi isolated from salt-adapted host plants can confer salinity stress tolerance to salt-sensitive crops. Therefore, we isolated fungal endophytes from shrubs along the shores of saline alkaline Lake Magadi and evaluated their ability to induce salinity stress tolerance in tomato seeds and seedlings. Of 60 endophytic fungal isolates, 95% and 5% were from Ascomycetes and Basidiomycetes phyla, respectively. The highest number of isolates (48.3%) were from the roots. Amylase, protease and cellulase were produced by 25, 30 and 27 isolates, respectively; and 32 isolates solubilized phosphate. Only eight isolates grew at 1.5 M NaCl. Four fungal endophytes (Cephalotrichum cylindricum, Fusarium equiseti, Fusarium falciforme and Aspergilus puniceus) were tested under greenhouse conditions for their ability to induce salinity tolerance in tomato seedlings. All four endophytes successfully colonized tomato seedlings and grew in 1.5 M NaCl. The germination of endophyte-inoculated seeds was enhanced by 23%, whereas seedlings showed increased chlorophyll and biomass content and decreased hydrogen peroxide content under salinity stress, compared with controls. The results suggest that the the four isolates can potentially be used to mitigate salinity stress in tomato plants in salt-affected soils.

Plant-endophyte communication: Scaling from molecular mechanisms to ecological outcomes

Diverse communities of fungal endophytes reside in plant tissues, where they affect and are affected by plant physiology and ecology. For these intimate interactions to form and persist, endophytes and their host plants engage in intricate systems of communication. The conversation between fungal endophytes and plant hosts ultimately dictates endophyte community composition and function and has cascading effects on plant health and plant interactions. In this review, we synthesize our current knowledge on the mechanisms and strategies of communication used by endophytic fungi and their plant hosts. We discuss the molecular mechanisms of communication that lead to organ specificity of endophytic communities and distinguish endophytes, pathogens, and saprotrophs. We conclude by offering emerging perspectives on the relevance of plant-endophyte communication to microbial community ecology and plant health and function.

Alleviating the drought stress and improving the plant resistance properties of Triticum aestivum via biopriming with aspergillus fumigatus

BACKGROUND

Wheat (Triticum aestivum L.) is one of the most widely grown and vital cereal crops, containing a high percentage of basic nutrients such as carbohydrates and proteins. Drought stress is one of the most significant limitations on wheat productivity. Due to climate change influences plant development and growth, physiological processes, grain quality, and yield. Drought stress has elicited a wide range of plant responses, namely physiological and molecular adaptations. Biopriming is one of the recent attempts to combat drought stress. Mitigating the harmful impact of abiotic stresses on crops by deploying extreme-habitat-adapted symbiotic microbes. The purpose of this study was to see how biopriming Triticum aestivum grains affected the effects of inoculating endophytic fungi Aspergillus fumigatus ON307213 isolated from stressed wheat plants in four model agricultural plants (Gemmiza-7, Sids-1, Sakha8, and Giza 168). And its viability in reducing drought stress through the use of phenotypic parameters such as root and shoot fresh and dry weight, shoot and root length, and so on. On a biochemical and physiological level, enzymatic parameters such as catalase and superoxidase dismutase are used. Total phenolics, flavonoids, and photosynthetic pigments are non-enzymatic parameters. Making use of molecular techniques such as reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

It has been found that using Aspergillus fumigatus as a biological biopriming tool can positively impact wheat plants experiencing drought stress. The total biomass of stressed wheat plants that had been bio-primed rose by more than 40% as compared to wheat plants that had not been bio-primed. A. fumigatus biopriming either increased or decreased the amount of enzymatic and non-enzymatic substances on biochemical scales, aside from the noticeable increase in photosynthetic pigment that occurs in plants that have been bio-primed and stressed. Drought-resistant genes show a biopriming influence in gene expression.

CONCLUSIONS

This is the first paper to describe the practicality of a. fumigatus biopriming and its effect on minimizing the degrading effects of drought through water limitation. It suggests the potential applications of arid habitat-adapted endophytes in agricultural systems.

The Wheat Endophyte Epicoccum layuense J4-3 Inhibits Fusarium graminearum and Enhances Plant Growth

Fungal endophytes are well-known for their ability to promote plant growth and hinder fungal diseases, including Fusarium head blight (FHB) caused by Fusarium graminearum. This study aimed to characterize the biocontrol efficacy of strain J4-3 isolated from the stem of symptomless wheat collected from Heilongjiang Province, China. It was identified as Epicoccum layuense using morphological characteristics and phylogenetic analysis of the rDNA internal transcribed spacer (ITS) and beta-tubulin (TUB). In a dual culture assay, strain J4-3 significantly inhibited the mycelial growth of F. graminearum strain PH-1 and other fungal pathogens. In addition, wheat coleoptile tests showed that lesion symptoms caused by F. graminearum were significantly reduced in wheat seedlings treated with hyphal fragment suspensions of strain J4-3 compared to the controls. Under field conditions, applying spore suspensions and culture filtrates of strain J4-3 with conidial suspensions of F. graminearum on wheat spikes resulted in the significant biocontrol efficacy of FHB. In addition, wheat seedlings previously treated with spore suspensions of strain J4-3 before sowing successfully resulted in FHB reduction after the application of conidial suspensions of F. graminearum at anthesis. More importantly, wheat seedlings treated with hyphal fragments and spore suspensions of strain J4-3 showed significant increases in wheat growth compared to the controls under greenhouse and field conditions. Overall, these findings suggest that E. layuense J4-3 could be a promising biocontrol agent (BCA) against F. graminearum, causing FHB and a growth-promoting fungus in wheat.

Current Scenario and Future Prospects of Endophytic Microbes: Promising Candidates for Abiotic and Biotic Stress Management for Agricultural and Environmental Sustainability

Globally, substantial research into endophytic microbes is being conducted to increase agricultural and environmental sustainability. Endophytic microbes such as bacteria, actinomycetes, and fungi inhabit ubiquitously within the tissues of all plant species without causing any harm or disease. Endophytes form symbiotic relationships with diverse plant species and can regulate numerous host functions, including resistance to abiotic and biotic stresses, growth and development, and stimulating immune systems. Moreover, plant endophytes play a dominant role in nutrient cycling, biodegradation, and bioremediation, and are widely used in many industries. Endophytes have a stronger predisposition for enhancing mineral and metal solubility by cells through the secretion of organic acids with low molecular weight and metal-specific ligands (such as siderophores) that alter soil pH and boost binding activity. Finally, endophytes synthesize various bioactive compounds with high competence that are promising candidates for new drugs, antibiotics, and medicines. Bioprospecting of endophytic novel secondary metabolites has given momentum to sustainable agriculture for combating environmental stresses. Biotechnological interventions with the aid of endophytes played a pivotal role in crop improvement to mitigate biotic and abiotic stress conditions like drought, salinity, xenobiotic compounds, and heavy metals. Identification of putative genes from endophytes conferring resistance and tolerance to crop diseases, apart from those involved in the accumulation and degradation of contaminants, could open new avenues in agricultural research and development. Furthermore, a detailed molecular and biochemical understanding of endophyte entry and colonization strategy in the host would better help in manipulating crop productivity under changing climatic conditions. Therefore, the present review highlights current research trends based on the SCOPUS database, potential biotechnological interventions of endophytic microorganisms in combating environmental stresses influencing crop productivity, future opportunities of endophytes in improving plant stress tolerance, and their contribution to sustainable remediation of hazardous environmental contaminants.

Coffee-Associated Endophytes: Plant Growth Promotion and Crop Protection

Endophytic microbes are a ubiquitous group of plant-associated communities that colonize the intercellular or intracellular host tissues while providing numerous beneficial effects to the plants. All the plant species are thought to be associated with endophytes, majorly constituted with bacteria and fungi. During the last two decades, there has been a considerable movement toward the study of endophytes associated with coffee plants. In this review, the main consideration is given to address the coffee-associated endophytic bacteria and fungi, particularly their action on plant growth promotion and the biocontrol of pests. In addition, we sought to identify and analyze the gaps in the available research. Additionally, the potential of endophytes to improve the quality of coffee seeds is briefly discussed. Even though there are limited studies on the subject, the potentiality of coffee endophytes in plant growth promotion through enhancing nitrogen fixation, availability of minerals, nutrient absorption, secretion of phytohormones, and other bioactive metabolites has been well recognized. Further, the antagonistic effect against various coffee pathogenic bacteria, fungi, nematodes, and also insect pests leads to the protection of the crop. Furthermore, it is recognized that endophytes enhance the sensory characteristics of coffee as a new field of study.

Inoculation with extreme endophytes improves performance and nutritional quality in crop species grown under exoplanetary conditions

Introduction

Technological advances have made possible long space travels and even exoplanetary colonies in the future. Nevertheless, the success of these activities depends on our ability to produce edible plants in stressful conditions such as high radiation, extreme temperatures and low oxygen levels. Since beneficial microorganisms, such as fungal endophytes from extreme environments, have helped agriculture cope with those difficulties, endophytic fungi may be a putative tool to ensure plant growth under exoplanetary conditions. Additionally, growing crops in polyculture has been shown to increase productivity and spatial efficiency, which is essential given the likely space restrictions in such conditions.

Methods

We evaluated the effect of the inoculation with a mix of two fungal endophytes from the Atacama Desert on performance (survival and biomass) and nutritional quality of three crop species (lettuce, chard and spinach) grown under exoplanetary conditions. In addition, we measured the amount of antioxidants (flavonoids and phenolics) as possible mechanisms to cope with such abiotic conditions. The exoplanetary conditions were; high UV radiation, low temperature, low water availability, and low oxygen levels. These crops were put in growing chambers in monoculture, dual culture and polyculture (the three species in the same pot) for 30 days.

Results and Discussion

Our results show that inoculation with extreme endophytes improved survival by ca. 15 - 35% and biomass by ca. 30 - 35% in all crop species. The most evident increase was when grown in polyculture, except for survival in spinach, where inoculated plants had higher survival only in dual culture. Nutritional quality and the amount of the antioxidant compounds antioxidants increased in all crop species when inoculated with the endophytes. Overall, fungal endophytes isolated from extreme environments such as the Atacama Desert, the driest desert in the world, could be a key biotechnological tool for future space agriculture, helping plants cope with environmental stress. Additionally, inoculated plants should be grown in polyculture to increase crop turnover and space-use efficiency. Lastly, these results provide useful insights to face the future challenges of space-farming.

Biostimulation of tomato growth and biocontrol of Fusarium wilt disease using certain endophytic fungi

BACKGROUND

Tomato plant (Solanum lycopersicum L.) suffers from numerous fungal pathogens that cause damage to yeild production qualitatively and quantitatively. One of the most destructive disease of tomato is Fusarium wilt that caused by soil borne fungus called F. oxysporum.

METHODS

In this study, the anti-Fusarium capabilities of the foliar application of fungal endophytes extracts have been investigated on tomato under Fusarium challenges. Antifungal assay, inhibition of conidial germination, disease severity, photosynthetic pigments, osmolytes, secondary metabolites, oxidative stress, peroxidase (POD) and polyphenol oxidases (PPO) isozymes were tested for potential resistance of tomato growing under Fusarium infection.

RESULTS

Ethyl acetate extracts of A. flavus MZ045563, A. fumigatus MZ045562 and A. nidulans MZ045561 exhibited antifungal activity toward F. oxysporum where inhibition zone diameters were 15, 12 and 20 mm, respectively. Moreover, extracts of all fungal isolates at concentration 7.5 mg/mL reduced conidia germination from 94.4 to 100%. Fusarium infection caused a destructive effects on tomato plant, high severity desiese index 84.37%, reduction in growth parameters, photosynthetic pigments, and soluble protein. However, contents of proline, total phenol, malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and antioxidant enzymes activity were increased in tomato plants grown under Fusarium wilt. Treatment of healthy or infected tomato plants by ethyl acetate fungal extracts showed improvements in morphological traits, photosynthetic pigments, osmolytes, total phenol and antioxidant enzymes activity. Besides, the harmful impacts of Fusarium wilt disease on tomato plants have also been reduced by lowering MDA and H₂O₂ levels. Also, treated tomato plants showed different responses in number and density of POD and PPO isozymes.

CONCLUSION

It could be suggested that application of ethyl acetate extracts of tested fungal endophytes especially combination of A. flavus, A. nidulans and A. fumigatus could be commercially used as safe biostimulation of tomato plants as well as biofungicide against tomato Fusarium wilt disease.

Unveiling chlorpyrifos mineralizing and tomato plant-growth activities of Enterobacter sp. strain HSTU-ASh6 using biochemical tests, field experiments, genomics, and in silico analyses

The chlorpyrifos-mineralizing rice root endophyte Enterobacter sp. HSTU-ASh6 strain was identified, which enormously enhanced the growth of tomato plant under epiphytic conditions. The strain solubilizes phosphate and grew in nitrogen-free Jensen's medium. It secreted indole acetic acid (IAA; 4.8 mg/mL) and ACC deaminase (0.0076 μg/mL/h) and hydrolyzed chlorpyrifos phosphodiester bonds into 3,5,6-trichloro-2-pyridinol and diethyl methyl-monophosphate, which was confirmed by Gas Chromatography - Tandem Mass Spectrometry (GC-MS/MS) analysis. In vitro and in silico (ANI, DDH, housekeeping genes and whole genome phylogenetic tree, and genome comparison) analyses confirmed that the strain belonged to a new species of Enterobacter. The annotated genome of strain HSTU-ASh6 revealed a sets of nitrogen-fixing, siderophore, acdS, and IAA producing, stress tolerance, phosphate metabolizing, and pesticide-degrading genes. The 3D structure of 28 potential model proteins that can degrade pesticides was validated, and virtual screening using 105 different pesticides revealed that the proteins exhibit strong catalytic interaction with organophosphorus pesticides. Selected docked complexes such as α/β hydrolase-crotoxyphos, carboxylesterase-coumaphos, α/β hydrolase-cypermethrin, α/β hydrolase-diazinon, and amidohydrolase-chlorpyrifos meet their catalytic triads in visualization, which showed stability in molecular dynamics simulation up to 100 ns. The foliar application of Enterobacter sp. strain HSTU-ASh6 on tomato plants significantly improved their growth and development at vegetative and reproductive stages in fields, resulting in fresh weight and dry weight was 1.8-2.0-fold and 1.3-1.6-fold higher in where urea application was cut by 70%, respectively. Therefore, the newly discovered chlorpyrifos-degrading species Enterobacter sp. HSTU-ASh6 could be used as a smart biofertilizer component for sustainable tomato cultivation.

The Neuroprotective Potential of Endophytic Fungi and Proposed Molecular Mechanism: A Current Update

Millions of people are affected by neuronal disorders that are emerging as a principal cause of death after cancer. Alzheimer's disease, ataxia, Parkinson's disease, multiple system atrophy, and autism comprise the most common ones, being accompanied by loss of cognitive power, impaired balance, and movement. In past decades, natural polyphenols obtained from different sources including bacteria, fungi, and plants have been utilized in the traditional system of medicine for the treatment of several ailments. Endophytes are one such natural producer of secondary metabolites, namely, polyphenols, which exhibit strong abilities to assist in the management of such affections, through modifying multiple therapeutic targets and weaken their complex physiology. Limited research has been conducted in detail on bioactive compounds present in the endophytic fungi and their neuroprotective effects. Therefore, this review aims to provide an update on scientific evidences related to the pharmacological and clinical potential along with proposed molecular mechanism of action of endophytes for neuronal protection.

Acrophialophora jodhpurensis: an endophytic plant growth promoting fungus with biocontrol effect against Alternaria alternata

In this study, efficiency of the endophytic fungal isolate Msh5 was evaluated on promoting tomato plant growth and controlling Alternaria alternata, the causal agent of early blight in tomatoes. Morphological and molecular (ITS and tub2 sequences) analyses revealed that the fungal isolate, Msh5, was Acrophialophora jodhpurensis (Chaetomium jodhpurense Lodha). This beneficial fungus was capable of producing indole-3-acetic acid (IAA), urease, siderophore, extracellular enzymes, and solubilized phosphate. Under laboratory conditions, the Msh5 isolate of A. jodhpurensis inhibited A. alternata growth in dual culture, volatile and non-volatile metabolites assays. The supernatant of this endophytic fungus was capable of reducing spore germination and altering the hyphal structure of A. alternata and the spores produced germ tubes showed vacuolization and abnormal structure compared to the control. Also, the effect of A. jodhpurensis on plant growth parameters (such as shoot and root weight and length) and suppressing A. alternata was investigated in vivo via seed inoculation with spores of A. jodhpurensis using 1% sugar, 0.5% carboxymethyl cellulose (CMC) or 0.5% molasses solution as stickers. Colonization of tomato roots by the endophytic fungus resulted in significant increasing plant growth parameters and reduction in the progress of the diseases caused by A. alternata compared to the controls. Among the different coating materials used as stickers, sugar was found to be the most effective for enhancing plant growth parameters and decreasing the disease progress. Therefore, A. jodhpurensis isolate Msh5 can be suggested as a potential biofertilizer and biocontrol agent for protecting tomato plants against A. alternata.

Living Fungi in an Opencast Limestone Mine: Who Are They and What Can They Do?

Opencast limestone mines or limestone quarries are considered challenging ecosystems for soil fungi as they are highly degraded land with specific conditions, including high temperature, prolonged sunlight exposure, and a lack of organic matter, moisture, and nutrients in soil. In such ecosystems, certain fungi can survive and have a crucial function in maintaining soil ecosystem functions. Unfortunately, we know very little about taxonomic diversity, potential functions, and the ecology of such fungi, especially for a limestone quarry in a tropical region. Here, we characterized and compared the living soil fungal communities in an opencast limestone mine, including mining site and its associated rehabilitation site (9 months post-rehabilitation), with the soil fungal community in a reference forest, using the amplicon sequencing of enrichment culture. Our results showed that living fungal richness in the quarry areas was significantly lower than that in the reference forest, and their community compositions were also significantly different. Living fungi in the mining sites mostly comprised of Ascomycota (Eurotiomycetes and Sordariomycetes) with strongly declined abundance or absence of Basidiomycota and Mucoromycota. After nine months of rehabilitation, certain taxa were introduced, such as Hypoxylon spp. and Phellinus noxius, though this change did not significantly differentiate fungal community composition between the mining and rehabilitation plots. The majority of fungi in these plots are classified as saprotrophs, which potentially produce all fifteen soil enzymes used as soil health indicators. Network analysis, which was analyzed to show insight into complex structures of living fungal community in the limestone quarry, showed a clear modular structure that was significantly impacted by different soil properties. Furthermore, this study suggests potential taxa that could be useful for future rehabilitation.

Overview of biofertilizers in crop production and stress management for sustainable agriculture

With the increase in world population, the demography of humans is estimated to be exceeded and it has become a major challenge to provide an adequate amount of food, feed, and agricultural products majorly in developing countries. The use of chemical fertilizers causes the plant to grow efficiently and rapidly to meet the food demand. The drawbacks of using a higher quantity of chemical or synthetic fertilizers are environmental pollution, persistent changes in the soil ecology, physiochemical composition, decreasing agricultural productivity and cause several health hazards. Climatic factors are responsible for enhancing abiotic stress on crops, resulting in reduced agricultural productivity. There are various types of abiotic and biotic stress factors like soil salinity, drought, wind, improper temperature, heavy metals, waterlogging, and different weeds and phytopathogens like bacteria, viruses, fungi, and nematodes which attack plants, reducing crop productivity and quality. There is a shift toward the use of biofertilizers due to all these facts, which provide nutrition through natural processes like zinc, potassium and phosphorus solubilization, nitrogen fixation, production of hormones, siderophore, various hydrolytic enzymes and protect the plant from different plant pathogens and stress conditions. They provide the nutrition in adequate amount that is sufficient for healthy crop development to fulfill the demand of the increasing population worldwide, eco-friendly and economically convenient. This review will focus on biofertilizers and their mechanisms of action, role in crop productivity and in biotic/abiotic stress tolerance.

Is Endophytic Colonization of Host Plants a Method of Alleviating Drought Stress? Conceptualizing the Hidden World of Endophytes

In the wake of changing climatic conditions, plants are frequently exposed to a wide range of biotic and abiotic stresses at various stages of their development, all of which negatively affect their growth, development, and productivity. Drought is one of the most devastating abiotic stresses for most cultivated crops, particularly in arid and semiarid environments. Conventional breeding and biotechnological approaches are used to generate drought-tolerant crop plants. However, these techniques are costly and time-consuming. Plant-colonizing microbes, notably, endophytic fungi, have received increasing attention in recent years since they can boost plant growth and yield and can strengthen plant responses to abiotic stress. In this review, we describe these microorganisms and their relationship with host plants, summarize the current knowledge on how they “reprogram” the plants to promote their growth, productivity, and drought tolerance, and explain why they are promising agents in modern agriculture.

Fungal endophytes from salt-adapted plants confer salt tolerance and promote growth in wheat (Triticum aestivum L.) at early seedling stage

With increasing human global population, increased yield under saline conditions is a desirable trait for major food crops. Use of endophytes, isolated from halophytic hosts, seems to be an exciting approach for conferring salt tolerance to a salt-sensitive crop. Therefore, in the current study, fungal endophytes were isolated from halophytic plants' roots and their ability to withstand in vitro salt stress was evaluated. The fungal endophytes could withstand up to 1M NaCl concentrations and this tolerance was independent of their host or tissue source. When inoculated on salt-sensitive wheat seeds/seedlings, several of the endophytes showed a positive impact on germination and biomass-related parameters upon salt stress, both in vitro and under glasshouse conditions. One of the isolates from dicot plants (identified as Microsphaeropsis arundinis) could successfully colonize wheat and promote its growth under salt and no-salt conditions. Amongst the fungal isolates that are known to be natural endophytes of wheat, Chaetomium globosum was the best performing isolate and has previously been reported to be an effective biocontrol agent. Based on the results of our preliminary study, we suggest that these fungal endophytes could prove beneficial for enhancing the salt stress tolerance of wheat crop.

Symbiotic Modulation as a Driver of Niche Expansion of Coastal Plants in the San Juan Archipelago of Washington State

Modern evolutionary theory and population genetics posit that adaptation and habitat expansion of plants result from processes exclusive to their genomes. Here, we present studies showing that plants can grow across complex habitat gradients by modulating symbiotic associations with Class 2 fungal endophytes. Endophyte analysis of three native (Leymus mollis, Distichlis spicata, and Salicornia pacifica) and one invasive (Spartina anglica) plant growing across adjacent microhabitats in the San Juan Archipelago altered associations with Class 2 fungal endophytes in response to soil salinity levels. At the microhabitat interfaces where the gradation of salinity varied, the plants were colonized by endophytes from both microhabitats. A reciprocal transplant study along a salt gradient demonstrated that Leymus mollis (dunegrass) required endophytes indigenous to each microhabitat for optimal fitness and/or survival. In contrast, when dunegrass and Grindelia integrifolia (gumweed) were found growing in low salinity, but high drought habitats, these plant species had their own unique dominant endophyte association regardless of geographic proximity and conferred drought but not high salt stress tolerance. Modulation of endophyte abundance occurred in planta based on the ability of the symbiont to confer tolerance to the stress imposed on plants. The ability of an endophyte to confer appropriate stress tolerance resulted in a significant increase of in planta fungal abundance. Conversely, the inability of an endophyte to confer stress tolerance resulted in a decrease of in planta fungal abundance. Our studies indicate that Class 2 fungal endophytes can provide a symbiotic mechanism for niche expansion and phenotypic plasticity across environmental gradients.

Plant Tolerance to Drought Stress in the Presence of Supporting Bacteria and Fungi: An Efficient Strategy in Horticulture

Increasing temperature leads to intensive water evaporation, contributing to global warming and consequently leading to drought stress. These events are likely to trigger modifications in plant physiology and microbial functioning due to the altered availability of nutrients. Plants exposed to drought have developed different strategies to cope with stress by morphological, physiological, anatomical, and biochemical responses. First, visible changes influence plant biomass and consequently limit the yield of crops. The presented review was undertaken to discuss the impact of climate change with respect to drought stress and its impact on the performance of plants inoculated with plant growth-promoting microorganisms (PGPM). The main challenge for optimal performance of horticultural plants is the application of selected, beneficial microorganisms which actively support plants during drought stress. The most frequently described biochemical mechanisms for plant protection against drought by microorganisms are the production of phytohormones, antioxidants and xeroprotectants, and the induction of plant resistance. Rhizospheric or plant surface-colonizing (rhizoplane) and interior (endophytic) bacteria and fungi appear to be a suitable alternative for drought-stress management. Application of various biopreparations containing PGPM seems to provide hope for a relatively cheap, easy to apply and efficient way of alleviating drought stress in plants, with implications in productivity and food condition.

The Potential Application of Endophytes in Management of Stress from Drought and Salinity in Crop Plants

Endophytic microorganisms present inside the host plant play an essential role in host fitness, nutrient supply and stress tolerance. Endophytes are often used in sustainable agriculture as biofertilizers, biopesticides and as inoculants to mitigate abiotic stresses including salinity, drought, cold and pH variation in the soil. In changing climatic conditions, abiotic stresses create global challenges to achieve optimum crop yields in agricultural production. Plants experience stress conditions that involve endogenous boosting of their immune system or the overexpression of their defensive redox regulatory systems with increased reactive oxygen species (ROS). However, rising stress factors overwhelm the natural redox protection systems of plants, which leads to massive internal oxidative damage and death. Endophytes are an integral internal partner of hosts and have been shown to mitigate abiotic stresses via modulating local or systemic mechanisms and producing antioxidants to counteract ROS in plants. Advancements in omics and other technologies have been made, but potential application of endophytes remains largely unrealized. In this review article, we will discuss the diversity, population and interaction of endophytes with crop plants as well as potential applications in abiotic stress management.

Enhancement of Seawater Stress Tolerance in Barley by the Endophytic Fungus Aspergillus ochraceus

Symbiotic plant-fungi interaction is a promising approach to alleviate salt stress in plants. Moreover, endophytic fungi are well known to promote the growth of various crop plants. Herein, seven fungal endophytes were screened for salt tolerance; the results revealed that Aspergillus ochraceus showed a great potentiality in terms of salt tolerance, up to 200 g L⁻¹. The indole acetic acid (IAA) production antioxidant capacity and antifungal activity of A. ochraceus were evaluated, in vitro, under two levels of seawater stress, 15 and 30% (v/v; seawater/distilled water). The results illustrated that A. ochraceus could produce about 146 and 176 µg mL⁻¹ IAA in 15 and 30% seawater, respectively. The yield of IAA by A. ochraceus at 30% seawater was significantly higher at all tryptophan concentrations, as compared with that at 15% seawater. Moreover, the antioxidant activity of ethyl acetate extract of A. ochraceus (1000 µg mL⁻¹) at 15 and 30% seawater was 95.83 ± 1.25 and 98.33 ± 0.57%, respectively. Crude extracts of A. ochraceus obtained at 15 and 30% seawater exhibited significant antifungal activity against F. oxysporum, compared to distilled water. The irrigation of barley plants with seawater (15 and 30%) caused notable declines in most morphological indices, pigments, sugars, proteins, and yield characteristics, while increasing the contents of proline, malondialdehyde, and hydrogen peroxide and the activities of antioxidant enzymes. On the other hand, the application of A. ochraceus mitigated the harmful effects of seawater on the growth and physiology of barley plants. Therefore, this study suggests that the endophytic fungus A. ochraceus MT089958 could be applied as a strategy for mitigating the stress imposed by seawater irrigation in barley plants and, therefore, improving crop growth and productivity.