Maqshoof Ahmad

The role of mycorrhizae and plant growth promoting rhizobacteria (PGPR) in improving crop productivity under stressful environments

Both biotic and abiotic stresses are major constrains to agricultural production. Under stress conditions, plant growth is affected by a number of factors such as hormonal and nutritional imbalance, ion toxicity, physiological disorders, susceptibility to diseases, etc. Plant growth under stress conditions may be enhanced by the application of microbial inoculation including plant growth promoting rhizobacteria (PGPR) and mycorrhizal fungi. These microbes can promote plant growth by regulating nutritional and hormonal balance, producing plant growth regulators, solubilizing nutrients and inducing resistance against plant pathogens. In addition to their interactions with plants, these microbes also show synergistic as well as antagonistic interactions with other microbes in the soil environment. These interactions may be vital for sustainable agriculture because they mainly depend on biological processes rather than on agrochemicals to maintain plant growth and development as well as proper soil health under stress conditions. A number of research articles can be deciphered from the literature, which shows the role of rhizobacteria and mycorrhizae alone and/or in combination in enhancing plant growth under stress conditions. However, in contrast, a few review papers are available which discuss the synergistic interactions between rhizobacteria and mycorrhizae for enhancing plant growth under normal (non-stress) or stressful environments. Biological interactions between PGPR and mycorrhizal fungi are believed to cause a cumulative effect on all rhizosphere components, and these interactions are also affected by environmental factors such as soil type, nutrition, moisture and temperature. The present review comprehensively discusses recent developments on the effectiveness of PGPR and mycorrhizal fungi for enhancing plant growth under stressful environments. The key mechanisms involved in plant stress tolerance and the effectiveness of microbial inoculation for enhancing plant growth under stress conditions have been discussed at length in this review. Growth promotion by single and dual inoculation of PGPR and mycorrhizal fungi under stress conditions have also been discussed and reviewed comprehensively.

Potassium-Solubilizing Bacteria and Their Application in Agriculture

Potassium (K) is one of the major macronutrients which play an important role in plant growth and development. Total soil potassium reserves are generally large; however, major portion of it exists in insoluble K minerals and very little potassium becomes available to plants. There are certain microorganisms which use a number of biological processes to make potassium available from unavailable forms. These potassium-solubilizing bacteria (KSB) can be used as a promising approach to increase K availability in soils, thus playing an important role for crop establishment under K-limited soils. Owing to naturally available source of potassium in soil and high price of synthetic potassium fertilizers, the importance of KSB is increasing day by day. The use of chemical fertilizers can be decreased by using KSB in agriculture that can lead to sustainable agriculture. A number of workers have demonstrated the role of KSB in crop improvement. The present review highlights the importance of KSB for enhancing crop production. The mechanisms used by KSB for K solubilization have been discussed. The work of various scientists regarding plant growth promotion through KSB has been reviewed in detail, and present constraints and future scope of this technology have also been discussed.

Rhizosphere Bacteria for Crop Production and Improvement of Stress Tolerance: Mechanisms of Action, Applications, and Future Prospects

Rhizosphere bacteria associated with plant roots can enhance crop productivity through a number of direct and indirect mechanisms. These beneficial bacteria attracted the scientists around the globe due to their significant contribution to mitigate adverse effects of environmental stresses on plants. These plant growth-promoting rhizobacteria (PGPR) have the potential to improve crop production under stress conditions solely and/or in combination with other microbes. The use of PGPR as co-inoculants with symbiotic bacteria is a potential biotechnological approach to promote nodulation for improving crop biomass and soil health. Multi-strain bacterial consortia are also proved useful for enhancing plant growth and development particularly in conditions where single inoculation was not so effective. The objectives of present review are to highlight the basic mechanisms used by such bacteria in general and the applied aspects of these bacteria for improving plant stress tolerance and ultimately crop productivity particularly. Certain examples highlighting their significant role for enhancing plant growth under biotic and abiotic stress conditions have been reviewed. The role of PGPR for improving nodulation when used with nitrogen-fixing bacteria has been discussed. The potential of genetically engineered rhizobacteria that possess the required trait necessary under certain environmental conditions has also been evaluated. The areas that need further research and future perspectives of this technology have been discussed in detail.

Agrochemicals and Soil Microbes: Interaction for Soil Health

To fulfill food and fiber demand of the ever-increasing population over the world, agrochemicals are being used in large quantities. These agrochemicals include chemicals (hormone, fungicide, or insecticide, pesticides, and fertilizers) manufactured or processed for agricultural use to increase crop yield for economic point of view. Soil microbes constitute the biosphere that is the most important fraction of soil involved in nutrient cycling thus maintaining soil fertility. Agrochemicals are used to enhance the productivity of crops but when entering into soil directly affect soil microbes which ultimately deteriorate soil health. Many biological functions of the soil are disrupted by the application of agrochemicals. The direct and indirect effects of these chemicals on soil biology are reduction in population, proliferation of beneficial soil microorganisms and their biotransformation, decrease in biological nitrogen fixation, and reduced mineralization of organic compounds. Soil microbial enzymatic activities are the indicators of soil biological health, fertility, and chemical status. Agrochemicals incorporated in the soil eradicate beneficial soil microbes which are involved in important enzymatic components like chain of reactions that play vital role in synchronizing important chemical processes in soil. On the other hand, many microbes in the soil have the ability to degrade or metabolize the agrochemical pollutants in the soil to ensure the soil health. Soil microorganisms have intrinsic nature for rapid degradation processes and genetic adaptation to chemicals in the environment. Agrochemicals of diverse nature could be remediated from soil and water with the use of potential microorganisms in the soil. In this chapter, the effect of agrochemicals on soil biology and the role of soil microbes in the degradation of agrochemicals have been reviewed and summarized.

Current source with low voltage controlled for surface Electrical Stimulation

Functional Electrical Stimulation (FES) is a promising way to restore mobility to Spinal Cord Injury (SCI) patients by applying low-level electrical current to the paralyzed muscles so as to enhance that persons ability to function and live independently. However, due to the limited number of commercially available FES assisted exerciser systems and their rather high cost, the conventional devices are unaffordable for most peoples. Thus, this paper makes a comparative study of the various design of a multiple purpose portable functional electrical stimulator which is used in surface stimulation for patients with spinal cord injuries. The functionality, circuit performance and reliability of the circuits are presented.

Knee joint impedance hybrid modeling and control of functional electrical stimulation (FES)-cyclingfor paraplegic: Free swinging trajectory

Functional electrical stimulation (FES) has been used to restore the function of paralyzed muscles due to spinal cord injury (SCI). FES induced movement control is a significantly challenging area due to complexity and nonlinearity of musculoskeletal system. A crucial issue of FES is the control of motor function by the artificial activation of paralyzed muscles due to the various characteristics of the underlying physiological/biomechanical system. Muscle response characteristics are nonlinear and time-varying with fatigue issues. In this approach only the quadriceps muscle is stimulated to perform the trajectory motion. This paper presents the initial development of control strategies using FLC and GA in order to optimize the system by FES-cycling trajectory control via Analog Digital Converter, ADC.

Role of Phytohormones in Stress Tolerance of Plants

Environmental stresses, both biotic and abiotic, cause negative impact on plant growth and development, and plants need to adopt certain strategies for maintaining proper growth under stress conditions. These strategies include certain physiological, biochemical, and molecular mechanisms to cope with these stresses. These mechanisms include the production of hormones (phytohormones) and osmolytes. Phytohormones are organic molecules that affect various plant physiological processes like growth, development, and cell differentiation. Phytohormones regulate key physiological events under normal and stress conditions. They play a vital role for enhancing the ability of plants to adapt to the harsh environmental conditions by mediating a wide range of adaptive responses. These responses enable the plants to acclimatize to adverse soil conditions. Various types of phytohormones play an important function in plants individually or in coordination with each other. The nature and level of these hormones in plants are major factors that influence plant processes and functions. The present chapter describes the potential role of phytohormones for promoting plant growth and development under stress conditions. The major classes of plant hormones and their source of production have been described. Metabolism of phytohormones and their physiological responses with special reference to their concentration-dependent or negative impact on plant growth have been discussed in detail. The impact of these hormones on plant growth under stress conditions has been reviewed and discussed with selected examples. Also, the role of microbes in phytohormone production has been elaborated with examples. Future perspectives of the area have also been discussed.

Preliminary study on phosphate solubilizing Bacillus subtilis strain Q3 and Paenibacillus sp. strain Q6 for improving cotton growth under alkaline conditions

Background Low phosphorus availability limits crop production in alkaline calcareous soils in semi-arid regions including Pakistan. Phosphate solubilizing bacteria may improve crop growth on alkaline calcareous soils due to their ability to enhance P availability. Methods Twenty rhizobacterial isolates (Q1–Q20) were isolated from rhizosphere of cotton and characterized for their growth promoting attributes in vitro. The selected phosphate solubilizing isolates were further screened for their ability to improve cotton growth under axenic conditions (jar trial). The phosphorus solubilization capacities of selected strains were quantified and these strains were identified through 16S rDNA sequencing. Results Isolates Q2, Q3, Q6, Q7, Q8, Q13 and Q14 were able to solubilize phosphate from insoluble sources. Most of these isolates also possessed other traits including catalase activity and ammonia production. The growth promotion assay showed that Q3 was significantly better than most of the other isolates followed by Q6. Maximum root colonization (4.34 × 106 cfu g−1) was observed in case of isolate Q6 followed by Q3. The phosphorus solubilization capacities of these strains were quantified, showing a maximum phosphorus solubilization by Q3 (optical density 2.605 ± 0.06) followed by the Q6 strain. The strain Q3 was identified as Bacillus subtilis (accession # KX788864) and Q6 as Paenibacillus sp. (accession # KX788865) through 16S rDNA sequencing. Discussion The bacterial isolates varied in their abilities for different growth promoting traits. The selected PGPR Bacillus subtilis strain Q3 and Paenibacillus sp. strain Q6 have multifarious growth promoting traits including ability to grow at higher EC and pH levels, and phosphorus solubilizing ability. These strains can efficiently colonize cotton roots under salt affected soils and help plants in phosphorus nutrition. It is concluded that both strains are potential candidates for promoting cotton growth under alkaline conditions, however further investigation is required to determine their potential for field application.

Zinc Solubilizing Bacteria for Zinc Biofortification in Cereals: A Step Toward Sustainable Nutritional Security

Food production and security for the ever-increasing population are becoming a key challenge for the scientists. The food security demands not only enhanced agricultural productivity but also improvement in produce quality while reducing adverse impact of agricultural practices on natural resources and the environment. Inadequate nutrition is popular among poor community. Malnutrition of micronutrients is also common due to less concentration present in food. The concentration of micronutrients is very low in cereals due to dependence on cereals; we are taking micronutrients far below the required ones in daily nutrition and are suffering the deficiency of these micronutrients. Among these, Zn is a part of enzymes that regulates the rate of metabolic reactions involved in the development and growth of crop plants and human beings. Zinc deficiency is a common issue not only in plants but in human being and animals as well. Approximately one third of total population of poor world is at high risk of Zn deficiency because they rely on cereals for their daily caloric intake. Its deficiency is a global problem for plants and can be found in every part of the world. More than 70% of Pakistani soils are zinc deficient. So, the cereal crops grown on these soils are zinc deficient. Zn deficiency is the largest cause of death and diseases in humans. This situation demands some effective strategies to overcome Zn deficiency in edible crops, to enhance the grain Zn content and to minimize adverse effects of Zn deficiency on humans thus reducing malnutrition. Many strategies are available to overcome the zinc deficiency in plants and human beings as well. Most important and sustainable strategy is the use of zinc solubilizing bacteria. Zinc solubilizing bacteria alone or with organic materials may also increase the bioavailability of native and applied zinc to the plants through different mechanisms of actions. In this chapter, importance of zinc with a special reference to zinc solubilizing bacteria and their mechanisms of action for improving the yield and quality of cereals to achieve the nutritional food security has been discussed in detail.