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Tomato is an important nutritional vegetable crop and its nutrient contents are affected by both biotic and abiotic stresses. The main objective of this study was to determine the effect of seed biopriming with Trichoderma pseudokoningii BHUR2 and vermiwash treatment on nutrient content of tomato and defense response against Sclerotium rolfsii under heat stress condition. The combined application of T. pseudokoningii BHUR2 and vermiwash increased fresh weight of root (4.8-fold) and shoot (5.8-fold), dry weight of root (6.9-fold) and shoot (6.4-fold) and number of fruits per plant (4.2-fold) as compared to control under S. rolfsii inoculated condition. Plants treated with T. pseudokoningii BHUR2 and vermiwash exhibited higher defense response against S. rolfsii, mediated by higher activity of superoxide dismutase (3.57-fold), peroxidase (2.05-fold) and phenylalanine ammonia lyase (2.98-fold) enzymes and accumulation of total phenol content (5.35-fold) as compared to control plants. In addition, combined treatment was found to have a positive impact on nutritional status (N, P, K and Ca and lycopene, total soluble sugar and total protein) in tomato fruit. These results suggest potential of T. pseudokoningii BHUR2 and vermiwash in enhancing tomato immunity against S. rolfsii under heat stress condition, which was due to (1) induction in the antioxidant activity and phenylpropanoid pathway, which minimize oxidative damage and reduce pathogen infection and (2) significant improvement in nutrient content leads to better plant growth. The formulation of Trichoderma BHUR2 can be used for field application to mitigate heat stress in plants.

To provide food security with quality crops for exponentially growing population brought intense pressure on the limited land and natural resources among developing countries. Abiotic stresses such as continuously rising temperature as consequences of global warming is adding pressure to existing problems by adversely affecting crop productivity through physiological changes in plants. Hence there is need of qualitatively potential vegetable crops that can withstand changing environmental conditions such as Okra (Abelmoschus spp.) holding high level of nutrients along with economic importance. But requirement of high temperature and humidity for its cultivation make the plant prone to several phytopathogens that ultimately leads to severe qualitative and quantitative losses depending upon the plant growth stage getting affected. Due to the unenviable problems of chemical fertilizers, biocontrol agents were applied as auxiliary treatments either single or in combination that possess fewer consequences on the environment. But due to increasing environmental and soil temperature, activities of these formulations are getting hindered. Therefore, there is an urgent requirement to procure high temperature stress tolerant strains along with antagonistic and plant growth promoting abilities. In the current study, we mainly focused on isolation of high temperature tolerant Trichoderma harzianum (BHU P4) strain with antagonistic abilities against fungal pathogen Sclerotium rolfsii causing collar rot disease. The strain was also studied for plant growth promoting attributes in okra plant which resulted in increased fresh weight, dry weight, chlorophyll content and nutrient content in comparison to control and pathogen challenged plants. This study was associated with an improvement in the level of total phenol, SOD, PO and PAL enzymes in order to regulate the host defense mechanism against its confrontation with S. rolfsii.

Based on natural and anthropogenic activities, the soil quality has depleted gradually which is also mediated through unpredictably changed environmental conditions. As a consequence, a challenge has been raised before farmers and nations to compensate the degraded soil quality. To replenish the soil quality, farmers deploy synthetic fertilizer which is an unsustainable practice and further lead conditions worse by the diminished biological activity, increased level of toxicity, decreased fertility, etc. As a comparatively safe and sustainable alternative, PGPRs have been characterized as they could always assist plants against various challenges like nutrient unavailability, abiotic stresses, and pathogens. Many of those PGPRs which have been studied for their beneficial impacts are now used on a commercial scale for alleviating abiotic and biotic stresses of crop plants. Some of the PGPRs with wonderful ex situ and in situ performances are Azospirillum brasilense, Azospirillum lipoferum, Bacillus, Pseudomonas, Acinetobacter, Alcaligenes faecalis, Stenotrophomonas, Pseudomonas, Rahnella, Pseudomonas fluorescens, Bacillus megaterium, Bacillus licheniformis, Proteus mirabilis, Achromobacter xylosoxidans, Gluconoacetobacter diazotrophicus, Azoarcus, Pseudomonas migulae, Brachybacterium saurashtrense, Brevibacterium casei, Haererohalobacter, and many more which have surely assisted plant including a list of Arabidopsis, maize, wheat, potato, tomato, capsicum, etc. This chapter unfolds important mechanisms and strategies used by PGPRs to help crop plant cope up the various biotic and abiotic stresses and increase soil and plant health.

Contaminated soil has adverse effects on legume symbiosis, which lead to disturbance in nitrogen metabolism in plants. Although several studies have been performed on response of biological nitrogen fixation (BNF) under stress condition, less is known about how leguminous plants adjust their BNF process under contaminated soil. Fenugreek (Trigonella foenum-graecum) is an annual plant belonging to legume family and majorly grown in Northern region of India for its medicinal property. Northern region of India is mainly affected with dynamic climate that ultimately cause adverse effect on plant cultivation. In addition, due to many functioning industries in this region, nearby agricultural lands are affected with their toxic effluents. These effluents contaminate agricultural soil with heavy metals and salts, where leguminous plants fail to perform rhizobia symbiosis. However, plant releases more number of antioxidants, flavonoids, or other phenolic compounds to cope with such a type of soil stress. In the present chapter, fenugreek plant property and its rhizobial symbiosis are discussed here. Some case studies also mentioned on role of exogenous flavonoids in alleviation of soil stress effects on nodule formation. The present study suggests the use of flavonoid compounds as plant biostimulants for improving BNF process in legume plant under soil stress conditions and also explores new study in this direction.

The soil microbial community hugely affects the growth and development of the plants through direct or indirect interactions. The rhizospheric microbial community dwelling in the soil are major drivers of this phenomenon. Manipulation of soil microbial population and community through various treatments of an array of beneficial microbes such as plant growth-promoting rhizobacteria, plant growth-promoting fungi, endophytic bacteria, biocontrol agents, etc. helps in alleviating various abiotic and biotic stresses of the plants. This, in turn, leads to the achievement of the yield which is close to the potential yield of the crop. Apart from increasing the yield of the crop, some of the beneficial microbes also enhance the nutrient content in the soil and availability of certain minerals to the plants eventually leading to conservation of soil health. Thus, manipulation of plant–soil microbiome paves the way for sustainable and green agriculture without imparting excessive monetary expenses, thereby creating increased crop production and embellishment of soil health. This chapter will so focus on the strategies and methods that are adopted to manipulate the plant–soil microbiome interactions, various mechanisms that are involved in the interactions, and the impact of this technology on the plant and soil.

Biological nitrogen fixation (BNF) is a sustainable approach to reduce negative effects of chemical N fertilizers on ecosystem. Therefore, BNF has gained special attention in researchers for enhancing its effectiveness among different crop plants. The genetic mutation approach in bacterial spp. towards efficient symbiosis and plant growth promotion is an attractive strategy nowadays. In addition, positive mutants of plant growth promoting rhizobacterial (PGPR) strains could survive under harsh conditions and promote plant growth also. The objectives of the present chapter are to highlight the basic mechanisms of induced mutation in bacteria and applied aspects of these mutated bacteria for improving nitrogen-fixing abilities in plants.

Salt tolerant bacteria can be helpful in improving a plant’s tolerance to salinity. Although plant–bacteria interactions in response to salt stress have been characterized, the precise molecular mechanisms by which bacterial inoculation alleviates salt stress in plants are still poorly explored. In the present study, we aimed to determine the role of a salt-tolerant plant growth-promoting rhizobacteria (PGPR) Sphingobacterium BHU-AV3 for improving salt tolerance in tomato through investigating the physiological responses of tomato roots and leaves under salinity stress. Tomato plants inoculated with BHU-AV3 and challenged with 200 mM NaCl exhibited less senescence, positively correlated with the maintenance of ion balance, lowered reactive oxygen species (ROS), and increased proline content compared to the non-inoculated plants. BHU-AV3-inoculated plant leaves were less affected by oxidative stress, as evident from a reduction in superoxide contents, cell death, and lipid peroxidation. The reduction in ROS level was associated with the increased antioxidant enzyme activities along with multiple-isoform expression [peroxidase (POD), polyphenol oxidase (PPO), and superoxide dismutase (SOD)] in plant roots. Additionally, BHU-AV3 inoculation induced the expression of proteins involved in (i) energy production [ATP synthase], (ii) carbohydrate metabolism (enolase), (iii) thiamine biosynthesis protein, (iv) translation protein (elongation factor 1 alpha), and the antioxidant defense system (catalase) in tomato roots. These findings have provided insight into the molecular mechanisms of bacteria-mediated alleviation of salt stress in plants. From the study, we can conclude that BHU-AV3 inoculation effectively induces antioxidant systems and energy metabolism in tomato roots, which leads to whole plant protection during salt stress through induced systemic tolerance.

Soil salinity is a major limiting factor for crop productivity worldwide and is continuously increasing owing to climate change. A wide range of studies and practices have been performed to induce salt tolerance mechanisms in plants, but their result in crop improvement has been limited due to lack of time and money. In the current scenario, there is increasing attention towards habitat-imposed plant stress tolerance driven by plant-associated microbes, either rhizospheric and/or endophytic. These microbes play a key role in protecting plants against various environmental stresses. Therefore, the use of plant growth-promoting microbes in agriculture is a low-cost and eco-friendly technology to enhance crop productivity in saline areas. In the present review, the authors describe the functionality of endophytic bacteria and their modes of action to enhance salinity tolerance in plants, with special reference to osmotic and ionic stress management. There is concrete evidence that endophytic bacteria serve host functions, such as improving osmolytes, anti-oxidant and phytohormonal signaling and enhancing plant nutrient uptake efficiency. More research on endophytes has enabled us to gain insights into the mechanism of colonization and their interactions with plants. With this information in mind, the authors tried to solve the following questions: (1) how do benign endophytes ameliorate salt stress in plants? (2) What type of physiological changes incur in plants under salt stress conditions? And (3), what type of determinants produced by endophytes will be helpful in plant growth promotion under salt stress?

Plant growth promoting rhizobacteria (PGPR) have been described for sustainable agriculture practices as being a vital agent for abiotic and biotic stress mitigation and growth promotion in plants. In the present research, the authors emphasize the role of drought tolerant PGPR namely, Pseudomonas simiae strain AU, in protection of soybean plants by modulating the gene expression profile and phytohormone biosynthesis responsible for drought tolerance in plants. The gene expression analysis confirmed the involvement of transcription factors (DREB/EREB), osmoprotectants (P5CS, GOLS), and water transporters (PIP & TIP), as these genes were up-regulated in P. simiae AU-inoculated plants leading to drought tolerance. In addition, enhanced production of abscisic acid (ABA) and salicylic acid (SA) hormones and reduction of ethylene emission, associated with promoting drought tolerance, was observed in bacterial-inoculated plants in comparison to non-inoculated plants. Higher proline and total soluble sugar contents in AU-inoculated soybean plants also contributed to increased tolerance to drought stress. Overall, P. simiae AU mediated drought-induced expression profiles of stress genes and plant hormones were determined in soybean plants.

Nitric oxide (NO), evolved during various biological processes occuring in soil, bacteria, and plants, is acting as signaling molecule to trigger different essential pathways involved in plant-microbe interactions. Reactive nitrogen species (RNS) is present at every developmental stage of plants and plays very important role in their life cycle. This valuable molecule also involved in signaling in response to biotic and abiotic stress in plants. Moreover, NO is very important or said to be a central molecule of nitrogen cycle. The NO is produced during different biological nitrogen transformation processes. Remarkably, the essential information of NO production and its efficient relations with plant and microbes are poorly characterized. This chapter covers the different processes of NO production in soil, bacteria, and plants and their role in different physiological processes. In particular, the role of NO is addressed as a signaling molecule in plant-microbe interactions including legume-rhizobium symbiosis.

Plant growth-promoting bacteria (PGPB) are capable of alleviating environmental stress and eliciting tolerance in plants to promote their growth. Several PGPB elicit physical and/or chemical changes related to plant defense in the form of induced systemic resistance (ISR) under biotic stress. Researchers emphasized that PGPB-elicited ISR has suppressed plant diseases caused by a range of pathogens in both the greenhouse and field. PGPB-elicited physical and chemical changes in plants result in enhanced tolerance to drought, salt, and other factors that have been described as a form of induced systemic tolerance under abiotic stress. This review will focus on recent research concerning interactions between PGPB and plants under biotic and abiotic stresses. The use of PGPB requires precise understanding of the interactions between plant-bacteria, among bacteria-microbiota, and how biotic and abiotic factors influence these relationships. Consequently, continued research is needed to develop new approaches to ameliorate the efficiency of PGPB and to understand the ecological, genetic, and biochemical relationships in their habitat.

This study explored several features related to salt tolerance in soybean plants through plant growth-promoting rhizobacteria (PGPR; Pseudomonas sp. strain AK-1, and Bacillus sp. strain SJ-5). We report the significant effect of 1-aminocyclopropane-1-carboxylate deaminase, indole-3-acetic acid production and exopolysaccharide production from both bacterial strains on physical parameters and biochemical activities in Glycine max plants under salt stress. In this report, we investigated the leaf water content, osmolyte accumulation, and activities of stress-responsive enzymes in the absence and presence of salt stress. Control (plants devoid of bacterial strains) and PGPR-inoculated soybean plants were grown in half Murashige and Skoog medium subjected to saline and non-saline conditions. Results showed that PGPR-inoculated plants had superior tolerance against salt stress, as shown by their enhanced plant biomass (fresh weight), higher water content, higher photosynthesis activity, and lower osmotic stress injury. The increased proline accumulation and lipoxygenase activity in PGPR-inoculated plant roots contributed to increased plant tolerance to salt stress. SJ-5-inoculated plants (0.414 U/mg protein) and AK-1-inoculated plants (0.403 U/mg protein) showed higher LOX activity than control plants (0.366 U/mg protein). Proline content was higher in SJ-5-(120 µg/g f.w.) and AK-1-(135 µg/g f.w.)inoculated plants than control plants (90 µg/g f.w.). Peroxidase activity was also higher in PGPR-inoculated plant roots during salinity. These results suggest that, in PGPR-inoculated roots, lipoxygenase plays a role in mitigating the adverse effect of salt stress. Furthermore, enhanced proline maintains osmotic balance and a positive water potential for water entrance into the roots, and peroxidase enzyme reduces oxidative damage by lowering reactive oxygen species level under salt stress. Our results indicated that both Pseudomonas and Bacillus are multifunctional PGPR strains that can promote plant growth, development and reduce salinity stress. However, our Bacillus bacterium strain had more ACC deaminase, phosphate solubilization, and siderophore activity under salt stress as compared to the Pseudomonas strain.

Bacterial released volatile compounds (VOCs) in air enable bacteria to interact with their surrounding environment. Soil bacterial volatiles are known to contribute to plant interactions, and several studies also identified their influence on plant stress tolerance. Plant growth-promoting rhizobacterial (PGPR)-mediated VOCs are reported to increase seedling emergence, plant weight, crop yield, and stress resistance. The present chapter describes the characterization of different bacterial VOCs and their roles in enhancement of plant abiotic stress tolerance, a new research area, with potential agriculture applications.

Wilt disease of soybean caused by a very common soil-borne fungus, Fusarium oxysporum is one of the most destructive diseases of the crop. The aim of the present study was to characterize plant growth-promotion activities and induced resistance of a rhizobacterial strain for the soybean plant against F. oxysporum. Rhizobacterium strain SJ-5 exhibited plant growth-promotion characteristics and antagonistic activity against the test pathogen on dual plate assay. It was identified as a Carnobacterium sp. A 950 bp PCR product was amplified from Carnobacterium sp. strain SJ-5, using zwittermicin A self-resistance gene-specific primers (zmaR). The strain produced indole 3-acetic acid (19 μg/ml) in the presence of salt stress and exhibited growth in Dworkin and Foster salt medium amended with 1-aminocyclopropane-1-carboxylate (ACC) through ACC deaminase activity (277 nmol/mg/h) as compared to the control. Strain seeds treated with the strain significantly enhanced the quorum of healthy plants after challenge inoculation at 14 days after seeding. An increase in the activity of stress enzymes after challenge inoculation with the test pathogen is reported. Treatment with the bacterium resulted in an increase in the chlorophyll content in the leaves in comparison with challenge-inoculated plants.

In the present study, two bacterial strains along with Pseudomonas sp. strain VS1 were employed and screened on the basis of plant growth-promotion characteristics. Strains showed in vitro antibiosis against the test fungal pathogen Fusarium oxysporum together with plant growth-promotion properties that included indole-3-acetic acid, 1-aminocyclopropane-1-carboxylic acid and inorganic phosphorus solubilization production. The activities of stress responsive enzymes that included lipoxygenase, phenylalanine ammonia-lyase, catalase, peroxidase and superoxide dismutase were reported in bacteria and control-treated soybean plants. Bacteria treated seeds showed higher enzymatic activities in leaves in comparison with fungal spore treated seeds and were considered as positive control. Treatment with bacteria resulted in remarkable increase in the chlorophyll content in leaves as compared to water (negative control) and fungal spore treated seeds (P

Soil salinity is a major abiotic factor which adversely affects the crop growth and productivity worldwide. Higher salt concentration caused ion imbalance and hyperosmotic stress which often lead to oxidative stress in plants. Soil salinization is mainly due to the poor irrigation management practices and natural causes. A total 20 % of the world’s cultivated lands and almost half of all irrigated lands are affected by high salinity. This chapter begins by stressing the importance of research into plant salt tolerance. After a brief outline of salinity-induced damage to both agricultural yield and growth of plants, strategies which plants adopt to deal with salinity are discussed, and current biotechnological efforts towards producing salt-tolerant crops are summarized. Particular attention is paid towards the application of plant growth-promoting bacteria in agriculture system for producing salt stress-tolerant crops and a fundamental understanding towards the mechanisms of beneficial plant–microbe interaction in the presence of salt.

In the present study, we employ Pseudomonas sp. strain VS1 showed in vitro plant growth-promotion characteristics and promoted soybean seed emergence under salt stress. Strain produced indole 3-acetic acid in the presence of salt stresses that exhibited high numbers of lateral root as compared to control. Bacterial strain exhibited growth in DF salt medium amended with 1-aminocyclopropane-1-carboxylate through ACC deaminase activity. Bacterial-treated soybean seeds were subjected to salt stress and significantly enhanced emergence at 7 days after seeding. Strain untreated soybean plants had a 33% seed germination when 200 mM NaCl was applied at 0 DAS and the root length was significantly decreased compared to the strain treated plants (LSD0.05 = 0.21). Most importantly, the application of 200 mM NaCl at 0 DAS resulted in only a 9% of lateral root in untreated plants as compared to strain treated plants.

In continuous agricultural systems, crop yields are directly dependent on the inherent soil fertility with microbial processes that governs the mineralization and mobilization of nutrients required for plant growth. The impact of different crop species that are used in various combinations is likely to be an important factor in determining the structure of plant benign microbial communities that function in nutrient cycling, the production of plant growth hormones, and suppression of root diseases. In the present scenario, a perceived role of biotechnology is to introduce multiple choreographed genes into plants that would elicit multiple benefits to the plants such as resistance to stress, productivity, and quality. Microbial genomes that have coevolved with native plant species may already be choreographed and compatible with a wide range of plant genomes and available in this vast unexplored genetic reservoir. Understanding of microbial genome and how it communicates with plant genome for their mutual welfare could lead to innovative methods of plant improvement. Increased adverse effects of abiotic and biotic stresses impacting productivity in principal crops are being witnessed all over the world. Extreme events like prolonged droughts, intense rains and flooding, heat waves, and frost damages are likely to further increase in future due to climate change. A wide range of adaptations and mitigation strategies are required to cope with such impacts. Efficient resource management and crop improvement for evolving better breeds can help to overcome abiotic stresses to some extent. However, such strategies being long drawn and cost intensive, there is a need to develop simple and low cost-effective biological methods for the management of abiotic stress, which can be used on long-term basis. Therefore, studies are needed to elucidate the molecular mechanisms that result from treatment of plants with benign microbes under stress conditions and only then will the full benefits of plant-microbe interaction be understood.

Salinity is a major limiting factor for soybean crop productivity. To enhance the tolerance of soybean against salt stress, it is essential to understand the diversity of microbiota harboured by soybean rhizosphere. Earlier studies have demonstrated that local adaptation of plants to habitat imposed stresses is driven by their closely associated microbes. The present study aimed to isolation and characterization of salt tolerant rhizobacteria with respect to their functional plant growth promotion ability. A total of 43 bacterial isolates were recovered from soybean rhizospheric soil grown in Bundi district, Rajasthan, India. Out of them, one bacterial isolate strain AU was found to tolerate 10% NaCl stress and significantly enhanced soybean seedlings growth under 100mM NaCl condition. Molecular phylogenetic analysis placed this isolate closely to Pseudomonas simiae OLiT with 99.93% similarity. Molecular characterization of functional genes revealed that AU bacterium possessed genes like IaaM (IAA production), g6pd (Pi-solubilization) and sid (siderophore production). Here, we show that soybean rhizosphere possessed a salt tolerant plant growth promoting bacterium strain AU, which may have impacts on alleviation and tolerance of salt stress in legume plants.