Priyanku Teotia

Rhizosphere Microbes: Potassium Solubilization and Crop Productivity – Present and Future Aspects

The plant rhizosphere harbor array of potassium-solubilizing microbes (KSMs), which solubilize the insoluble and inaccessible potassium (K) to accessible forms of potassium for plant uptake and transport, is one of the inevitable elements for growth and yield. The process of potassium solubilization is performed by specific rhizosphere microbes, which include bacteria and fungi; the prominent are Bacillus sp. (B. megaterium, B. mucilaginosus, B. edaphicus, B. circulans, Acidithiobacillus ferrooxidans, Pseudomonas putida, Arthrobacter sp., and Paenibacillus sp.) Aspergillus spp., and Aspergillus terreus. The agricultural soil particulates contain minerals such as orthoclase, illite, biotite, feldspar, and mica which contain potassium, though this is not available to the plants due to its immobilized form. Intermittently, potassium is an important element after N and P in soil chemistry; therefore, the rhizosphere microbes play a significant role in mobilizing the unavailable form of potassium to the plant roots. The potential rhizosphere K-solubilizing microbes such as Pseudomonas, Bacillus, and Aspergillus excrete organic acids, which solubilize the unavailable potassium and make available to plant roots. Till date, most of the work has been done on nitrogen-fixing and phosphate-solubilizing microbes; moreover, the available biofertilizer with solubilized K (readily available) needs more attention at commercial scale. The current chapter addresses the information gaps related to potassium-solubilizing/potassium-mobilizing microorganisms in soil and analyzing current and future aspects of potassium-solubilizing microbes for the crop productivity.

Endophytic Probiotics and Plant Health: Toward a Balanced Accost

The endophytic probiotic microorganisms have been reported to be found in virtually each plant studied, where endophytes colonize the internal tissues of the host plant and they might form a variety of dissimilar and distinct associations that include but not limited to interdependency, positive and neutral cooperative, mutualistic, commensalistic, and also trophobiotic. Most of the endophytic microbiomes appear to originate either from the plant rhizosphere or the phyllosphere. However, some of the endophytes may also be transmitted through the seed. Probable endophytic microbes can enhance and accelerate the plant growth and production and, moreover, can also act as potential biocontrol agents. There are numerous potential fungal and bacterial endophytes that make indispensable secondary metabolites such as phytohormones, siderophores, volatile organic compounds, HCN production that support the development and progression of the host plant. Certain compounds produced by endophytes act as antibiotics which have possible antibacterial, antifungal, and insecticidal properties. These compounds intensely restrain the growth of pathogenic microorganisms, including the probable plant pathogens. On the other hand, these probable endophytic microbes can also be precious to human beings by producing a variety of natural products that could be utilized for the possible employment in medication, agronomy, or commerce. Additionally, it has been shown that endophytes too have the potential to eliminate the soil contaminants by enhancing bioremediation and phytoremediation process and, therefore, may play a remarkable role in soil fertility augmentation through notable and striking valuable processes such as biological nitrogen fixation, phosphate solubilization, metal chelation, and potassium mobilization. There is a growing and vested interest in development of biotechnological applications of probable endophytic microbes for improving crop production, phytoremediation, and sustainable production of food crops for biomass as well as biofuel production, which is a feasible and practical step toward the sustainable form of agriculture.

Environmental Biodegradation of Xenobiotics: Role of Potential Microflora

As a significance of industrial growth and advancement, ecological pollution triggered by release of varied types of inorganic and organic compounds has posed serious magnitudes. Worldwide, several thousands of dangerous and risky waste dumping sites have been created resulting in the accumulation of xenobiotics in water and soil since long time. Many unnatural compounds such as nitroaromatic compounds (NACs) and polycyclic aromatics and hydrocarbons (PAHs) are the by-products of crude petro products. Along with these, also the halogenated organic compounds constitute a huge and varied group of chemicals that are accountable for causing extensive environmental pollution. The conventional physicochemical corrective strategies to cleanse the sites contaminated by these pollutants are not cost economical. Consequently, much research work has been focused on biological means and techniques for degradation and removal of such pollutants. The sites contaminated by these compounds demand serious corrective answers, and the research has exposed a varied range of microflora that can exploit these xenobiotic compounds as carbon substrates, mineralizing them or changing them into innocuous products. Novel genes, enzymes, and metabolic ways involved in microbial biodegradation of PAHs, NACs, and other halogenated organic compounds (HOCs) have also been discovered; moreover, advanced technologies have also been developed which allow unearthing and broad flexibility of microbes in the environment cleaning. More studies are needed to understand the interface between xenobiotics and benign microbes in the environment to crisscross with biochemical and biotechnological areas. Such a novel approach will definitely provide the ground for effective interferences into environmental procedures and eventually lead to the enhanced tactics for appointing microbial diversity for effectual and actual bioremediation of xenobiotics.

Induced Systemic Resistance by Rhizospheric Microbes

In a natural ecosystem, plants copiously form advantageous and constructive relations with soil microbiomes that are significant and vital for plant growth survival and, as such, influence plant biodiversity and overall ecosystem performance. Conventional and typical examples of symbiotic microbes are ecto- and endomycorrhizal fungi that assist in water and nutrients uptake and Rhizobium bacteria that fixes free atmospheric nitrogen for plant. Advantageous microorganisms in the overall microbiome of plant roots zone enhance the plant vigor. Induced systemic resistance (ISR) developed as a significant and imperative means and way by which the selected and potential plant growth-promoting microbes in the rhizosphere influence the whole plant structure for higher and better defense against the broad range of pathogens and insect herbivores. A plethora of root-associated mutualistic microbes, including mainly common microbes such as Pseudomonas, Bacillus, Trichoderma, and ecto- and endomycorrhizal species, trigger and induce the plant’s immune system for boosted defense without precisely activating the expensive defenses. A lot of research work and evidences advocate that advantageous microorganisms are firstly established as possible plant invaders, after which the plant’s immune system is triggered, while, at delayed stages of the plant-microbe interaction, the mutualists are able to trigger the plant defense mechanism to enable efficacious colonization of the plant roots.

Molecular Tools for Strain Improvement in Aspergillus

Abstract Aspergillus is an important eukaryotic microorganism that influences our day-to-day lives in diverse areas such as food feed and agriculture, pharmaceuticals, and in fundamental science. Long ago scientists used the native or wild strains of Aspergillus for microbiological and other industrial uses. The quality and efficiency of the commercially employed strains was improved using prevailed traditional techniques such as mutagenesis. With the initiation of molecular tools, several attempts have been made to it to augment the expression level of heterologous genes, which are responsible for many beneficial traits in any fungal strain. The knowledge of novel molecular tools has been developed by the deep insight of basic and genetic research. Heterologous gene expression can be controlled or limited during transcription, posttranscription, during translation and posttranslation levels. To improve gene functionality and to diminish the expression constrains, numerous genetic strategies have been developed. The common strategies employed could be the multicopy introduction of desired genes, AT-rich sequence modification, fusion of a gene with its good expression, employment of resilient promoters and signal sequences, the construction and use of a particular enzyme-deficient or overproducing strains and the use of RNA interference techniques. These techniques have led to the expected escalation in the expression of heterologous or desired genes. With the accessibility of a huge pool of wild Aspergillus isolates, isolation of a great number of genes, which encode chosen and anticipated traits, could help in obtaining improved strains with superior desired functional performance.

Probiotic Microbiome: Potassium Solubilization and Plant Productivity

The rhizosphere of plant roots supports a range of potassium-solubilizing microbes (KSMs). These KSMs solubilize the insoluble and unavailable potassium (K) to forms of K available for uptake and transport by the plant. Potassium is one of the unavoidable elements required for growth and yield. The specific rhizospheric microbes that perform the process of K solubilization include both bacteria and fungi, the foremost of which are: Bacillus sp. (B. Mucilaginosus, B. megaterium, B. globisporus, B. edaphicus) Pseudomonas putida, Enterobacter hormaechei, Acidothiobacillus ferrooxidans, Paenibacillus sp., and Arthrobacter sp.) Aspergillus terresus, Fusarium oxysporum, Aspergillus fumigatus, and Aspergillus niger. Agricultural soil particulates hold minerals such as illite, biotite, orthoclase, mica, and feldspar that contain potassium; however, this is not accessible to plants due to its immobilized form. In soil chemistry, after N and P, K is an important element; a major role is played by the rhizosphric microbes in mobilizing the inaccessible form of K to the roots of the plant. The rhizospheric K-solubilizing microbes such as Bacillus, Pseudomonas, and Aspergillus expel organic acids, which solubilize the insoluble K and make it available to plant roots. Most of the research work in this area has been conducted on nitrogen fixing and phosphate-solubilizing microbes. Solubilized K (quickly available) in addition to the existing biofertilizers needs additional consideration at a profitable scale. The current chapter presents information to fill the knowledge gaps about K-solubilizing/mobilizing microorganisms in soil, and looks at the current and future facets of K-solubilizing microbes for enhanced crop production.

Metabolomics-Mediated Characterization of Endophytic Species in Recalcitrant Tree Species

The implication for metabolomics is to capture the endophytic microbes known to promote plant health and overall growth and development. A series of supportable effects on the number of events are mediated and understood by metabolic relations. Current developments in omics world have been made with regard to revealing metabolite release by phyto-microsymbionts, reflecting that they may produce a series of diverse metabolites. These ingredients have a function in resistance and race that may also be required for explicit communication with the plant host. Additionally, a few instances of mutual metabolite manufacturing are recognized and endophytes can moderate a plant–metabolite combination as well. This chapter is focused on a metabolomics tool and understanding the metabolic relations between plants and endophytes. We further discuss the efficient use of helpful plant–microbe interactions in terms of microbial existence in addition to scanning bioactive molecules of commercial interest.

Mobilization of Micronutrients by Mycorrhizal Fungi

Mycorrhizal fungus constitutes heterogeneous fungal taxa embracing an array of plant species. This group is found allied with the roots of beyond 90% of the plant species in this world. There is a range of mycorrhizal associations, among which arbuscular and ectotrophic mycorrhizal interactions are of high biological and economic significance. This chapter gives details about habitation, host range, and structural components of these mycorrhizal groups, along with a meticulous discussion on the mineral absorption, mechanisms involved in different absorption pathways. In addition to enhancement of mineral nutrient uptake by plants in soil, several mycorrhizal fungi execute an important task in mobilizing mineral nutrients from inaccessible organic substrate, mineral particles, and rock surfaces. Mycorrhizal fungi adopt various methods to achieve the purpose effectively, like greater area of absorption for the roots of plant, liberation of biochemical compounds, and consortium with different microbes. Furthermore, mycorrhizal fungi also provide an imperative C sink in soil other than mobilizing nutrients, consequently playing an important role in the cycling of these mineral elements. The role of every partner in a mycorrhizal association is to be exposed by the application of molecular and genetic tools, coupled with high-throughput sequencing and advanced microscopy. The signaling pathways between plants and fungi have recently been elucidated, and recognition of a range of novel nutrient transporters has unveiled a number of cellular processes which are fundamental to the mycorrhizal symbiosis. Various transporters, particularly proton-coupled phosphate transporters, have been documented on both the fungal and plant membranes which contribute to transmission of phosphate from fungi to plants. Even though much work has been formerly done on several aspects, such as symbioses, the extent to which these are functionally essential in agriculture remains uncertain. It is a vital need to spotlight on the questions, whose answers will offer novel perspectives on mycorrhizal utility.

Regeneration from Nodal Explants of Field-Grown Litchi ( Litchi chinensis Sonn.) Fruit Trees

Mass propagation of Litchi chinensis (Sonn.) via seeds is understood as detrimental because of the highly heterozygous nature of the plant due to cross-pollination. The conservative methods of vegetative propagation utilized for litchi are air layering or marcottage, grafting, and budding which are slow and incompetent as evinced by several reports. In the recent past numerous efforts for clonal propagation of litchi were made with marginal success. Earlier our group have reported multiple shoot induction and plant regeneration in litchi from the nodal cuttings and cotyledonary nodes and by in planta treatment of the axillary bud regions. In this, we highlight a research protocol which has a comprehensive discussion. It addresses the technical inputs for reproducible and efficient method of in vitro regeneration of elite litchi trees appropriate for clonal propagation. The protocol that has been referred has been proven advantageous to the horticulturists and the industry for recalcitrant trees, those that can be developed as true to the parental type.

The Lychee Fruit: Post Harvest Handling Techniques

Lychee fruit (Lychee chinensis Sonn.) is harvested under vivid humid and subtropical conditions in India and China, economically a significant fruit crop at health scale due to its beautiful skin color and bizarre and outlandish flavor. The fruit has a coarse pericarp surrounding the juicy succulent, edible aril with a seed in center. Cultivators are still in fancy for its commercialization; the reasons are pericarp browning, postharvest decay, and minor racking among the numerous key constraints influencing the quality of lychee during storage and transportation. Aridness of pericarp invites inflammatory damage owing to untimely postharvest handling practices. Cracking is expected at preharvest and fruit developmental stages. Pre- and postharvest stages are owing to the modest handling practices and sorting line operations. We address cracking problems of lychee pericarp which offers points of entry to the invasion of postharvest microbial pathogens during cold storage and transport. It is advisable that pericarp skin browning which is triggered by withering is not only limited to the corporeal attributes of lychees, involuntary injury, and postharvest deterioration; rather it leads to deadly effects on sensory attributes of lychee aril. We tried to develop an explicit understanding on pericarp skin browning during postharvest and transportation and further suggest adoption mechanism of SO2 fumigation in elite lychee cultivars. Moreover, we count the health issues on post fumigation which leaves the residual effects, changes fruit taste, and must be measured at ground level.