Current applications of nanotechnology to develop plant growth inducer agents as an innovation strategy

Abstract

Nanotechnology has been proposed as an important tool and strategy for applying new products in agriculture at the nanometer scale in order to improve the food crop at sustainability and productivity levels for contributing with the agriculture security. Nanoparticles (NPs) have been planted as an intelligent material with a large contact surface per unit mass respect to bulk-products, allowing its effect to be exerted with greater efficiency in a specific point on a plant target. Currently, NPs have been studied to be applied to various species of monocotyledonous and dicotyledonous plants. Some NPs properties such as concentration, shape, size, composition and surface functionality have the ability to regulate the NPs growth effects on the plant during germination and seedling stages under controlled and field conditions. Furthermore, several studies have tried to explain the mechanism of uptake, translocation and accumulation of NPs inside the plant at the organ and cell level, but further studies are needed to determine specific mechanisms and exact action. Nevertheless, evaluation of the toxicity effects of NPs on physiological indexes of the plant is needed to determine the effective dose without producing adverse effects on the plant and food chain. It is noteworthy that studies have indicated that nanoparticles, regardless of their nature, can be efficient inducers of plant growth. However, a series of laboratory tests are required to optimize their application conditions and their specific physiological impact on plants. In this review, we summarize the knowledge about NPs application to induce plant growth to direct future studies in order to propose NPs for technological innovation.     

Biosynthesized silver nanoparticles induce phytotoxicity in Vigna radiata L.

With the recent developments in the field of nanotechnology, the biosynthesis of nanoparticles has increased tremendously. Silver nanoparticles (SNPs) are among the most synthesized nanoparticles and this extensive synthesis can elevate the amounts of SNPs in the environment, which, consequently, pose a serious threat to the ecosystem and can bring unwanted environmental effects. As plants are an important part of ecosystem, investigation of toxic effects of SNPs on plants is particularly interesting. This study evaluates the potential risk of SNPs interaction with plants. For this, seeds of Vigna radiata L. were screened in presence of SNPs (20 mgL⁻¹) using the germination, growth, and biochemical parameters as a phototoxicity criterion. The 19.57 nm average-sized SNPs were synthesized via the biosynthesis method. These biosynthesized SNPs were then applied on two varieties of V. radiata (Azri and High cross 404) and found to have variety dependent toxic effects on seed germination, growth, and biochemical parameters. Seed germination, root length, shoot length, fresh weight, chlorophyll, carotenoid, sugar content, and total proteins were reduced by 20, 46, 50, 18, 55, 62, 82, and 67%, respectively, in High cross 404, when compared with control (distilled water). The variety Azri was less sensitive than the variety High cross 404. In conclusion, the results demonstrated that SNPs affect seed germination and seedling growth when internalized and accumulated in plants, revealing that SNPs were responsible for the side effects. More in-depth research is required, in the form of different concentrations of SNPs or different plant species, to draw a logical conclusion and develop legislation about the safe use of biosynthesized SNPs.Supplementary Information The online version contains supplementary material available at 10.1007/s12298-021-01073-4.     

Effects of Silver Nanoparticle Exposure on Germination and Early Growth of Eleven Wetland Plants

The increasing commercial production of engineered nanoparticles (ENPs) has led to concerns over the potential adverse impacts of these ENPs on biota in natural environments. Silver nanoparticles (AgNPs) are one of the most widely used ENPs and are expected to enter natural ecosystems. Here we examined the effects of AgNPs on germination and growth of eleven species of common wetland plants. We examined plant responses to AgNP exposure in simple pure culture experiments (direct exposure) and for seeds planted in homogenized field soils in a greenhouse experiment (soil exposure). We compared the effects of two AgNPs–20-nm polyvinylpyrrolidine-coated silver nanoparticles (PVP-AgNPs) and 6-nm gum arabic coated silver nanoparticles (GA-AgNPs)–to the effects of AgNO₃ exposure added at equivalent Ag concentrations (1, 10 or 40 mg Ag L⁻¹). In the direct exposure experiments, PVP-AgNP had no effect on germination while 40 mg Ag L⁻¹ GA-AgNP exposure significantly reduced the germination rate of three species and enhanced the germination rate of one species. In contrast, 40 mg Ag L⁻¹ AgNO₃ enhanced the germination rate of five species. In general root growth was much more affected by Ag exposure than was leaf growth. The magnitude of inhibition was always greater for GA-AgNPs than for AgNO₃ and PVP-AgNPs. In the soil exposure experiment, germination effects were less pronounced. The plant growth response differed by taxa with Lolium multiflorum growing more rapidly under both AgNO₃ and GA-AgNP exposures and all other taxa having significantly reduced growth under GA-AgNP exposure. AgNO₃ did not reduce the growth of any species while PVP-AgNPs significantly inhibited the growth of only one species. Our findings suggest important new avenues of research for understanding the fate and transport of NPs in natural media, the interactions between NPs and plants, and indirect and direct effects of NPs in mixed plant communities.     

Ethylene reduces plant gas exchange and growth of lettuce grown from seed to harvest under hypobaric and ambient total pressure

Naturally occurring high levels of ethylene can be a problem in spaceflight and controlled environment agriculture (CEA) leading to sterility and irregular plant growth. There are engineering and safety advantages of growing plants under hypobaria (low pressure) for space habitation. The goals of this research were to successfully grow lettuce (Lactuca sativa cv. Buttercrunch) in a long-term study from seed to harvest under hypobaric conditions, and to investigate how endogenously produced ethylene affects gas exchange and plant growth from seed germination to harvest under hypobaric and ambient total pressure conditions. Lettuce was grown under two levels of total gas pressure [hypobaric or ambient (25 or 101 kPa)] in a long-term, 32-day study. Significant levels of endogenous ethylene occurred by day-15 causing reductions in photosynthesis, dark-period respiration, and a subsequent decrease in plant growth. Hypobaria did not mitigate the adverse ethylene effects on plant growth. Seed germination was not adversely affected by hypobaria, but was reduced by hypoxia (6 kPa pO₂). Under hypoxia, seed germination was higher under hypobaria than ambient total pressure. This research shows that lettuce can be grown from seed to harvest under hypobaria (≅25% of normal earth ambient total pressure).     

Effect of liquid seaweed extracts on growth of tomato seedlings (Solanum lycopersicum L.)

Seaweed extracts are used as nutrient supplements, biostimulants, or biofertilizers in agriculture and horticulture to increase plant growth and yield. In this study, we examined the effect of liquid seaweed extracts (LSEs) made from Ulva lactuca, Caulerpa sertularioides, Padina gymnospora, and Sargassum liebmannii as biostimulants on the germination and growth of tomato (Solanum lycopersicum) under laboratory and greenhouse conditions using foliar and soil drench applications of LSEs. We assessed LSEs at different concentrations (0.2, 0.4, and 1.0 %) on germination parameters (percentage, index, mean time, energy, and seedling vigor index) and growth parameters (plumule length, radical length, shoot length, root length, fresh weight, and dry weight) of tomato seedlings. Our results indicate that seeds treated with LSEs of U. lactuca and P. gymnospora at lower concentrations (0.2 %) showed enhanced germination (better response in germination rate associated with lower mean germination time, high germination index and germination energy, and consequently greater seedling vigor and greater plumule and radicle length). Application as a soil drench was found to be more effective in influencing the height of the plant (up to 79 cm) than the foliar spray application (75 cm). Plants receiving LSEs of U. lactuca and P. gymnospora showed increased shoot length, root length, and weight. Furthermore, U. lactuca and P. gymnospora were found to be more successful and better candidates for developing effective biostimulants to improve the growth of tomato plants. This study provides important information on the identification and utilization of Mexican seaweed resources for agriculture and is the first study to report on the uses of these seaweeds as a source of liquid extracts as biostimulants in agriculture.     

Use of Gold Nanoparticles to Detect Water Uptake in Vascular Plants

Direct visualization of water-conducting pathways and sap flows in xylem vessels is important for understanding the physiology of vascular plants and their sap ascent. Gold nanoparticles (AuNPs) combined with synchrotron X-ray imaging technique is a new promising tool for investigating plant hydraulics in opaque xylem vessels of vascular plants. However, in practical applications of AuNPs for real-time quantitative visualization of sap flows, their interaction with a vascular network needs to be verified in advance. In this study, the effect of AuNPs on the water-refilling function of xylem vessels is experimentally investigated with three monocot species. Discrepancy in the water uptakes starts to appear at about 20 min to 40 min after the supply of AuNP solution to the test plant by the possible gradual accumulation of AuNPs on the internal structures of vasculature. However conclusively, it is observed that the water-refilling speeds in individual xylem vessels are virtually unaffected by hydrophilically surface-modified AuNPs (diameter ∼20 nm). Therefore, the AuNPs can be effectively used as flow tracers in the xylem vessels in the first 20∼30 min without any physiological barrier. As a result, AuNPs are found to be useful for visualizing various fluid dynamic phenomena occurring in vascular plants.     

Modifying plants for biofuel and biomaterial production

The productivity of plants as biofuel or biomaterial crops is established by both the yield of plant biomass per unit area of land and the efficiency of conversion of the biomass to biofuel. Higher yielding biofuel crops with increased conversion efficiencies allow production on a smaller land footprint minimizing competition with agriculture for food production and biodiversity conservation. Plants have traditionally been domesticated for food, fibre and feed applications. However, utilization for biofuels may require the breeding of novel phenotypes, or new species entirely. Genomics approaches support genetic selection strategies to deliver significant genetic improvement of plants as sources of biomass for biofuel manufacture. Genetic modification of plants provides a further range of options for improving the composition of biomass and for plant modifications to assist the fabrication of biofuels. The relative carbohydrate and lignin content influences the deconstruction of plant cell walls to biofuels. Key options for facilitating the deconstruction leading to higher monomeric sugar release from plants include increasing cellulose content, reducing cellulose crystallinity, and/or altering the amount or composition of noncellulosic polysaccharides or lignin. Modification of chemical linkages within and between these biomass components may improve the ease of deconstruction. Expression of enzymes in the plant may provide a cost‐effective option for biochemical conversion to biofuel.     

A biofuel cell with enhanced performance by multilayer biocatalyst immobilized on highly ordered macroporous electrode

A one-compartment glucose/O(2) biofuel cell based on an electrostatic layer-by-layer (LbL) technique on three-dimensional ordered macroporous (3DOM) gold electrode was described. A 3DOM gold electrode was synthesized electrochemically by an inverted colloidal crystal template technique. Then the macroporous gold electrodes were functionalized with Au nanoparticles (AuNPs) and enzyme, glucose dehydrogenase (GDH) or laccase. The (AuNPs/GDH)(n) multilayer modified macroporous gold electrode showed excellent bioelectrocatalytic activity towards glucose. The direct electroreduction towards oxygen was realized at (AuNPs/laccase)(n) films on 3DOM gold electrodes. The maximum power density of the cell with the macroporous film as matrix was 178muWcm(-2) at 226mV, which was 16 times larger than that of the biofuel cell with the flat electrode under the same condition. The proposed method is simple and would be applicable to enhance the power output of miniaturized biofuel cell.     

In vitro embryotoxicity and mode of antibacterial mechanistic study of gold and copper nanoparticles synthesized from Angelica keiskei (Miq.) Koidz. leaves extract

The present study demonstrated the in vitro embryotoxicity assessment of gold nanoparticles (AuNPs) and copper nanoparticles (CuNPs) prepared from the leaves extract of Angelica keiskei (Miq.) Koidz. and addressed their mode of antibacterial mechanisms. Both AuNPs and CuNPs were rapidly synthesized and the formations were observed within 1 h and 24 h, respectively. Further the morphological images of the nanoparticles were confirmed through transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The high-resolution X-ray diffraction (HR-XRD) analysis of the biosynthesized AuNPs and CuNPs were matched with joint committee on powder diffraction standards (JCPDS) file no of 04-0784 and 89-5899, respectively. A strong prominent Au and Cu signals were observed through energy dispersive spectroscopy (EDS) analysis. Fourier transform infrared spectroscopy (FT-IR) analysis confirmed the responsible phytochemicals for the synthesis of AuNPs and CuNPs. In order to assess the toxic effects of AuNPs and CuNPs, bactericidal activity was performed against few of the test pathogens in which the effective inhibition was observed against Gram-negative bacteria than the Gram-positive bacteria. The mode of action and interaction of nanoparticles were performed on the bacterial pathogens and the results concluded that the interaction of nanoparticles initially initiated on the surface of the cell wall adherence followed by ruptured the cells and caused the cell death. In addition to the antibacterial activity, in vitro embryotoxicity studies were performed against zebrafish embryos and the results confirmed that 200 µg/ml concentration of AuNPs showed the embryotoxicity, whereas 2 µg/ml of CuNPs resulted the embryotoxicity. Furthermore, the morphological anomalies of zebrafish embryos revealed the toxic nature of the synthesized nanoparticles.     

Effect of biologically synthesized silver nanoparticles on Bacopa monnieri (Linn.) Wettst. plant growth metabolism

In this present study, interactions of biologically synthesized silver nanoparticles on hydroponically grown Bacopa monnieri (Linn.) Wettst. plant growth metabolism were documented. Estimates of protein, carbohydrate, total phenols, in addition antioxidant enzymes, catalase and peroxidise were assayed in various parts of the plants grown in hydroponic solution. The silver nanoparticles used in this study were synthesized by treating AgNO₃ with aqueous leaves extracts of Acalypha indica Linn., a medicinal herb as a source of reductants. Enhanced peroxidase and catalase activity, simulated the stress conditions induced by the silver nitrate treatment. No severe toxic effects were observed in silver nanoparticles treated plants in the morphological studies under scanning electron microscopy (SEM) while structural aberrations were observed in the light microscopic evaluation of root and stem anatomy. Further, the uptake of silver in the root and stem tissues of B. monnieri (Linn.) Wettst. was confirmed using atomic absorption spectrophotometer (AAS).     

Does endophyte symbiosis resist allelopathic effects of an invasive plant in degraded grassland?

Allelopathic effects and plant associated systemic endophytic fungi are often thought to play a role in the invasion of exotic plant species. Here, we tested the inhibitory effects of the aqueous extracts of the hemiparasitic weed Pedicularis kansuensis on seed germination and seedling growth of endophyte-free (E−) and -infected (E+) grass species, Stipa purpurea and Elymus tangutorum. The weed extracts significantly inhibited both seed germination and seedling growth of the target grass species. Extracts from the inflorescences gave greater inhibition than those from the stems or roots, while the concentration of the extract had a direct effect on the extent of inhibition. The E+ target plants were less susceptible to the extracts than their E-counterparts. Our results suggest that the allelopathic potential of P. kansuensis will lead to increased frequencies of endophyte infected plants in grass populations.     

Microbial synthesis of spherical nanosilver and nanogold for mosquito control

Biosynthesis of metal nanoparticles using microorganisms is an important area of research in nanobiotechnology, which is an emerging eco-friendly science of well-defined sizes, shapes and controlled monodispersity. The present study proposed a green process for the extracellular production of silver (Ag) and gold (Au) nanoparticles (NPs) using the soil fungi Chrysosporium keratinophilum and Verticillium lecanii. The synthesized NPs were formed fairly uniform with spherical shape determined by Transmission Electron Microscope (TEM) and confirmed by Scanning Electron Microscope (SEM). Elemental analysis on single particle was carried by EDX analysis. The results were further supported by UV-vis spectrophotometry. In addition, we have also investigated the effect of synthesized AgNPs and AuNPs against the larvae and pupae of Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti. The efficacy test was performed at different concentrations for periods of different lengths by the probit analysis. The larvae and pupae of Cx. quinquefasciatus, An. stephensi and Ae. aegypti were found highly susceptible to the synthesized AgNPs than the AuNPs. The larvae of Cx. quinquefasciatus and Ae. aegypti were found to be more susceptible to the AgNPs and AuNPs synthesized using the C. keratinophilum and V. lecanii compared with the larvae of An. stephensi. The pupae of Ae. aegypti have shown higher mortality against the synthesized AgNPs than the pupa of Cx. quinquefasciatus, while no adverse effects could be observed in the pupa of An. stephensi. By this approach, it is suggested that this rapid synthesis of nanoparticles would be useful for developing a biological process for mosquito control.     

Nano carriers for nitric oxide delivery and its potential applications in plant physiological process: A mini review

Nitric oxide (NO) plays a key role in plant growth and defense. Since NO is a small molecule, devoid of charge and relatively lipophilic, it easily crosses cell membranes, acting as an important signaling messenger. Recently, several papers described the beneficial effects due to application of small molecular weight NO donors in plants. Exogenous NO donors break seed dormancy, stimulate plant germination and greening, control iron homeostasis in plants, and improve plant tolerance to salinity, metal toxicity, temperature and drought stress. However, these NO donors are thermally and photochemically unstable. A promising strategy that has been successfully used in biomedical applications is the combination of NO donors with nanomaterials. The encapsulation of NO donors in nanoparticles/nanotubes is able to control the release of therapeutic amounts of NO, thus improving its beneficial effects. Although nanomaterials have been used successfully to carry agrochemicals in plants, the delivery of NO is still to be studied. In this context, the present review highlights the advantages of applications of NO donors in plants, the uses of nanotechnology in agriculture, and the necessity to develop new strategies based on the combination of NO and nanomaterials in agriculture. Therefore, this review hopes to open up new perspectives in the area of nanobiotechnology, NO and agriculture.     

Assessment of heavy metal induced stress responses in pea (Pisum sativum L.)

Exposure of plants to heavy metals severely affects their growth and physiological processes. Nevertheless, different plants show variable responses to different heavy metals, generally in a concentration-dependent manner. In this study, phytotoxic effects of cadmium (Cd), cobalt (Co) and lead (Pb) applied as chlorides at concentration 500, 750, 1000 and 1250 ppm were evaluated on seed germination, early seedling growth and dry biomass of pea (Pisum sativum L.). A lower concentration (500 ppm) of Pb promoted seed germination but declined other growth parameters. Higher concentration had a phytotoxic influence on the pea. Cd and Co severely affected germination and seedling growth of pea resulting in complete failure of germination and seedling growth at higher metal concentration. Tolerance index (TI) calculated for seed germination and dry biomass indicated that tested plant had zero tolerance to 1250 ppm of Cd as well as 750 ppm and higher concentrations of Co. The order of heavy metals for their phytotoxic effects was Co > Cd > Pb. The study suggests that P. sativum is relatively tolerant to Pb but highly sensitive to Co and Cd.     

Impacts of Carpobrotus edulis (L.) N.E.Br. on the Germination,Establishment and Survival of Native Plants: A Clue for Assessing Its Competitive Strength

Does Carpobrotus edulis have an impact on native plants? How do C. edulis’ soil residual effects affect the maintenance of native populations? What is the extent of interspecific competition in its invasion process? In order to answer those questions, we established pure and mixed cultures of native species and C. edulis on soil collected from invaded and native areas of Mediterranean coastal dunes in the Iberian Peninsula. We examined the impact of the invader on the germination, growth and survival of seeds and adult plants of two native plant species (Malcolmia littorea (L.) R.Br, and Scabiosa atropurpurea L.) growing with ramets or seeds of C. edulis. Residual effects of C. edulis on soils affected the germination process and early growth of native plants in different ways, depending on plant species and density. Interspecific competition significantly reduced the germination and early growth of native plants but this result was soil, density, timing and plant species dependent. Also, at any density of adult individuals of C. edulis, established native adult plants were not competitive. Moreover, ramets of C. edulis had a lethal effect on native plants, which died in a short period of time. Even the presence of C. edulis seedlings prevents the recruitment of native species. In conclusion, C. edulis have strong negative impacts on the germination, growth and survival of the native species M. littorea and S. atropurpurea. These impacts were highly depended on the development stages of native and invasive plants. Our findings are crucial for new strategies of biodiversity conservation in coastal habitats.     

Evaluation of the antifungal activity of Rumex vesicarius L. and Ziziphus spina-christi (L) Desf. Aqueous extracts and assessment of the morphological changes induced to certain myco-phytopathogens

Many Plant extracts had proved a potential antifungal activity against a wide range of phytopathogenic fungi. The aim of this study was to evaluate the antifungal activity of the aqueous extracts of Rumex vesicarius L. and Ziziphus spina-christi (L) Desf. against some fungal species. The effect on growth inhibition, conidia germination, sporogenesis, morphological, and ultrastructural characterizations of fungal growth by scanning and transmission electron microscopes, have been investigated. Both plant extracts exhibited an antifungal activity against Fusarium, Helminthosporium, Alternaria, and Rhizoctonia species, besides, the sporogenesis of Alternaria and Fusarium species was suppressed. Both plants induced severe morphological changes in the hyphal shape and surface. We concluded that the aqueous extracts of these plants had strong antifungal activities. More investigations should be performed to evaluate the possible applications in agriculture and in vivo.     

Effect of pinene isomers on germination and growth of maize

Terpenes, secondary metabolites that are present in the essential oils of aromatic plants, are responsible for the biochemical interaction between plants, known as allelopathy. Monoterpenes are a major component of essential oils. Pinene is a monoterpene well-known for its phytotoxic action, but little is known about the allelopathic effect of its isomers. The aim of this study is to determine the effect of pinene's structural isomers and enantioisomers [(−)-α-pinene; (+)-α-pinene; (−)-β-pinene and (+)-β-pinene] at 0.16 mM, on certain physiological parameters (growth, dry weight, phenol, photosynthetic pigments and abscisic acid content) in both the germination and growth of maize (Zea mays L.). In germination bioassays, neither of the α-pinene stereoisomers showed change when compared to the control with respect to seed vigour; but root growth was increased, while β-pinene (racemic mixture) inhibited germination and plant length. In the growth bioassay, all of the pinene isomers decreased the plant length. In general, β-pinene terpene was more phytotoxic than α-pinene in both bioassays. Differences in germination and growth of maize treated with the pinene isomers can be attributed to different action mechanisms which depends both on the growth phases of maize and on the particular pinene isomers.     

Exploitation of marine bacteria for production of gold nanoparticles

Background

Gold nanoparticles (AuNPs) have found wide range of applications in electronics, biomedical engineering, and chemistry owing to their exceptional opto-electrical properties. Biological synthesis of gold nanoparticles by using plant extracts and microbes have received profound interest in recent times owing to their potential to produce nanoparticles with varied shape, size and morphology. Marine microorganisms are unique to tolerate high salt concentration and can evade toxicity of different metal ions. However, these marine microbes are not sufficiently explored for their capability of metal nanoparticle synthesis. Although, marine water is one of the richest sources of gold in the nature, however, there is no significant publication regarding utilization of marine micro-organisms to produce gold nanoparticles. Therefore, there might be a possibility of exploring marine bacteria as nanofactories for AuNP biosynthesis.

Results

In the present study, marine bacteria are exploited towards their capability of gold nanoparticles (AuNPs) production. Stable, monodisperse AuNP formation with around 10?nm dimension occur upon exposure of HAuCl₄ solution to whole cells of a novel strain of Marinobacter pelagius, as characterized by polyphasic taxonomy. Nanoparticles synthesized are characterized by Transmission electron microscopy, Dynamic light scattering and UV-visible spectroscopy.

Conclusion

The potential of marine organisms in biosynthesis of AuNPs are still relatively unexplored. Although, there are few reports of gold nanoparticles production using marine sponges and sea weeds however, there is no report on the production of gold nanoparticles using marine bacteria. The present work highlighted the possibility of using the marine bacterial strain of Marinobacter pelagius to achieve a fast rate of nanoparticles synthesis which may be of high interest for future process development of AuNPs. This is the first report of AuNP synthesis by marine bacteria.     

Developing Transgenic Jatropha Using the SbNHX1 Gene from an Extreme Halophyte for Cultivation in Saline Wasteland

Jatropha is an important second-generation biofuel plant. Salinity is a major factor adversely impacting the growth and yield of several plants including Jatropha. SbNHX1 is a vacuolar Na⁺/H⁺ antiporter gene that compartmentalises excess Na⁺ ions into the vacuole and maintains ion homeostasis. We have previously cloned and characterised the SbNHX1 gene from an extreme halophyte, Salicornia brachiata. Transgenic plants of Jatropha curcas with the SbNHX1 gene were developed using microprojectile bombardment mediated transformation. Integration of the transgene was confirmed by PCR and Rt-PCR and the copy number was determined by real time qPCR. The present study of engineering salt tolerance in Jatropha is the first report to date. Salt tolerance of the transgenic lines JL2, JL8 and JL19 was confirmed by leaf senescence assay, chlorophyll estimation, plant growth, ion content, electrolyte leakage and malondialdehyde (MDA) content analysis. Transgenic lines showed better salt tolerance than WT up to 200 mM NaCl. Imparting salt tolerance to Jatropha using the SbNHX1 gene may open up the possibility of cultivating it in marginal salty land, releasing arable land presently under Jatropha cultivation for agriculture purposes. Apart from this, transgenic Jatropha can be cultivated with brackish water, opening up the possibility of sustainable cultivation of this biofuel plant in salty coastal areas.     

Mitigation of salinity-induced negative impact on the growth and yield of wheat by plant growth-promoting rhizobacteria in naturally saline conditions

Salinity is one of the major environmental threats for successful crop production, hampering plant growth due to the osmotic effect and nutritional and hormonal imbalances. The application of naturally occurring plant growth-promoting rhizobacteria (PGPR) is an emerging technology aimed at ameliorating the negative impact of salinity. However, the results obtained in the laboratory can sometimes not be reproduced in the field. The aim of the study reported here was to evaluate the effect of PGPR inoculation on seed germination in a saline environment under axenic conditions and on enhancement of the growth and yield of wheat under natural salt-affected field conditions. Wheat seeds were inoculated with pre-isolated strains of Pseudomonas putida, Enterobacter cloacae, Serratia ficaria, and Pseudomonas fluorescens and sown at different salinity levels (1, 2, 3, 6, 9, 12, 15 dS m^-1). Inoculation with these strains was found to enhance the germination percentage, germination rate, and index of wheat seeds up to 43, 51, and 123 %, respectively, over the uninoculated control at the highest salinity level. The potential of these PGPR for improving the growth and yield of wheat was also evaluated at two natural salt-affected sites. Inoculation with PGPR resulted a significant increase in the growth and yield parameters of wheat at both sites. The inoculated plants also improved the nutrient status of the wheat plants. The inoculated plants had low sodium and high nitrogen, phosphorus, and potassium contents. Our results show that such rhizobacterial strains may be used as an effective tool for enhancing plant growth under salinity stress and for maximizing the utilization of salt-affected soils.