Naveen Kumar Arora

Effect of Indole-3-Acetic Acid (IAA) Produced by Pseudomonas aeruginosa in Suppression of Charcoal Rot Disease of Chickpea

The production of indole-3-acetic acid (IAA), by rhizobacteria, has been associated with plant growth promotion, especially root initiation and elongation. Isolate TO3 selected from 103 fluorescent pseudomonads, identified as Pseudomonas aeruginosa, showed maximum production of IAA. Isolate TO3 having biocontrol activity against Macrophomina phaseolina also showed production of siderophore and HCN was used to screen the role of bacterial IAA in reducing the level of charcoal rot disease occurrence in chickpea. Four IAA defective stable mutants of isolate TO3 having biocontrol activity against M. phaseolina were developed through 5-bromouracil mutagenesis. Mutant TO52 showed 76.47% reduction in production of IAA. Standard IAA was used in similar concentration as present in cell-free culture supernatant of wild isolate TO3 and its mutant TO52. The in vitro and in vivo study showed that IAA-defective mutant TO52 caused reduced biocontrol and plant growth promotory activity than wild isolate TO3. Standard IAA showed comparable biocontrol activity to the culture supernatant. To some extent better biocontrol and growth promotory activity in supernatant than standard IAA indicates the synergistic role of siderophore and HCN. The study clearly reports the role of bacterial IAA in suppression of charcoal rot disease of chickpea.

Plant Growth Promoting Rhizobacteria: Constraints in Bioformulation, Commercialization, and Future Strategies

Bioformulations for plant growth promotion continue to inspire research and development in many fields. Increase in soil fertility, plant growth promotion, and suppression of phytopathogens are the targets of the bioformulation industry that leads to the development of ecofriendly environment. The synthetic chemicals used in the agriculture to increase yields, kill pathogens, pests, and weeds, have a big harmful impact on the ecosystem. But still the chemicals rule the agroindustry. The aim of the review is to assess the constraints associated with the effective development of bioinoculant industry particularly in developing countries. Another objective of the review is to evaluate what should be explored in the future to uplift the stature of the bioinoculants. Bioformulations offer an environmentally sustainable approach to increase crop production and health, contributing substantially in making the twenty-first century the age of biotechnology.

Multifaceted Plant-Associated Microbes and Their Mechanisms Diminish the Concept of Direct and Indirect PGPRs

It is an old saying that when we take from nature, we have to give back also; this give-and-take phenomenon leads to sustainability and is important for growth of a relationship. This is also applicable in plant–microbial world. The association of microbes with plants can be exploited and used to gain the benefits not only for the associated organisms but also for the ecosystem as a whole. When we view it in a holistic way, it is clear that multifaceted and diverse mechanisms of plant-associated microbes (PAMs) participate in promoting plant growth; protecting plant health; strengthening plant–microbe association under stress-, pollutant-, or contaminant-affected conditions; and protecting plants from the attack of phytopathogens through biological control. The multiple functions performed by microbes in the vicinity of plants (rhizosphere, phyllosphere, or other regions) are extremely interwoven and interlinked and are inseparable from each other. At present, the plant growth promoting rhizobacteria (PGPR) and mechanisms by which they function or help their respective host plant have been broadly classified into direct or indirect. However, the scenario is not as simple, plain, or should we say two-dimensional. Several PGPRs and the metabolites they produce can function in multiple ways in same or diverse conditions diminishing the concept of direct and indirect. Several examples discussed in this chapter dilute the boundary between direct and indirect and raise questions for the researchers to gather more knowledge on the intricately woven relationship and functions of the metabolites and mechanisms as a whole. A microbial metabolite in the rhizosphere cannot only perform a big role which is quite apparent but also several other functions which are less visible or obvious but are equally important. Several examples cited in the literature prove that the so-called direct mechanisms (like nutrient acquisition, phytohormone production, iron chelation, phosphate solubilization, and nitrogen fixation) also help the plant in other (indirect) ways and similarly the so-called indirect mechanisms (like antimicrobial metabolites for biocontrol and induced systemic resistance (ISR)) perform several different (direct) functions. Diverse mechanisms function simultaneously in the soil and do not work individually, strengthening the concept of universal and holistic approach.

PGPR for Protection of Plant Health Under Saline Conditions

The economy of many countries relies on agriculture. Salinity is one of the major constraints that limit crop productivity, particularly in arid and semiarid regions. The development of salt-tolerant crops is not an easy and economical approach for sustainable agriculture, whereas microbial inoculation to alleviate salt tolerance is a better option because it minimizes production costs and environmental hazards. The aim of the present review is to point out the status of salinization and constraints related with it, and to draw the focus on future research strategies for the development of better inoculants in saline-affected regions, particularly in context to the developing countries.

Biopesticides: Where We Stand?

Chemical pesticides are well known for their effective role in disease management because not only they act on a broad host range but production technology is also less expensive. However, the devastating part is their huge negative impact on the environment including the living beings of the planet. In spite of this, in the absence of suitable alternative, the use of synthetic pesticides has dominated around the globe. By the advent of greener approach of developing and using biopesticides, the situation is gradually changing but in fact can move far more swiftly in this direction which will be sustainable and eco-friendly. Although biopesticides are slowly replacing the chemical pesticides, a complete global look at the scenario indicates that the former and particularly the industries based on them are still in an insecure position in comparison to the chemicals which rule the agriculture. We can say that the biopesticides, although show a great promise, have not come up to the desired level so as to displace the dominance of chemicals. In this chapter, the global scenario of biopesticides is discussed emphasizing upon the current demand, use, constraints, and remedies.

Plant growth promoting rhizobacteria to alleviate soybean growth under abiotic and biotic stresses

Abstract Soybean (Glycine max (L.) Merr.), the “golden bean” of the twenty-first century, is among the most important legumes. It is a legume crop, but it is broadly used as oilseed. Soybean is a great source of nutrients and proteins. It can supply much needed protein to the human diet, with more than 40% protein of high quality and all the essential amino acids, especially glycine, tryptophan, and lysine, similarly to cow’s milk and animal proteins. Soybean also has about 20% oil including lecithin (an important fatty acid) and vitamins A and D. The 4% mineral salts of soybeans are a high source of phosphorus and calcium. The importance of soybean crops, economically and socially, is well known worldwide, providing about 64% of the world’s oil (the major source of oil), and about 28% of total production. Also, the crop has greatly enhanced the rural economy by improving the living standards of soybean farmers, especially women and children. In some parts of Asia, between 30% and 60% of the average cash income derives from soybean crop sales used to buy material inputs. Nowadays the production of soybean crops is being hampered by several abiotic and biotic stressors. These stressors cause losses of millions of dollars as a result of the average yield of soybean declining. Development of stress-tolerant genotypes of soybean is not without its difficulties, whereas repeated use of chemicals and fertilizers adversely affects soil ecology. Hence a better approach to enhance the growth and production of this important crop is by utilizing biological methods including plant growth promoting rhizobacteria (Pgpr). Such bacteria are able to enhance soybean growth and yield under stress by utilizing various mechanisms. Some of the most important aspects and related details have been reviewed and analyzed.

Effects of Soil Environment on Field Efficacy of Microbial Inoculants

Although many microorganisms show good performance in specific trials, this is often not translated into consistent, effective plant growth promotion and biocontrol in diverse field situations. The key factors involved in the lack of success are rapid decline in the size of populations of active cells to levels ineffective to achieve the objective and variable production of required metabolites or poor colonization, following the introduction into soil. The physical, chemical, and physicochemical nature of soil and its indigenous microorganisms and predators influence the microbial population both quantitatively and qualitatively. Soil abiotic factors (e.g., texture, pH, temperature, and moisture) exert their (direct) effect on inoculant population dynamics by imposing stresses. On the other side, trophic competitions and antagonistic/synergic and predatory interactions with the resident microbial and fauna populations determine the field efficiency of inoculants. The aim of this review is to throw light on different soil environmental conditions that affect the survival of inoculated microbial strains in the field. A proper characterization of target soils and rhizospheres as habitats for introduced microbes is a key to the development of bioformulations that support beneficial microorganisms in the soil.

Transactions Among Microorganisms and Plant in the Composite Rhizosphere Habitat

Root exudates selectively influence the growth of microorganisms that colonize the rhizosphere by altering the chemistry of soil in the vicinity of the plant roots and by serving as signal molecules and selective growth substrates for soil microorganisms. Microbial signals to plants influence the cell metabolism and plant nutrition and growth. It is increasingly apparent that, in nature, microbes function less as individuals and more as coherent groups that are able to inhabit multiple ecological niches. Because of current public concerns about the side effects of agrochemicals, there is an increasing interest in improving the understanding of cooperative activities among plants and rhizosphere microbial populations. This review provides a better understanding of processes such as stimulation of microbial activity by root exudates, competition between microorganisms and roots for nutrients, and molecular talk between roots and microorganisms and among microorganisms in the rhizosphere. Various positive plant–microbe–microbe interactions along with their multifaceted communications are highlighted that should be studied in an integrated manner for the development of sustainable agriculture with global applicability.

Rhizobial Bioformulations: Past, Present and Future

The nitrogen fixing bacterial group known as rhizobia are very important and are used as biological fertilizers for two main purposes; one is to fulfil the nutritional requirements of increasingly populated world and other to overcome the problems arising due to chemical fertilizers. Rhizobial bioformulations are in the market since more than a century and can be the solution for deficiency of nitrogen in our food and soils. Rhizobia maintain the soil fertility along with higher crop yields due to the capability of biological nitrogen fixation (BNF). Currently, various types of rhizobial biofertilizers are commercially available in the market all over the world for agricultural purposes. These can be solid carrier based formulations (organic and inorganic), liquid formulations (with and without additives), synthetic polymer based formulations or metabolite based formulations, but there still is a great room for improvement. However, over the years there have been subtle changes in the rhizobial inoculants in terms of production and application.

Plant Growth-Promoting Microbes: Diverse Roles in Agriculture and Environmental Sustainability

The need for environmental sustainability to create a balance between the future’s need and resources available is a key issue at the global level. The world’s population is increasing day by day, and natural resources are being exploited rapidly. In this situation, enhancement of agricultural productivity for feeding expanding population is a matter of concern. Conventional agricultural practices for enhancing productivity pose a threat to agroecosystems. Experience with the indiscriminate use of chemical fertilizers and pesticide is bitter. Similarly, the impact of anthropogenic activities and global climate change on the environment is detrimental and created irreversible changes in the agroecosystems. In this scenario, a major focus on plant growth-promoting microbes (PGPM) for restoring the agroecosystems to their original shape is gaining the attention of agronomists and environmentalists. Work on rhizospheric bacteria and fungi has already shown potential in the management of various agricultural problems, and especially their use in the form of biofertilizers and biopesticides has resulted in lesser reliance on synthetic agrochemicals. However, a fresh perspective suggests the role of PGPM in the remediation of ecosystems through removal of recalcitrant compounds and as alleviators of abiotic stresses, thus also helping to combat the impact of climate change. Although PGPM are proving promising tools for environmental sustainability, yet more work needs to be carried out for establishing their firm position to manage agroecosystems in a sustainable manner. Greater knowledge and revelation of the secret of plant–microbe interactions will provide a state-of-the-art solution for food security in terms of quality, quantity, and environmental sustainability.