Influence of salt tolerant Trichoderma spp. on growth of maize (Zea mays) under different salinity conditions

Application of Trichoderma harzianum enhances salt tolerance and yield of Indian mustard through increasing antioxidant enzyme activity

Growth and yield reduction of crops due to salt stress have become a serious issue worldwide. Trichoderma is very well known as a plant growth-promoting fungi under abiotic stress conditions. Therefore, this study was designed to investigate the effect of Trichoderma harzianum on the growth, yield, nutrient uptake, and antioxidant activity of three Indian mustard genotypes under saline condition (EC 9.28 dS m-1). A two-factorial (Trichoderma and Indian mustard genotypes) pot experiment was conducted following a completely randomized design (CRD) with four replicates. Trichoderma was applied to soil as compost and suspension. The BD-7104 genotype showed better performance than Tori-7 under saline conditions. Compared to control, application of T. harzianum showed better performance in enhancing growth and yield of all the genotypes by increasing plants' tolerance to salt stress. Again, Trichoderma application increased the chlorophyll, proline, and oil content of Indian mustard. The generation of antioxidant enzymes viz., SOD, CAT, APX, and POD was significantly increased and, synthesis of H2O2 and MDA was decreased to a variable degree under different Trichoderma treatments. On average, application of Trichoderma as compost enhanced seed yield by 23 % than control. The better growth and yield in Trichoderma treated plants were the results of better uptake and assimilation of N, P, S, Ca, Mg, and K and reduced uptake of Na with a lower Na/K. Overall, BD-7104 genotype can be grown in soil treated with Trichoderma as compost at a rate of TdC12.5 for obtaining better yield and nutritional quality under salinity stress condition.

Co-application of biochars and Piriformospora indica improved the quality of coastal saline soil and promoted the growth of forage

Soil quality is defined as the ability of soil to maintain the soil environment and the biosphere. Due to the limitation of salt and alkali stress, soil quality can be reduced, which in turn affects agricultural production. Biochar is widely used in saline-alkali land improvement because of its special pore structure and strong ion exchange ability, while Piriformospora indica is widely used in saline-alkali land improvement because it can symbiose with plants and improve plant stress resistance. However, the synergistic effect of combined biochar application and inoculation of P. indica on the quality of saline-alkali soil and plant development is uncertain. Hence, we investigated the combined influences of biochar and P. indica on the soil physicochemical characteristics, as well as the growth and chlorophyll florescence of sorghum-sudangrass hybrids (Sorghum bicolor × Sorghum sudane) in our study. The results indicated that after applying biochar and P. indica together, there was a considerable drop in soil pH, conductivity, Na+, and Cl- concentrations. Meanwhile, the soil organic matter (SOM), available phosphorus (AP), and alkaline hydrolyzable nitrogen (AN) increased by 151.81%, 50.84%, and 103.50%, respectively, when the Bamboo biochar was combined with 120 ml/pot of P. indica. Eventually, sorghum-sudangrass hybrid biomass, transpiration rate, and chlorophyll content increased by 111.69%, 204.98%, and 118.54%, respectively. According to our findings, using P. indica and biochar together can enhance soil quality and plant growth. The results also provide insights to enhance the quality of saline-alkali soils and the role of microorganisms in nutrient cycling.

Trichoderma and Bacillus multifunctional allies for plant growth and health in saline soils: recent advances and future challenges

Saline soils pose significant challenges to global agricultural productivity, hindering crop growth and efficiency. Despite various mitigation strategies, the issue persists, underscoring the need for innovative and sustainable solutions. One promising approach involves leveraging microorganisms and their plant interactions to reclaim saline soils and bolster crop yields. This review highlights pioneering and recent advancements in utilizing multi-traits Trichoderma and Bacillus species as potent promoters of plant growth and health. It examines the multifaceted impacts of saline stress on plants and microbes, elucidating their physiological and molecular responses. Additionally, it delves into the role of ACC deaminase in mitigating plant ethylene levels by Trichoderma and Bacillus species. Although there are several studies on Trichoderma-Bacillus, much remains to be understood about their synergistic relationships and their potential as auxiliaries in the phytoremediation of saline soils, which is why this work addresses these challenges.

Wastewater irrigation and Trichoderma colonization in tomato plants: effects on plant traits, antioxidant activity, and performance of the insect pest Macrosiphum euphorbiae

The scarcity of freshwater for agriculture in many regions has led to the application of sewage and saline water for irrigation. Irrigation with non-conventional water sources could become a non-harmful process for plant cultivation, and the effects of their use on crops should be monitored in order to develop optimal management strategies. One possibility to overcome potential barriers is to use biostimulants such as Trichoderma spp. fungi. Tomato is a crop of great economic importance in the world. This study investigated the joint effects of Trichoderma afroharzianum T-22 on tomato plants irrigated with simulated unconventional waters. The experiment consisted of a control and three water treatments. In the control, the plants were watered with distilled water. The three water treatments were obtained by using an irrigation water added with nitrogen, a wastewater effluent, and a mixed groundwater-wastewater effluents. Potted tomato plants (variety Bobcat) were grown in a controlled growth chamber. Antioxidant activity, susceptibility to the aphids Macrosiphum euphorbiae, and tomato plant growth parameters were estimated. Trichoderma afroharzianum T-22 had a positive effect on plant growth and antioxidant defenses when plants were irrigated with distilled water. Instead, no significant morphological effects induced by T. afroharzianum T-22 on plants were observed when unconventional water was used for irrigation. However, inoculation with T. afroharzianum T-22 activated a stress response that made the colonized plants more susceptible to aphid development and increased their fecundity and longevity. Thanks to this study, it may be possible for the first time to open a new discussion on the practical possibility of using reclaimed wastewater for crop irrigation with the addition of a growth-promoting fungal symbiont.

Harnessing Rhizospheric Microbes for Eco-friendly and Sustainable Crop Production in Saline Environments

Soil salinization is a global issue that negatively impacts crop yield and has become a prime concern for researchers worldwide. Many important crop plants are susceptible to salinity-induced stresses, including ionic and osmotic stress. Approximately, 20% of the world's cultivated and 33% of irrigated land is affected by salt. While various agricultural practices have been successful in alleviating salinity stress, they can be costly and not environment-friendly. Therefore, there is a need for cost-effective and eco-friendly practices to improve soil health. One promising approach involves utilizing microbes found in the vicinity of plant roots to mitigate the effects of salinity stress and enhance plant growth as well as crop yield. By exploiting the salinity tolerance of plants and their associated rhizospheric microorganisms, which have plant growth-promoting properties, it is possible to reduce the adverse effects of salt stress on crop plants. The soil salinization is a common problem in the world, due to which we are unable to use the saline land. To make proper use of this land for different crops, microorganisms can play an important role. Looking at the increasing population of the world, this will be an appreciated effort to make the best use of the wasted land for food security. The updated information on this issue is needed. In this context, this article provides a concise review of the latest research on the use of salt-tolerant rhizospheric microorganisms to mitigate salinity stress in crop plants.

Effect of salt stress on the photosynthetic characteristics and endogenous hormones, and: A comprehensive evaluation of salt tolerance in Reaumuria soongorica seedlings

Salinity is a major limiting factor in desert ecosystems, where Reaumuria soongarica is a dominant species. It is crucial to study the growth and physiological response mechanisms of R. soongorica under salt stress for the protection and restoration of the desert ecosystems. However, the effects of salt concentration and stress duration on endogenous hormonal content and photosynthetic efficiency and salt injury index of R. soongorica leaves have not been reported. Currently, there is no systematic evaluation system to determine physiological adaptation strategies of R. soongorica seedlings in response to salt stress. In this study, simulation experiments were performed with NaCl solution mixed with soil. Enzyme-linked immunosorbent assay and LI-6800 portable photosynthesis analyzer were used to measure indole acetic acid (IAA), corn nucleoside hormone (ZR), abscisic acid (ABA), and photosynthesis-related parameters in leaves of R. soongorica seedlings at 0 (24-48 h after salt treatment), 3, 6, and 9 days. At the same time, growth indicators (salt injury index, root-to-shoot ratio), reactive oxygen species content, superoxide dismutase enzyme (SOD) activity, osmolyte content, membrane peroxidation, and leaf pigment content were measured at different salt concentrations and treatment times. Finally, principal component analysis and membership function method were used to comprehensively evaluate the salt tolerance of seedlings. The results showed that treatment with 200 mM NaCl for 3 days significantly increased SOD activity, the content of osmotic adjustment substances (proline, soluble protein), endogenous hormone content (ABA, ZR), root-to-shoot ratio, and Chla/Chlb values but decreased malondialdehyde content (MDA) in the leaves of R. soongorica seedlings. Leaf water content (LRWC), net photosynthetic rate (Pn), transpiration rate (Tr), water use efficiency (WUE), and IAA content in R. soongorica seedlings were lower than those in the control, when exposed to 400 and 500 mM NaCl solutions. Finally, the principal component analysis revealed endogenous hormone content and antioxidant enzyme activity to be useful for the comprehensive evaluation of salt tolerance in R. soongorica seedlings. The R. soongorica seedlings showed the strongest salt tolerance when exposed to 200 mM NaCl for 3 days. This study provides a theoretical foundation for gene mining and breeding of salt-tolerant species in the future.

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.

Effects of Vermicompost Substrates and Coconut Fibers Used against the Background of Various Biofertilizers on the Yields of Cucumis melo L. and Solanum lycopersicum L

Vermicompost has been promoted as a viable substrate component owing to its physicochemical properties, nutrient richness, and status as an excellent soil improver. It is considered the best organic fertilizer and is more eco-friendly than chemical fertilizers. Plant-growth-promoting microorganisms (PGPMs) are defined as plant biofertilizers that improve nutritional efficiency—that is, they transform nutrients within substrates from organic to inorganic forms, making them available for plants. The main objective of this research study is to evaluate the effects of the application of three PGPM microbial consortia on different mixtures of organic substrates based on vermicompost (V) and coconut fiber (CF) on two different horticultural crops. We performed a yield analysis and drainage nutrient tests and determined the plant nutritional status and enzymatic activity in organic substrates based on the two crops, Cucumis melo L. and Solanum lycopersicum L. A multivariate analysis of variance and principal component analysis was conducted using substrate types and PGPMs as factors. Differences (p < 0.05) in yield, dehydrogenase activity, the nutrient concentrations in a petiole sap, and drainage were observed at 30, 60, 75, and 90 days after transplant. PGPMs such as Trichoderma sp. and plant-growth-promoting rhizobacteria (PGPR) in organic substrates (40V + 60CF) can significantly improve the nutritional status of plants for use in organic soilless container agriculture. Biofertilization with PGPMs and suitable mixtures of organic substrates together with aqueous extracts (tea) of vermicompost, as nutrient solutions applied by fertigation, has allowed us to achieve an adequate level of production through environmentally friendly techniques. The results obtained allowed us to affirm that it was possible to replace conventional fertilization using chemical products and ensure adequate crop nutrition by supplying the main macronutrients.

Synergistic action of Trichoderma koningiopsis and T. asperellum mitigates salt stress in paddy

Intensive cultivation increases the salinity and alkalinity of soil leading to its degradation. Such soil lead to abiotic stress conditions in plants causing ROS-mediated cellular damage. Microbes constitute an important group of bio-stimulants, which are promising alternatives to reduce ROS-mediated abiotic stresses and improve plant growth. In the present study synergistic activity of stress-tolerant Trichoderma koningiopsis NBRI-PR5 (MTCC 25372) and T. asperellum NBRI-K14 (MTCC 25373) (TrichoMix) was assessed in paddy crop under salt stress conditions. Improved soil microbial biomass carbon (MBC), total organic carbon (TOC), and available nutrients N/P/K by 2-3 folds was observed in the pot experiment using the TrichoMix. It restored the heterogeneous microbial population of the paddy rhizosphere during salt stress and modulated the soil enzyme activities. The anatomical distortions in rice roots due to salt stress were stabilized in presence of the TrichoMix. Different stress marker genes (OsMAPK5, OsAPX, OsGST, OsUSP, OsBADH, OsLYSO, OsNRAMP6, and OsBz8) were differentially modulated by the TrichoMix in presence of salt stress as compared to the control. The TrichoMix increased the yield by 10% in marginally stressed fields; however, it enhanced the yield by approximately 60% when used with the 50% recommended dose of NPK. In the integrated treatment, Fe and Zn were fortified by approximately 40% and 29% respectively in the grains. From the present study, it was concluded that the TrichoMix stimulated the rice plants to accumulate osmoprotectants, improved the anatomical features, modulated the plant defense system, and improved the grain yield and quality. Therefore, the NBRI-PR5 and NBRI-K14 mixture may be used as a bio-stimulant to increase productivity in the rapidly deteriorating soil and reduce the NPK inputs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01192-6.

Salt Stress Alleviation in Triticum aestivum Through Primary and Secondary Metabolites Modulation by Aspergillus terreus BTK-1

We report the growth promoting potential in wheat under saline conditions by an endophytic fungus Aspergillus terreus BTK-1. The isolated BTK-1 from the root of Chenopodium album was identified as Aspergillus terreus through 18S rDNA sequence analysis. BTK-1 secreted indole acetic acid (IAA), exhibited 1- aminocyclopropane-1- carboxylate deaminase (ACC) and siderophores activity, and solubilized phosphate. Wheat seedlings were exposed to a saline environment (0, 60, 120, and 180 mM) with or without BKT-1 inoculation. Seedlings inoculated with BTK-1 showed higher concentrations of IAA and gibberellins, whereas they showed low concentrations of abscisic acid compared to the BTK-1 non-inoculated plants. Also, BTK-1 inoculated wheat plants revealed significantly (P = 0.05) longer shoots and roots, biomass, and chlorophyll contents. On the contrary, plants without BTK-1 inoculation indicated significantly (P = 0.05) low amounts of carbohydrates, phenolics, prolines, potassium, magnesium, and calcium, with high amounts of Na and malonaldehyde under salt stress. Likewise, BTK-1 inoculated wheat plants showed high activity of reduced glutathione, and low activity of ascorbate, catalase, and peroxidase under salt stress. The mitigation of salinity stress by BTK-1 inoculated wheat plants suggested its use as a bio-stimulator in salt affected soils.

Understanding the potential of root microbiome influencing salt-tolerance in plants and mechanisms involved at the transcriptional and translational level

Soil salinity severely affects plant growth and development and imparts inevitable losses to crop productivity. Increasing the concentration of salts in the vicinity of plant roots has severe consequences at the morphological, biochemical, and molecular levels. These include loss of chlorophyll, decrease in photosynthetic rate, reduction in cell division, ROS generation, inactivation of antioxidative enzymes, alterations in phytohormone biosynthesis and signaling, and so forth. The association of microorganisms, viz. plant growth-promoting rhizobacteria, endophytes, and mycorrhiza, with plant roots constituting the root microbiome can confer a greater degree of salinity tolerance in addition to their inherent ability to promote growth and induce defense mechanisms. The mechanisms involved in induced stress tolerance bestowed by these microorganisms involve the modulation of phytohormone biosynthesis and signaling pathways (including indole acetic acid, gibberellic acid, brassinosteroids, abscisic acid, and jasmonic acid), accumulation of osmoprotectants (proline, glycine betaine, and sugar alcohols), and regulation of ion transporters (SOS1, NHX, HKT1). Apart from this, salt-tolerant microorganisms are known to induce the expression of salt-responsive genes via the action of several transcription factors, as well as by posttranscriptional and posttranslational modifications. Moreover, the potential of these salt-tolerant microflora can be employed for sustainably improving crop performance in saline environments. Therefore, this review will briefly focus on the key responses of plants under salinity stress and elucidate the mechanisms employed by the salt-tolerant microorganisms in improving plant tolerance under saline environments.

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.

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.

Effect of zinc-resistant Lysinibacillus species inoculation on growth, physiological properties, and zinc uptake in maize (Zea mays L.)

Soil contamination by heavy metals is one of the major abiotic stresses that cause retarded plant growth and low productivity. Among the heavy metals, excessive accumulations of zinc (Zn) cause toxicity to plants. The toxicity caused by Zn could be managed by application of Zn-tolerant plant growth-promoting (PGP) bacteria. In this study, five Zn-tolerant bacteria (100-400 mg^-1 Zn resistant) were selected and identified as Lysinibacillus spp. based on 16S rRNA gene sequencing. The PGP properties of the Lysinibacillus spp. showed the production of indole acetic acid (60.0-84.0 μg/ml) and siderophore, as well as solubilization of potassium. Furthermore, the isolates were evaluated under greenhouse condition with 2 g kg^-1 Zn stress and without Zn stress along with control on Zea mays. The results showed that Lysinibacillus spp. coated seeds enhanced plant growth attributes and biomass yield in both conditions compared with control plants. The enhancement of root growth ranged from 49.2 to 148.6% and shoot length from 83.3 to 111.7% under Zn-stressed soils. Also, the inoculated seedlings substantially enhanced chlorophyll a and b, proline, total phenol, and ascorbic acid. The uptake of Zn by maize root ranged from 31.5 to 210.0% compared with control plants. Therefore, this study suggested that the tested Zn-tolerant Lysinibacillus spp. may be used for cultivation of Z. mays in Zn-contaminated agricultural lands.

Biological function of Klebsiella variicola and its effect on the rhizosphere soil of maize seedlings

BACKGROUND

Deterioration of the ecological environment in recent years has led to increasing soil salinization, which severely affects the cultivation of agricultural crops. While research has focused on improving soil environment through the application of pollution-free microbial fertilizers, there are relatively few plant growth-promoting bacteria suitable for saline-alkali environments. Although Klebsiella variicola can adapt to saline-alkali environments to successfully colonize rhizosphere microenvironments, only a few studies have investigated its role in promoting crop growth. Its effect on the crop rhizosphere soil microenvironment is especially unclear.

METHODS

In this study, the biological function of K. variicola and its colonization in maize seedling rhizosphere soil were studied in detail through selective media and ultraviolet spectrophotometry. The effects of K. variicola on the rhizosphere soil microenvironment and the growth of maize seedlings in saline-alkali and neutral soils were systematically analysed using the colorimetric method, the potassium dichromate volumetric method, and the diffusion absorption method.

RESULTS

Our results showed that K. variicola played a role in indole acetic acid, acetoin, ammonia, phosphorus, and potassium production, as well as in nitrogen fixation. A high level of colonization was observed in the rhizosphere soil of maize seedlings. Following the application of K. variicola in neutral and saline-alkali soils, the nutrient composition of rhizosphere soil of maize seedlings increased in varying degrees, more notably in saline-alkali soil. The content of organic matter, alkali-hydrolysable nitrogen, available phosphorus, available potassium, alkaline phosphatase, sucrase, urease, and catalase increased by 64.22%, 117.39%, 175.64%, 28.63%, 146.08%, 76.77%, 86.60%, and 45.29%, respectively, insaline-alkalisoil.

CONCLUSION

K.variicola, therefore, performed a variety of biological functions to promote the growth of maize seedlings and effectively improve the level of soil nutrients and enzymes in the rhizosphere of maize seedlings, undersaline-alkali stress conditions. It played an important role in enhancing the rhizosphere microenvironment of maize seedlings under saline-alkali stress.

Amelioration effect of salt-tolerant plant growth-promoting bacteria on growth and physiological properties of rice (Oryza sativa) under salt-stressed conditions

For sustainable agriculture in saline soil, extensive exploitation of salt-tolerant plant growth-promoting (PGP) bacteria and other symbiotic bacteria is required. This study was carried out to evaluate the efficiency of native salt-tolerant rice rhizobacteria for plant growth promotion under salt stress. A total of 188 bacteria were screened for assessing salt-tolerant capacity and nine isolates tolerating 12% NaCl (w/v) concentration were selected. Biochemical and molecular identification revealed that the salt-tolerant bacteria belonged to Bacillus sp, Exiguobacterium sp, Enterobacter sp, Lysinibacillus sp, Stenotrophomonas sp, Microbacterium sp, and Achromobacter sp. The increase in NaCl concentration from 2 to 4% decreases the PGP activities such as IAA production, P solubilization, K solubilization, and nitrate reduction. The effects of inoculation of salt-tolerant bacteria on the growth and different physiological properties of rice (Oryza sativa) were studied. It was found that the salinity affected the root and shoot length of the control plants; however, bacterial inoculant were found to effectively promote the growth of paddy under salinity stress. Further, bacterial inoculants substantially enhanced total chlorophyll, proline, total phenol, and oxidative damage such as electrolyte leakage and membrane stability index under salt stress. This study suggests that salt-tolerant PGP bacteria may be used for cultivation of O. sativa in salinized agricultural lands.

Seed Biopriming with Salt-Tolerant Endophytic Pseudomonas geniculata-Modulated Biochemical Responses Provide Ecological Fitness in Maize (Zea mays L.) Grown in Saline Sodic Soil

Under changing climate, soil salinity and sodicity is a limiting factor to crop production and are considered a threat to sustainability in agriculture. A number of attempts are being made to develop microbe-based technologies for alleviation of toxic effects of salts. However, the mechanisms of salt tolerance in agriculturally important crops are not fully understood and still require in-depth study in the backdrop of emerging concepts in biological systems. The present investigation was aimed to decipher the microbe-mediated mechanisms of salt tolerance in maize. Endophytic Pseudomonas geniculate MF-84 was isolated from maize rhizosphere and tagged with green fluorescent protein for localization in the plant system. Confocal microphotographs clearly indicate that MF-84 was localized in the epidermal cells, cortical tissues, endodermis and vascular bundles including proto-xylem, meta-xylem, phloem and bundle sheath. The role of P. geniculate MF-84 in induction and bioaccumulation of soluble sugar, proline and natural antioxidants enzymes in maize plant was investigated which lead not only to growth promotion but also provide protection from salt stress in maize. Results suggested that application of P. geniculate MF-84 reduces the uptake of Na+ and increases uptake of K+ and Ca2+ in maize roots indicative of the role of MF-84 in maintaining ionic balance/homeostasis in the plant roots under higher salt conditions. It not only helps in alleviation of toxic effects of salt but also increases plant growth along with reduction in crop losses due to salinity and sodicity.

Characterization of Trichoderma asperellum RM-28 for its sodic/saline-alkali tolerance and plant growth promoting activities to alleviate toxicity of red mud

Red mud (RM) is a highly alkaline, saline and sodic solid by-product released by alumina industries, which pose an economical and environmental problem and establishment of vegetation on these sites is a big challenge. In the present study, a fungus RM-28 exhibiting high tolerance to alkaline (pH 12), saline/sodic (NaCl 4%) was isolated from RM flooded rhizosphere soil of bermudagrass and tested its ability to reduce RM toxicity and promote the growth of sorghum-sudangrass seedlings. This fungus also exhibited high tolerance to heavy metal(loid)s (HMs) and desirable plant growth-promoting traits. This fungus was identified as Trichoderma asperellum based on its internal transcribed spacer (ITS) of rDNA and translation elongation factor-1α (TEF 1α) gene analysis. This fungus was effective in reducing the pH and solubilizing tricalcium phosphate under high alkaline and saline conditions in vitro. Further, RM-28 inoculation significantly lowered the pH and EC of the red mud from 11.8 to 8.2 and 2.23 to 1.42, respectively. Inoculation of RM-28 significantly improved the growth, chlorophyll content and reduced the oxidative stress of sorghum-sudangrass seedlings grown in red mud leachate. These observations suggest that T. asperellum RM-28 serves as potential source for the establishment of vegetation on red mud/red mud contaminated soils.

Alleviation of the effects of saline-alkaline stress on maize seedlings by regulation of active oxygen metabolism by Trichoderma asperellum

This study investigated the influence of Trichoderma asperellum on active oxygen production in maize seedlings under saline-alkaline stress conditions. Two maize cultivars were tested: 'Jiangyu 417' ('JY417'), which can tolerate saline-alkaline stress; and, 'Xianyu 335' ('XY335'), which is sensitive to saline-alkaline stress. The seedlings were grown on natural saline-alkaline soil (pH 9.30) in plastic pots. To each liter of saline-alkaline soil, 200 mL of T. asperellum spore suspension was applied; three fungal suspensions were used, namely, 1 × 103, 1 × 106, and 1 × 109 spores/L. A control with only the vehicle applied was also established, along with a second control in which untreated meadow soil (pH 8.23) was used. Root and leaf samples were collected when the seedlings had three heart-shaped leaves and the fourth was in the developmental phase. Physical and biochemical parameters related to oxidation resistance were assessed. The results indicated that the 'JY417' and 'XY335' seedlings showed different degrees of oxidative damage and differences in their antioxidant defense systems under saline-alkaline stress. As the spore density of the fungal suspension increased, the K+ and Ca2+ contents in the seedlings increased, but Na+ content decreased. Moreover, fungal treatment promoted the synthesis or accumulation of osmolytes, which enhanced the water absorbing capacity of the cells, increased antioxidant enzyme activities, enhanced the content of non-enzyme antioxidants, and reduced the accumulation of reactive oxygen species. Fungal treatment alleviated oxidative damage caused by the saline-alkaline stress in roots and leaves of the seedlings. The application of T. asperellum overcame the inhibitory effect of saline-alkaline soil stress on the growth of maize seedlings. In the present experiment, application with 1 × 109 spores/L gave the optimal results.

Salinity fluctuation influencing biological adaptation: growth dynamics and Na+ /K+ -ATPase activity in a euryhaline bacterium

Although salinity fluctuation is a prominent characteristic of many coastal ecosystems, its effects on biological adaptation have not yet been fully recognized. To test the salinity fluctuations on biological adaptation, population growth dynamics and Na⁺ /K⁺ -ATPase activity were investigated in the euryhaline bacterium Idiomarina sp. DYB, which was acclimated at different salinity exposure levels, exposure times, and shifts in direction of salinity. Results showed: (1) bacterial population growth dynamics and Na⁺ /K⁺ -ATPase activity changed significantly in response to salinity fluctuation; (2) patterns of variation in bacterial growth dynamics were related to exposure times, levels of salinity, and shifts in direction of salinity change; (3) significant tradeoffs were detected between growth rate (r) and carrying capacity (K) on the one hand, and Na⁺ /K⁺ -ATPase activity on the other; and (4) beneficial acclimation was confirmed in Idiomarina sp. DYB. In brief, this study demonstrated that salinity fluctuation can change the population growth dynamics, Na⁺ /K⁺ -ATPase activity, and tradeoffs between r, K, and Na⁺ /K⁺ -ATPase activity, thus facilitating bacterial adaption in a changing environment. These findings provide constructive information for determining biological response patterns to environmental change.