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Phosphorus (P) is an essential macronutrient, crucial for intensification of agricultural production. Although P is a vital nutrient for all life forms but in natural ecosystem it is least available owing to its high reactive nature. Plants have developed diverse adaptive strategies to improve Pi acquisition and utilization under inadequate condition. They undergo numerous modifications at morphological, physiological, and biochemical level to maintain P homeostasis under deplete conditions of P. In last decades, notable development has been made in utilizing microbes for regulating P supply in soil solution. In this review, we focused on the understanding of P uptake from soil, mobilization within plants, phosphate starvation responses and efficacy of microorganisms in facilitating external P to plants. Moreover, other metabolism in microorganism viz. phosphate accumulation is an important trait of microbes to maintain labile P in soil solution. Application of phosphate accumulating microbes is well known in enhanced biological phosphorus removal (EBPR) system and heavy metal remediation. This review also discussed the phosphate accumulation mechanism in microbes and their importance in regulating P supply in soil. Current knowledge and further exploration of mechanism involved by P accumulating microbes may offer better insight of the regulatory events controlling P homeostasis. It will be beneficial for developing more efficient sustainable technologies to augment P use efficiency in soil for better plant growth promotion and nutrient starvation alleviation.

The study aimed to explicate the role of microbial co-inoculants for the mitigation of arsenic (As) toxicity in rice. Arsenate (AsV) reducer yeast Debaryomyces hansenii NBRI-Sh2.11 (Sh2.11) with bacterial strains of different biotransformation potential was attempted to develop microbial co-inoculants. An experiment to test their efficacy (yeast and bacterial strains) on plant growth and As uptake was conducted under a stressed condition of 20 mg kg-1 of arsenite (AsIII). A combination of Sh2.11 with an As(III)-oxidizer, Citrobacter sp. NBRI-B5.12 (B5.12), resulted in ∼90% decrease in grain As content as compared to Sh2.11 alone (∼40%). Reduced As accumulation in rice roots under co-treated condition was validated with SEM-EDS analysis. Enhanced As expulsion in the selected combination under in vitro conditions was found to be correlated with higher As content in the soil during their interaction with plants. Selected co-inoculant mediated enhanced nutrient uptake in association with better production of indole acetic acid (IAA) and gibberellic acid (GA) in shoot, support microbial co-inoculant mediated better biomass under stressful condition. Boosted defense response in association with enhanced glutathione-S-transferase (GST) and glutathione reductase (GR), activities under in vitro and in vivo conditions were observed. These results indicated that the As(III) oxidizer-B5.12 accelerated the As detoxification property of the As(V) reducer-Sh2.11. Henceforth, the results confer that the coupled reduction-oxidation process of the co-inoculant reduces the accumulation of As in rice grain. These co-inoculants can be further developed for field trials to achieve higher biomass with alleviated As toxicity in rice.

Arsenic (As) has become natural health hazard for millions of people across the world due to its distribution in the food chain. Naturally, it is present in different oxidative states of inorganic [As(V) and As(III)] and organic (DMA, MMA and TMA) forms. Among different mitigation approaches, microbe mediated mitigation of As toxicity is an effective and eco-friendly approach. The present study involves the characterization of bacterial strains containing arsenite methyltransferase (Pseudomonas oleovorans, B4.10); arsenate reductase (Sphingobacterium puteale, B4.22) and arsenite oxidase (Citrobacter sp., B5.12) activity with plant growth promoting (PGP) traits. Efficient reduction of grain As content by 61 % was observed due to inoculation of methyltransferase containing B4.10 as compared to B4.22 (47 %) and B5.12 (49 %). Reduced bioaccumulation of As in root (0.339) and shoot (0.166) in presence of B4.10 was found to be inversely related with translocation factor for Mn (3.28), Fe (0.073), and Se (1.82). Bioaccumulation of these micro elements was found to be associated with the modulated expression of different mineral transporters (OsIRT2, OsFRO2, OsTOM1, OsSultr4;1, and OsZIP2) in rice shoot. Improved dehydrogenase (407 %), and β-glucosidase (97 %) activity in presence of P. oleovorans (B4.10) as compared to arsenate reductase (198 and 50 %), and arsenite oxidase (134 and 69 %) containing bacteria was also observed. Our finding confers the potential of methyltransferase positive P. oleovorans (B4.10) for As stress amelioration. Reduced grain As uptake was found to be mediated by improved plant growth and nutrient uptake associated with enhanced soil microbial activity.

Citral and geraniol are dominating constituents of lemon and rose scented essential oils of Cymbopogon spp. Here, we report their antifungal activity against some pathogenic fungi Drechsler...

Plant pathogens are an emerging threat to global food security leading to severe losses of economically important food crops. Rice, catering 40% of global population, faces tremendous yield and economic losses due to pathogen incidences. Today, agriculture practices are more bound to the use of chemical pesticides and fertilizers for disease management and improved crop yields. Thus, the crop protection product sector is becoming a fast developing industry in order to compel with the growing population and need to minimize crop damage. This entails the usage of chemicals for crop protection in a judicious manner within the national, confined regulatory framework. However, the application of high doses of chemical pesticides and fertilisers in intensive farming practices negatively affects both human health and natural ecosystems. Hence, there is the urgent demand for the use of safer, environmentally sound and sustainable alternative technologies for profitable crop production. Therefore, the present chapter fosters majorly on the different biological and molecular approaches for disease management.

Soil contaminants have adversely affected the natural ecosystem and are a major concern. Overlong confinement of these pollutants in soil and their distribution in crops and groundwater has made the situation worse. Evacuation of these pollutants to bring their level below threshold is the requirement of the present scenario. Phytoremediation is a sustainable substitute to physicochemical methods for remediation of contaminated sites. Combined use of plants and microbes to enhance phytoremediation efficacy is an emerging approach. Microbes evolve different strategies which aid in reducing contaminants level. In addition, the use of genetic engineering techniques, namely, gene silencing or overexpression of genes involved in uptake, sequestration, and transportation of contaminants has unfastened new prospects of phytoremediation. Several attempts of using microbial genes have been made for enhanced remediation potential. The present chapter provides a critical review of the potential role of microbes, plants, and their interaction along with biotechnological approaches using microbial genes for enhanced phytoremediation potential.

Silicon (Si) has gained considerable attention for its utility in improved plant health under biotic and abiotic stresses through alteration of physiological and metabolic processes. Its interaction with arsenic (As) has been the compelling area of research amidst heavy metal toxicity. However, microbe mediated Si solubilization and their role for reduced As uptake is still an unexplored domain. Foremost role of Bacillus amyloliquefaciens (NBRISN13) in impediment of arsenite (AsIII) translocation signifies our work. Reduced grain As content (52-72%) during SN13 inoculation under feldspar supplementation (Si+SN+As) highlight the novel outcome of our study. Upregulation of Lsi1, Lsi2 and Lsi3genes in Si+SN+As treated rice plants associated with restricted As translocation, frames new propositions for future research on microbemediated reduced As uptake through increased Si transport. In addition to low As accumulation, alleviation of oxidative stress markers by modulation of defense enzyme activities and differential accumulation of plant hormones was found to be associated with improved growth and yield. Thus, our findings confer the potential role of microbe mediated Si solubilization in mitigation of As stress to restore plant growth and yield.

Silicon (Si), the second most abundant element on earth, remains unavailable for plants’ uptake due to its poor solubility. Microbial interventions to convert it in soluble forms are well documented. However, studies on discrimination of Si and P solubilizing microbes due to common estimation method and sharing of solubilisation mechanism are still obscure. A defined differential media, i.e., silicon solubilizing media (NBRISSM) is developed to screen Si solubilizers. NBRISN13 (B. amyloliquefaciens), a Si solubilizer, exhibiting antagonistic property against Rhizoctonia solani, was further validated for disease resistance. The key finding of the work is that NBRISSM is a novel differential media for screening Si solubilizers, distinct from P solubilizers. Dominance of Pseudomonas and Bacillus spp. for the function of Si solubilization was observed during diversity analysis of Si solubilizers isolated from distinct rhizospheres. Sphingobacterium zeae, a different strain other than Pseudomonas and Bacillus sp, is identified as Si solubilizer along with a novel strain of Pseudomonas sp. Role of acidic phosphatase during Si solubilization has been firstly reported in our study in addition to other pH dependent phenomenon. Study also showed the combinatorial effect of feldspar and NBRISN13 on elicited immune response through (i) increased Si uptake, (ii) reduced disease incidences, (iii) modulation of cell wall degrading and antioxidative enzyme activities, and (iv) induced defense responsive gene expression.

Rice grown in arsenic (As) contaminated areas contributes to high dietary exposure of As inducing multiple adverse effects on human health. The As contamination and application of phosphate fertilizers during seedling stage creates a high P and As stress condition. The flooded paddy fields are also conducive for algal growth and microbial activity. The present study proposes potential role of microalgae, Chlorella vulgaris (CHL) and bacteria, Pseudomonas putida (RAR) on rice plant grown under excess As and phosphate (P) conditions. The results show synchronized interaction of CHL + RAR which, reduces As uptake through enhanced P:As and reduced As:biomass ratio by modulating P trafficking. Gene expression analysis of different phosphate transporters exhibited correlation with reduced As uptake and other essential metals. The balancing of reactive oxygen species (ROS), proline accumulation, hormone modulation, and As sequestration in microbial biomass were elucidated as possible mechanisms of As detoxification. The study concludes that RAR and CHL combination mitigates the As stress during P-enriched conditions in rice by: (i) reducing As availability, (ii) modulating the As uptake, and (iii) improving detoxification mechanism of the plant. The study will be important in assessing the role and applicability of P solubilizing biofertilizers in these conditions.

Arsenic (As) is a serious threat for environment and human health. Rice, the main staple crop is more prone to As uptake. Bioremediation strategies with heavy metal tolerant rhizobacteria are well known. The main objective of the study was to characterize arsenic-resistant yeast strains, capable of mitigating arsenic stress in rice. Three yeast strains identified as Debaryomyces hansenii (NBRI-Sh2.11), Candida tropicalis (NBRI-B3.4) and Candida dubliniensis (NBRI-3.5) were found to have As reductase activity. D. hansenii with higher As tolerance has As expulsion ability as compared to other two strains. Inoculation of D. hansenii showed improved detoxification through scavenging of reactive oxygen species (ROS) by the modulation of SOD and APX activity under As stress condition in rice. Modulation of defense responsive gene (NADPH, GST, GR) along with arsR and metal cation transporter are the probable mechanism of As detoxification as evident with improved membrane (electrolyte leakage) stability. Reduced grain As (~40% reduction) due to interaction with D. hansenii (NBRI-Sh2.11) further validated it's As mitigation property in rice. To the best of our knowledge D. hansenii has been reported for the first time for arsenic stress mitigation in rice with improved growth and nutrient status of the plant.

Environmental pollution is an ever-increasing problem being faced by the world in the present era. Soil pollution is increasing, owing to dumping of all kinds of wastes, mining and using of agrochemicals and other anthropogenic activities. These pollutants include many recalcitrant organic compounds, e-wastes, isotopic wastes and heavy metals. Heavy metals are essentially polluting agricultural fields and thus affect productivity and quality of the produce. Accumulation of these toxic metals in plants leads to their subsequent transfer and biomagnification in the food chain. Therefore, their toxicity is an area of concern for ecological, evolutionary, nutritional and environmental reasons. Several strategies are being employed for remediation of agricultural soils, mycoremediation being one of them. Mycoremediation is an eco-friendly ‘green-clean’ technology that has tremendous potential to be utilized in the cleaning up of heavy metals and organic pollutants. Association of plant and fungi can detoxify toxic metals, translocate and accumulate them in the above-ground biomass, which has to be then harvested for metal recovery. Despite tremendous potential for the application of mycoremediation in the cleaning up of contaminated soil, sediment and water, it has not been commercialized and used extensively on a large scale. The present chapter discusses the strategies and applicability of mycoremediation mechanisms for heavy metal resistance/tolerance in plants.