Improvement of Maize Yield by Foliar Application of Azospirillum brasilense Az39

Journal of Plant Growth Regulation - Azospirillum brasilense is a plant growth promoting bacteria (PGPB) widely used as an inoculant in diverse species, including maize (Zea mays L.) to improve...     

EFFECT OF METAL TOLERANT PLANT GROWTH PROMOTING BACTERIA ON GROWTH AND METAL ACCUMULATION IN ZEA MAYS PLANTS GROWN IN FLY ASH AMENDED SOIL

The present study was undertaken to examine the effect of the application of fly ash (FA) into Garden soil (GS), with and without inoculation of plant growth promoting bacteria (PGPB), on the growth and metal uptake by Zea mays plants. Three FA tolerant PGPB strains, Pseudomonas sp. PS5, PS14, and Bacillus sp. BC29 were isolated from FA contaminated soils and assessed for their plant growth promoting features on the Z. mays plants. All three strains were also examined for their ability to solubilize phosphate and to produce Indole Acetic Acid (IAA), siderophores, and hydrogencynide acid (HCN) production. Although inoculation of all strains significantly enhanced the growth of plants at both the concentration of FA but maximum growth was observed in plants inoculated with BC29 and PS14 at low level (25%) of FA concentration. The experimental results explored the plant growth promoting features of selected strains which not only enhanced growth and biomass of plants but also protected them from toxicity of FA.     

Elemental composition of strawberry plants inoculated with the plant growth‐promoting bacterium Azospirillum brasilense REC3, assessed with scanning electron microscopy and energy dispersive X‐ray analysis

The elemental composition of strawberry plants (Fragaria ananassa cv. Macarena) inoculated with the plant growth‐promoting bacterium Azospirillum brasilense REC3, and non‐inoculated controls, was studied using scanning electron microscopy (SEM) and energy dispersive X‐ray (EDS) analysis. This allowed simultaneous semi‐quantification of different elements in a small, solid sample. Plants were inoculated and grown hydroponically in 50% or 100% Hoagland solution, corresponding to limited or optimum nutrient medium, respectively. Bacteria‐inoculated plants increased the growth index 45% and 80% compared to controls when grown in 100% and 50% Hoagland solution, respectively. Thus, inoculation with A. brasilense REC3 in a nutrient‐limited medium had the strongest effect in terms of increasing both shoot and root biomass and growth index, as already described for Azospirillum inoculated into nutrient‐poor soils. SEM‐EDS spectra and maps showed the elemental composition and relative distribution of nutrients in strawberry tissues. Leaves contained C, O, N, Na, P, K, Ca and Cu, while roots also had Si and Cl. The organic fraction (C, O and N) accounted for over 96.3% of the total chemical composition; of the mineral fraction, Na had higher accumulation in both leaves and roots. Azospirillum‐inoculated and control plants had similar elemental quantities; however, in bacteria‐inoculated roots, P was significantly increased (34.33%), which constitutes a major benefit for plant nutrition, while Cu content decreased (35.16%).     

Microbial inoculation of plants

Summary Seed of maize, tomato, and wheat was inoculated with cultures of Azotobacter, Clostridium, and a nitrogen-fixing facultative Bacillus and grown in a nutrient-deficient sand and a highly fertile silt loam.In sand, wheat showed a significant positive response to inoculation with Azotobacter and Clostridium but maize and tomato were unaffected by inoculation.When inoculated seed was planted in Lima silt loam there were significant increases in the growth of maize, tomato, and wheat to treatment with Clostridium, inoculated maize and wheat responded to Azotobacter inoculation while only wheat responded to inoculation with the facultative Bacillus.In pure-culture studies of the ability of these cultures to establish upon plant roots it was shown that Azotobacter did not colonize the roots of lucerne, maize, tomato, or wheat to any great extent. Bacillus and Clostridium were moderate colonizers of plant roots reaching from 1 to 20 per cent the levels reached byPseudomonas fluorescens on the same plants.The author held a Fulbright Travel Grant for the 1961–1962 academic year.Agronomy Paper No. 595. Supported in part by funds provided by Regional Research Project NE 39.     

Azospirillum sp. Promotes Root Hair Development in Tomato Plants through a Mechanism that Involves Ethylene

Tomato seeds were inoculated with the plant growth–promoting rhizobacteria Azospirillum brasilense FT326, and changes in parameters associated with plant growth were evaluated 15 days after inoculation. Azospirilla were localized on roots and within xylematic tissue. An increase in shoot and root fresh weight, main root hair length, and root surface indicated that inoculation with A. brasilense FT 326 resulted in plant growth improvement. The levels of indole-3-acetic acid (IAA) and ethylene, two of the phytohormones related to plant growth, were higher in inoculated plants. Exogenously supplied ethylene mimicked the effect of inoculation, and the addition of an inhibitor of its synthesis or of its physiological activity completely blocked A. brasilense growth promotion. Based on our results, we propose that the process of growth promotion triggered by A. brasilense inoculation involves a signaling pathway that has ethylene as a central, positive regulator.     

Enhanced Cd extraction of oilseed rape (Brassica napus) by plant growth-promoting bacteria isolated from Cd hyperaccumulator Sedum alfredii Hance

Four plant growth-promoting bacteria (PGPB) were used as study materials, among them two heavy metal-tolerant rhizosphere strains SrN1 (Arthrobacter sp.) and SrN9 (Bacillus altitudinis) were isolated from rhizosphere soil, while two endophytic strains SaN1 (Bacillus megaterium) and SaMR12 (Sphingomonas) were identified from roots of the cadmium (Cd)/zinc (Zn) hyperaccumulator Sedum alfredii Hance. A pot experiment was carried out to investigate the effects of these PGPB on plant growth and Cd accumulation of oilseed rape (Brassica napus) plants grown on aged Cd-spiked soil. The results showed that the four PGPB significantly boosted oilseed rape shoot biomass production, improved soil and plant analyzer development (SPAD) value, enhanced Cd uptake of plant and Cd translocation to the leaves. By fluorescent in situ hybridization (FISH) and green fluorescent protein (GFP), we demonstrated the studied S. alfredii endophytic bacterium SaMR12 were able to colonize successfully in the B. napus roots. However, all four PGPB could increase seed Cd accumulation. Due to its potential to enhance Cd uptake by the plant and to restrict Cd accumulation in the seeds, SaMR12 was selected as the most promising microbial partner of B. napus when setting up a plant–microbe fortified remediation system.     

Azospirillum brasilense Sp 245 produces ABA in chemically-defined culture medium and increases ABA content in arabidopsis plants

Azospirillum sp. are plant growth promoting bacteria (PGPB) that increase grain yield in cereals and other species via growth promotion and/or stress alleviation. The PGPB beneficial effects have been partially attributed to bacterial production of plant hormones, especially growth promoters like auxins, gibberellins and cytokinins. This paper reports the characterization of the stress-like plant hormone abscisic acid (ABA) by GC-EIMS in cultures of A. brasilense Sp 245 after 120 h of incubation in chemically-defined media, and chemically-defined media with moderate stress (100 mM NaCl). Chemical characterization of ABA was done by gas chromatography-electron impact mass spectrometry (GC-EIMS) and quantification by selected ion monitoring (SIM) with a stable isotope of the hormone as internal standard in the media. A. brasilense cultures produced higher amounts of ABA per ml of culture when NaCl was incorporated in the culture medium. Inoculation of Arabidopsis thaliana with A. brasilense Sp 245 enhanced two-fold the plant’s ABA content. These results contribute to explain, at least to some extent, the beneficial effects of Azospirillum sp. previously found in inoculated plants placed under adverse environmental conditions.     

Potential of efficient and resistant plant growth‐promoting rhizobacteria in lead uptake and plant defence stimulation in Lathyrus sativus under lead stress

• The ability of plant growth‐promoting rhizobacteria (PGPR) to enhance Lathyrus sativus tolerance to lead (Pb) stress was investigated.
• Ten consortia formed by mixing four efficient and Pb‐resistant PGPR strains were assessed for their beneficial effect in improving Pb (0.5 mM) uptake and in inducing the host defence system of L. sativus under hydroponic conditions based on various physiological and biochemical parameters.
• Lead stress significantly decreased shoot (SDW) and root (RDW) dry weight, but PGPR inoculation improved both dry weights, with highest increases in SDW and RDW of plants inoculated with I5 (R. leguminosarum (M5) + P. fluorescens (K23) + Luteibacter sp. + Variovorax sp.) and I9 (R. leguminosarum (M5) + Variovorax sp. + Luteibacter sp. + S. meliloti) by 151% and 94%, respectively. Additionally, inoculation significantly enhanced both chlorophyll and soluble sugar content, mainly in I5 inoculated leaves by 238% and 71%, respectively, despite the fact that Pb decreased these parameters. We also found that PGPR inoculation helps to reduce oxidative damage and enhances antioxidant enzyme activity, phenolic compound biosynthesis, carotenoids and proline content. PGPR inoculation increased Pb uptake in L. sativus, with highest increase in shoots of plants inoculated with I5 and I7, and in roots and nodules of plants inoculated with I1. Moreover, PGPR inoculation enhanced mineral homeostasis for Ca, Cu and Zn under Pb stress, mainly in plants inoculated with I1, I5, I7 and I9.
• Results of our study suggest the potential of efficient and Pb‐resistant PGPR in alleviating harmful effects of metal stress via activation of various defence mechanisms and enhancing Pb uptake that promotes tolerance of L. sativus to Pb stress.

     

Bacterial inoculation of maize affects carbon allocation to roots and carbon turnover in the rhizosphere

To assess the influence of bacteria inoculation on carbon flow through maize plant and rhizosphere,¹⁴C allocation after¹⁴CO₂ application to shoots over a 5-day period was determined. Plants were grown on C- and N-free quartz sand in two-compartment pots, separating root and shoot space. While one treatment remained uninoculated, treatments two and three were inoculated withPantoea agglomerans (D5/23) andPseudomonas fluorescens (Ps I A12), respectively, five days after planting. Bacterial inoculation had profound impacts on carbon distribution within the system. Root/rhizosphere respiration was increased and more carbon was allocated to roots of plants being inoculated. After five days of¹⁴CO₂ application, more ethanol-soluble substances were found in roots of inoculated treatments and lower rhizodeposition indicated intensive C turnover in the rhizosphere. In both inoculated treatments the intensity of photosynthesis measured as net-CO₂-assimilation rates were increased when compared to the uninoculated plants. However, high C turnover in the rhizosphere reduced shoot growth of D5/23 inoculated plants, with no effect on shoot growth of Ps I A12 inoculated plants. A separation of labeled compounds in roots and rhizodeposition revealed that neutral substances (sugars) constituted the largest fraction. The relative fractions of sugars, amino acids and organic acids in roots and rhizodeposition suggest that amino acid exudation was particularly stimulated by bacterial inoculation and that turnover of this substance group is high in the rhizosphere.     

Co-inoculation Effects of Rhizobium sullae and Pseudomonas sp. on Growth,Antioxidant Status,and Expression Pattern of Genes Associated with Heavy Metal Tolerance and Accumulation of Cadmium in Sulla coronaria

Recently, phytoremediation assisted by soil bacteria has emerged as a potential tool to clean up the metal-contaminated/polluted environment. Three plant-growth-promoting bacteria (PGPBs): Rhizobium sullae, Pseudomonas fluorescens, and Pseudomonas sp. were found to tolerate cadmium (Cd) stress. Sulla coronaria inoculated with these PGPBs, and grown under different Cd concentrations (0, 100, and 200 µM), showed increases in dry biomass and proline content. Notable increases in different gas-exchange characteristics such as photosynthesis rate (A), transpiration rate (E), and water-use efficiency (WUE), as well as increases in nitrogen (N) and Cd accumulations were also recorded in inoculated plants compared to non-inoculated Cd stressed plants. The activities of antioxidant enzymes superoxide dismutase (SOD), guaiacol peroxidase (GPOX), catalase (CAT), and ascorbate peroxidase (APX) in S. coronaria roots increased under Cd stress after PGPB co-inoculation, suggesting that these PGPB species could be used for amelioration of stress tolerance in S. coronaria. The expression patterns of ScPCS, ScMT, ScF-box, ScGR, and ScGST in roots of S. coronaria indicated that these genes are differentially expressed under Cd treatments, suggesting their possible roles in Cd and heavy metal stress responses. The results indicate that co-inoculation with R. sullae and Pseudomonas sp. could alleviate Cd toxicity in S. coronaria. In the present study, the obtained data suggest that the application of PGPBs could be a promising strategy for enhancing the phytostabilization efficiency of Cd-contaminated soils.

     

Characterization of bacterial communities associated with Brassica napus L. growing on a Zn-contaminated soil and their effects on root growth

The interaction between plant growth-promoting bacteria (PGPB) and plants can enhance biomass production and metal tolerance of the host plants. This work aimed at isolating and characterizing the cultivable bacterial community associated with Brassica napus growing on a Zn-contaminated site, for selecting cultivable PGPB that might enhance biomass production and metal tolerance of energy crops. The effects of some of these bacterial strains on root growth of B. napus exposed to increasing Zn and Cd concentrations were assessed. A total of 426 morphologically different bacterial strains were isolated from the soil, the rhizosphere, and the roots and stems of B. napus. The diversity of the isolated bacterial populations was similar in rhizosphere and roots, but lower in soil and stem compartments. Burkoholderia, Alcaligenes, Agrococcus, Polaromonas, Stenotrophomonas, Serratia, Microbacterium, and Caulobacter were found as root endophytes exclusively. The inoculation of seeds with Pseudomonas sp. strains 228 and 256, and Serratia sp. strain 246 facilitated the root development of B. napus at 1,000 µM Zn. Arthrobacter sp. strain 222, Serratia sp. strain 246, and Pseudomonas sp. 228 and 262 increased the root length at 300 µM Cd.     

固氮菌接种对棉苗氮磷钾吸收、某些酶活性及产量的影响(英文)

Spermospheremodels和盆栽试验结果表明 ,海岛棉 (GossypiumbarbadenseL .)苗接种自生固氮菌(Azotobactersp .)、巴西固氮螺菌NO40 (AzospirillumbrasilenseNO40 )、多粘芽孢杆菌 (BacilluspolymyxaCF)和根瘤菌 (Rhizobium) ,和以自生固氮菌分别与其它 3种供试菌种两者的混合菌 ,能增强棉花根际固氮酶活性和棉苗对氮的吸收 ,提高功能叶中氮、磷和叶绿素含量 ,从而有利于提高生物学产量 ,尤以自生固氮菌的促进效应最为显著。另一方面 ,混合菌处理较单一菌株处理 ,可以显著提高棉苗对氮的吸收 ,增加干物质积累提高皮棉产量 ,其中尤以固氮菌分别与根瘤菌或巴西固氮螺菌NO40的协同效应最显著     

Root discoloration and shoot symptoms in silver birch after Phytophthora infection in vitro

• There are no records of established plant pathogenic Phytophthora species in Finnish forests, but they are likely in the future. Therefore, the effects of Phytophthora inoculations on young, ca. 2‐month‐old silver birch (Betula pendula) seedling roots and shoots were investigated.
• Visual inspection of dark discoloration, direct PCR and re‐isolation, and detailed root morphology analyses were used to evaluate the effects of Phytophthora inoculation on roots. Symptoms in leaves and stems were also recorded.
• Phytophthora was successfully re‐isolated from 67% of the surface‐sterilized roots of inoculated seedlings, but not from the non‐inoculated control seedlings. Dark discolorations were found more often in the root segments of inoculated seedlings than in control seedlings. In the Phytophthora‐treated seedlings, discoloured root segments were usually linked and found primarily in the main root or lateral roots attached to it, whereas in the control seedlings a few single discoloured root segments were scattered throughout the root systems. The number of root segments was lower in the inoculated than in the control seedlings, indicating root loss after Phytophthora inoculation. In the shoots of inoculated birches, leaf and shoot wilting was observed.
• The appearance of wilting in shoots without visible dark discoloration in the base of stems indicated that symptoms originated from roots inoculated with Phytophthora.

     

Effects of growth-promoting rhizobacteria on maize growth and rhizosphere microbial community under conservation tillage in Northeast China

Conservation tillage in conjunction with straw mulching is a sustainable agricultural approach. However, straw mulching reduces the soil temperature, inhibits early maize growth and reduces grain yield in cold regions. To address this problem, we investigated the effects of inoculation of plant growth-promoting rhizobacteria (PGPR) on maize growth and rhizosphere microbial communities under conservation tillage in Northeast China. The PGPR strains Sinorhizobium sp. A15, Bacillus sp. A28, Sphingomonas sp. A55 and Enterobacter sp. P24 were isolated from the maize rhizosphere in the same area and inoculated separately. Inoculation of these strains significantly enhanced maize growth, and the strains A15, A28 and A55 significantly increased grain yield by as much as 22%–29%. Real-time quantitative PCR and high-throughput sequencing showed that separate inoculation with the four strains increased the abundance and species richness of bacteria in the maize rhizosphere. Notably, the relative abundance of Acidobacteria_Subgroup_6, Chloroflexi_KD4-96, and Verrucomicrobiae at the class level and Mucilaginibacter at the genus level were positively correlated with maize biomass and yield. Inoculation with PGPR shows potential for improvement of maize production under conservation tillage in cold regions by regulating the rhizosphere bacterial community structure and by direct stimulation of plant growth.     

A novel morphological response of maize (Zea mays) adult roots to heterogeneous nitrate supply revealed by a split‐root experiment

Approximately 35–55% of total nitrogen (N) in maize plants is taken up by the root at the reproductive stage. Little is known about how the root of an adult plant responds to heterogeneous nutrient supply. In this study, root morphological and physiological adaptations to nitrate‐rich and nitrate‐poor patches and corresponding gene expression of ZmNrt2.1 and ZmNrt2.2 of maize seedlings and adult plants were characterized. Local high nitrate (LoHN) supply increased both lateral root length (LRL) and density of the treated nodal roots of adult maize plants, but only increased LRL of the treated primary roots of seedlings. LoHN also increased plant total N acquisition but not N influx rate of the treated roots, when expressed as per unit of root length. Furthermore, LoHN markedly increased specific root length (m g^?1) of the treated roots but significantly inhibited the growth of the lateral roots outside of the nitrate‐rich patches, suggesting a systemic carbon saving strategy within a whole root system. Surprisingly, local low nitrate (LoLN) supply stimulated nodal root growth of adult plants although LoLN inhibited growth of primary roots of seedlings. LoLN inhibited the N influx rate of the treated roots and did not change plant total N content. The gene expression of ZmNrt2.1 and ZmNrt2.2 of the treated roots of seedlings and adult plants was inhibited by LoHN but enhanced by LoLN. In conclusion, maize adult roots responded to nitrate‐rich and nitrate‐poor patches by adaptive morphological alterations and displayed carbon saving strategies in response to heterogeneous nitrate supply.     

L-Tryptophan-dependent biosynthesis of indole-3-acetic acid (IAA) improves plant growth and colonization of maize by <Emphasis Type="BoldItalic">Burkholderia phytofirmans</Emphasis> PsJN

Burkholderia phytofirmans PsJN is a well-known plant growth-promoting bacterium that establishes rhizospheric and endophytic colonization in different plants. PsJN inoculation promotes growth of different horticultural crops. L-Tryptophan (L-TRP) application may further improve its effectiveness, due to substrate (L-TRP)-dependent inoculum (PsJN)-derived auxins in the rhizosphere. In the present study, the substrate (L-TRP)-dependent response of PsJN inoculation to maize growth and auxin biosynthesis was evaluated under pot conditions. In vitro auxin biosynthesis by PsJN was determined in the absence and presence of L-TRP, a physiological precursor of auxins. Surface-disinfected seeds were treated with peat-based inoculum and L-TRP solutions (10^?4 and 10^?5 M). Results revealed that L-TRP application and PsJN inoculation, when applied separately, significantly increased the growth parameters of maize compared to untreated control. However, PsJN inoculation supplemented with L-TRP (10^?5 M) gave the most promising results and significantly increased plant height, photosynthesis, chlorophyll content, root biomass and shoot biomass up to 18, 16, 45, 62 and 55 %, respectively, compared to the uninoculated control. Similarly, higher values of N, P and IAA content were observed with precursor (L-TRP)–inoculum (PsJN) interaction. The inoculant strain efficiently colonized maize seedlings and was recovered from the rhizosphere, root and shoot of plants. The results imply that substrate (L-TRP)-derived IAA biosynthesis in the rhizosphere by PsJN inoculation could be a useful approach for improving the growth, photosynthesis and nutrient content of maize plants.     

Inoculation and production of container-grown red alder seedlings

Summary The inoculation ofAlnus rubra (red alder) withFrankia sp. can lead to a highly efficient symbiosis. Several factors contribute to the successful establishment of nitrogenfixing nodules: (1) quantity and quality ofFrankia inoculant; (2) time and method of inoculation; (3) nutritional status of the host plant.Frankia isolates were screened for their ability to nodulate and promote plant growth of container-grown red alder. Inoculations were performed on seedlings and seeds. Apparent differences in symbiotic performance could be seen when seeds or seedlings were inoculated. Plants inoculated at planting performed significantly better than those inoculated four weeks later in terms of shoot height, nodule number and shoot dry weight. If inoculation was delayed further, reduction in shoot height, nodule number and shoot dry weight resulted. The effect of fertilizer was also investigated with regard to providing optimal plant growth after inoculation. Plants receiving 1/5 Hoagland's solution minus nitrogen showed maximal plant growth with abundant nodulation. Plants receiving 1/5 Hoagland's solution with nitrogen showed excellent plant growth with significantly reduced nodulation.     

Mycorrhizas in agroforestry: spread and sharing of arbuscular mycorrhizal fungi between trees and crops: complementary use of molecular and microscopic approaches

The spread of arbuscular mycorrhizal (AM) fungi from tree to crop roots was examined by molecular and microscopic methods in a glasshouse study. Growth of Calliandra calothyrsus Meissner trees inoculated with isolates of the AM fungi Glomus etunicatum Becker and Gerdemann and Gigaspora albida Schenck and Smith was monitored over an 18-month period. Three successive ‘intercrops’ of beans or maize were sown at 25, 50 and 75 cm distances from the tree and harvested during this period. At each crop harvest, the distribution of tree and crop roots and the spread of the inoculant fungi were determined using traditional microscopic methods and fungal specific primers. Both inoculants greatly improved the growth of the trees and colonization spread to the crops once the trees were 6 months old. However, benefits of inoculation to crop growth were not observed due to increased competition from the larger inoculated trees growing in a restricted soil volume. Of the two inoculant fungi, Glomus etunicatum appeared to be more mobile as it spread more rapidly, formed higher levels of colonization at increasing distances from the tree and was responsible for most of the mycorrhizal cross-contamination. In contrast, colonization of tree and crop roots by Gigaspora albida was higher nearest the tree. This work demonstrated the benefits of mycorrhizal fungus inoculation for tree growth and confirmed that trees and crops share the same AM fungi. Trees may therefore act as reservoirs of mycorrhizal fungi, either inoculant or indigenous, for surrounding crops or other annual vegetation. It was also shown that tree pruning, the normal practice in agroforestry systems, did not reduce mycorrhizal colonization or prevent spread to crops. However, the slow rates of inoculant spread found here suggest that it may take years before inoculants benefit the growth of crops sown several metres from the tree. The work also demonstrated that microscopic quantification of mycorrhizal colonization and the use of molecular probes to identify specific fungi within roots can complement each other effectively. Molecular probes were more sensitive at detecting mycorrhizal fungi than microscopic methods, but did not discriminate between full mycorrhizal structures and traces of hyphae.