Effects Of Root Colonization Research Articles

Azospirillum brasilense Inoculation in a Maize–Urochloa–Rice Cropping System Promotes Soil Chemical and Biological Changes and Increases Productivity

Large quantities of cover crop residues in the soil, combined, or not, with the inoculation of seeds with diazotrophic bacteria, can increase organic matter (OM) and protect soil microorganisms, such as arbuscular mycorrhizal fungi (AMF) and dark septate endophytic (DSE) fungi. Thus, the use of these sustainable biotechnologies can benefit microbial interactions, soil fertility and rice production in the Brazilian Cerrado region. In this study, we evaluated the effects of maize and Urochloa ruziziensis, intercropped or individually, as cover crops and an inoculation of Azospirillum brasilense on the chemical (fertility) and biological (C–microbial biomass and C–CO2 released) attributes of soil and the effects of root colonization by AMF and DSE on the yield of rice grown in succession in highlands. The experiment was conducted under field conditions, in a typical dystrophic Red Oxisol. The experimental design consisted of randomized blocks arranged in strips, incorporating a combination of eight residual cover crops: ((1) maize, (2) maize–I (I = inoculation of seeds with A. brasilense), (3) Urochloa (U. ruziziensis), (4) Urochloa–I, (5) maize + Urochloa–I, (6) maize + Urochloa–I, (7) maize–I + Urochloa and (8) maize–I + Urochloa–I). This was accompanied by two treatments of rice as a successor crop (inoculated or not with A. brasilense), with four replicates, totaling 64 experimental units. A cover crop and rice seed inoculation prompted increases in OM and AMF relative to DSE, while the inoculation of rice, regardless of the cover crop treatment, increased the soil’s P content. The combination of maize + Urochloa–I and inoculated rice as the next crop generated increases in its sum of bases (SBs) and cation exchange capacity (CEC). There was a 19% increase in rice grain yields when the seed was inoculated.

Development of a Pseudomonas-based biocontrol consortium with effective root colonization and extended beneficial side effects for plants under high-temperature stress

The root microbiota plays a crucial role in plant performance. The use of microbial consortia is considered a very useful tool for studying microbial interactions in the rhizosphere of different agricultural crop plants. Thus, a consortium of 3 compatible beneficial rhizospheric Pseudomonas strains previously isolated from the avocado rhizosphere, was constructed. The consortium is composed of two compatible biocontrol P. chlororaphis strains (PCL1601 and PCL1606), and the biocontrol rhizobacterium Pseudomonas alcaligenes AVO110, which are all efficient root colonizers of avocado and tomato plants. These three strains were compatible with each other and reached stable levels both in liquid media and on plant roots. Bacterial strains were fluorescent tagged, and colonization-related traits were analyzed in vitro, revealing formation of mixed biofilm networks without exclusion of any of the strains. Additionally, bacterial colonization patterns compatible with the different strains were observed, with high survival traits on avocado and tomato roots. The bacteria composing the consortium shared the same root habitat and exhibited biocontrol activity against soil-borne fungal pathogens at similar levels to those displayed by the individual strains. As expected, because these strains were isolated from avocado roots, this Pseudomonas-based consortium had more stable bacterial counts on avocado roots than on tomato roots; however, inoculation of tomato roots with this consortium was shown to protect tomato plants under high-temperature stress. The results revealed that this consortium has side beneficial effect for tomato plants under high-temperature stress, thus improving the potential performance of the individual strains. We concluded that this rhizobacterial consortium do not improve the plant protection against soil-borne phytopathogenic fungi displayed by the single strains; however, its inoculation can show an specific improvement of plant performance on a horticultural non-host plant (such as tomato) when the plant was challenged by high temperature stress, thus extending the beneficial role of this bacterial consortium.

Phosphate solubilizing Pseudomonas and Bacillus combined with rock phosphates promoting tomato growth and reducing bacterial canker disease.

Nowadays, sustainable agriculture approaches are based on the use of biofertilizers and biopesticides. Tomato (Solanum lycopersicum L.) rhizosphere could provide rhizobacteria with biofertilizing and biopesticide properties. In this study, bacteria from the rhizosphere of tomato were evaluated in vitro for plant growth promotion (PGP) properties. Five Pseudomonas isolates (PsT-04c, PsT-94s, PsT-116, PsT-124, and PsT-130) and one Bacillus isolate (BaT-68s), with the highest ability to solubilize tricalcium phosphate (TCP) were selected for further molecular identification and characterization. Isolates showed phosphate solubilization up to 195.42 μg mL-1. All isolates showed phosphate solubilization by organic acid production. The six isolates improved seed germination and showed effective root colonization when tomato seeds were coated with isolates at 106 cfu g-1 in axenic soil conditions. Furthermore, the selected isolates were tested for beneficial effects on tomato growth and nutrient status in greenhouse experiments with natural rock phosphate (RP). The results showed that inoculated tomato plants in the presence of RP have a higher shoot and root lengths and weights compared with the control. After 60 days, significant increases in plant Ca, Na, P, protein, and sugar contents were also observed in inoculated seedlings. In addition, inoculated tomato seedlings showed an increase in foliar chlorophyll a and b and total chlorophyll, while no significant changes were observed in chlorophyll fluorescence. In greenhouse, two Pseudomonas isolates, PsT-04c and PsT-130, showed ability to trigger induced systemic resistance in inoculated tomato seedlings when subsequently challenged by Clavibacter michiganensis subsp. michiganensis, the causal agent of tomato bacterial canker. High protection rate (75%) was concomitant to an increase in the resistance indicators: total soluble phenolic compounds, phenylalanine-ammonia lyase, and H2O2. The results strongly demonstrated the effectiveness of phosphate-solubilizing bacteria adapted to rhizosphere as biofertilizers for tomato crops and biopesticides by inducing systemic resistance to the causal agent of tomato bacterial canker disease.

Pre-inoculation with arbuscular mycorrhizal fungi affects essential oil quality and the reproduction of root lesion nematode in Cymbopogon citratus.

Cymbopogon citratus (lemongrass) is an important medicinal and aromatic plant containing citral-rich essential oil, of which the quality and quantity may be affected by nematode infection. Research has shown that arbuscular mycorrhizal fungi (AMF) may act as nematode biocontrol agents and improve the chemical composition of plants. Three experiments were conducted to assess the effects of AMF inoculation on vegetative growth, essential oil composition, induction of defense-related proteins, and control of Pratylenchus brachyurus in C. citratus. Seedlings were transplanted into pots inoculated with one of two AMF species (Rhizophagus clarus or Claroideoglomus etunicatum). At 30days after AMF inoculation, plants were inoculated with P. brachyurus. Evaluations were performed at 75days after nematode inoculation. Although both AMF treatments led to effective root colonization (> 84%), fungus inoculation was not effective in reducing P. brachyurus population density. Nevertheless, C. etunicatum promoted an increase in shoot weight, and AMF treatments contributed to preserving essential oil composition in nematode-infected plants. In addition, both AMF treatments enhanced polyphenol oxidase activity and R. clarus increased peroxidase activity after nematode inoculation.

Biofilms and nanoparticles: applications in agriculture.

A profound need to explore eco-friendly methods to practice sustainable agriculture leads to the research and exploration of plant growth-promoting rhizobacteria (PGPRs). Biofilms are assemblages of microbial communities within a self-secreted exopolymeric matrix, adhering to different biotic and abiotic surfaces and performing a variety of desired and undesired functions. Biofilm formation by PGPRs is governed by effective root colonization of the host plant in providing plant growth promotion and stress management. Biofilms can also provide a suitable environment for the synthesis and entrapment of nanoparticles. Together, nanoparticles and PGPRs may contribute towards biocontrol and crop management. This review discusses the significance of biofilms in agriculture and their confluence with different types of nanoparticles for plant protection and improved crop production.

Effect of Root Colonization by Arbuscular Mycorrhizal Fungi on Growth, Productivity and Blast Resistance in Rice

BackgroundArbuscular mycorrhizal (AM) fungi form symbiotic associations with roots in most land plants. AM symbiosis provides benefits to host plants by improving nutrition and fitness. AM symbiosis has also been associated with increased resistance to pathogen infection in several plant species. In rice, the effects of AM symbiosis is less studied, probably because rice is mostly cultivated in wetland areas, and plants in such ecosystems have traditionally been considered as non-mycorrhizal. In this study, we investigated the effect of AM inoculation on performance of elite rice cultivars (Oryza sativa, japonica subspecies) under greenhouse and field conditions, focusing on growth, resistance to the rice blast fungus Magnaporthe oryzae and productivity.ResultsThe response to inoculation with either Funneliformis mosseae or Rhizophagus irregularis was evaluated in a panel of 12 rice cultivars. Root colonization was confirmed in all rice varieties. Under controlled greenhouse conditions, R. irregularis showed higher levels of root colonization than F. mosseae. Compared to non-inoculated plants, the AM-inoculated plants had higher Pi content in leaves. Varietal differences were observed in the growth response of rice cultivars to inoculation with an AM fungus, which were also dependent on the identity of the fungus. Thus, positive, negligible, and negative responses to AM inoculation were observed among rice varieties. Inoculation with F. mosseae or R. irregularis also conferred protection to the rice blast fungus, but the level of mycorrhiza-induced blast resistance varied among host genotypes. Rice seedlings (Loto and Gines varieties) were pre-inoculated with R. irregularis, transplanted into flooded fields, and grown until maturity. A significant increase in grain yield was observed in mycorrhizal plants compared with non-mycorrhizal plants, which was related to an increase in the number of panicles.ConclusionResults here presented support that rice plants benefit from the AM symbiosis while illustrating the potential of using AM fungi to improve productivity and blast resistance in cultivated rice. Differences observed in the mycorrhizal responsiveness among the different rice cultivars in terms of growth promotion and blast resistance indicate that evaluation of benefits received by the AM symbiosis needs to be carefully evaluated on a case-by-case basis for efficient exploitation of AM fungi in rice cultivation.

Designing a multi-species inoculant of phosphate rock-solubilizing bacteria compatible with arbuscular mycorrhizae for plant growth promotion in low-P soil amended with PR

Four phosphate rock-solubilizing bacteria (PRSB) (Asaia lannensis Vb1, Pseudomonas sp. Vr14, Rahnella sp. Sr24, and Pantoea sp. Vr25) isolated from the mycorrhizosphere of maize were evaluated as inoculants, individually or in different combinations, together with Rhizophagus irregularis DAOM 197198, under greenhouse conditions. To create an effective bacterial mix for P solubilization and growth promotion, parameters such as the ability of the strains (individually or in mixture) to mobilize phosphate rock (PR), their biocompatibility, and their capacity for biofilm formation over PR particles and root colonization were tested. Accompanying PR solubilization, the bacteria produced organic acids and reduced the pH of the medium, produced exopolysaccharides, and had variable capacity to colonize the roots of maize plantlets. In low-phosphorus soil amendment with PR, all strains, regardless of their capacity to solubilize PR, increased dry weight, nutrient (N, P, and K) uptake, and the percentage of indigenous arbuscular mycorrhizae (iAM) root colonization in maize plants, compared to the non-inoculated control. However, mixed inoculation of the strains showed significantly better results. Addition of Rhizophagus irregularis resulted in further growth stimulation. Overall results showed that two combinations—Rahnella sp. Sr24 + Pantoea sp. Vr25 + R. irregularis, and Pantoea sp. Vr25 + Pseudomonas sp. Vr14 + R. irregularis—were better inoculants. We concluded that an effective PRSB combination of biocompatible strains with capacity for PR solubilization, successful biofilm formation, effective root colonization, different growth promotion traits, and the addition of AM has potential as inoculants for more sustainable agriculture in low-phosphorus soils amended with low-reactivity PR.

Residual effects of biochar and phosphorus on growth and nutrient accumulation by maize (Zea mays L.) amended with microbes in texturally different soils

The purpose of study was to examine the residual effects of two types of biochar amendments, two phosphorus (P) fertilizer levels, phosphorus solubilizing bacteria (PSB) and arbuscular mycorrhizal fungs (AMF) on plant growth, nutrients absorption and root architecture of Zea mays L. in texturally different soils. Biochar signficantly increased nutrients absorption and plant biomass production with P-fertilization and microbial inoculantion. Texturally different soils enhanced the plant biomass and nutrients absorption in their independent capacity on addition of biochar, microbial inoculants and P-fertilization. It was shown that mycorrhizal inoculation had positive influence on plant root and shoot biomass in both soils irrespective to the biochar type used. Root colonization was notably increased in biochar + mycorrhizae (B + M) inocultaed plants. It was shown that mycorrhizal inoculation had positive influence on nutrients absorption by plant roots and it had high content of P, potassium, calcium and magnesium in plants at all biochar and P levels. Without P fertilization, biochar amendments significantly promoted shoot P content and root colonization. The P application significantly influenced soil microbial activity in terms of nutrient concentration and plant growth. Root attributes were significantly inclined by microbial inoculation. Residual effects of biochar and P significantly enhanced the nutreints absorption and maize plant growth. Thus, we concluded that residual biochar and P fertilizer showed positive effects on nutrients absorption and maize plant growth promotion in differently textured soils. Microbial inoculants further stimulated the plant biomass production and nutrients absorption due to effective root colonization.

Colonization of polycyclic aromatic hydrocarbon-degrading bacteria on roots reduces the risk of PAH contamination in vegetables

This is a primary investigation on the mitigation of polycyclic aromatic hydrocarbon (phenanthrene as a model PAH) contamination in vegetables including water spinach (Ipomoea aquatica Forsk), pakchoi (Brassica campestris) and Chinese cabbage (Brassica chinensis) using a gfp-labeled PAH-degrading bacterium (RS1-gfp). Effective root colonization led to dense RS1-gfp populations inhabiting the rhizosphere and endosphere of the vegetables, which subsequently led to a reduction in phenanthrene accumulation and risk in vegetables. When compared with the controls without RS1-gfp, the amount of phenanthrene accumulation due to strain RS1-gfp colonization reduced by up to ~93.7% in roots and ~75.2% in shoots of vegetables, respectively. The estimated incremental lifetime cancer risk (ILCR) for adults due to phenanthrene in vegetables was reduced by 24.6%–48% through RS1-gfp inoculation. The proposed method was developed to circumvent the risk of phenanthrene contamination in vegetables by inoculating PAH-degrading bacteria. The findings provide an in-depth understanding of PAH detoxification in agricultural plants grown on contaminated sites by exploiting bacteria like RS1-gfp, which portray both rhizo- and endophytic lifestyles.

Chryseobacterium nankingense sp. nov. WR21 effectively suppresses Ralstonia solanacearum growth via intensive root exudates competition

Previous studies demonstrated that the Chryseobacterium sp. WR21 could effectively control the bacterial wilt disease caused by Ralstonia solanacearum through effective root colonization. The strain WR21 exhibited a low level of DNA homology with Chryseobacterium strains DSM 15235T (24.1%), DSM 17724T (24.8%), and DSM 18014T (10.4%), suggesting that WR21 may represent a novel species, for which the name Chryseobacterium nankingense sp. nov. is proposed. The in vitro competition experiments with strain WR21 indicated it significantly inhibited growth of the pathogen in co-culture with six of nine tested nutrients (e.g. root exudates) that could be utilized by strain WR21 and R. solanacearum. Similar trends were observed in co-culturing experiments using tissue exudates of tomato. A positive relationship (r = 0.785) was noticed between the differences in the average growth rate of both strains and the disease suppression effects. In conclusion, Chryseobacterium nankingense sp. nov. WR21 exhibits antagonism through nutrient competition that might be used for achieving biocontrol of Ralstonia solanacearum induced wilts.

Colonization and plant growth-promotion of tomato by Burkholderia tropica

Several diazotrophic Burkholderia species have been described to exhibit some activities involved in plant growth promotion and biological control. In this work seedlings of tomato plants were inoculated with this bacterium in order to study colonization of different vegetal tissues and plant growth promoting ability under greenhouse conditions. Tomato seedlings inoculated with Burkholderia tropica strain MTo-293 and two derivative strains containing the marker genes gusA and gfp, respectively (constructions described in this work), were grown under gnotobiotic conditions. Colonization was monitored both by colony counting of bacterial suspensions from homogenized tissues with or without previous surface disinfection and by microscopic observation of entire plant tissues. In another set of experiments tomato seedlings were inoculated with B. tropica MTo-293 for evaluation of tomato production under greenhouse conditions. Tomato yields were determined by quantifying total tomato production throughout the crop in two different seasons. B. tropica could be isolated from root surfaces (>7.0 logCFUg−1 fresh weight) and from surface-disinfected and disrupted roots (>5.0 logCFUg−1 fresh weight) and stems (>4.0 logCFUg−1 fresh weight) of inoculated plants. Microscopic studies showed colonizing bacteria on root hairs, root tips, lateral root emergence sites, and stomata. In greenhouse experiments inoculated plants showed a consistent increase of both number and weight of fruits as compared to uninoculated controls. Although this enhancement in fruit production was only statistically significant for fruit weight in the first crop season, our results show a consistent tendency to a higher yield (5–15%) for the inoculated treatments also in the second year. These results show that seedling inoculation with B. tropica led to effective root colonization of tomato plants followed by bacterial spreading to aerial tissues. This significant colonization was accompanied by an enhancement of tomato production in two different crop seasons.

Effects of root colonization by symbiotic arbuscular mycorrhizal fungi on the yield of pharmacologically active compounds in Angelica archangelica L.

The major effects of arbuscular mycorrhizal fungi (AMF) colonization on plant growth, monoterpenoids and coumarins were determined in two genotypes of angelica (Angelica archangelica L., Apiaceae). Genetically uniform experimental plants were used, which was achieved by in vitro propagation of two genotypes (individual plants). The effects of Glomus mosseae (Funneliformis mosseae, BEG 12), Glomus intraradices (Rhizophagus intraradices, BB-E) and the AMF mixture Symbivit® were tested against a negative (without AMF and without additional phosphorus) and a positive (KH2PO4 without AMF) control in five plants per treatment. All in all 50 plants were investigated. Fifteen monoterpenoid and seven coumarin compounds were quantitatively determined in the rhizome and coarse root fractions by means of GC/MS using an internal standard. The sum of the monoterpenoids and coumarins was calculated. Concentrations of compounds rather slightly decreased upon inoculation with AMF when compared to the control. In contrast, biomass increased showing the highest amounts for plants treated with G. mosseae. These results finally caused a marked increase in yield for G. mosseae treated plants compared to the control. Phosphorus treatment led to the lowest yield with significant results for coumarins and in particular for osthole compared to G. mosseae treatment. This is also evidence of an independent effect from an increased phosphorus uptake due to root colonization by AMF. In summary, the results showed a marked increase in yield of all investigated compounds through treatment with G. mosseae compared to the control group, even if the level of significance was just barely missed presumably on account of the small sample size.

The computational-based structure of Dwarf14 provides evidence for its role as potential strigolactone receptor in plants

BackgroundStrigolactones (SLs) are recently identified plant hormones modulating root and shoot branching. Besides their endogenous role within the producing organism, SLs are also key molecules in the communication of plants with arbuscular mycorrhizal (AM) fungi and parasitic weeds. In fact SLs are exuded into the rhizosphere where they act as a host-derived signal, stimulating the germination of the seeds of parasitic plants which would not survive in the absence of a host root to colonize. Similarly, their perception by AM fungi causes extensive hyphal branching; this is a prerequisite for effective root colonization, since it increases the number of potential contact points with the host surface. In spite of the crucial and multifaceted biological role of SLs, there is no information on the receptor(s) which bind(s) such active molecules, neither in the producing plants, or in parasitic weeds or AM fungi.ResultsIn this work, we applied homology modelling techniques to investigate the structure of the protein encoded by the gene Dwarf14, which was first identified in rice as conferring SLs insensitivity when mutated. The best sequence identity was with bacterial RsbQ. Both proteins belong to the superfamily of alpha/beta-fold hydrolases, some members of which play a role in the metabolism or signalling of plant hormones. The Dwarf14 (D14) structure was refined by means of molecular dynamics simulations. In order to support the hypothesis that D14 could be an endogenous SLs receptor, we performed docking experiments with a natural ligand.ConclusionsIt is suggested that D14 interacts with and thereby may act as a receptor for SLs in plants. This hypothesis offers a starting point to experimentally study the mechanism of its activity in vivo by means of structural, molecular and genetic approaches. Lastly, knowledge of the putative receptor structure will boost the research on analogues of the natural substrates as required for agricultural applications.

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A pot culture experiment was conducted to develop quality standards for the Arbuscular Mycorrhiza (AM) inoculum in terms of spore density in order to ensure the efficacy of the AM product when used for crop production as a P mobilizing biofertilizer. Plant growth parameters like root volume and total plant dry weight of maize (PEHM5) which was used as trap crop skyrocketed to its maximum when inoculated with 5-6 spores g-1 of AM inoculum. Effective root colonization of 100% was recorded in maize when 5-6 spores, was present. Total root length colonization of the maize variety PEHM5 was registered to be more than 90%, when treated with an AM inoculum containing 5-6 spores g-1. Moreover, a significant increase of the spore number was observed, when sterilized vermiculite + 10% soil was used as sub- strate for the AM inoculum production with increased spore density of 5-6 spores g -1 . Thus, spore density of 5-6 spores was standardized to

Impact of a beneficial and of a pathogenic Fusarium strain on the fingerprinting-based structure of microbial communities in tomato ( Lycopersicon esculentum Milll.) rhizosphere

Fusarium solani strain FsK (FsK), isolated from a plant pathogen-suppressive compost, grows endophytically in tomato roots and controls infestations by Fusarium oxysporum f.sp . radicis- lycopersici (FORL). The effect of root colonization by the two fungi on the diversity of rhizosphere microbial community was studied. Tomato plants were inoculated with FsK and/or FORL and rhizosphere soil was collected 8, 15 and 30 days post inoculation (dpi) and analyzed by denaturating gradient gel electrophoresis (DGGE) of PCR-amplified internal transcribed spacer (ITS) sequences of fungi and 16S rRNA gene sequences of common rhizosphere bacterial guilds like alpha-proteobacteria and pseudomonads. Cluster analysis of DGGE fingerprints showed that FsK had a transient impact on the fungal and alpha-proteobacterial community only during its endophytic stage (15 dpi), while FORL had a readily distinguished and persistent effect on the fungal community. The changes observed in the rhizosphere fungal and bacterial communities may depict the interactions of the two fungal inocula with the plant. Cloning of selected DGGE bands stimulated by FsK showed that the responsive bacteria were closely related to species known to include biological control agents (BCA). Overall, the inoculation of FsK in tomato rhizosphere did not appear to have a significant impact on the diversity of non-target microbial groups inhabiting plant rhizosphere.

Greenhouse and field studies on Cr, Cu, Pb and Zn phytoextraction by Brassica napus from contaminated soils in the Apulia region, Southern Italy

In the framework of a project aiming to phytoremediate heavy metal contaminated soils in the Apulia region, Southern Italy, a series of greenhouse experiments followed by field trials were performed in order to optimize heavy metal phytoextraction by Brassica napus. The effects of root colonization by Bacillus licheniformis BLMB1 and of addition of municipal solid waste (MSW) composts on the capacity of B. napus to tolerate and accumulate Cr, Cu, Pb and Zn were evaluated. B. napus was able to accumulate high amount of metals in greenhouse conditions, whereas it grew with difficulty or not at all in the open field, and metal accumulation in plant fractions was relatively low. The accumulation of metals in the plant fractions was in the order: Cr > Zn > Cu > Pb. The presence of either compost or B. licheniformis BLMB1 strain enhanced metal accumulation, Cr in particular, in the experimental conditions used. This effect can be useful in the phytoextraction of Cr from contaminated soils.

Biological control of Macrophomina phaseolina by chemotactic fluorescent Pseudomonas aeruginosa PN1 and its plant growth promotory activity in chir-pine

Ten strains of Pseudomonas aeruginosa (PN1 ˜ PN10) isolated from rhizosphere of chir-pine were tested for their plant growth promontory properties and antagonistic activities against Macrophomina phaseolina in vitro and in vivo. P. aeruginosa PN1 produced siderophore, IAA, cyanogen and solubilized phosphorus, besides producing chitinase and β-1,3-glucanase. In dual culture, P. aeruginosa PN1 caused 69% colony growth inhibition. However, cell free culture filtrate also posed inhibitory effect but to a lesser extent. After 90 days, P. aeruginosa PN1 increased plant growth and biomass in pots trial containing M. phaseolina-infested soil. PN1 showed the strong chemotaxis toward root exudates resulting in effective root colonization. Moreover, increased population in rhizosphere of these bacteria was also recorded after 90 days of treatment. Thus, chemotactic fluorescent P. aeruginosa PN1 exhibited strong antagonistic property against M. phaseolina, suppressed the disease and improved plant growth of the seedlings of chir-pine proving potential biocontrol agent.

Assessment of SCAR markers to design real‐time PCR primers for rhizosphere quantification of Azospirillum brasilense phytostimulatory inoculants of maize

To assess the applicability of sequence characterized amplified region (SCAR) markers obtained from BOX, ERIC and RAPD fragments to design primers for real-time PCR quantification of the phytostimulatory maize inoculants Azospirillum brasilense UAP-154 and CFN-535 in the rhizosphere. Primers were designed based on strain-specific SCAR markers and were screened for successful amplification of target strain and absence of cross-reaction with other Azospirillum strains. The specificity of primers thus selected was verified under real-time PCR conditions using genomic DNA from strain collection and DNA from rhizosphere samples. The detection limit was 60 fg DNA with pure cultures and 4 x 10(3) (for UAP-154) and 4 x 10(4) CFU g(-1) (for CFN-535) in the maize rhizosphere. Inoculant quantification was effective from 10(4) to 10(8) CFU g(-1) soil. BOX-based SCAR markers were useful to find primers for strain-specific real-time PCR quantification of each A. brasilense inoculant in the maize rhizosphere. Effective root colonization is a prerequisite for successful Azospirillum phytostimulation, but cultivation-independent monitoring methods were lacking. The real-time PCR methods developed here will help understand the effect of environmental conditions on root colonization and phytostimulation by A. brasilense UAP-154 and CFN-535.

Effect of Arbuscular Mycorrhization on the Accumulation of Hydroxycinnamic Acid Derivatives in Date Palm Seedlings Challenged with Fusarium oxysporum f. sp. albedinis

AbstractThe effect of root colonization with arbuscular mycorrhizal fungi on the content of phenolic compounds was determined in date palm seedlings challenged with Fusarium oxysporum f. sp. albedinis (Foa), the pathogen causing the bayoud disease. The examination of phenolic compounds revealed no qualitative difference between arbuscular mycorrhized plants and non‐mycorrhized ones. However, after Foa infection, the accumulation of non‐constitutive hydroxycinnamic acid derivatives, such as the sinapic derivative I2, known to play a crucial role in resistance of date palm to Foa was more pronounced in mycorrhized seedlings. No accumulation of these compounds was detected in mycorrhized seedlings not challenged with Foa. The potential immunization of date palm seedlings with mycorrhizal fungi is discussed.

Plant growth promoting rhizobacteria improve growth and essential oil yield in Origanum majorana L.

Effects of root colonization by plant growth promoting rhizobacteria (PGPR) on biomass, and qualitative and quantitative composition of essential oils, were determined in the aromatic crop Origanum majorana L. (sweet marjoram). PGPR strains evaluated were Pseudomonas fluorescens, Bacillus subtilis, Sinorhizobium meliloti, and Bradyrhizobium sp. Only P. fluorescens and Bradyrhizobium sp. showed significant increases in shoot length, shoot weight, number of leaf, number of node, and root dry weight, in comparison to control plants or plants treated with other PGPR. Essential oil yield was also significantly increased relative to non-inoculated plants, without alteration of oil composition. P. fluorescens has clear commercial potential for economic cultivation of O. majorana.