Zinc Solubilization Research Articles

Impact of Sources, Levels of Zinc and Zinc Solubilizing Bacteria on the Growth and Yield of Maize in Calcareous Soil

A pot culture experiment was conducted with TNAU maize hybrid CO 6 at Tamil Nadu Agricultural University, Coimbatore to evaluate the effect of application of zinc and zinc solubilizing bacteria on the growth and productivity of maize in calcareous soil. The experimental soil was a black calcareous soil with clay loam texture, which belongs to Periyanaickenpalayam series (Typic Haplustert). The experiment was laid out in factorial completely randomized design (FCRD) with three factors replicated thrice. The treatments consisted of two sources of Zn (ZnSO4 and Zn3(PO4) 2) with three levels (0, 5, 7.5 kg Zn ha-1), with and without zinc solubilizing bacteria (ZSB). Among the sources, ZnSO4 performed better than Zn3(PO4) 2 with respect to growth, yield attributes and yield. Increasing levels of Zn had a favourable influence on maize crop and highest growth and yield parameters were recorded with 7.5 kg Zn ha1. With the application of 7.5 kg Zn ha-1, 11.3% mean grain yield increase was observed over no Zn application. ZSB inoculation increased the mean grain and stover yield of maize by 4.2% over the treatments without ZSB inoculation. Considering the overall performance, application of 7.5 kg Zn ha-1 as ZnSO4 along with ZSB was found to be the best Zn management strategy for enhancing maize growth and productivity in calcareous soil.

ISOLATION AND SCREENING OF SOIL YEASTS FOR PLANT GROWTH PROMOTING TRAITS

Soil microorganisms are the key player of biochemical and biological processes of the soil and govern the soil health and sustain agricultural production. Yeast is one of the potential plant growth promoting organisms when compared to bacteria and filamentous fungi. In this study, potential plant growth promoting yeast isolates were isolated from garden land soil. All the yeast isolates were screened based on morphological and antibiotic resistance. Several plant growth promoting abilities of the yeast isolates were investigated. The yeast isolates were tested for mineral solubilization of Zinc, phosphate, and potassium (K). Among the isolates, SY7 showed maximum Zn solubilization potential. For P solubilization and K releasing, SY10 yeast isolate showed maximum potential when compared to others. The results revealed that SY2 yeast isolate, produced the maximum amount of indole acetic acid (IAA), Gibberellic acid (GA3). The isolate, SY6 exhibited better siderophore activity and positive for HCN production. Hence, it is concluded that soil yeast may be considered as potential plant growth promoting agents. .

Genetic diversity and growth promoting characteristics of diazotrophic bacteria isolated from 20 genotypes of Brachiaria spp.

Diazotrophic bacteria, including those of the genus Azospirillum and Nitrospirillum, colonize Brachiaria genotypes and contribute to plant development through nitrogen fixation, production of phytohormones and bioavailability of nutrients. This study aimed to determine the phylogenetic positioning and evaluate the functional abilities of diazotrophic bacteria isolated from Brachiaria genotypes. Diazotrophic bacterial counting and isolation were carried out with rhizosphere soil and root samples from 20 Brachiaria genotypes after inoculation in nitrogen-free semi-solid NFb and LGI media. The isolates were analyzed using 16S rRNA and nifH sequences, and tested for their functional abilities to produce auxin and siderophores, to solubilize phosphate and zinc, and to degrade cellulose. The diazotrophic population ranged from 102 to 108 g−1 rhizosphere soil or roots. Sequencing of 16S rRNA from 213 isolates confirmed the presence of genera Azospirillum and Nitrospirillum, and revealed the presence of 14 other diazotrophic genera. The genus Nitrospirillum was detected colonizing all niches of most Brachiaria species. A PCA analysis showed a positive correlation between the ability to produce siderophores with the ability to produce IAA; and between phosphate and zinc solubilisation. The results showed a high diversity of diazotrophic bacterial species colonizing 20 Brachiaria genotypes and revealed the presence of bacteria with variable growth-promoting characteristics, highlighting their potential as good candidates for the development of biofertilizers.

Residual effect of zinc applied to rice on zinc nutrition of succeeding wheat crop inoculated with zinc solubilizing microbial consortium

Large scale deficiency of Zn results in low crops yields and the problem of Zn malnutrition in humans and livestock. To economize crop production on Zn deficient soils, two-year field experiments were undertaken with two wheat varieties to evaluate the performance of seed inoculation with a consortium of three bacterial strains in combination with varying doses of Zn fertilizer applied to 1 year rice crop on yields, Zn concentration and Zn uptake of wheat. Seed coating of wheat with bacterial consortium significantly increased grain yields, Zn concentration and uptake in grains and straw and total Zn uptake over the control. It also helped to increase the apparent recoveries of soil applied Zn fertilizer to 1 year rice by succeeding wheat crops and DTPA extractable Zn in soil after 2 year wheat in comparison to the control. Seed inoculation in combination with low dosage of Zn also significantly decreased phytic acid: Zn ratio but increased methionine concentration in wheat grains.

Isolation, screening and application of a potent PGPR for enhancing growth of Chickpea as affected by nitrogen level

ABSTRACT Chickpea (Cicer arietinum L.) can obtain much of its N requirement through nitrogen fixation, but plant productivity also relies on N fertilization. Nitrogen capture from fertilizers by the plant is highly inefficient and can have a negative impact on the environment. Plant growth promoting rhizobacteria (PGPR) can improve efficiency of N fertilizer use and support optimum plant growth under low N input to soil. Chickpea plants were grown in pots and treated with low and optimum N input supplemented with PGPR. Bacteria isolated from chickpea rhizosphere exhibited potential growth promoting production of ammonia, indole acetic acid and phytase and solubilization of inorganic phosphate and zinc. A PGPR strain, identified as Cedecea davisae RS3, was selected by principal component analysis and its effect on plant growth promotion evaluated in chickpea plants under N-appropriate (N+), N-deficit with RS3 (N−RS3) and N-appropriate with RS3 (N+RS3) treatments. Overall performance of chickpea plants grown under N−RS3 was better than that of N+ and N+RS3 plants. The improved performance under N-RS3 could be related to enhancement of root nodulation and nitrogenase activity. The PGPR with N-RS3 might be used to obtain sustainable production of chickpea under reduced N.

The nematicide Serratia plymuthica M24T3 colonizes Arabidopsis thaliana, stimulates plant growth, and presents plant beneficial potential.

Nine bacterial strains were previously isolated in association with pinewood nematode (PWN) from wilted pine trees. They proved to be nematicidal in vitro, and one of the highest activities, with potential to control PWN, was showed by Serratia sp. M24T3. Its ecology in association with plants remains unclear. This study aimed to evaluate the ability of strain M24T3 to colonize the internal tissues of the model plant Arabidopsis thaliana using confocal microscopy. Plant growth-promoting bacteria (PGPB) functional traits were tested and retrieved in the genome of strain M24T3. In greenhouse conditions, the bacterial effects of all nematicidal strains were also evaluated, co-inoculated or not with Bradyrhizobium sp. 3267, on Vigna unguiculata fitness. Inoculation of strain M24T3 increased the number of A. thaliana lateral roots and the confocal analysis confirmed effective bacterial colonization in the plant. Strain M24T3 showed cellulolytic activity, siderophores production, phosphate and zinc solubilization ability, and indole acetic acid production independent of supplementation with L-tryptophan. In the genome of strain M24T3, genes involved in the interaction with the plants such as 1-aminocyclopropane-1-carboxylate (ACC) deaminase, chitinolytic activity, and quorum sensing were also detected. The genomic organization showed ACC deaminase and its leucine-responsive transcriptional regulator, and the activity of ACC deaminase was 594.6nmol α-ketobutyrateμg protein-1μl-1. Strain M24T3 in co-inoculation with Bradyrhizobium sp. 3267 promoted the growth of V. unguiculata. In conclusion, this study demonstrated the ability of strain M24T3 to colonize other plants besides pine trees as an endophyte and displays PGPB traits that probably increased plant tolerance to stresses.

Screening of Rice Apoplast Associated Endophytic Bacterial Isolates for Moisture Stress Tolerance and Plant Growth Promoting Traits

Investigations were made to identify, screen and characterize rice apoplastic fluid endophytic bacterial strains for osmotic stress tolerance and plant growth promoting activity. These bacterial strains were identified phylogentically as Bacillus subtilis TSAC5, Bacillus subtilis TSAA2, Bacillus sp. R2AA10, Bacillus cereus R2AA7, Bacillus marisflavi TSAC7, Cupriavidus alkaliphilus TSAC1, Delftia sp. TSAC2, Janibacter melonis R2AA1, Microbacterium oleivorans R2AA6, Kocuria rosea R2AA5, Pseudomonas aeruginosa NAAI3 and Sphingobium yanoikuyae R2AI1. Of these 12 strains, eight were obtained from drought tolerant rice varieties such as Anna R4 and IR DRT 64 and four from normal rice variety CO51. These endophytes exhibited varied level of osmotic stress tolerance created using different concentrations of PEG 6000 (-1.5, -3.0, -4.0, -4.5, -5.0 and -5.5 MPa) under in vitro conditions in liquid and solid medium. Among the 12 strains, Cupriavidus alkaliphilus TSAC1, Delftia sp. TSAC2, Bacillus marisflavi TSAC7, Janibacter melonis R2AA1, Kocuria rosea R2AA5, Pseudomonas aeruginosa NAAI3 and Sphingobium yanoikuyae R2AI1 showed moisture stress tolerance up to -5.5 MPa. Further increase in moisture stress of -6.0 MPa inhibited growth of 12 tested strains. These strains also exhibited Indole acetic acid (IAA), gibberellic acid (GA3) and extracellular polysaccharide (EPS) production and also showed ACC deaminase (ACCD) activity. Maximum extracellular proline production was found in Bacillus marisflavi TSAC7 under both normal and water stressed conditions. Higher IAA productivity was registered in Janibacter melonis R2AA1 followed by Cupriavidus alkaliphilus TSAC1 and Sphingobium yanoikuyae R2AI1 in the absence of PEG 6000. In the presence of PEG 6000 Delftia sp. TSAC2 recorded maximum IAA productivity. Bacillus subtilis TSAA2 showed greater ACC deaminase activity. EPS production was in the order of Pseudomonas aeruginosa NAAI3 followed by Sphingobium yanoikuyae R2AI1. Sphingobium yanoikuyae R2AI1 produced maximum quantity of GA3 both under normal and water stressed condition. None of the tested strains indicated insoluble phosphate, silicate and zinc solubilisation.

Biofertilizer/biopesticide potentiality of zinc solubilizing Pseudomonas aeruginosa FA-9 and Enterobacter sp. FA-11 isolated from the wheat rhizosphere grown in arid zone

Bacterial strains were obtained from wheat rhizosphere and screened for zinc solubilization on agar plates. Two strains FA-9 and FA-11 were found efficient for Zn solubilizing activity and were identified as Pseudomonas aeruginosa and Enterobacter sp. by 16S rRNA and gyrase (gyrB) genes analysis, respectively. The strain FA-9 produced a clear zone diameter of 63 mm, 60 mm and 51 mm on agar plate amended with different zinc ores. The strain FA-11 produced a zone diameter of 17 mm with zinc carbonate and 20 mm with zinc oxide while no zone was observed with zinc phosphate. Both strains showed no visible activity with ZnS ore. Similarly, FA-9 and FA-11 increased maximum soluble zinc content (102 µg ml−1 and 45 µg ml−1) from zinc carbonate ore as compared to zinc oxide ore (102 µg ml−1 and 45 µg ml−1) in liquid broth. It was noted that both strains exhibited less potential (7 µg ml−1 and 0.57 µg ml−1) to solubilize ZnS ore in liquid broth. A comparison between agar plate assay and liquid broth quantification shows that agar plate assay does not present the solubilizing potential of ZSB precisely. The strains FA-9 and FA-11 produced auxin with l-tryptophan (3.25 µg ml−1 and 2.86 µg ml−1) and without l-tryptophan (1.23 µg ml−1 and 1.02 µg ml−1). Both strains expressed exo-polysaccharides (EPS) and siderophores activity along with phosphate (P) solubilization, ACC deaminase and antifungal activities. The ACC deaminase and N-fixation activity was confirmed by the amplification of acdS and nifH genes respectively.

Synergism of Pseudomonas aeruginosa (LSE-2) nodule endophyte with Bradyrhizobium sp. (LSBR-3) for improving plant growth, nutrient acquisition and soil health in soybean.

The present study was aimed to assess the scope of native potential endophyte Pseudomonas aeruginosa (LSE-2) strain (KX925973) with recommended Bradyrhizobium sp. (LSBR-3) (KF906140) for synergistic effect to develop as consortium biofertilizer of soybean. A total of 28 non-rhizobial endophytic bacteria were isolated from cultivated and wild sp. of soybean. All isolates were screened for multifarious PGP traits viz. Indole-3-acetic acid (IAA), phosphate (P) and zinc (Zn) solubilization, siderophore, cell wall degrading enzymes and pathogenicity. Compatible of LSBR-3 and LSE-2 enhanced IAA, P-solubilization, 1-aminocyclopropane-carboxylate deaminase and biofilm formation over the single inoculant treatment. Further, consortium was evaluated in vivo for growth, symbiotic traits, nutrient acquisition, soil quality parameters and yield attributes of soybean. Improvement in growth parameters were recorded with dual inoculant LSBR-3 + LSE-2 as compared to LSBR-3 alone and un-inoculated control treatments. Significantly (p ≥ 0.05) high symbiotic and soil quality parameters (phosphatase and soil dehydrogenase activity) was recorded with LSBR-3 + LSE-2 at vegetative and flowering stage as compared to LSBR-3 alone and un-inoculated control treatments. Single inoculation of LSBR-3 improved grain yield by 4.25% over the un-inoculated control treatment, further, enhancement in yield was recorded with consortium inoculant (LSBR-3 and LSE-2) by 3.47% over the LSBR-3 alone. Application of consortium inoculant (LSBR-3 + LSE-2) gave an additional income of Rs. 5089/ha over the un-inoculated control treatment. The results, thus strongly suggest that endophytic diazotroph LSE-2 can be used as potent bio-inoculant along with LSBR-3 as bio-enhancer for improving soybean productivity in a sustainable system.

Potential of Novel Sequence Type of Burkholderia cenocepacia for Biological Control of Root Rot of Maize (Zea mays L.) Caused by Fusarium temperatum.

In this study, two Burkholderia strains, strain KNU17BI2 and strain KNU17BI3, were isolated from maize rhizospheric soil, South Korea. The 16S rRNA gene and multilocus sequence analysis and typing (MLSA-MLST) were used for the identification of the studied strains. Strain KNU17BI2, which belonged to Burkholderia cenocepacia, was of a novel sequence type (ST) designated ST-1538, while strain KNU17BI3 had a similar allelic profile with the seven loci of Burkholderia contaminans strain LMG 23361. The strains were evaluated in vitro for their specific plant growth promoting (PGP) traits, such as zinc solubilization, phosphate solubilization, ammonia production, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, indole acetic acid (IAA) production, siderophore, and hydrolytic enzyme activity. Interestingly, the strains exhibited a positive effect on all of the tested parameters. The strains also showed broad-spectrum antifungal activity against economically important phytopathogens in the dual culture assay. Furthermore, the strains were evaluated under greenhouse conditions for their in vivo effect to promote plant growth and to suppress the root rot of maize that is caused by Fusarium temperatum on four Korean maize cultivars. The results of the greenhouse study revealed that both of the strains were promising to significantly suppress fusarium root rot and enhance plant growth promotion on the four maize cultivars. This study, for the first time, reported in vitro antifungal potential of B. cenocepacia of novel ST against economically important plant pathogens viz., F. temperatum, Fusarium graminearum, Fusarium moniliforme, Fusarium oxysporum f.sp. melonis, Fusarium subglutinans, Phytophthora drechsleri, and Stemphylium lycopersici. This is also the first report of zinc solubilization by B. cenocepacia. Moreover, the present research work reports, for the first time, about the potential of B. cenocepacia and B. contaminans to control the root rot of maize that is caused by F. temperatum. Therefore, we recommend further studies to precisely identify the bioactive chemical compounds behind such activities that would be novel sources of natural products for biological control and plant growth promotion of different crops.

Actinobacteria for sustainable agriculture

Actinobacteria is a phylum and class of Gram-positive bacteria. The phylum Actinobacteria are classified into six classes namely Acidimicrobiia, Actinobacteria, Coriobacteriia, Nitriliruptoria, Rubrobacteria and Thermoleophilia. Members of phylum Actinobacteria are ubiquitous in nature. Actinobacteria can be utilized as biofertilizers for sustainable agriculture as they can enhance plant growth and soil health though different plant growth promoting attributes such as solubilization of phosphorus, potassium and zinc, production of Fe-chelating compounds, phytohormones hormones such indole acetic acids, cytokinin, and gibberellins as well as by biological nitrogen fixation. The Actinobacteria also plays an important role in mitigation of different abiotic stress conditions in plants. The members of phylum Actinobacteria such as Actinomyces, Arthrobacter, Bifidobacterium, Cellulomonas, Clavibacter, Corynebacterium, Frankia, Microbacterium, Micrococcus, Mycobacterium, Nocardia, Propionibacterium, Pseudonocardia, Rhodococcus, Sanguibacter and Streptomyces exhibited the multifarious plant growth promoting attributes and could be used as biofertilizers for crops growing under natural as well as under the abiotic stress conditions for plant growth and soil health for sustainable agriculture.

Biodiversity of methylotrophic microbial communities and their potential role in mitigation of abiotic stresses in plants

Methylotrophic bacterial community is very important group of bacteria utilizing reduced carbon compounds and plays significant role in plant growth promotion (PGP), crop yield and soil fertility for sustainable agriculture. Abiotic and biotic stresses are very important factors affecting PGP in agriculture. A vast number of microbial communities play an important role in abiotic stress tolerance. The PGP methylotrophic microbes have been reported well enough to mitigate different types of biotic and abiotic stresses. The abiotic stress tolerance was well documented by several methylotrophic bacterial communities such as Hyphomicrobium, Methylarcula, Methylobacillus, Methylobacterium, Methylocapsa, Methylocella, Methyloferula, Methylohalomonas, Methylomonas, Methylophilus, Methylopila, Methylosinus, Methylotenera, Methylovirgula and Methylovorus. The abiotic stress tolerance ability of different methylotrophs and their colonization in different parts of plants under severe low temperature, high temperature, drought and salt stress conditions have been investigated in various studies. The methylotrophic communities help in proliferation of plant directly through solubilization of phosphorus, potassium and zinc, production of phytohormones viz., auxins and cytokinins; production of Fe-chelating compound, biological nitrogen fixation and ACC-deaminase activities or indirectly through productions of ammonia, siderophores and secondary metabolites. The auxin and cytokinin secreted by methylotrophs influence seed germination and plant root growth and help plants to endure water stress. On the plant surface, the abundant methylotrophs exude osmo-protectants such as sugars and alcohols which ultimately help to protect the plants from desiccation and excessive radiations. The utilisation of these potent methylotrophic strains may facilitate proper crop production, PGP by ameliorating abiotic stresses.

Effect of zinc and zinc solubilizing bacteria on the yield and nutrient uptake by maize in calcareous soil

Investigations were conducted for assessing the impact of different sources and levels of zinc and zinc solubilizing bacteria on the yield and nutrient uptake by maize in calcareous soil. The study was conducted at Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu on TNAU maize hybrid CO 6. The experiment was laid out in factorial completely randomized design (FCRD) with three factors replicated thrice. The treatments consisted of two sources of Zn [ZnS4Oand Zn3 (PO4)2] with three levels (0, 5, 7.5 kg Zn/ha) with and without zinc solubilizing bacteria (ZSB). ZnSO4 application performed better than Zn3(PO4)2 in improving the grain and stover yield. Among the levels of Zn, 7.5 kg Zn/ha registered significantly highest grain and stover yield. When compared to the treatments without ZSB inoculation, 4.2 per cent increase in mean grain and stover yield was registered with ZSB inoculation. With respect to uptake of nutrients, ZSB showed a significant increase in the grain, stover and total uptake of P, K, Zn, Fe, Mn and Cu. In addition sources of Zn also significantly increased the P uptake in grain and stover and Zn3 (PO4)2 registered higher P uptake than ZnSO. Sources and levels of Zn had no effect on the uptake of K, Fe, Mn and Cu whereas Zn uptake increased with increase in the levels of Zn and the highest uptake of Zn by maize was observed when Zn was applied at 7.5 kg/ha as ZnSO4.

Application of Plant Growth Promoting Rhizobacteria in Growth Enhancement of a Multipurpose crop Crotalaria Juncea (Sunhemp) in Saline Soil

Salinity is a major abiotic stress which limits the crop productivity. In this study salt tolerant bacteria were isolated from root nodules of Crotalaria juncea plant collected from different salt affected sites. Salt tolerance activity of all the isolates was checked and it was observed that 47% of the isolates showed up to 8% salt tolerance. On the basis of morphological, biochemical and physiological characterization isolates were found to be Gram negative, rod shaped and motile bacteria that belong to rhizobia. All the isolates also showed nodulation in host plant. Most of the isolates were positive for various plant growth promoting attributes. On the basis of salt tolerance and plant growth promoting characterization isolate CR6 was selected for further studies. CR6 showed positive results for phosphate and zinc solubilisation, and was able to produce indole acetic acid (IAA), siderophore and exopolysaccharides (EPS). CR6 also showed nitrogen fixation and ACC deaminase activity. CR6 was applied on Crotalaria plant to enhance growth in saline soil. After application of CR6 seed germination rate and various growth parameters such as root length, shoot length, nodule number, fresh weight, dry weight, leaves count, chlorophyll and proline content of plants were enhanced in comparison to control, hence CR6 can be used as an efficient bioinoculant to enhance crop growth in saline soil.

In vitro study of biocontrol potential of rhizospheric Pseudomonas aeruginosa against Fusarium oxysporum f. sp.\xa0cucumerinum

Fusarium wilt is an economically important disease of cucumber caused by the fungus Fusarium oxysporum f. sp. cucumerinum (Foc). It causes severe losses in the yield and quality of cucumber and is extremely difficult to control conventionally using chemical fungicides. Biological control offers an eco-friendly alternative to chemical pesticide for sustainable plant disease management. In this context, biocontrol activity of rhizosphere soil bacteria was investigated against Foc in vitro. Thirty-five rhizobacterial isolates were screened for antagonistic activity in dual culture, and isolate BA5 showed the highest antagonistic activity (58.33% mycelial growth inhibition) against Foc. Maximum fungal biomass reduction (90.20%) was found in King’s B broth in shake flask culture. Cell-free culture filtrate and ethyl acetate crude extract inhibited mycelial growth of Foc by 56.66 and 25.0%, respectively. Further, the selected isolate produced siderophores, volatile compound(s), hydrocyanic acid, and protease. Siderophores and volatile compound(s) were involved in the isolate-induced antagonism. In addition, the isolate exhibited several plant growth-promoting traits, including phosphate and zinc solubilization, ammonia production, organic acid production, and in vitro biofilm formation. Based on the morphological, physiological, biochemical characteristics, and phylogeny analysis, the isolate BA5 was identified as Pseudomonas aeruginosa, and the 16S rDNA sequence was submitted in the NCBI GenBank under the strain name RKA5. Because of the novel antifungal and plant growth promotion potentials, the strain can be used as a promising biocontrol agent against the fungal pathogen Foc.

Corn sap bacterial endophytes and their potential in plant growth-promotion

Plants interact with many different bacteria at various stages of their life. A mutualistic relationship between a plant and an endophytic bacterium occurs when a plant provides a safe habitat and a secure food supply to the microbe and it, in return, benefits the plants’ capacity to function in its environment. In this study, corn sap was screened for the diversity and functionality of culturable bacterial endophytes, and a total of 437 bacterial endophytes were isolated, identified, and characterized for their possible role as biofertilizers and biocontrol agents. The growth promoting traits that were characterized included siderophore production, phosphate and zinc solubilization, nitrogen fixation, indole acetic acid production, and antifungal activity against several plant pathogens. Most isolates (71.8%) were found to fix nitrogen and solubilize phosphate (66.8%), close to half (42.5%) could solubilize zinc, and 28.3% of the corn bacterial endophytes could sequester iron. Most isolates (77.3%) displayed antifungal activity, and 186 of the 437 isolates tested were found to promote plant growth in a gnotobiotic assay. These results suggest that growth promotion from these bacterial endophytes is the outcome of multiple biochemical and microbiological mechanisms.

Prospecting endophytes from different Fe or Zn accumulating wheat genotypes for their influence as inoculants on plant growth, yield, and micronutrient content

The plant microbiome is known to play a significant role in improving plant productivity and quality of produce, and the endophytic component was explored toward developing inoculants for enhancing micronutrient concentration in grains. A set of 213 endophytes (201 bacteria and 12 fungi) were isolated, from a set of 13 wheat genotypes, identified through preliminary screening as low and high iron and zinc accumulating genotypes. A pot experiment, with two low accumulator genotypes and eight selected endophytes, was undertaken, followed by field evaluation with both high and low Zn or Fe accumulator genotypes. Screening of these endophytes identified 11 bacteria and 2 fungi as being efficient for zinc solubilization, while 10 bacteria and 2 fungi were promising siderophore producers. Zinc and iron uptake were enhanced by one to several folds over the recommended dose of NPK (RDF) in the pot experiment. Two sets of promising endophytes, identified as Bacillus subtilis (DS-178) and Arthrobacter sp. (DS-179) for zinc accumulation, and Arthrobacter sulfonivorans (DS-68) and Enterococcus hirae (DS-163) for iron acquisition in grains, were selected. Significant increase of 14–20% in plant growth and yield was recorded in field experiment, with 75% increase, over RDF, in terms of Fe or Zn accumulation in wheat grains. Phytic acid, an anti-nutritional factor, was significantly lower in grains from endophyte inoculated treatments in the wheat genotypes evaluated. This illustrated the promise of these endophytes in improving both the translocation of micronutrients and enhancing the quality of wheat grains.

Solubilization of insoluble zinc compounds by zinc solubilizing bacteria (ZSB) and optimization of their growth conditions.

In this research, the optimum growth conditions for two zinc solubilizing bacteria (ZSB) have been studied for their potential application as bioinoculants to overcome Zn unavailability in soils. For this purpose, a laboratory-scale experiment was carried out to evaluate the zinc solubilizing ability of 80 plant growth promoting bacteria (PGPB) strains isolated from the rhizosphere of barley and tomato plants. To select effective ZSB, isolates were evaluated on Tris-mineral medium supplemented separately with zinc oxide, zinc carbonate, and zinc phosphate at a concentration of 0.1%. Two strains (Agrobacterium tumefaciens and Rhizobium sp.) were selected, based on a clear halo zone around their colonies in the solid medium supplemented with zinc oxide after 10days of incubation at 29°C. Results of solubilization at different pH values showed that these strains had solubilization activity in the range of pH 8-10 while no solubilization was observed at pH 6 and 7. The maximum Zn solubilization values were noted at pH 9: 51.4mgL-1 (Agrobacterium tumefaciens) and 72.1mgL-1 (Rhizobium sp). According to findings, bacterial growth was affected by different NaCl concentrations under in vitro condition. The salt concentration required for 50% inhibition of absorbance was 2.11 and 2.27% NaCl for Agrobacterium tumefaciens and Rhizobium sp., respectively. The maximum bacterial growth was observed at about 0.8% NaCl concentration.

Effectiveness of multi-trait Burkholderia contaminans KNU17BI1 in growth promotion and management of banded leaf and sheath blight in maize seedling

Plant growth promoting (PGP) bacteria enhance plant growth and are a green alternative to chemical fertilizers. In our study, an effective plant growth promoting rhizobacteria (PGPR) strain, KNU17BI1, was isolated from rhizospheric soil of maize, South Korea. The strain was tested in vitro for specific PGP and antifungal traits, such as phosphate solubilization, zinc solubilization, indole acetic acid (IAA) production, ammonia production, nitrogen fixation, 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, siderophore hydrogen cyanide production (HCN) and hydrolytic enzyme activity. Furthermore, in viro antifungal activity was done in a laboratory and in vivo effect of KNU17BI1 on banded leaf and sheath blight intensity as well as plant growth promotion on maize seedling were conducted under greenhouse conditions. The strain was found to be highly effective toward all the parameters except HCN production. The strain KNU17BI1 was identified on the basis of 16S RNA and multilocus sequence analysis (MLSA) and confirmed as Burkholderia contaminans. This study for the first time demonstrated potent in vitro antifungal activity of B. contaminans against Rhizoctonia solani AG-1(IA), Pythium graminicola, Fusarium moniliforme, Alternaria alternata, Alternaria solani, Fusarium graminearum, Stemphylium botryosum Wallr, Colletotrichum dematium, Stemphylium lycopersici and Fusarium oxysporum f.sp. melonis. Furthermore, in this study, for the first time, the potential of B. contaminans stain KNU17BI1 in controlling banded leaf and sheath blight of maize caused by R. solani AG-1(IA) was reported. Therefore, further studies are warranted on the structural identification of actual compounds behind such activities that would be exploited further for biocontrol as well as plant growth promotion.

Application of Rhizobium-Pseudomonas consortia for enhanced production of mungbean in sustainable manner

In this study plant growth promoting rhizobacteria (PGPR) were isolated from root nodules of Vigna radiata and rhizospheric soil of Abrus precatorius respectively. On the basis of morphological, biochemical and physiological characterization, isolate R5 (from root nodules of V. radiata) was identified as Rhizobium and P21 (from rhizosphere of A. precatorius) as Pseudomonas. Isolates R5 and P21 showed positive results for phosphate solubilization, zinc solubilization, nitrogen fixation, production of indole acetic acid (IAA), siderophore and exopolysaccharides (EPS). Isolates (R5 and P21) were applied as coinoculant on mungbean (V. radiata) to check their impact on its growth in laboratory conditions and pot trials. Seed germination rate and growth analysis of plants were observed by measuring growth parameters (root length, shoot length, leaves count, root nodule count, fresh weight, dry weight and chlorophyll content). It was observed that R5 and P21 significantly enhanced the plant growth in comparison to control (without treatment), but consortial inoculation was more effective in comparison to mono-inoculation of R5 and P21.