Halophilic rhizobacteria from <Emphasis Type="Italic">Distichlis spicata</Emphasis> promote growth and improve salt tolerance in heterologous plant hosts

Rhizobacteria are central components of the plant microbiome and influence root development and function. Desciphering how rhizobacteria contribute to plant performance under adverse environments is a major research challenge. The aims of the present study were to isolate and characterize rhizobacteria from the halophilic grass Distichlis spicata and to test their possible growth promoting and salt protective properties in Arabidopsis thaliana, Cucumis sativus, and Citrullus lanatus. To determine their possible plant growth promoting properties, 38 rhizobacterial isolates were co-cultivated with Arabidopsis seedlings in vitro. Out of these, two halophilic bacteria, LBEndo1 and KBEcto4, were selected following their strong shoot and root biostimulation. 16S rRNA sequencing identified LBEndo1 as Bacillus sp. and KBEcto4 as Pseudomonas lini. Both strains improved growth under standard and saline conditions, which correlated with IAA and siderophore production, as well as phosphate solubilization. Additionally, the KBEcto4 strain expresses the ACC deaminase enzyme (acdS gene), and slightly increases auxin redistribution within Arabidopsis roots expressing an auxin-inducible gene construct. These data reveal the potential of saltgrass (Distichlis spicata) rhizobacteria to promote growth and confer salt tolerance to Arabidopsis and crop plants.     

Alleviation of Mercury Toxicity in Wheat by the Interaction of Mercury-Tolerant Plant Growth-Promoting Rhizobacteria

Heavy metal contamination of agricultural soils has increased along with industrialization. Mercury is a toxic heavy metal and a widespread pollutant in the ecosystem. Mercury-tolerant and plant growth-promoting rhizobacteria (PGPR) HG 1, HG 2, and HG 3 were isolated from the rhizosphere of plants growing in a mercury-contaminated site. These isolates were able to grow in the presence of mercury ranging from 10 to 200 µM in minimal medium and 25 to 500 µM in LB medium. The strains were characterized by morphological, biochemical, and plant growth-promoting traits. In the present study, these PGPR strains were analyzed for their involvement in metal stress tolerance in Triticum aestivum (wheat). Two bacterial strains, namely, Enterobacter ludwigii (HG 2) and Klebsiella pneumoniae (HG 3), showed better growth promotion of T. aestivum seedlings under metal stress. Different growth parameters like, water content and biochemical properties were analyzed in the PGPR-inoculated wheat plants under 75 µM HgCl₂. Shoot length, root length, shoot dry weight, root dry weight and relative water content (RWC) were significantly higher in inoculated plants compared to uninoculated plants under stress condition. Proline content, electrolyte leakage, and malondialdehyde content (shoots and roots) were significantly lower in inoculated plants with respect to uninoculated plants under mercury stress. Therefore, it could be assumed that all these parameters collectively improve plant growth under mercury stress conditions in the presence of PGPR. Hence, these PGPRs can serve as promising candidates for increasing plant growth and also have immense potential for bioremediation of mercury-contaminated soils.     

Molecular diversity of 1-aminocyclopropane-1-carboxylate (ACC) deaminase producing PGPR from wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) rhizosphere

Aims

The present study was planned to investigate the diversity of 1-aminocyclopropane-1-carboxylate (ACC) deaminase producing bacteria from the rhizosphere of wheat plants and subsequent evaluation of selected PGPR on growth enhancement of wheat seedlings under drought and saline conditions.

Methods

ACC deaminase producing plant growth promoting rhizobacteria (PGPR) were isolated from the rhizosphere of wheat and identified using 16S rRNA gene sequence analysis. Isolates were evaluated for various direct and indirect plant growth promoting (PGP) traits. Plant inoculation experiment was conducted using isolates IG 19 and IG 22 in wheat to assess their plant growth promotion potential under salinity and drought stress.

Results

Thirty-eight ACC deaminase producing PGPR were isolated which belonged to 12 distinct genera and falling into four phyla γ-proteobacteria, β-proteobacteria, Flavobacteria and Firmicutes. Klebsiella sp. was the most abundant genera and followed by Enterobacter sp. The isolates exhibited ACC deaminase activities ranging from 0.106–0.980 μM α- ketobutyrate μg protein^?1 h^?1. The isolates showed multiple PGP traits such as IAA production, phosphate, zinc, potassium solubilization and siderophore production. Enterobacter cloacae (IG 19) and Citrobacter sp. (IG 22) inoculated wheat seedlings showed notable increases in fresh and dry biomass under non-stress as well as under stressed condition.

Conclusion

To the best of our knowledge this is the first report of presence of ACC deaminase activity and other PGP traits from the genus Citrobacter and Empedobacter. Our finding revealed that the γ-proteobacteria group dominated the wheat rhizosphere. Plant inoculation with PGPR could be a sustainable approach to alleviate abiotic stresses in wheat plants. These native PGPR isolates could be used as potential biofertilizers for sustainable agriculture.

     

Drought-induced acclimatization of a fast-growing plant decreases insect performance in leaf-chewing and sap-sucking guilds

An initial destabilization of functions triggered by drought stress in plants is followed by acclimatization and acquisition of tolerance; however, knowledge remains limited on drought-mediated changes in plant quality for herbivores. We tested whether a water-stressed fast-growing plant negatively affects host-specialist insects in both sap-sucking and leaf-chewing feeding guilds. Collards (Brassica oleracea var. acephala) were grown in well-watered, slightly water-stressed and severely water-stressed conditions. Decreasing soil moisture adversely affected plant development, assessed as a reduction in leaf number and size, stomatal size and relative water content. Severely stressed plants had less fiber and glucosinolates; however, they showed more total nitrogen and lipids. Larval survival, pupal weight, reproductive rate (Ro) and rate of population growth (r) were lower when the leaf-chewing Plutella xylostella was reared with severely stressed collards. In multiple-choice tests, moths laid fewer eggs on leaf discs of collard that were exposed to drought. The fecundity of the sap-sucking Brevicoryne brassicae was higher and the development of alates was lower when insects were fed on plants kept in well-watered regime as compared to slight-stress and severe-stress. Despite higher nitrogen content and fewer glucosinolates, a higher level of leaf surface wax in severely stressed collards possibly decreased food quality for both herbivores. Thus, host-specific herbivores of different guilds showed similar responses to drought-stressed, fast-growing plants. Water-stressed crops could discourage the attack of specialist insects, but the intensity of the stress that is required to achieve this effect will greatly reduce crop production, in terms of plant growth or foliage increment.     

Water stress amelioration and plant growth promotion in wheat plants by osmotic stress tolerant bacteria

Soil microorganisms with potential for alleviation of abiotic stresses in combination with plant growth promotion would be extremely useful tools in sustainable agriculture. To this end, the present study was initiated where forty-five salt tolerant bacterial isolates with ability to grow in high salt medium were obtained from the rhizosphere of Triticum aestivum and Imperata cylindrica. These bacteria were tested for plant-growth-promoting rhizobacteria traits in vitro such as phosphate solubilization, siderophore, ACC deaminase and IAA production. Of the forty-five isolates, W10 from wheat rhizosphere and IP8 from blady grass rhizosphere, which tested positive in all the tests were identified by morpholological, biochemical and 16SrDNA sequencing as Bacillus safensis and Ochrobactrum pseudogregnonense respectively and selected for in vivo studies. Both the bacteria could promote growth in six varieties of wheat tested in terms of increase in root and shoot biomass, height of plants, yield, as well as increase in chlorophyll content. Besides, the wheat plants could withstand water stress more efficiently in presence of the bacteria as indicated by delay in appearance of wilting symptoms increases in relative water content of treated water stressed plants in comparison to untreated stressed ones, and elevated antioxidant responses. Enhanced antioxidant responses were evident as elevated activities of enzymes such as catalase, peroxidase, ascorbate peroxidase, superoxide dismutase and glutathione reductase as well as increased accumulation of antioxidants such as carotenoids and ascorbate. Results clearly indicate that the ability of wheat plants to withstand water stress is enhanced by application of these bacteria which also function as plant growth promoting rhizobacteria.     

Effect of auxin producing and phosphate solubilizing bacteria on mobility of soil phosphorus,growth rate,and P acquisition by wheat plants

Microorganisms capable of mobilizing phosphate promote plant growth, this activity being frequently accompanied by production of plant hormones auxins. However, the extent of contribution of these characteristics to promotion of plant growth remains unclear. Paenibacillus illinoisensis IB 1087 and Pseudomonas extremaustralis IB-Ki-13-1A strains were selected for their capacity to mobilize phosphates and to synthesize auxins in vitro. The effects of inoculating these bacteria on the content of mobile phosphorus in the soil as well as on the phosphorus and hormone content in wheat plants were studied and the observed responses were related to the changes in plant growth. Inoculation of bacteria into the soil increased P concentration in the plants suggesting their increased capacity for the efficient acquisition of phosphorus compounds, while concentration of mobile phosphorus in the soil was increased by its inoculation with bacteria only in the absence of plants. The treatment increased plants mass (to greater extent in the case of P. illinoisensis) in accordance with the increased level of auxins in the treated plant. Increased mass accumulation did not correlate with the potential ability of bacteria strains for production of auxins or phosphate mobilization in vitro. Our data indicate importance of increased auxin content in the plants for the stimulation of root growth and capacity for P uptake as influenced by growth-promoting bacteria.     

Photosynthetic and antioxidative upregulation in drought-stressed sesame (<Emphasis Type="Italic">Sesamum indicum</Emphasis> L.) subjected to foliar-applied salicylic acid

Insufficient attention has been paid to the physiological responses of sesame to drought and it is unclear if exogenous plant growth regulators are beneficial to drought-stressed sesame. Thus, a field study was conducted on seven Sesamum indicum genotypes affected by two levels of irrigation (60 and 80% depletions in available soil water) and by foliar-applied salicylic acid (SA; 0 and 0.6 mM). Water deficit led to depressions in net photosynthetic rate, stomatal conductance, leaf area index, chlorophyll a, b, and total chlorophyll contents, maximum quantum efficiency of PSII, and plant dry matter and seed yield, despite increases in carotenoid concentration, superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase activities. SA was found beneficial in ameliorating the depressions in all of the above characteristics, indicating that it could be applied for lessening the harmful effects of the drought stress.     

Evaluation of rhizobacteria in upland rice in Brazil: growth promotion and interaction of induced defense responses against leaf blast (<Emphasis Type="Italic">Magnaporthe oryzae</Emphasis>)

Blast and the initial vigor of upland rice plants are the main challenges facing rice crops in Brazilian no-tillage systems. The aim of this study was to evaluate the growth promotion and interactions of defense responses against Magnaporthe oryzae in rice plants treated with rhizobacteria Bacillus sp. (BRM 32110) and Serratia sp. (BRM 32114). The seeds of the rice were microbiolized, and 14 days after the plants emerged, the soil was drenched with rhizobacterial suspensions. Growth promotion was evaluated by root and shoot biomass, root and shoot length, foliar area, and nitrate reductase (NR) activity. The defense response was evaluated by quantification of the rice blast severity (RBS), disease progress, pathogenesis-related protein (PRP) activity, and salicylic acid content (SA). The length and biomass of the roots and shoots and the foliar area of the plants treated with BRM 32114 isolate increased; however, the NR activity was 43% lower compared to the control. Both isolates reduced the severity and progress of the disease. Principal component analysis showed that RBS, β-1,3-glucanase (GLU), peroxidase (POX), and phenylalanine ammonia lyase (PAL) were the main sources of the first components of variance, whereas lipoxygenase (LOX) and SA were the main sources of the second components and were negatively correlated. Serratia sp. isolate BRM 32114 can be used as a growth-promoting agent and has potential for inducing resistance in rice plants. The results suggest that the interaction among the levels and timing of the PRP activity and the levels of SA play important roles in the defense responses against M. oryzae.     

Effects of mycorrhizal fungi inoculation and soil amendment with hydrogel on leaf anatomy,growth and physiology performance of olive plantlets under two contrasting water regimes

Abiotic stresses present a real environmental problem in agriculture field. In our paper, we examine the significance of arbuscular mycorrhizal fungi (AMF) and soil amendment with water retaining superpolymers (hydrogel) on growth and physiology performance of olive plantlets. Our experiment was carried out in nursery conditions, to test the impact of hydrogel (TH) and mycorrhizal fungi (TM), used individually or combined (THM), and compare them with non inoculated plants (TC), to understand and reduce the water stress damage in olive plantlets (cv. Chemlali). We also evaluate interactions between hydrogel, mycorrhizal treatments and water regimes. Results of mycorrhization (M%) show that roots colonized by Rhizophagus irregularis of well-watered plants were about 40.87%. In combined treatment (THM), M% was about 32.14%. Compared to TC treatment, TM treatment enhances significantly the dry weights of the whole plant under the two water regimes. The TM treatment had the highest relative water content (66.50%) and Chl (a?+?b) (0.83 mg g^??1) in stressed conditions. We found also that under water stress, the maximal quantum efficiency of the photosystem II measurements in leaves were significantly improved by 50.70% in TH treatment compared to control. For phenolic contents, TH treatment decreased significantly total phenols by 50.10% compared to TC. Our study gives evidence that the use of AMF and the hydrogel separately or in combination may enhance the capacity to avoid drought damages of olive plantlets and improve olive performances.     

Beneficial native bacteria improve survival and mycorrhization of desert truffle mycorrhizal plants in nursery conditions

Sixty-four native bacterial colonies were isolated from mycorrhizal roots of Helianthemum almeriense colonized by Terfezia claveryi, mycorrhizosphere soil, and peridium of T. claveryi to evaluate their effect on mycorrhizal plant production. Based on the phylogenetic analysis of the 16S rDNA partial sequence, 45 different strains from 17 genera were gathered. The largest genera were Pseudomonas (40.8 % of the isolated strains), Bacillus (12.2 % of isolated strains), and Varivorax (8.2 % of isolated strains). All the bacteria were characterized phenotypically and by their plant growth-promoting rhizobacteria (PGPR) traits (auxin and siderophore production, phosphate solubilization, and ACC deaminase activity). Only bacterial combinations with several PGPR traits or Pseudomonas sp. strain 5, which presents three different PGPR traits, had a positive effect on plant survival and growth. Particularly relevant were the bacterial treatments involving auxin release, which significantly increased the root-shoot ratio and mycorrhizal colonization. Moreover, Pseudomonas mandelii strain 29 was able to considerably increase mycorrhizal colonization but not plant growth, and could be considered as mycorrhiza-helper bacteria. Therefore, the mycorrhizal roots, mycorrhizosphere soil, and peridium of desert truffles are environments enriched in bacteria which may be used to increase the survival and mycorrhization in the desert truffle plant production system at a semi-industrial scale.     

Water sources and water-use efficiency of desert plants in different habitats in Dunhuang,NW China

To understand habitat associated differences in desert plant water-use patterns, water stable oxygen isotope composition was used to determine water source and leaf carbon isotope composition (δ ¹³C) was used to estimate long-term water-use efficiency in three typical habitats (saline land, sandy land and Gobi) in Dunhuang. The primary findings are: (1) in the three habitats, plant species used mainly deep soil water (>120 cm), except for Kalidium foliatum in the saline land, which relied primarily on 0–40 cm soil water; (2) in the saline land and Gobi habitat, Alhagi sparsifolia had the most negative foliar δ ¹³C; in the sandy land, Elaeagnus angustifolia leaf was enriched in ¹³C than the other three species in 2011, but no species differences in foliar δ ¹³C was observed among the four species in 2012; (3) common species (Tamarix ramosissima and A. sparsifolia) may alter their water sources to cope with habitat differences associated changes in soil water availability with deeper water sources were used in the Gobi habitat with lower soil water content (SWC) compared to in the saline land and sandy land; (4) we detected significant habitat differences in foliar δ ¹³C in A. sparsifolia which may have resulted from differences in SWC and soil electrical conductivity. However, no habitat differences in foliar δ ¹³C were observed in T. ramosissima, which may attribute to the strong genetic control in T. ramosissima or the ability to access stable deep soil water. Overall, the results suggest that extremely arid climate, root distribution and soil properties worked together to determine plant water uptake in Dunhuang area.     

Effects of using different host plants and long-term fertilization systems on population sizes of infective arbuscular mycorrhizal fungi

The effect of cultivation of mycorrhizal and non-mycorrhizal plants and mineral fertilization on the arbuscular mycorrhizal fungal (AMF) community structure of maize (Zea mays L.) plants was studied. Soil samples were collected from two field experiments treated for 5 years with three fertilization systems (Control – no fertilization; Mineral – NPK fertilization; and Organic – Farmyard manure fertilization). Soil samples containing soil and root fragments of rapeseed (Brassica napus L., non-mycorrhizal plant) and wheat (Triticum aestivum L., mycorrhizal plant) collected from the field plots were used as native microbial inoculum sources to maize plants. Maize plants were sown in pots containing these inoculum sources for four months under glasshouse conditions. Colonization of wheat roots by AMF, AMF community structure, AMF diversity (Shannon’s index), AMF dominance (Simpson’s index) and growth of maize were investigated. Sixteen AMF species were identified from rhizosphere soil samples as different species of genera Acaulospora, Claroideoglomus, Dentiscutata, Funneliformis, Gigaspora, Quatunica, Racocetra, and Rhizoglomus. Maize plants grown in manure-fertilized soils had a distinct AMF community structure from plants either fertilized with mineral NPK-fertilizer or non-fertilized. The results also showed that inoculum from non-mycorrhizal plants combined with mineral fertilization decreased AMF diversity (Shannon’s index), AMF dominance (Simpson’s index) and growth of maize. Our findings suggest that non-mycorrhizal plants, such as B. napus, can negatively affect the presence and the effects of soil inoculation on maize growth. Also, our results highlight the importance of considering the long-term effect of rapeseed cultivation system on the reduction of population sizes of infective AMF, and its effect on succeeding annual crops.     

Nutrient concentration in wheat and soil under allelopathy treatments

Allelopathy is related to soil nutrient availability and allelochemicals can change the soil and therefore the plant nutrient status. Wheat is one of the most important crops for the production of human food in the world. Alhagi maurorum and Cardaria draba are the most important weeds in wheat fields. We performed experiments to assess the allelopathic effect of A. maurorum and C. draba shoots on mineral nutrient concentrations in pot-grown wheat plants and soil. The presence of dry powder of A. maurorum and C. draba shoots reduced concentrations of macronutrients (NO₃ ^?, K⁺, Ca²⁺ and P) and micronutrients (Fe²⁺ and Cu²⁺) in roots and shoots of wheat plants, whereas it did not affect concentrations of Mg²⁺, Mn²⁺ and Zn²⁺. Allelopathic effect of A. maurorum was significantly greater than that of C. draba. There was a significantly positive correlation between wheat growth and ion concentration. There was a significantly negative correlation between the soil nutrient concentration and plant nutrient concentration across the treatments. These results suggest that allelopathy increases the nutrient availability in the soil because of the decrease in absorption by plants.     

Induction of water deficit tolerance in wheat due to exogenous application of plant growth regulators: membrane stability,water relations and photosynthesis

Our experiment was carried out in order to explore effects of plant growth regulators (PGR; thidiazuron, paclobutrazol, and ascorbic acid) on physiological traits of wheat genotypes under water surplus and deficit conditions. Study revealed that relative water content, membrane stability index, chlorophyll content, photosynthetic rate (P_N), and maximal quantum yield of PSII improved with PGRs application across the genotypes both under irrigation and water stress. The response of HD 2733 genotype was more positive toward PGRs treatment as compared to other genotypes under water stress. Higher P_N and chlorophyll contents were observed in HD 2987 followed by C 306 genotype under water-stress conditions. Moreover, Rubisco small subunit (SSU) expression was lower in wheat genotypes under water stress as compared to irrigated conditions. Application of PGRs led to upregulation of SSU under water stress, while no significant change was found in Rubisco level and activity under irrigated condition in dependence on PGRs treatments. Yield-related traits showed also significant reduction under water-stress conditions, while application of PGRs enhanced the yield and its components. Results indicated that the PGRs exhibited a positive interaction and synergetic effect on water stressed wheat plants in terms of photosynthetic machinery and yield.     

Physiological and biochemical changes in tomato cultivar PT-3 with dual inoculation of mycorrhiza and PGPR against root-knot nematode

Arbuscular mycorrhizal fungi (AMF) and plant growth promoting rhizobacteria (PGPR) have potential to control soil-borne diseases including plant-parasitic nematodes. First, the effects of dual inoculation of mycorrhiza (Rhizophagus irregularis) and two stains of pseudomonads (Pseudomonas jessenii strain R62 and Pseudomonas synxantha strain R81) on tomato (Solanum lycopersicum cv. PT-3) growth were tested. Further, the physiological and biochemical changes caused by these beneficial organisms during infection by the root-knot nematode Meloidogyne incognita were studied. The experiment was conducted under glass house conditions and carried out up to one month after nematode inoculation. Plants treated with dual or individual inoculation of AMF and PGPR showed significantly enhanced plant growth and reduced nematode infection. In addition, they exhibited potent activity of phenolics (28 %) and defensive enzymes i.e. peroxidase (PO; 1.26 fold), polyphenyloxidase (PPO; 1.35 fold) and superoxide dismutase (SOD; 1.09 fold) while a significant reduction in malondialdehyde (MDA; 1.63 fold) and hydrogen peroxide (H₂O₂; 1.30 fold) content was recorded when compared to the nematode-infected plants. These findings indicate the feasibility of AMF and PGPR individually or in combinations as potential biocontrol agents for the management of root-knot nematodes.     

Bacteria endemic to saline coastal belt and their ability to mitigate the effects of salt stress on rice growth and yields

Increase in soil salinity adversely affects the metabolism and lowers the yield of rice (Oryza sativa L). Application of plant growth-promoting rhizobacteria (PGPR) to ameliorate the effects of salt stress on sensitive rice can be both effective and sustainable. In this study, 20 bacterial strains were isolated from the soil of saline-prone regions of Satkhira, north of the Sundarbans in coastal Bangladesh. Three bacteria among these grew well in the presence of 3 M salt (NaCl) and were Gram positive and non-motile. Their 16S rRNA sequence revealed that they belong to the Halobacillus genus. Two of them were identified as Halobacillus dabanensis strain SB-26 and the other one as Halobacillus sp. GSP 34. A couple of mechanisms by which these microbes could play beneficial role if associated with plants, such as nitrogen fixation and indole acetic acid (IAA) production, were identified. The two bacterial strains showed positive results for nitrogen fixation and indole acetic acid (IAA) activity under salt stress. Their effect on the physiology and yield of a farmer popular but sensitive BRRI dhan 28 rice variety was investigated under both control and salt stress. At the seedling stage, inoculated plants had significantly greater root length, shoot height, total weight, chlorophyll content, but lower electrolyte leakage both in control and salt stress (0, 40, and 80 mM). Performance of the plants was even better when both bacteria were used in combination. At the reproductive stage, the plants also showed better phenology in presence of the inoculated bacteria. Under stress (50 mM NaCl), these plants showed significantly greater plant height, lower spikelet damage, and yield reduction compared to untreated plants. The identified Halobacillus strains can therefore be used to improve the yield of rice by exploiting their plant growth promotion activities in coastal areas affected by moderate salinity, such as those with an ionic conductivity of up to 5 dS m^?1.     

Co-inoculation with <Emphasis Type="Italic">Enterobacter</Emphasis> and Rhizobacteria on Yield and Nutrient Uptake by Wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) in the Alluvial Soil Under Indo-Gangetic Plain of India

The aim of this work was to evaluate the effects of co-inoculation with phosphate-solubilizing and nitrogen-fixing rhizobacteria on growth promotion, yield, and nutrient uptake by wheat. Out of twenty-five bacteria isolated from the rhizosphere soils of cereal, vegetable, and agro-forestry plants in eastern Uttar Pradesh, three superior most plant growth-promoting (PGP) isolates were characterized as Serratia marcescens, Microbacterium arborescens, and Enterobacter sp. based on their biochemical and 16S rDNA gene sequencing data and selected them for evaluating their PGP effects on growth and yield of wheat. Among them, Enterobacter sp. and M. arborescens fixed significantly higher amounts (9.32?±?0.57 and 8.89?±?0.58 mg Ng^?1 carbon oxidized, respectively) of atmospheric nitrogen and produced higher amounts (27.06?±?1.70 and 26.82?±?1.63 TP 100 µg mL^?1, respectively) of IAA in vitro compared to S. marcescens (8.32?±?0.39 mg Ng^?1 carbon oxidized and 21.29?±?0.99 TP 100 µg mL^?1). Although both M. arborescens and S. marcescens solubilized remarkable amounts of phosphate from tricalcium phosphate likely through production of organic acids, however, Enterobacter sp. was inactive. The effects of these three rhizobacteria were evaluated on wheat in alluvial soils of the Indo-Gangetic Plain by inoculation of plants with bacterial isolates either alone or in combinations in both pot and field conditions for two successive years. Rhizobacterial inoculation either alone or in consortium of varying combinations significantly (P?≤?0.05) increased growth and yield of wheat compared to mock inoculated controls. A consortium of two or three rhizobacterial isolates also significantly increased plant height, straw yield, grain yield, and test weight of wheat in both pot and field trials compared to single application of any of these isolates. Among the rhizobacterial treatment, co-inoculation of three rhizobacteria (Enterobacter, M. arborescens and S. marcescens) performed best in promotion of growth, yield, and nutrient (N, P, Cu, Zn, Mn, and Fe) uptake by wheat. Taken together, our results suggest that co-inoculation of Enterobacter with S. marcescens and M. arborescens could be used for preparation of an effective formulation of PGP consortium for eco-friendly and sustainable production of wheat.     

Early plant growth and biochemical responses induced by <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> Sp245 lipopolysaccharides in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) seedlings are attenuated by procyanidin B2

This study analyzes the effects of procyanidin B2 on early wheat plant growth and plant biochemical responses promoted by lipopolysaccharides (LPS) derived from the rhizobacteria Azospirillum brasilense Sp245. Measurements of leaf, root length, fresh weight, and dry weight showed in vitro plant growth stimulation 4 days after treatment with A. brasilense as well as LPS. Superoxide anion (O₂ ^·?) and hydrogen peroxide (H₂O₂) levels increased in seedling roots treated with LPS (100 μg mL^?1). The chlorophyll content in leaf decreased while the starch content increased 24 h after treatment in seedling roots. The LPS treatment induced a high increase in total peroxidase (POX) (EC 1.11.1.7) activity and ionically bound cell wall POX content in roots, when compared to respective controls. Early plant growth and biochemical responses observed in wheat seedlings treated with LPS were inhibited by the addition of procyanidin B2 (5 μg mL^?1), a B type proanthocyanidin (PAC), plant-derived polyphenolic compound with binding properties of LPS. All results suggest first that the ionically bound cell wall POX enzymes could be a molecular target of A. brasilense LPS, and second that the recognition or association of LPS by plant cells is required to activate plant responses. This last event could play a critical role during plant growth regulation by A. brasilense LPS.