Application of Plant-Growth-Promoting Fungi Trichoderma longibrachiatum T6 Enhances Tolerance of Wheat to Salt Stress through Improvement of Antioxidative Defense System and Gene Expression

Alleviation potential of green-synthesized selenium nanoparticles for cadmium stress in Solanum lycopersicum L: modulation of secondary metabolites and physiochemical attributes

KEY MESSAGE

Selenium nanoparticles reduce cadmium absorption in tomato roots, mitigating heavy metal effects. SeNPs can efficiently help to enhance growth, yield, and biomolecule markers in cadmium-stressed tomato plants. In the present study, the effects of selenium nanoparticles (SeNPs) were investigated on the tomato plants grown in cadmium-contaminated soil. Nanoparticles were synthesized using water extract of Nigella sativa and were characterized for their size and shape. Two application methods (foliar spray and soil drench) with nanoparticle concentrations of 0, 100, and 300 mg/L were used to observe their effects on cadmium-stressed plants. Growth, yield, biochemical, and stress parameters were studied. Results showed that SeNPs positively affected plant growth, mitigating the negative effects of cadmium stress. Shoot length (SL), root length (RL), number of branches (NB), number of leaves per plant (NL), and leaf area (LA) were significantly reduced by cadmium stress but enhanced by 45, 51, 506, 208, and 82%, respectively, by soil drench treatment of SeNPs. Similarly, SeNPs increased the fruit yield (> 100%) and fruit weight (> 100%), and decreased the days to fruit initiation in tomato plants. Pigments were also positively affected by the SeNPs, particularly in foliar treatment. Lycopene content was also enhanced by the addition of NPs (75%). Furthermore, the addition of SeNPs improved the ascorbic acid, protein, phenolic, flavonoid, and proline contents of the tomato plants under cadmium stress, whereas stress enzymes also showed enhanced activities under cadmium stress. It is concluded from the present study that the addition of selenium nanoparticles enhanced the growth and yield of Cd-stressed plants by reducing the absorption of cadmium and increasing the stress management of plants.

Halotolerant and plant growth-promoting endophytic fungus Aspergillus terreus CR7 alleviates salt stress and exhibits genoprotective effect in Vigna radiata

Soil salinity is one of the major environmental stresses that results in reduction of cultivable land and decreased productivity. In the present study, halotolerant and plant growth-promoting endophytic fungi were isolated from Catharanthus roseus, and their effect in mitigating salt stress in Vigna radiata was evaluated. An isolate CR7, identified to be Aspergillus terreus, showing plant growth promotion activities, viz. IAA production (23.43 ± 0.79 μg/ml), phosphate solubilization (133.63 ± 6.40 μg/ml), ACC deaminase activity (86.36 ± 2.70 μmol α-ketobutyrate/h/mg protein) etc. and ability to grow at 15% NaCl was selected for further in vivo studies. Colonization of CR7 was carried out in V. radiata which was subjected to different concentrations of salt (150, 200, and 250 mM NaCl). Under salt stress, A. terreus CR7 inoculated plants showed substantially improved root and shoot length, biomass, chlorophyll content, relative water content, phenolics, protein content, and DPPH scavenging activity. Endogenous IAA level was enhanced by 5.28-fold in treated plants at maximum salt stress. Inoculation of A. terreus CR7 affected oxidative stress parameters, exhibiting an increase in catalase and superoxide dismutase and reduction in proline, electrolyte leakage, and malondialdehyde content. Fluorescent microscopic analysis of roots revealed improved cell viability and decreased levels of glutathione and hydrogen peroxide under salt stress in treated plants. The isolate A. terreus CR7 also protected against DNA damage induced by salt stress which was evaluated using comet assay. A decrease in DNA tail length, tail moment, and olive tail moment to the extent of 19.87%, 19.76%, and 24.81%, respectively, was observed in A. terreus CR7-colonized plants under salt stress. It can be concluded that A. terreus CR7 can be exploited for alleviating the impact of salt stress in crop plants.

Endophytic colonization of five Trichoderma species and their effects on growth of a Eucalyptus hybrid

The study aimed to evaluate the effectiveness of endophytic colonization via leaf and root inoculation of five Trichoderma species in a Eucalyptus hybrid, as well as the effects of inoculation on plant growth. The experimental design was completely randomized in a 6 × 2 factorial scheme. Plant growth was evaluated during the experimental period at three different times: 20 days after inoculation (d.a.i), 40 d.a.i., and 60 d.a.i. A statistical difference was observed between the inoculation methods during each period and between the Trichoderma species. Plants inoculated with T. asperellum showed the greatest growth among the treatments. Root-inoculated plants produced the greatest growth response. This showed that the presence of Trichoderma in the roots assisted in nutrient assimilation, promoted greater plant growth, when compared with leaf-inoculated plants. Evaluation of the effectiveness of endophytic colonization was performed at each sampling period by collecting leaf samples, and at 60 d.a.i., by collecting leaf, stem, and root samples. T. longibrachiatum and T. harzianum were isolated from leaves at 20 d.a.i., with an increase in the number of colonized plants throughout the evaluation of leaf-inoculated plants. In root-inoculated plants, treatment with T. longibrachiatum, T. harzianum, and T. asperellum presented the highest endophytic colonization in the stem and root samples (at 60 d.a.i.).

Partial substitution of chemical fertilizer by Trichoderma biofertilizer improved nitrogen use efficiency in wolfberry (Lycium chinense) in coastal saline land

A two-year field trial was conducted to investigate the effects of partial substitution of chemical fertilizer (CF) by Trichoderma biofertilizer (TF) on nitrogen (N) use efficiency and associated mechanisms in wolfberry (Lycium chinense) in coastal saline land. As with plant biomass and fruit yield, apparent N use efficiency and plant N accumulation were also higher with TF plus 75% CF than 100% CF, indicating that TF substitution promoted plant growth and N uptake. As a reason, TF substitution stabilized soil N supply by mitigating steep deceases in soil NH4 +-N and NO3 -N concentrations in the second half of growing seasons. TF substitution also increased carbon (C) fixation according to higher photosynthetic rate (Pn) and stable 13C abundance with TF plus 75% CF than 100% CF. Importantly, leaf N accumulation significantly and positively related with Pn, biomass, and fruit yield, and structural equation modeling also confirmed the importance of the causal relation of N accumulation coupled with C fixation for biomass and yield formation. Consequently, physiological and agronomical N use efficiencies were significantly higher with TF plus 75% CF than 100% CF. Overall, partial substitution of CF by TF improved N use efficiency in wolfberry in coastal saline land by stabilizing soil N supply and coupling N accumulation with C fixation.

Effect of Metarhizium anisopliae (MetA1) on growth enhancement and antioxidative defense mechanism against Rhizoctonia root rot in okra

Rhizoctonia solani is an important necrotrophic pathogenic fungus that causes okra root disease and results in severe yield reduction. Many biocontrol agents are being studied with the intent of improving plant growth and defense systems and reducing crop loss by preventing fungal infections. Recently, a member of the Hypocrealean family, Metarhizium anisopliae, has been reported for insect pathogenicity, endophytism, plant growth promotion, and antifungal potentialities. This research investigated the role of M. anisopliae (MetA1) in growth promotion and root disease suppression in okra. The antagonism against R. solani and the plant growth promotion traits of MetA1 were tested in vitro. The effects of endophytic MetA1 on promoting plant growth and disease suppression were assessed in planta. Dual culture and cell-free culture filtrate assays showed antagonistic activity against R. solani by MetA1. Some plant growth promotion traits, such as phosphate solubilization and catalase activity were also exhibited by MetA1. Seed primed with MetA1 increased the shoot, root, leaves, chlorophyll content, and biomass content compared to control okra plants. The plants challenged with R. solani showed the highest hydrogen peroxide (H2O2) and lipid peroxidation (MDA) contents in the leaves of okra. Whereas MetA1 applied plants showed a reduction of H2O2 and MDA by 5.21 and 14.96%, respectively, under pathogen-inoculated conditions by increasing antioxidant enzyme activities, including catalase (CAT), peroxidase (POD), glutathione S-transferase (GST), and ascorbate peroxidase (APX), by 30.11, 10.19, 5.62, and 5.06%, respectively. Moreover, MetA1 increased soluble sugars, carbohydrates, proline, and secondary metabolites, viz., phenol and flavonoid contents in okra resulting in a better osmotic adjustment of diseases infecting plants. MetA1 reduced disease incidence by 58.33% at 15 DAI compared to the R. solani inoculated plant. The results revealed that MetA1 improved plant growth, elevated the plant defense system, and suppressed root diseases caused by R. solani. Thus, MetA1 was found to be an effective candidate for the biological control program.

Priming of Citrullus lanatus var. Colocynthoides seeds in seaweed extract improved seed germination, plant growth and performance under salinity conditions

Citrullus lanatus var. Colocynthoide "Gurum" is an unconventional crop that can be utilized as a new source of edible oil and has the ability to grow in a variety of harsh conditions. To mitigate the adverse effects of salinity on seed germination and plant performance of C. lanatus, seeds were primed in the aqueous extracts of the seaweed Ulva lactuca before planting under greenhouse conditions. The aqueous extract of U. lactuca at 8% w/v led to maximal seed germination percentage and seedling growth of C. lanatus. Moreover, U. lactuca extract counteracted the negative effects of salt stress on the plant by significantly increasing the activity of SOD, CAT, and POD. The bioactive components of U. lactuca, e.g. glycine betaine and phenolic compounds can account for such beneficial role of algal extract on C. lanatus. Thus, priming of C. lanatus seeds in U. lactuca extract with various concentrations of U. lactuca extract can be employed as an effective practice for successful seed germination, improved plant growth and enhanced salt resistance, probably as a result of increased antioxidant enzymes activity and photosynthetic pigments.

Dual RNA-Seq Profiling Unveils Mycoparasitic Activities of Trichoderma atroviride against Haploid Armillaria ostoyae in Antagonistic Interaction Assays

Armillaria ostoyae, a species among the destructive forest pathogens from the genus Armillaria, causes root rot disease on woody plants worldwide. Efficient control measures to limit the growth and impact of this severe underground pathogen are under investigation. In a previous study, a new soilborne fungal isolate, Trichoderma atroviride SZMC 24276 (TA), exhibited high antagonistic efficacy, which suggested that it could be utilized as a biocontrol agent. The dual culture assay results indicated that the haploid A. ostoyae-derivative SZMC 23085 (AO) (C18/9) is highly susceptible to the mycelial invasion of TA. In the present study, we analyzed the transcriptome of AO and that of TA in in vitro dual culture assays to test the molecular arsenal of Trichoderma antagonism and the defense mechanisms of Armillaria. We conducted time-course analysis and functional annotation and analyzed enriched pathways and differentially expressed genes including biocontrol-related candidate genes from TA and defense-related candidate genes from AO. The results indicated that TA deployed several biocontrol mechanisms when confronted with AO. In response, AO initiated multiple defense mechanisms to protect against the fungal attack. To our knowledge, the present study offers the first transcriptome analysis of a biocontrol fungus attacking AO. Overall, this study provides insights that aid the further exploration of plant pathogen-biocontrol agent interaction mechanisms. IMPORTANCE Armillaria species can survive for decades in the soil on dead woody debris, develop rapidly under favorable conditions, and harmfully infect newly planted forests. Our previous study found Trichoderma atroviride to be highly effective in controlling Armillaria growth; therefore, our current work explored the molecular mechanisms that might play a key role in Trichoderma-Armillaria interactions. Direct confrontation assays combined with time course-based dual transcriptome analysis provided a reliable system for uncovering the interactive molecular dynamics between the fungal plant pathogen and its mycoparasitic partner. Furthermore, using a haploid Armillaria isolate allowed us to survey the deadly prey-invading activities of the mycoparasite and the ultimate defensive strategies of its prey. Our current study provides detailed insights into the essential genes and mechanisms involved in Armillaria defense against Trichoderma and the genes potentially involved in the efficiency of Trichoderma to control Armillaria. In addition, using a sensitive haploid Armillaria strain (C18/9), with its complete genome data already available, also offers the opportunity to test possible variable molecular responses of Armillaria ostoyae toward diverse Trichoderma isolates with various biocontrol abilities. Initial molecular tests of the dual interactions may soon help to develop a targeted biocontrol intervention with mycoparasites against plant pathogens.

New seed coating containing Trichoderma viride with anti-pathogenic properties

Background

To ensure food security in the face of climate change and the growing world population, multi-pronged measures should be taken. One promising approach uses plant growth-promoting fungi (PGPF), such as Trichoderma, to reduce the usage of agrochemicals and increase plant yield, stress tolerance, and nutritional value. However, large-scale applications of PGPF have been hampered by several constraints, and, consequently, usage on a large scale is still limited. Seed coating, a process that consists of covering seeds with low quantities of exogenous materials, is gaining attention as an efficient and feasible delivery system for PGPF.

Methods

We have designed a new seed coating composed of chitin, methylcellulose, and Trichoderma viride spores and assessed its effect on canola (Brassica napus L.) growth and development. For this purpose, we analyzed the antifungal activity of T. viride against common canola pathogenic fungi (Botrytis cinerea, Fusarium culmorum, and Colletotrichum sp.). Moreover, the effect of seed coating on germination ratio and seedling growth was evaluated. To verify the effect of seed coating on plant metabolism, we determined superoxide dismutase (SOD) activity and expression of the stress-related RSH (RelA/SpoT homologs).

Results

Our results showed that the T. viride strains used for seed coating significantly restricted the growth of all three pathogens, especially F. culmorum, for which the growth was inhibited by over 40%. Additionally, the new seed coating did not negatively affect the ability of the seeds to complete germination, increased seedling growth, and did not induce the plant stress response. To summarize, we have successfully developed a cost-effective and environmentally responsible seed coating, which will also be easy to exploit on an industrial scale.

Inoculation with Azorhizobium caulinodans ORS571 enhances plant growth and salt tolerance of switchgrass (Panicum virgatum L.) seedlings

BACKGROUND

Switchgrass (Panicum virgatum L.) is an important biofuel crop that may contribute to replacing petroleum fuels. However, slow seedling growth and soil salinization affect the growth and development of switchgrass. An increasing number of studies have shown that beneficial microorganisms promote plant growth and increase tolerance to salinity stress. However, the feasibility of inoculating switchgrass with Azorhizobium caulinodans ORS571 to enhance the growth and salt tolerance of its seedlings is unclear. Our previous study showed that A. caulinodans ORS571 could colonize wheat (Triticum aestivum L.) and thereby promote its growth and development and regulate the gene expression levels of microRNAs (miRNAs).

RESULTS

In this study, we systematically studied the impact of A. caulinodans ORS571 on switchgrass growth and development and the response to salinity stress; we also studied the underlying mechanisms during these biological processes. Inoculation with A. caulinodans ORS571 significantly alleviated the effect of salt stress on seedling growth. Under normal conditions, A. caulinodans ORS571 significantly increased fresh plant weight, chlorophyll a content, protein content, and peroxidase (POD) activity in switchgrass seedlings. Under salt stress, the fresh weight, dry weight, shoot and root lengths, and chlorophyll contents were all significantly increased, and some of these parameters even recovered to normal levels after inoculation with A. caulinodans ORS571. Soluble sugar and protein contents and POD and superoxide dismutase (SOD) activities were also significantly increased, contrary to the results for proline. Additionally, A. caulinodans ORS571 may alleviate salt stress by regulating miRNAs. Twelve selected miRNAs were all upregulated to different degrees under salt stress in switchgrass seedlings. However, the levels of miR169, miR171, miR319, miR393, miR535, and miR854 were decreased significantly after inoculation with A. caulinodans ORS571 under salt stress, in contrast to the expression level of miR399.

CONCLUSION

This study revealed that A. caulinodans ORS571 increased the salt tolerance of switchgrass seedlings by increasing their water content, photosynthetic efficiency, osmotic pressure maintenance, and reactive oxygen species (ROS) scavenging abilities and regulating miRNA expression. This work provides a new, creative idea for improving the salt tolerance of switchgrass seedlings.

Alleviation of the adverse effects of NaCl stress on tomato seedlings (Solanum lycopersicum L.) by Trichoderma viride through the antioxidative defense system

BACKGROUND

Trichoderma viride are well known for their biocontrol capabilities, but little is known about how they stimulate plant development and increase their resistance to salt stress. One of the main abiotic factors limiting crop development and yield is salt stress. Therefore, the purpose of this work was to ascertain how NaCl effects on T. viride growth as well as on the seedlings morphological and physio-biochemical parameters of tomato (Solanum lycopersicum L.) under plate culture conditions. Additionally, a pot experiment was conducted to determine how T. viride affected the development characteristics of tomato plants subjected to various salt concentrations (50 and 100 mM NaCl). T. viride's contribution to tomato seedling stress tolerance was also closely examined.

RESULTS

Results showed that 100 mM NaCl decreased the colony diameter of T. viride by 13.4% compared to the control. Under plate and greenhouse conditions, tomato seedlings exposed to salt exposure exhibited an overall decline in growth. Also, a reduction in relative water content (RWC) and protein contents occurred under salt stress. At the same time, increases were found in proline, total phenolics, flavonoids, H₂O₂ content, malondialdehyde, likewise the activities of peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), and ascorbate peroxidase (APX) enzymes. Even though, with T. viride application, the salt negative effects on both morphological and physio-biochemical parameters were mitigated to a greater extent. T. viride increased proline and total antioxidant capacity (TAC) in tomato seedlings at 100 mM NaCl by an average of 20.66 and 43.82% compared to their comparable control. T. viride increased the activities of CAT, PPO, and APX enzymes by 74.6, 58.48, and 61.61% at 50 mM NaCl compared to non-saline control seedlings. As well, T. viride decreased MDA and H₂O₂ contents by an average of 14 and 24.8% in tomato seedlings at 50 mM NaCl compared to their comparable control. Also, under 100 mM NaCl, the T. viride-treated tomato seedlings showed increased total phenolics (17.85%) and flavonoids (33.17%) compared to non- treated one.

CONCLUSION

Hence, our research sheds new insight on the pathways by which T. viride can boost tomato seedling tolerance to salt stress at morphological and physio-biochemical levels by activating both enzymatic and non-enzymatic antioxidant defense systems.

Climate change challenges, plant science solutions

Climate change is a defining challenge of the 21st century, and this decade is a critical time for action to mitigate the worst effects on human populations and ecosystems. Plant science can play an important role in developing crops with enhanced resilience to harsh conditions (e.g. heat, drought, salt stress, flooding, disease outbreaks) and engineering efficient carbon-capturing and carbon-sequestering plants. Here, we present examples of research being conducted in these areas and discuss challenges and open questions as a call to action for the plant science community.

Selenium Regulates Antioxidant, Photosynthesis, and Cell Permeability in Plants under Various Abiotic Stresses: A Review

Plant growth is affected by various abiotic stresses, including water, temperature, light, salt, and heavy metals. Selenium (Se) is not an essential nutrient for plants but plays important roles in alleviating the abiotic stresses suffered by plants. This article summarizes the Se uptake and metabolic processes in plants and the functions of Se in response to water, temperature, light, salt, and heavy metal stresses in plants. Se promotes the uptake of beneficial substances, maintains the stability of plasma membranes, and enhances the activity of various antioxidant enzymes, thus alleviating adverse effects in plants under abiotic stresses. Future research directions on the relationship between Se and abiotic stresses in plants are proposed. This article will further deepen our understanding of the relationship between Se and plants.

Improving Wheat Salt Tolerance for Saline Agriculture

Salinity is a major abiotic stress that threatens crop yield and food supply in saline soil areas. Crops have evolved various strategies to facilitate survival and production of harvestable yield under salinity stress. Wheat (Triticum aestivum L.) is the main crop in arid and semiarid land areas, which are often affected by soil salinity. In this review, we summarize the conventional approaches to enhance wheat salt tolerance, including cross-breeding, exogenous application of chemical compounds, beneficial soil microorganisms, and transgenic engineering. We also propose several new breeding techniques for increasing salt tolerance in wheat, such as identifying new quantitative trait loci or genes related to salt tolerance, gene stacking and multiple genome editing, and wheat wild relatives and orphan crops domestication. The challenges and possible countermeasures in enhancing wheat salinity tolerance are also discussed.

The Use of Mycoendophyte-Based Bioformulations to Control Apple Diseases: Toward an Organic Apple Production System in the Aurès (Algeria)

The present study aims to investigate the effectiveness of bioformulations based on endophytic fungi to control apple scab and Valsa canker disease in two orchards in the Aurès region (Algeria). In both orchards, the results showed that the treatment of senescent apple leaves by invert emulsions containing Trichoderma longibrachiatum and Chaetomium globosum harmed the ascogenesis of winter forms of Venturia inaequalis by reducing the number of ascospore-ejecting asci, the number of morphologically mature asci, and a considerable increase in the immature asci number. This antifungal activity was more essential in soil-incorporated leaves, showing the importance of the combination of treatments with cultural practices to efficiently control the apple scab disease. Furthermore, the disease incidence decreased by 52.63% and 50.68% in R'haouat and Bouhmama orchards, respectively. Moreover, the treatment of Valsa ceratosperma cankers with a biogel containing the endophytic yeast Metschnikowia sp. led to wound healing varying from 43.52% and 87.97% after 120 days but remained more considerable than conventional treatment with Folicur (tebuconazol). The current results open real opportunities concerning the implementation of eco-friendly and potent apple protection systems.

Trichoderma longibrachiatum TG1 increases endogenous salicylic acid content and antioxidants activity in wheat seedlings under salinity stress

Several studies have reported the deleterious effects of excessive salt stress on Triticum aestivum L. seedlings. Seed pretreatment with exogenous salicylic acid (SA) enhances plants to tolerate salt stress. Herein, the present study aims to investigate the potential of plant-growth-promoting fungus Trichoderma longibrachiatum (TG1) to increase the plant growth and enhance the salicylic acid (SA) contents and antioxidants activity in wheat seedlings under different concentrations of salt stress. Wheat seeds were pretreated in TG1 spore suspension before exposure to different salt stresses. Compared with 0, 50, 100, 150 salt stresses, the TG1 and NaCl increased the wheat seeds germination rate, germination potential and germination index significantly; the shoot height and root length were increased by an average of 39.45% and 29.73%, respectively. Compared to NaCl stress across the four concentrations (0, 50, 100, and 150 mM), the TG1 treated wheat seedlings increased SA concentration and phenylalanine ammonia-lyase activity (PAL) by an average of 55.87% and 24.10% respectively. In addition, the TG1+NaCl-treated seedlings increased superoxide dismutase (SOD), peroxidases (POD), and catalase (CAT) activities in the shoot by an average of 47.68%, 23.68%, and 38.65% respectively compared to NaCl-stressed seedlings. Significantly, the genes, SOD, CAT, and POD were relatively up-regulated in the salt-tolerant TG1-treated seedlings at all NaCl concentrations in comparison to the control. Wheat seedlings treated with TG1+NaCl increased the transcript levels of SOD, POD and CAT by 1.35, 1.85 and 1.04-fold at 50 mM NaCl concentration, respectively, compared with 0 mM NaCl concentration. Our results indicated that seeds pretreatment with TG1 could increase endogenous SA of plants and promote seedling growth under salt stress by improving enzymatic antioxidant activities and gene expression.

A novel PGPF Penicillium olsonii isolated from the rhizosphere of Aeluropus littoralis promotes plant growth, enhances salt stress tolerance, and reduces chemical fertilizers inputs in hydroponic system

The hydroponic farming significantly enhances the yield and enables multiple cropping per year. These advantages can be improved by using plant growth-promoting fungi (PGPF) either under normal or stress conditions. In this study, the fungal strain (A3) isolated from the rhizosphere of the halophyte plant Aeluropus littoralis was identified as Penicillium olsonii based on sequence homology of its ITS region. The A3 fungus was shown to be halotolerant (up to 1 M NaCl) and its optimal growth was at 27°C, but inhibited at 40°C. In liquid culture medium, the A3 produced indole acetic acid (IAA) especially in the presence of L-tryptophan. Tobacco plants grown under hydroponic farming system were used to evaluate the promoting activity of the direct effect of A3 mycelium (DE) and the indirect effect (IDE) of its cell-free culture filtrate (A3CFF). The results showed that for the two conditions (DE or IDE) the tobacco seedlings exhibited significant increase in their height, leaf area, dry weight, and total chlorophyll content. Interestingly, the A3CFF (added to the MS liquid medium or to nutrient solution (NS), prepared from commercial fertilizers) induced significantly the growth parameters, the proline concentration, the catalase (CAT) and the superoxide dismutase (SOD) activities of tobacco plants. The A3CFF maintained its activity even after extended storage at 4°C for 1 year. Since the A3 is a halotolerant fungus, we tested its ability to alleviate salt stress effects. Indeed, when added at 1:50 dilution factor to NS in the presence of 250 mM NaCl, the A3CFF enhanced the plant salt tolerance by increasing the levels of total chlorophyll, proline, CAT, and SOD activities. In addition, the treated plants accumulated less Na⁺ in their roots but more K⁺ in their leaves. The A3CFF was also found to induce the expression of five salt stress related genes (NtSOS1, NtNHX1, NtHKT1, NtSOD, and NtCAT1). Finally, we proved that the A3CFF can reduce by half the chemical fertilizers inputs. Indeed, the tobacco plants grown in a hydroponic system using 0.5xNS supplemented with A3CFF (1:50) exhibited significantly higher growth than those grown in 0.5xNS or 1xNS. In an attempt to explain this mechanism, the expression profile of some growth related genes (nitrogen metabolism (NR1, NRT1), auxin (TRYP1, YUCCA6-like), and brassinosteroid (DET2, DWF4) biosynthesis) was performed. The results showed that all these genes were up-regulated following plant treatment with A3CFF. In summary the results revealed that the halotolerant fungus P. olsonii can stimulates tobacco plant growth, enhances its salt tolerance, and reduces by half the required chemical fertilizer inputs in a hydroponic farming system.

Cryopreservation and germinative behavior of Passiflora spp. seeds

Cryopreservation is an interesting strategy for the long-term conservation of the seeds of the majority of cultivated plants as well as many of the corresponding wild parents. The objective of this study was to evaluate the response of the seeds of different passion fruit species to cryopreservation, as well as to apply multivariate tools to better understand the germinative behavior after thawing, to support the application and repeatability of these methods with other Passiflora species. Seeds of P. coccinea, P. edulis, P. gibertii, P. maliformis, P. morifolia, P. setacea, P. suberosa and P. tenuifila were submitted to cryopreservation, and after thawing the following variables were analyzed: emergence percentage (%); mean emergence time (days); mean emergence speed (plantlets.day-1); uncertainty (bit); and synchrony (bit). We applied multivariate analysis of variance (MANOVA) and canonical discriminant analysis (CDA) to the data. The seeds of all the species withstood the freezing well, indicating that cryopreservation is a viable alternative for long-term conservation of Passiflora genetic material. The emergence percentage, average emergence speed and average emergence time were the variables that contributed the most to separation of the species in the first canonical discriminant function (Can1). The seeds of the species studied were found to be tolerant to desiccation because they remained viable even with low water content. The results showed that seeds could be cryopreserved successfully both with and without prior desiccation.

Comparative Transcriptomics Suggests Early Modifications by Vintec® in Grapevine Trunk of Hormonal Signaling and Secondary Metabolism Biosynthesis in Response to Phaeomoniella chlamydospora and Phaeoacremonium minimum

Given their well-known antifungal abilities, species of the genus Trichoderma are of significant interest in modern agriculture. Recent studies have shown that Trichoderma species can induce plant resistance against different phytopathogens. To further extend this line of investigation, we investigate herein the transcriptomic response of grapevine trunk to Vintec^®, which is a Trichoderma atroviride SC1-based commercial formulation for biological control of grapevine trunk diseases and which reduces wood colonization. The aim of the study is to understand whether the biocontrol agent Vintec^® modifies the trunk response to Phaeoacremonium minimum and Phaeomoniella chlamydospora, which are two esca-associated fungal pathogens. An analysis of transcriptional regulation identifies clusters of co-regulated genes whose transcriptomic reprogramming in response to infection depends on the absence or presence of Vintec^®. On one hand, the results show that Vintec^® differentially modulates the expression of putative genes involved in hormonal signaling, especially those involved in auxin signaling. On the other hand, most significant gene expression modifications occur among secondary-metabolism-related genes, especially regarding phenylpropanoid metabolism and stilbene biosynthesis. Taken together, these results suggest that the biocontrol agent Vintec^® induces wood responses that counteract disease development.

Effects of Dark Septate Endophytes on the Performance and Soil Microbia of Lycium ruthenicum Under Drought Stress

In the current study, we explored the effects of dark septate endophytes (DSE) (Neocamarosporium phragmitis, Alternaria chlamydospore, and Microascus alveolaris) on the performance and rhizosphere soil microbial composition of Lycium ruthenicum Murr under drought stress. Differences in plant growth and physiological indexes, soil parameters, and microbial composition under different treatments were studied. Three DSE species could form good symbiotic relationships with L. ruthenicum plants, and the symbionts depended on DSE species and water availability. Inoculation of DSE had the greatest benefit on host plants under drought conditions. In particular, N. phragmitis and A. chlamydospore had a significant positive influence on the biomass, morphological and physiological indexes of host plants. Additionally, the content of arbuscular mycorrhiza (AM) fungi, gram-negative bacteria, and actinomycetes in the soil was significantly elevated after DSE inoculation in the absence of water. Based on a variance decomposition analysis, DSE was the most important factor affecting the growth and physiological parameters of host plants, and DSE inoculation combined with water conditions significantly affected the contents of soil microbial communities. Structural equation model (SEM) analysis showed that the positive effects of DSE on L. ruthenicum varied with DSE species and plant parameters under different water conditions. These results are helpful to understand the ecological function of DSE and its potential application in the cultivation of L. ruthenicum plants in drylands.

A Diaporthe Fungal Endophyte From a Wild Grass Improves Growth and Salinity Tolerance of Tritordeum and Perennial Ryegrass

Some microbiome components can provide functions that extend the capabilities of plants, increasing the environmental adaptability and performance of holobionts. Festuca rubra subsp. pruinosa is a perennial grass adapted to rocky sea cliffs, where soil and nutrients are very limited, and exposure to salinity is continuous. This study aimed to investigate if a Diaporthe fungal endophyte belonging to the core microbiome of Festuca rubra roots could improve the performance of two agricultural grasses. In a greenhouse experiment, plants of tritordeum (Triticum durum x Hordeum chilense) and perennial ryegrass (Lolium perenne) were inoculated with Diaporthe strain EB4 and subjected to two salinity conditions (0 and 200 mM NaCl). Biomass production, mineral elements, proline, hormone profiles, antioxidant capacity, and total phenolic compounds were examined in plants, and fungal functions potentially related to the promotion of plant growth were determined. The inoculation with Diaporthe promoted plant growth of both grasses, increasing leaf biomass (84% in tritordeum and 29% in perennial ryegrass), root biomass, nutrient content (N, Ca, Mg, and Fe), and the production of indole 3-acetic acid, regardless of the salinity treatment. Improved growth and nutrient uptake might occur because Diaporthe produces several extracellular enzymes capable of recycling organic nutrient pools. In addition, the fungus produced indole 3-acetic acid in vitro and modulated the production of this phytohormone in the plant. Under salinity, the activity of Diaporthe ameliorated the stress, increasing proline, nutrient uptake in roots, gibberellins, and indole 3-acetic acid, which in turn results into improved growth. Thus, this fungus can transfer to alternative hosts some advantages useful at its original habitat.

Potential use of beneficial fungal microorganisms and C-phycocyanin extract for enhancing seed germination, seedling growth and biochemical traits of Solanum lycopersicum L

Background

Biopriming as a new technique of seed treatment involves the application of beneficial microorganisms on the seed surface to stimulate seed germination, plant growth, and protect the seed from soil and seed-borne pathogens. The present investigation was carried out on seed germination, seedling vigor and biochemical traits of one of the most important vegetable crops (Tomato, Solanum lycopersicum L.). The treatments comprised viz. T1: Non primed seeds (Control), T2: Hydropriming, T3: Biopriming with C-phycocyanin (C-PC) (Spirulina platensis extract), T4: Biopriming with Trichoderma asperellum, T5: Biopriming with T. viride, T6: Biopriming with Beauveria bassiana.

Results

Extraction and purification of C-phycocyanin (C-PC) from the dry S. platensis powder using various methods was performed. The purity after dialyses was 0.49 and its ultimate purity (A₆₂₀/A₂₈₀) after ion-exchange chromatography was 4.64. The results on tomato seedlings revealed that the maximum germination percentage (100%), germination index (15.46 and 15.12), seedling length (10.67 cm), seedling dry weight (1.73 and 1.97 mg) and seedling length vigor index (1066.7) were recorded for tomato biopriming with T. viride, and B. bassiana (T5 and T6). Moreover, the quantitative estimation of total carbohydrates and total free amino acids contents in bioprimed tomato seedlings indicated a significantly higher amount with T. viride, followed by those bioprimed with T. asperellum, B. bassiana and C-PC extract.

Conclusion

Thus, our results indicated that biopriming of tomato seeds with beneficial fungal inoculants and C-PC was very effective. The most operative biostimulants were those bioprimed with T. viride and B. bassiana compared to other biostimulants (T. asperellum and C-PC). Therefore, to ensure sustainable agriculture, this study offers new possibilities for the biopriming application as an alternative and ecological management strategy to chemical treatment and provides a valuable basis for improving seed germination.

Trichoderma: The Current Status of Its Application in Agriculture for the Biocontrol of Fungal Phytopathogens and Stimulation of Plant Growth

Rhizosphere filamentous fungi of the genus Trichoderma, a dominant component of various soil ecosystem mycobiomes, are characterized by the ability to colonize plant roots. Detailed knowledge of the properties of Trichoderma, including metabolic activity and the type of interaction with plants and other microorganisms, can ensure its effective use in agriculture. The growing interest in the application of Trichoderma results from their direct and indirect biocontrol potential against a wide range of soil phytopathogens. They act through various complex mechanisms, such as mycoparasitism, the degradation of pathogen cell walls, competition for nutrients and space, and induction of plant resistance. With the constant exposure of plants to a variety of pathogens, especially filamentous fungi, and the increased resistance of pathogens to chemical pesticides, the main challenge is to develop biological protection alternatives. Among non-pathogenic microorganisms, Trichoderma seems to be the best candidate for use in green technologies due to its wide biofertilization and biostimulatory potential. Most of the species from the genus Trichoderma belong to the plant growth-promoting fungi that produce phytohormones and the 1-aminocyclopropane-1-carboxylate (ACC) deaminase enzyme. In the present review, the current status of Trichoderma is gathered, which is especially relevant in plant growth stimulation and the biocontrol of fungal phytopathogens.

Reactive Oxygen Species, Antioxidant Responses and Implications from a Microbial Modulation Perspective

Simple Summary

Environmental conditions are subject to unprecedented changes due to recent progressive anthropogenic activities on our planet. Plants, as the frontline of food security, are susceptible to these changes, resulting in the generation of unavoidable byproducts of metabolism (ROS), which eventually affect their productivity. The response of plants to these unfavorable conditions is highly intricate and depends on several factors, among them are the species/genotype tolerance level, intensity, and duration of stress factors. Defensive mechanisms in plant systems, by nature, are concerned primarily with generating enzymatic and non-enzymatic antioxidants. In addition to this, plant-microbe interactions have been found to improve immune systems in plants suffering from drought and salinity stress.

Abstract

Plants are exposed to various environmental stresses in their lifespan that threaten their survival. Reactive oxygen species (ROS), the byproducts of aerobic metabolism, are essential signalling molecules in regulating multiple plant developmental processes as well as in reinforcing plant tolerance to biotic and abiotic stimuli. However, intensified environmental challenges such as salinity, drought, UV irradiation, and heavy metals usually interfere with natural ROS metabolism and homeostasis, thus aggravating ROS generation excessively and ultimately resulting in oxidative stress. Cellular damage is confined to the degradation of biomolecular structures, including carbohydrates, proteins, lipids, pigments, and DNA. The nature of the double-edged function of ROS as a secondary messenger or harmful oxidant has been attributed to the degree of existing balance between cellular ROS production and ROS removal machinery. The activities of enzyme-based antioxidants, catalase (CAT, EC 1.11.1.6), monodehydroascorbate reductase (MDHAR, E.C.1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), and guaiacol peroxidase (GPX, EC 1.11.1.7); and non-enzyme based antioxidant molecules, ascorbate (AA), glutathione (GSH), carotenoids, α-tocopherol, prolines, flavonoids, and phenolics, are indeed parts of the defensive strategies developed by plants to scavenge excess ROS and to maintain cellular redox homeostasis during oxidative stress. This review briefly summarises current knowledge on enzymatic and non-enzymatic antioxidant machinery in plants. Moreover, additional information about the beneficial impact of the microbiome on countering abiotic/biotic stresses in association with roots and plant tissues has also been provided.

Impact of Soil Chemical Properties on the Growth Promotion Ability of Trichoderma ghanense, T. tomentosum and Their Complex on Rye in Different Land-Use Systems

Microbial-based biostimulants that increase plant performance and ensure sustainable restoration of degraded soils are of great importance. The aim of the present study was to evaluate the growth promotion ability of indigenous Trichoderma ghanense, T. tomentosum and their complex on early rye seedlings in sustained grassland and arable soil. The impact of soil chemical properties on the ability of selected Trichoderma strains and their complex to promote plant growth was determined by the evaluation of the rye (Secale cereale L.) early seedling growth—measuring the length of shoots and roots as well as their dry weight. Trichoderma species were tested for their ability to produce extracellular degradative enzymes on solid media. Furthermore, the soil properties and CM-cellulase activity of soil were estimated. The indigenous Trichoderma strains possess the capacity to produce enzymes such as peroxidase, laccase, tyrosinase, and endoglucanase. The results indicated a significant (p < 0.05) increase in plant growth and the improvement of some soil chemical properties (total N, mobile humic and fulvic acids, exchangeable K₂O, soil CM-cellulase activity) in inoculated soils when compared to the control. The growth of the roots of rye seedlings in sustained grassland was enhanced when T. tomentosum was applied (p = 0.005). There was an increase in total weight and shoot weight of rye seedlings when T. ghanense was used in the arable soil (p = 0.014 and p = 0.024). The expected beneficial effect of Trichoderma spp. complex on rye growth promotion was not observed in any tested soil. The results could find application in the development of new and efficient biostimulants, since not only do physiological characteristics of fungi play an important role but also the quality of the soil has an impact.

Potential of Trichoderma harzianum and Its Metabolites to Protect Wheat Seedlings against Fusarium culmorum and 2,4-D

Wheat is a critically important crop. The application of fungi, such as Trichoderma harzianum, to protect and improve crop yields could become an alternative solution to synthetic chemicals. However, the interaction between the fungus and wheat in the presence of stress factors at the molecular level has not been fully elucidated. In the present work, we exposed germinating seeds of wheat (Triticum aestivum) to the plant pathogen Fusarium culmorum and the popular herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in the presence of T. harzianum or its extracellular metabolites. Then, the harvested roots and shoots were analyzed using spectrometry, 2D-PAGE, and MALDI-TOF/MS techniques. Although F. culmorum and 2,4-D were found to disturb seed germination and the chlorophyll content, T. harzianum partly alleviated these negative effects and reduced the synthesis of zearalenone by F. culmorum. Moreover, T. harzianum decreased the activity of oxidoreduction enzymes (CAT and SOD) and the contents of the oxylipins 9-Hode, 13-Hode, and 13-Hotre induced by stress factors. Under the influence of various growth conditions, changes were observed in over 40 proteins from the wheat roots. Higher volumes of proteins and enzymes performing oxidoreductive functions, such as catalase, ascorbate peroxidase, cytochrome C peroxidase, and Cu/Zn superoxide dismutase, were found in the Fusarium-inoculated and 2,4-D-treated wheat roots. Additionally, observation of the level of 12-oxo-phytodienoic acid reductase involved in the oxylipin signaling pathway in wheat showed an increase. Trichoderma and its metabolites present in the system leveled out the mentioned proteins to the control volumes. Among the 30 proteins examined in the shoots, the expression of the proteins involved in photosynthesis and oxidative stress response was found to be induced in the presence of the herbicide and the pathogen. In summary, these proteomic and metabolomic studies confirmed that the presence of T. harzianum results in the alleviation of oxidative stress in wheat induced by 2,4-D or F. culmorum.

Changes in Volatile Organic Compounds from Salt-Tolerant Trichoderma and the Biochemical Response and Growth Performance in Saline-Stressed Groundnut

Soil salinity is one of the major obstacles that is limiting the growth and yield of groundnut. This study aims to investigate the effect of growth-promoting fungi, Trichoderma, on groundnut plants that were cultivated in saline conditions. Five different Trichoderma isolates were grown in four different NaCl concentrations. Selected Trichoderma were then applied to the groundnut seeds and their growth and development were monitored during the study. Growth inhibition, volatile organic compounds, chlorophylls, carotenoids, total phenolics and flavonoids, and minerals were assessed between the Trichoderma treatments. Increasing the salt concentration from 0.25–0.75 M decreased the growth of the Trichoderma isolates. The amounts and profiles of the volatile organic compounds from the T. asperellum isolate were significantly different to those in the T. virens isolate. In the vegetative growth stage, increased chlorophyll content was recorded in both the T. asperellum and T. virens-treated groundnut. The leaves that were obtained from the groundnut that was treated with T. virens T.v4 contained significantly higher indole-3-acetic acid (420 µg IAA/g) than the same plants’ roots (113.3 µg IAA/g). Compared to the control groundnut, the T. asperellum T.a8-treated groundnut showed increased phenolics (31%) and flavonoids (43%) and increased shoots and biomass weight at the generative growth stage. This study demonstrates that Trichoderma, with their plant growth promotion ability, could potentially be used to improve the growth of groundnut growing under salinity stress. Importantly, salt-tolerant Trichoderma could be regarded as a beneficial and sustainable way to improve the survival of salt-sensitive crops.

Trichoderma longibrachiatum (TG1) Enhances Wheat Seedlings Tolerance to Salt Stress and Resistance to Fusarium pseudograminearum

Salinity is abiotic stress that inhibits seed germination and suppresses plant growth and root development in a dose-dependent manner. Fusarium pseudograminearum (Fg) is a plant pathogen that causes wheat crown rot. Chemical control methods against Fg are toxic to the environment and resistance has been observed in wheat crops. Therefore, an alternative approach is needed to manage this devastating disease and the effects of salinity. Our research focused on the mycoparasitic mechanisms of Trichoderma longibrachiatum (TG1) on Fg and the induction of defenses in wheat seedlings under salt and Fg stress at physiological, biochemical and molecular levels. The average inhibition rate of TG1 against Fg was 33.86%, 36.32%, 44.59%, and 46.62%, respectively, in the four NaCl treatments (0, 50, 100, and 150 mM). The mycoparasitic mechanisms of TG1 against Fg were coiling, penetration, and wrapping of Fg hyphae. In response to inoculation of TG1 with Fg, significant upregulation of cell wall degrading enzymes (CWDEs) was observed. The expression of β-1, 6-glucan synthase (PP4), endochitinase precursor (PH-1), and chitinase (chi18-15) increased by 1. 6, 1. 9, and 1.3-fold on day 14 compared with day 3. Wheat seedlings with combined TG1 + Fg treatments under different NaCl stress levels decreased disease index by an average of 51.89%; increased the superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity by an average of 38%, 61%, and 24.96%, respectively; and decreased malondialdehyde (MDA) and hydrogen peroxide (H2O2) content by an average of 44.07% and 41.75% respectively, compared with Fg treated seedlings. The combined TG1 + Fg treatment induced the transcription level of plant defense-related genes resulting in an increase in tyrosin-protein kinase (PR2), chitinase class I (CHIA1), and pathogenesis-related protein (PR1-2) by an average of 1.15, 1.35, and 1.37-fold, respectively compared to Fg treatment. However, the expression levels of phenylalanine ammonia-lyase (PAL) increased 3.40-fold under various NaCl stresses. Our results suggest that TG1 enhances wheat seedling growth and controls wheat crown rot disease by strengthening the plant defense system and upregulating the expression of pathogenesis-related genes under both Fg and salt stress.

Niche differentiation of belowground microorganisms and their functional signatures in Assam type tea (Camellia sinensis var. assamica)

We employed an Illumina-based high-throughput metagenomics sequencing approach to unveil the rhizosphere and root endosphere microbial community associated with an organically grown Camellia population located at the Experimental Garden for Plantation Crops, Assam (India). The de novo assembled tea root endosphere metagenome contained 24,231 contigs (total 7,771,089 base pairs with an average length of 321 bps), while tea rhizosphere soil metagenome contained 261,965 sequences (total 230,537,174 base pairs, average length 846). The most prominent rhizobacteria belonged to the genera, viz., Bacillus (10.35%), Candidatus Solibacter (6.36%), Burkholderia (5.19%), Pseudomonas (3.9%), Streptomyces (3.52%), and Bradyrhizobium (2.77%), while the root endosphere was dominated by bacterial genera, viz., Serratia (46.64%), Methylobacterium (8.02%), Yersinia (5.97%), Burkholderia (2.05%), etc. The presence of few agronomically important bacterial genera, Bradyrhizobium, Rhizobium (each 0.93%), Sinorhizobium (0.34%), Azorhizobium, and Flavobacterium (0.17% each), was also detected in the root endosphere. KEGG pathway mapping indicated the presence of microbial metabolic pathway genes related to tyrosine metabolism, tryptophan metabolism, glyoxylate, and dicarboxylate metabolism which play important roles in endosphere activities, including survival, growth promotion, and host adaptation. The root endosphere microbiome also contained few important plant growth promoting traits related to phytohormone production, abiotic stress alleviation, mineral solubilization, and plant disease suppression.

Salt-Tolerant Compatible Microbial Inoculants Modulate Physio-Biochemical Responses Enhance Plant Growth, Zn Biofortification and Yield of Wheat Grown in Saline-Sodic Soil

A wide range of root-associated mutualistic microorganisms have been successfully applied and documented in the past for growth promotion, biofertilization, biofortification and biotic and abiotic stress amelioration in major crops. These microorganisms include nitrogen fixers, nutrient mobilizers, bio-remediators and bio-control agents. The present study aimed to demonstrate the impact of salt-tolerant compatible microbial inoculants on plant growth; Zn biofortification and yield of wheat (Triticum aestivum L.) crops grown in saline-sodic soil and insight of the mechanisms involved therein are being shared through this paper. Field experiments were conducted to evaluate the effects of Trichoderma harzianum UBSTH-501 and Bacillus amyloliquefaciens B-16 on wheat grown in saline-sodic soil at Research Farm, ICAR-Indian Institute of Seed Sciences, Kushmaur, India. The population of rhizosphere-associated microorganisms changed dramatically upon inoculation of the test microbes in the wheat rhizosphere. The co-inoculation induced a significant accumulation of proline and total soluble sugar in wheat at 30, 60, 90 and 120 days after sowing as compared to the uninoculated control. Upon quantitative estimation of organic solutes and antioxidant enzymes, these were found to have increased significantly in co-inoculated plants under salt-stressed conditions. The application of microbial inoculants enhanced the salt tolerance level significantly in wheat plants grown in saline-sodic soil. A significant increase in the uptake and translocation of potassium (K⁺) and calcium (Ca²⁺) was observed in wheat co-inoculated with the microbial inoculants, while a significant reduction in sodium (Na⁺) content was recorded in plants treated with both the bio-agents when compared with the respective uninoculated control plants. Results clearly indicated that significantly higher expression of TaHKT-1 and TaNHX1 in the roots enhances salt tolerance effectively by maintaining the Na⁺/K⁺ balance in the plant tissue. It was also observed that co-inoculation of the test inoculants increased the expression of ZIP transporters (2–3.5-folds) which ultimately led to increased biofortification of Zn in wheat grown in saline-sodic soil. Results suggested that co-inoculation of T. harzianum UBSTH-501 and B. amyloliquefaciens B-16 not only increased plant growth but also improved total grain yield along with a reduction in seedling mortality in the early stages of crop growth. In general, the present investigation demonstrated the feasibility of using salt-tolerant rhizosphere microbes for plant growth promotion and provides insights into plant-microbe interactions to ameliorate salt stress and increase Zn bio-fortification in wheat.

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.

Microbial amelioration of salinity stress in HD 2967 wheat cultivar by up-regulating antioxidant defense

An experiment was conducted to investigate the potential of Piriformospora indica and plant growth-promoting bacteria (PGPB) to ameliorate salinity stress in HD 2967 wheat cultivar. Plants were treated with four different levels of salinity viz. 0, 50, 100 and 200 mM NaCl (electrical conductivity value 0.01, 5.84, 11.50 and 21.4 mS cm⁻¹, respectively) under greenhouse conditions, using a completely randomized design experiment. Plants inoculated with PGPB and P. indica showed decrease in lipid peroxidation, relative membrane permeability and lipoxygenase enzyme (LOX) activity as compared to uninoculated plants. The result of this study showed that PGPB and P. indica inoculated HD 2967 wheat plants accumulated higher content of proline, α-tocopherol and carotenoid as compared to uninoculated plants. The HD 2967 wheat plants either inoculated with PGPB or P. indica showed significantly higher activities of antioxidant enzymes viz. superoxide dismutase, catalase and ascorbate peroxidase than that of the uninoculated plants. Moreover, PGPB inoculated plants showed greater activity of antioxidant enzymes than the plants inoculated with P. indica. Salinity stress tolerance was more pronounced in the PGPB inoculated than P. indica inoculated plants. This study revealed the potentiality of PGPB and P. indica as bio-ameliorator under salinity stress, and suggests that this plant microbial association could be a promising biotechnological tool to combat the deleterious effects of salinity stress.

Effects of mixed culture fermentation of Bacillus amyloliquefaciens and Trichoderma longibrachiatum on its constituent strains and the biocontrol of tomato Fusarium wilt

AIMS

To study the effects of mixed culture fermentation (MCF) of Bacillus amyloliquefaciens and Trichoderma longibrachiatum on its constituent strains and the application values for agricultural production, with the intention of developing efficient and environmentally friendly biocontrol agents.

METHODS AND RESULTS

In this study, an in vitro antifungal growth experiment showed that the inhibitory rate of the MCF broth on pathogenic fungi (Fusarium oxysporum f. sp. lycopersici, Botrytis cinerea, Trichothecium roseum and Colletotrichum gloeosporioides) was less than that of B. amyloliquefaciens culture fermentation (BCF). Moreover, the content and gene expression of lipopeptide antibiotics were also lower than that in the BCF group. However, the pot experiments based on irrigation with appropriately diluted fermentation broth showed that the biocontrol effect of MCF on tomato Fusarium wilt was significantly higher than that of TCF (T. longibrachiatum culture fermentation) and BCF, and was approximately 15.79% higher than that of the BTF group which made by mixing equivalent amounts of BCF and TCF. In MCF broth, two micro-organisms antagonized and coexisted, and the growth of T. longibrachiatum was inhibited. Using transcriptomic analysis, we speculated that MCF can upregulate the expression of genes related to carbon and nitrogen metabolism, oxidation-reduction activity, sporulation, environmental information response and chemotaxis, and biosynthesis of secondary metabolites of B. amyloliquefaciens, which might enhance the nutrient substances metabolism and competitiveness, survival ability, colonization and adaptability to the environment to increase its biocontrol potential.

CONCLUSIONS

Mixed culture fermentation could promote the more reasonable and effective utilization of biocontrol micro-organisms though improving biocontrol effect, enhancing strains survival and competitiveness, increasing beneficial metabolites, combined with resistance induction or synergistic control.

SIGNIFICANCE AND IMPACT OF THE STUDY

Using MCF agronomically utilizes biocontrol agents in an efficient way, which has a good potential for commercial implementation and could reduce production costs.

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.

Saline-alkaline stress in growing maize seedlings is alleviated by Trichoderma asperellum through regulation of the soil environment

A significant proportion of the land area of Heilongjiang Province, China, is composed of saline-alkaline soil, which severely inhibits maize growth. Although Trichoderma treatment is widely regarded as a promising strategy for improving the soil environment and promoting plant growth, the mechanism through which Trichoderma asperellum enhances maize resistance to saline-alkaline stress is not clear. In this study, we explored the effect of T. asperellum application at different concentrations to soil saline-alkaline environment on the seedlings of two maize cultivars, assessing the biochemical parameters related to oxidation resistance. Increasing spore densities of T. asperellum suspension effectively regulated the soil ion balance in the rhizosphere of maize seedlings, reduced the soil pH by 2.15-5.76% and sodium adsorption ratios by 22.70-54.13%, increased soil nutrient content and enzyme activity, and improved the soil environment for seedling growth. Additionally, T. asperellum treatment increased the maize seedling content of osmo-regulating substances and rate of glutathione:oxidised glutathione (43.86-88.25%) and ascorbate:oxidised ascorbate (25.26-222.32%) by affecting the antioxidant enzyme activity in the roots, increasing reactive oxygen species scavenging, and maintaining the osmotic balance and metabolic homeostasis under saline-alkaline stress. T. asperellum also improved the saline-alkaline tolerance of maize seedlings by improving the root growth characteristics. Moreover, results showed that Trichoderma applied at high concentration had the greatest effect. In conclusion, improvement in the saline-alkaline tolerance of maize seedlings by T. asperellum under saline-alkaline soil conditions may be achieved through diverse effects that vary among maize cultivars.

Endophytic Fungi: Biological Control and Induced Resistance to Phytopathogens and Abiotic Stresses

Plant diseases cause losses of approximately 16% globally. Thus, management measures must be implemented to mitigate losses and guarantee food production. In addition to traditional management measures, induced resistance and biological control have gained ground in agriculture due to their enormous potential. Endophytic fungi internally colonize plant tissues and have the potential to act as control agents, such as biological agents or elicitors in the process of induced resistance and in attenuating abiotic stresses. In this review, we list the mode of action of this group of microorganisms which can act in controlling plant diseases and describe several examples in which endophytes were able to reduce the damage caused by pathogens and adverse conditions. This is due to their arsenal of molecules generated during the interaction by which they form a kind of biological shield in the plant. Furthermore, considering that endophytic fungi can be an important tool in managing for biotic and abiotic stresses due to the large amount of biologically active substances produced, bioprospecting this class of microorganisms is tending to increase and generate valuable products for agriculture.

Bioprospecting of Rhizosphere-Resident Fungi: Their Role and Importance in Sustainable Agriculture

Rhizosphere-resident fungi that are helpful to plants are generally termed as 'plant growth promoting fungi' (PGPF). These fungi are one of the chief sources of the biotic inducers known to give their host plants numerous advantages, and they play a vital role in sustainable agriculture. Today's biggest challenge is to satisfy the rising demand for crop protection and crop yield without harming the natural ecosystem. Nowadays, PGPF has become an eco-friendly way to improve crop yield by enhancing seed germination, shoot and root growth, chlorophyll production, and fruit yield, etc., either directly or indirectly. The mode of action of these PGPF includes the solubilization and mineralization of the essential micro- and macronutrients needed by plants to regulate the balance for various plant processes. PGPF produce defense-related enzymes, defensive/volatile compounds, and phytohormones that control pathogenic microbes' growth, thereby assisting the plants in facing various biotic and abiotic stresses. Therefore, this review presents a holistic view of PGPF as efficient natural biofertilizers to improve crop plants' growth and resistance.

Trichoderma asperellum Inoculation as a Tool for Attenuating Drought Stress in Sugarcane

Drought stress is an important concern worldwide which reduces crop yield and quality. To alleviate this problem, Trichoderma asperellum has been used as a plant growth-promoting fungus capable of inducing plant tolerance to biotic and abiotic stresses. Here, we examined the effect of T. asperellum inoculation on sugarcane plant above and belowground development under drought stress and investigated the role of this fungus on inducing tolerance to drought at physiological and biochemical levels. The experiment was performed in pots under greenhouse conditions, with four treatments and four replicates. The treatments consisted of sugarcane plants inoculated or not with T. asperellum and grown under drought stress and adequate water availability. Drought-stressed sugarcane plants inoculated with T. asperellum changed the crop nutrition and chlorophyll and carotenoid concentrations, resulting in increased photosynthesis rate, stomatal conductance, and water use efficiency compared to the non-inoculated plants. In addition, the antioxidant metabolism also changed, increasing the superoxide dismutase and peroxidase enzyme activities, as well as the proline concentration and sugar portioning. These cascade effects enhanced the root and stalk development, demonstrating that T. asperellum inoculation is an important tool in alleviating the negative effects of drought stress in sugarcane. Future studies should be performed to elucidate if T. asperellum should be reapplied to the sugarcane ratoons.

Differential Responses of Cucurbita pepo to Podosphaera xanthii Reveal the Mechanism of Powdery Mildew Disease Resistance in Pumpkin

Powdery mildew is one of the most destructive diseases and the major cause to the production losses of cucurbit worldwide. A number of strategies have been developed and applied to discover suitable and safer methods to manage the occurrence of powdery mildew disease in pumpkins (Cucurbita pepo L.), but information is limited in screening tolerant germplasms and exploring their mechanisms in preventing the disease occurrence at physiological, biochemical, and molecular levels. Therefore, we investigated the responses of two commercial pumpkin cultivars to Podosphaera xanthii infection. Compared with mock-inoculated seedlings, few small and sparse powdery areas were observed on the leaves of the Sixing F1 cultivar on the 13th day after inoculation with P. xanthii, whereas a large number of diseased powdery areas and a layer of white powdery mildew were observed on the surface of Jin12 F1 leaves. The inoculation duration (7, 9, 11, and 13 days) significantly and continuously increased the disease incidence and index of pumpkin seedlings. The contents of H2O2, MDA, lignin, and total phenolics in the leaves of Sixing F1 and Jin12 F1 cultivars were markedly increased after inoculation with P. xanthii. However, the Sixing F1 cultivar exhibited much less reactive oxygen species (ROS) accumulation, a lower rate of lipid peroxidation, and a higher level of lignin and total phenolics contents after inoculation than the Jin12 F1 cultivar. Compared with untreated control pumpkin seedlings, significantly higher activities and gene expressions of the phenylpropanoids pathway enzymes (PAL and PPO), ROS scavenging defense enzymes (SOD, CAT, POD, and APX), and other salicylic acid (SA) signaling pathway marker genes were observed in the leaves of both cultivars after P. xanthii inoculation at different inoculation time points. These enhancements were significantly higher in Sixing F1 than Jin12 F1. Our results indicate that the Sixing F1 cultivar exhibited a much stronger ability in resistance to P. xanthii infection than the Jin12 F1 cultivar. Our results suggest that one possible mechanism of C. pepo cultivars to prevent the pathogen P. xanthii infection is by activating and enhancing the activity and gene expression of the phenylpropanoids pathway to synthesize phenolic substances and lignin, ROS scavenging defense enzymes to eliminate the harmful effects of ROS, and signaling pathway marker gene expression to improve plant disease resistance.

Biocontrol Mechanisms of Trichoderma koningiopsis PSU3-2 against Postharvest Anthracnose of Chili Pepper

Several mechanisms are involved in the biological control of plant pathogens by the soil-borne Trichoderma spp. fungi. The aim of this study was to characterize a new strain of Trichoderma as a potential biological control agent to control the postharvest anthracnose of chili pepper caused by Colletotrichumgloeosporioides. A total of nine strains of Trichoderma spp. were screened for their antifungal activity using a dual culture assay against C.gloeosporioides. Trichoderma koningiopsis PSU3-2 was shown to be the most effective strain, with a percentage inhibition of 79.57%, which was significantly higher than that of other strains (p < 0.05). In the sealed plate method, T. koningiopsis PSU3-2 suppressed the growth of C.gloeosporioides by 38.33%. Solid-phase microextraction (SPME) was applied to trap volatiles emitted by T. koningiopsis PSU3-2, and the GC/MS profiling revealed the presence of antifungal compounds including azetidine, 2-phenylethanol, and ethyl hexadecanoate. The production of cell-wall-degrading enzymes (CWDEs) was assayed through cell-free culture filtrate (CF) of PSU3-2, and the enzyme activity of chitinase and β-1,3-glucanase was 0.06 and 0.23 U/mL, respectively, significantly higher than that in the control (p < 0.05). Scanning electron microscopy of the mycelium incubated in cell-free CF of T. koningiopsis PSU3-2 showed the abnormal shape of C.gloeosporioides hyphae. Application of T. koningiopsis PSU3-2 by the dipping method significantly reduced the lesion size (p < 0.05) after inoculation with C.gloeosporioides compared to the control, and there was no disease symptom development in T. koningiopsis PSU3-2-treated chili pepper. This study demonstrates that T. koningiopsis PSU3-2 is an effective antagonistic microorganism and a promising biocontrol agent against postharvest anthracnose of chili pepper, acting with multiple mechanisms.

Potential of indigenous crop microbiomes for sustainable agriculture

The intimate interactions of indigenous crops with their associated microbiomes during long-term co-evolution strengthen the capacity and flexibility of crops to cope with biotic and abiotic stresses. This represents a promising untapped field for searching novel tools to sustainably increase crop productivity. However, the current capability of harnessing the power of indigenous crop microbiomes for sustainable crop production is limited due to low efficiency of separating the targeted functional microbes. Here, we highlight the potential benefits and existing challenges of utilizing indigenous crop microbiomes to reduce agrochemical inputs and increase crop resistance to biotic and abiotic stresses. We propose a framework using Raman-spectroscopy-based single-cell-sorting technology combined with a synthetic community approach to design and optimize a functionally reliable 'beneficial biome' under controlled conditions. This framework will offer opportunities for sustainable agriculture and provide a new direction for future studies.

Effects of soaking seeds in exogenous vitamins on active oxygen metabolism and seedling growth under low-temperature stress

This study investigated the influence of the exogenous application of vitamin B2 (V_B2), B12 (V_B12), biotin (V_H), and nicotinic acid (V_PP) on oxygen production in maize (Zea mays L.) seedlings at 5 °C for day 1, 3, 5 and 7. The seeds were soaked in V_B2, V_B12, V_H, and V_PP solutions for 24 h at the concentration of 100 mg/L, and control was soaked in distilled water. A total of 50 seeds were used for each treatment in germination boxes was repeated three times. The germination box was placed in a hypothermic incubator for 1, 3, 5, and 7 days in the dark at 5 °C, then moved to a plant growth room and kept for seven days. Compared with the V_H and V_PP treatments, the V_B2 and V_B12 treatments had higher thiobarbituric acid reactive substances, proline, and soluble sugars. The V_B2 and V_B12 treatments also increased the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) than other treatments. The V_B2 and V_B12 treatments reduced the contents of hydrogen peroxide (H₂O₂ ^-), superoxide anion (O₂ ^-), and the damage of reactive oxygen species (ROS) to cells, increased the stability of the cell membrane and the content of cell osmoregulation substances. Moreover, V_B2 and V_B12 had higher seedling growth, germination rate, and index. Treatments V_B2 and V_B12 could promote maize seed germination and growth under low-temperature stress. Exogenous vitamins in crop production can be a valuable tool for protecting plants against low-temperature stress.

A Beginner's Guide to Osmoprotection by Biostimulants

Water is indispensable for the life of any organism on Earth. Consequently, osmotic stress due to salinity and drought is the greatest threat to crop productivity. Ongoing climate change includes rising temperatures and less precipitation over large areas of the planet. This is leading to increased vulnerability to the drought conditions that habitually threaten food security in many countries. Such a scenario poses a daunting challenge for scientists: the search for innovative solutions to save water and cultivate under water deficit. A search for formulations including biostimulants capable of improving tolerance to this stress is a promising specific approach. This review updates the most recent state of the art in the field.

Transcriptomics of Biostimulation of Plants Under Abiotic Stress

Plant biostimulants are compounds, living microorganisms, or their constituent parts that alter plant development programs. The impact of biostimulants is manifested in several ways: via morphological, physiological, biochemical, epigenomic, proteomic, and transcriptomic changes. For each of these, a response and alteration occur, and these alterations in turn improve metabolic and adaptive performance in the environment. Many studies have been conducted on the effects of different biotic and abiotic stimulants on plants, including many crop species. However, as far as we know, there are no reviews available that describe the impact of biostimulants for a specific field such as transcriptomics, which is the objective of this review. For the commercial registration process of products for agricultural use, it is necessary to distinguish the specific impact of biostimulants from that of other legal categories of products used in agriculture, such as fertilizers and plant hormones. For the chemical or biological classification of biostimulants, the classification is seen as a complex issue, given the great diversity of compounds and organisms that cause biostimulation. However, with an approach focused on the impact on a particular field such as transcriptomics, it is perhaps possible to obtain a criterion that allows biostimulants to be grouped considering their effects on living systems, as well as the overlap of the impact on metabolism, physiology, and morphology occurring between fertilizers, hormones, and biostimulants.

Partial Substitution of K by Na Alleviates Drought Stress and Increases Water Use Efficiency in Eucalyptus Species Seedlings

Eucalyptus, the most widely planted tree genus worldwide, is frequently cultivated in soils with low water and nutrient availability. Sodium (Na) can substitute some physiological functions of potassium (K), directly influencing plants' water status. However, the extent to which K can be replaced by Na in drought conditions remains poorly understood. A greenhouse experiment was conducted with three Eucalyptus genotypes under two water conditions (well-watered and water-stressed) and five combination rates of K and Na, representing substitutions of 0/100, 25/75, 50/50, 75/25, and 100/0 (percentage of Na/percentage of K), to investigate growth and photosynthesis-related parameters. This study focused on the positive effects of Na supply since, depending on the levels applied, the Na supply may induce plants to salinity stress (>100 mM of NaCl). Plants supplied with low to intermediate K replacement by Na reduced the critical level of K without showing symptoms of K deficiency and provided higher total dry matter (TDM) than those Eucalyptus seedlings supplied only with K in both water conditions. Those plants supplied with low to intermediate K replacement by Na had improved CO₂ assimilation (A), stomatal density (Std), K use efficiency (UE _K ), and water use efficiency (WUE), in addition to reduced leaf water potential (Ψw) and maintenance of leaf turgidity, with the stomata partially closed, indicated by the higher values of leaf carbon isotope composition (δ¹³C‰). Meanwhile, combination rates higher than 50% of K replacement by Na led to K-deficient plants, characterized by the lower values of TDM, δ¹³C‰, WUE, and leaf K concentration and higher leaf Na concentration. There was positive evidence of partial replacement of K by Na in Eucalyptus seedlings; meanwhile, the ideal percentage of substitution increased according to the drought tolerance of the species (Eucalyptus saligna < Eucalyptus urophylla < Eucalyptus camaldulensis).

Identification and characterization of a novel multi-stress responsive gene in Arabidopsis

Abiotic stresses especially salinity, drought and high temperature result in considerable reduction of crop productivity. In this study, we identified AT4G18280 annotated as a glycine-rich cell wall protein-like (hereafter refer to as GRPL1) protein as a potential multistress-responsive gene. Analysis of public transcriptome data and GUS assay of pGRPL1::GUS showed a strong induction of GRPL1 under drought, salinity and heat stresses. Transgenic plants overexpressing GRPL1-3HA showed significantly higher germination, root elongation and survival rate under salt stress. Moreover, the 35S::GRPL1-3HA transgenic lines also showed higher survival rates under drought and heat stresses. GRPL1 showed similar expression patterns with Abscisic acid (ABA)-pathway genes under different growth and stress conditions, suggesting a possibility that GRPL1 might act in the ABA pathway that is further supported by the inability of ABA-deficient mutant (aba2-1) to induce GRPL1 under drought stress. Taken together, our data presents GRPL1 as a potential multi-stress responsive gene working downstream of ABA.

Trichoderma Enhances Net Photosynthesis, Water Use Efficiency, and Growth of Wheat (Triticum aestivum L.) under Salt Stress

Soil salinity is one of the most important abiotic stresses limiting plant growth and productivity. The breeding of salt-tolerant wheat cultivars has substantially relieved the adverse effects of salt stress. Complementing these cultivars with growth-promoting microbes has the potential to stimulate and further enhance their salt tolerance. In this study, two fungal isolates, Th4 and Th6, and one bacterial isolate, C7, were isolated. The phylogenetic analyses suggested that these isolates were closely related to Trichoderma yunnanense, Trichoderma afroharzianum, and Bacillus licheniformis, respectively. These isolates produced indole-3-acetic acid (IAA) under salt stress (200 mM). The abilities of these isolates to enhance salt tolerance were investigated by seed coatings on salt-sensitive and salt-tolerant wheat cultivars. Salt stress (S), cultivar (C), and microbial treatment (M) significantly affected water use efficiency. The interaction effect of M x S significantly correlated with all photosynthetic parameters investigated. Treatments with Trichoderma isolates enhanced net photosynthesis, water use efficiency and biomass production. Principal component analysis revealed that the influences of microbial isolates on the photosynthetic parameters of the different wheat cultivars differed substantially. This study illustrated that Trichoderma isolates enhance the growth of wheat under salt stress and demonstrated the potential of using these isolates as plant biostimulants.

Keystone metabolites of crop rhizosphere microbiomes

The role of microbes in sustaining agricultural plant growth has great potential consequences for human prosperity. Yet we have an incomplete understanding of the basic function of rhizosphere microbial communities and how they may change under future stresses, let alone how these processes might be harnessed to sustain or improve crop yields. A reductionist approach may aid the generation and testing of hypotheses that can ultimately be translated to agricultural practices. With this in mind, we ask whether some rhizosphere microbial communities might be governed by 'keystone metabolites', envisioned here as microbially produced molecules that, through antibiotic and/or growth-promoting properties, may play an outsized role in shaping the development of the community spatiotemporally. To illustrate this point, we use the example of redox-active metabolites, and in particular phenazines, which are produced by many bacteria found in agricultural soils and have well-understood catalytic properties. Phenazines can act as potent antibiotics against a variety of cell types, yet they also can promote the acquisition of essential inorganic nutrients. In this essay, we suggest the ways these metabolites might affect microbial communities and ultimately agricultural productivity in two specific scenarios: firstly, in the biocontrol of beneficial and pathogenic fungi in increasingly arid crop soils and, secondly, through promotion of phosphorus bioavailability and sustainable fertilizer use. We conclude with specific proposals for future research.

Mycosynthesis of ZnO Nanoparticles Using Trichoderma spp. Isolated from Rhizosphere Soils and Its Synergistic Antibacterial Effect against Xanthomonas oryzae pv. oryzae

The Plant Growth Promoting Fungi (PGPF) is used as a source of biofertilizers due to their production of secondary metabolites and beneficial effects on plants. The present work is focused on the co-cultivation of Trichoderma spp. (T. harzianum (PGT4), T. reesei (PGT5) and T. reesei (PGT13)) and the production of secondary metabolites from mono and co-culture and mycosynthesis of zinc oxide nanoparticles (ZnO NPs), which were characterized by a UV visible spectrophotometer, Powder X-ray Diffraction (PXRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDAX) and Transmission Electron Microscope (TEM) and Selected Area (Electron) Diffraction (SAED) patterns. The fungal secondary metabolite crude was extracted from the mono and co-culture of Trichoderma spp. And were analyzed by GC-MS, which was further subjected for antibacterial activity against Xanthomonas oryzae pv. Oryzae, the causative organism for Bacterial Leaf Blight (BLB) in rice. Our results showed that the maximum zone of inhibition was recorded from the co-culture of Trichoderma spp. rather than mono cultures, which indicates that co-cultivation of beneficial fungi can stimulate the synthesis of novel secondary metabolites better than in monocultures. ZnO NPs were synthesized from fungal secondary metabolites of mono cultures of Trichoderma harzianum (PGT4), Trichoderma reesei (PGT5), Trichoderma reesei (PGT13) and co-culture (PGT4 + PGT5 + PGT13). These ZnO NPs were checked for antibacterial activity against Xoo, which was found to be of a dose-dependent manner. In summary, the biosynthesized ZnO NPs and secondary metabolites from co-culture of Trichoderma spp. are ecofriendly and can be used as an alternative for chemical fertilizers in agriculture.