Induced defense-related proteins in soybean (Glycine max L. Merrill) plants by Carnobacterium sp. SJ-5 upon challenge inoculation of Fusarium oxysporum

The aim of the present study was to analyze induced expression of defense-related proteins in the soybean plants by rhizobacterial stain Carnobacterium sp. SJ-5 upon challenge inoculation with Fusarium oxysporum. Determination of the enzymatic activity of the different defense-related enzymes, phenylalanine ammonia lyase (PAL), lipoxygenase (LOX), peroxidase (POD) and polyphenol oxidase (PPO) was performed in the major parts of Glycine max L. Merrill using spectrophotometric method. Native-polyacrylamide gel electrophoresis analysis of the POD and PPO was employed followed by activity staining to find out the isoforms of respective enzymes. Activities of the PAL, LOX, POD and PPO were found to be highest in the bacterized root tissue of the soybean plants challenged with F. oxysporum. Isoform analysis revealed that PPO1, PPO4 and POD2 isoforms were expressed at higher levels in bacterized soybean root tissues challenge inoculated with the pathogen. Conclusively it was found that bacterial strain Carnobacterium sp. SJ-5 protect soybean plants from wilt disease caused by F. oxysporum by elicitation of the defense-related enzymes.     

Identification and evaluation of a potential biocontrol agent,Bacillus subtilis,against Fusarium sp. in apple seedlings

To find a potential biocontrol agent against Fusarium sp. in apple seedlings, an endophytic bacterium strain was isolated from apple tree tissues. The inhibitive efficiency of the isolated strain against the hyphal growth of Fusarium sp. and Rhizoctonia solani was tested. Strain Y-1 showed significant inhibitory effects against Fusarium oxysporum, F. moniliforme, F. proliferatum, F. solani and R. solani. Its antifungal activity against F. oxysporum was the highest, reaching up to 64.90 %. In vivo tests indicated that strain Y-1 effectively protects apple from F. oxysporum infections. The control effect reached 92.26 % when bacterial inoculation was performed 3 days prior to pathogen inoculation. Strain Y-1 could colonize the rhizosphere and tissues within 30 days. It was also able to induce systemic resistance in apple seedlings as shown by the activities of SOD and POD. Strain Y-1 significantly increased the root length, root wet and dry weights, and plant height of the apple seedlings compared with the control group. The homology analysis of the 16S rRNA sequence, together with morphological, physical, and biochemical analyses, revealed that strain Y-1 is Bacillus subtilis.     

Staurosporine from the endophytic Streptomyces sp. strain CNS-42 acts as a potential biocontrol agent and growth elicitor in cucumber

Chinese medicinal plants and their surrounding rhizospheric soil serve as promising sources of actinobacteria. A total of 180 actinobacteria strains were isolated from the rhizosphere soil, leaves, stems, and roots of nine selected plants and have been identified as potential biocontrol agents against Fusarium oxysporum f. sp. cucumerinum. An endophytic strain CNS-42 isolated from Alisma orientale showed the largest zone of inhibition demonstrating a potent effect against F. oxysporum f. sp. cucumerinum and a broad antimicrobial activity against bacteria, yeasts, and other pathogenic fungi. The in vivo biocontrol assays showed that the disease severity index was significantly reduced (P < 0.05), and plant shoot fresh weight and height increased greatly (P < 0.05) in plantlets treated with strain CNS-42 compared to the negative control. This isolate was identified as Streptomyces sp. based on cultural, physiological, morphological characteristics, and 16S rRNA gene analysis. Further bioassay-guided isolation and purification revealed that staurosporine was responsible for its antifungal and plant growth promoting activities and the latter property of staurosporine is reported for the first time. The in vivo assay was further performed and indicated that staurosporine showed good growth promoting effect on the plant shoot biomass of cucumber. This is the first critical evidence identifying CNS-42 as a biocontrol agent for the soil borne pathogen, F. oxysporum f. sp. cucumerinum.     

ACC Deaminase-Containing Bacillus subtilis Reduces Stress Ethylene-Induced Damage and Improves Mycorrhizal Colonization and Rhizobial Nodulation in Trigonella foenum-graecum Under Drought Stress

This study was aimed at protecting Trigonella plants by reducing stress ethylene levels through ACC (1-aminocyclopropane-1-carboxylic acid) deaminase-containing Bacillus subtilis (LDR2) and promoting plant growth through improved colonization of beneficial microbes like Ensifer meliloti (Em) and Rhizophagus irregularis (Ri) under drought stress. A plant growth-promoting rhizobacterium strain possessing high levels of ACC deaminase characterized as B. subtilis was selected. Application of this strain considerably protected Trigonella plants under severe drought stress conditions; this protection was correlated with reduced levels of ACC (responsible for generation of stress ethylene). The experiment consisted of eight inoculation treatments with different combinations of ACC deaminase-containing rhizobacteria LDR2, Ri, and Em under three water regimes. The tripartite combination of LDR2 + Ri + Em acted synergistically to induce protective mechanisms against decreased soil water availability in Trigonella plants and improved plant weight by 56 % with lower ACC concentration (39 % less than stressed noninoculated plants) under severe drought conditions. Drought-induced changes in biochemical markers like reduced chlorophyll concentration, increased proline content, and higher lipid peroxidation were monitored and clearly indicated the protective effects of LDR2 under drought stress. Under drought conditions, apart from alleviating ethylene-induced damage, LDR2 enhanced nodulation and arbuscular mycorrhizal fungi colonization in the plants resulting in improved nutrient uptake and plant growth.     

Performance of cowpea as influenced by native strain of rhizobia,lime and phosphorus in Samaru,Nigeria

Arsenic (As) is a toxic metalloid that has gained special interest in the past years as a global environmental problem. Groundwater in Córdoba province (Argentina) presents high As concentrations which can be absorbed by plants or be used for artificial irrigation. The aim of this research was to elucidate the differential responses of symbiotic interactions established with three bacterial strains and soybean plants to realistic doses of arsenic. The reference strain Bradyrhizobium diazoefficiens USDA110 and the native isolate Bradyrhizobium sp. Per 3.64 were able to grow up to 13 mM As(V) whereas the native strain Bradyrhizobium sp. Per 3.61 grew up to 9.5 mM As(V). Metalloid addition did not modify the soybean plant growth at 6 μM As(V). Nevertheless, it was enough to induce oxidative stress as observed by an increase on lipid peroxidation. The soybean-Bradyrhizobium sp. assay at 6 μM As(V) showed no changes in growth variables (shoot and root dry weight) in plants inoculated with the reference microsymbiont or Bradyrhizobium sp. Per 3.61. Regarding As uptake by plants, metalloid accumulation followed the same distribution pattern among strains. Remarkably, at 6 μM As(V), soybean inoculation with Bradyrhizobium sp. Per 3.61 revealed a significantly lower translocation factor (TF) in comparison to other inoculated strains promoting As phytostabilization. At the highest As(V) concentration tested, only Bradyrhizobium diazoefficiens USDA110 was able to nodulate the legume, however, a significant decrease in the number and dry weight of nodules and nitrogen content was observed. In conclusion, the inoculation of soybean plants with the reference strain Bradyrhizobium diazoefficiens USDA110 exposed to high As(V) concentration represents an effective and promising symbiotic interaction that allows the development of the legume due to the minimal effects on plant growth. However, in low As(V) concentration environments, the native isolate Bradyrhizobium sp. Per 3.61, is shown to be the best inoculant among the tested strains, owing to the limitation of metalloid translocation and accumulation to edible parts of the legume, avoiding fruit contamination and human poisoning.     

Plant growth-promotion (PGP) activities and molecular characterization of rhizobacterial strains isolated from soybean (Glycine max L. Merril) plants against charcoal rot pathogen, Macrophomina phaseolina

Charcoal rot disease, caused by the fungus Macrophomina phaseolina, leads to significant yield losses of soybean crops. One strategy to control charcoal rot is the use of antagonistic, root-colonizing bacteria. Rhizobacteria A₅F and FPT₇21 and Pseudomonas sp. strain GRP₃ were characterized for their plant growth-promotion activities against the pathogen. Rhizobacterium FPT₇21 exhibited higher antagonistic activity against the pathogen on dual plate assay compared to strain A₅F and GRP₃. FPT₇21 and GRP₃ gave decreased disease intensity in terms of average number of pathogen-infested plants. Lipoxygenase (LOX), phenylalanine ammonia-lyase (PAL), and peroxidase (POD) activities were estimated in extracts of plants grown from seeds that were treated with rhizobacteria, and inoculated with spore suspension of M. phaseolina. The activity of these enzymes after challenge with the test pathogen increased. Strains FPT₇21 and GRP₃ exhibited maximum increases in LOX, PAL and POD activity (U mg⁻¹ fresh leaf wt) compared to strain A₅F.     

Induction of defense-related proteins in tomato roots treated with Pseudomonas fluorescens Pf1 and Fusarium oxysporum f. sp. lycopersici

Pseudomonas fluorescens isolate Pf1 was found to protect tomato plants from wilt disease caused by Fusarium oxysporum f. sp. lycopersici. Induction of defense proteins and chemicals by P. fluorescens isolate Pf1 against challenge inoculation with F. oxysporum f. sp. lycopersici in tomato was studied. Phenolics were found to accumulate in bacterized tomato root tissues challenged with F. oxysporum f. sp. lycopersici at one day after pathogen challenge. The accumulation of phenolics reached maximum at the 5^th day after pathogen challenge. In pathogen-inoculated plants, the accumulation started at the 2^nd day and drastically decreased 4 days after the pathogen inoculation. Activities of phenylalanine ammonia-lyase (PAL), peroxidase (PO) and polyphenol oxidase (PPO) increased in bacterized tomato root tissues challenged with the pathogen at one day after pathogen challenge and activities of PAL and PO reached maximum at the 4^th day while activity of PPO reached maximum at the 5^th day after challenge inoculation. Isoform analysis revealed that a unique PPO1 isoform was induced and PO1 and PPO2 isoforms were expressed at higher levels in bacterized tomato root tissues challenge inoculated with the pathogen. Similarly, -1,3 glucanase, chitinase and thaumatin-like proteins (TLP) were induced to accumulate at higher levels at 3-5 days of challenge inoculation in bacterized plants. Western blot analysis showed that chitinase isoform Chi2 with a molecular weight of 46 kDa was newly induced due to P. fluorescens isolate Pf1 treatment challenged with the pathogen. TLP isoform with molecular weight of 33 kDa was induced not only in P. fluorescens isolate Pf1-treated root tissues challenged with the pathogen but also in roots treated with P. fluorescens isolate Pf1 alone and roots inoculated with the pathogen. These results suggest that induction of defense enzymes involved in phenylpropanoid pathway and accumulation of phenolics and PR-proteins might have contributed to restriction of invasion of F. oxysporum f. sp. lycopersici in tomato roots.     

Effect of nitric oxide signaling in bacterial-treated soybean plant under salt stress

To understand protective roles of nitric oxide against salt stress, the effects of exogenous sodium nitroprusside on activities of lipoxygenase, peroxidase, phenylalanine ammonialyase, catalase, superoxide dismutase enzymes, proline accumulation, and distribution of sodium in soybean plants under salt were determined. Application of sodium nitroprusside + bacterium enhanced plant growth-promotion characteristics, activities of different enzymes, and proline accumulation in the presence of sodium nitroprusside under salt stress. Treatment with NaCl at 200 mM and sodium nitroprusside (0.1 mM) reduced Na⁺ levels but increased K⁺ levels in leaves in comparison with the NaCl-treated plants. Correspondingly, the plants treated with exogenous sodium nitroprusside and NaCl maintained a lower ratio of [Na⁺]/[K⁺] in NaCl-stressed plants.     

Variations of Phenoloxidase Activities as a Consequence of Stresses that Induce Resistance to Fusarium Wilt of Tomato

The variations over 7–8 day of peroxidase (PO) and polyphenoloxidase (PPO) activity have been investigated in tomato plants the roots of which had been subjected to stresses (heat, chloroform and a non-pathogenic form of Fusarium oxysporum) that induce resistance to Fusarium oxysporum f. sp. lycopersici. All treatments induced increase of PO and PPO activity that reached a maximum 3 days after the treatments in leaves, 4 days in stem and roots and were higher in leaves than in other parts. Activity decreased to levels for the control plants after 8 days. Inoculation with Fusarium oxysporum f. sp. lycopersici further stimulated PO and PPO activity in all treated plants over that caused by the treatments alone. Again, activity of treated plants was lower than in controls 7 days after inoculation. It is concluded that 1. increased PO and PPO activity in tomato is a systemic response to cellular injury caused in the root by heat, chloroform and non-pathogenic Fusarium oxysporum, 2. these treatments do no prevent the pathogen from interacting with the plants and inducing further enzyme increase, 3. treated plants react more strongly to the challenge inoculation than untreated plants.     

Endophytic bacteria enhancing growth and disease resistance of potato (Solanum tuberosum L.)

Priming plants by non-pathogenic bacteria allows the host to save energy and to reduce time needed for development of defense reaction during a pathogen attack. However, information on the role of endophytes in plant defense is limited. Here, the ability of endophytic bacteria to promote growth and resistance of potato plants towards infection by the necrotroph Pectobacterium atrosepticum was studied. A Pseudomonas sp. strain was selected due to antagonism towards bacterial pathogens and a Methylobacterium sp. strain because of efficient plant colonization. The aim of this study was to find if there is any correlation between plant growth promotion and induction of resistance by endophytes of potato, as well as to study the putative mechanisms of endophytes interacting with the plant during resistance induction. Both tested strains promoted growth of potato shoots but only the Pseudomonas sp. increased potato resistance towards the soft rot disease. Induction of disease resistance by the Methylobacterium sp. was inversely proportional to the size of bacterial population used for inoculation. The plant antioxidant system was moderately activated during the induction of resistance by the biocontrol strains. qPCR data on expression of marker genes of induced systemic resistance and acquired systemic resistance in endophyte-infected Arabidopsis plants showed activation of both salicylic acid and jasmonate/ethylene-dependent pathways after challenge inoculation with the pathogen. We suggest that some endophytes have the potential to activate both basal and inducible plant defense systems, whereas the growth promotion by biocontrol strains may not correlate with induction of disease resistance.     

Interaction of endophytic diazotrophic bacteria and Fusarium oxysporum f. sp. cubense on plantlets of banana ‘Maça’

The objective of this work was to evaluate the effect of endophytic diazotrophic bacteria Herbaspirillum and Burkholderia on the Fusarium oxysporum f. sp. cubense (Foc) establishment and on the plantlets growth of the ‘Maçã’ banana (Musa spp., group ABB). Two assays were carried out in a greenhouse at the National Center of Tropical Agroindustry in Fortaleza city, Ceará State (Brazil), using randomized block designs in the factorial arrangements 4?×?2 and 8?×?2. On the first trial plantlets were inoculated with the Burkholderia sp. AB202; Herbaspirillum sp., BA227, both of strains and controls bacteria, with and without Foc and cultivated in pots filled with an autoclaved mixture of washed sand and vermiculite (ratio 3:2 v v^?1), during 4 months. On a second assay, plants were subjected to following conditions: absence and presence of strains AB202, AB213 (Burkholderia spp.), BA227, BA234 (Herbaspirillum-like), AB202 plus BA227, AB213 plus BA234, the mixture of the four bacterial strain, absence and presence of the Foc; and cultivated in pots filled with autoclaved Haplic Arenosol, during 2 months. The plant association with diazotrophs and the Foc was confirmed, and factors interacted significantly on the most probable number of bacteria and the colony forming units of the pathogen on roots and plant rhizomes. The potential of the endophytes on the inhibition of Foc propagate units and on the plant growth promotion was demonstrated. The higher biomass was observed four and 2 months after plant inoculation with AB202 and BA234. Results showed that these endophytes may be used as potential biofertilizer and biocontrol agents.     

Incorporation into the transplant soil plug of the plant protective agent Paenibacillus alvei strain K165 confers protection to melon against Fusarium wilt

Fusarium oxysporum f.sp. melonis (FOM) is a plant pathogen affecting melon production worldwide. An environmental friendly disease management strategy is the use of biocontrol agents (BCAs). Towards this direction, two BCA release strategies, seed coating and amendment of the transplant soil plug with the BCA strain Paenibacillus alvei K165 at various ratios, were evaluated against FOM in planta and in vitro. A reduction in Fusarium wilt symptom development was observed in melon plants, after mixing the transplant soil plug with K165 (10⁷ cfu g^?1 powder) at a ratio of 10 % (v/v). The monitoring of K165 rhizosphere population in the different treatments revealed a possible existence of a threshold population level that has to be attained before suppression of disease occurs. The data of the present study suggest that K165 plant protective activity against FOM can be possibly attributed to antibiosis and the triggering of Chit1 and Pal1 gene expression.     

Characterization of As(III) oxidizing <Emphasis Type="Italic">Achromobacter</Emphasis> sp. strain N2: effects on arsenic toxicity and translocation in rice

Achromobacter sp. strain N2 was isolated from a pyrite-cinder-contaminated soil and presented plant growth promoting traits (ACC deaminase activity, production of indole-3-acetic and jasmonic acids, siderophores secretion, and phosphate solubilization) and arsenic transformation abilities. Achromobacter sp. strain N2 was resistant to different metals and metalloids, including arsenate (100 mM) and arsenite (5 mM). The strain was resistant to ionic stressors (i.e., arsenate and NaCl), whereas bacterial growth was impaired by osmotic stress. Strain N2 was able to oxidize 1.0 mmol L^?1 of arsenite to arsenate in 72 h. This evidence was supported by the retrieval of an arsenite oxidase AioA gene highly homologous to arsenite oxidases of Achromobacter and Alcaligenes species. Rice seeds of Oryza sativa (var. Loto) were bio-primed with ACCD-induced and non-induced cells in order to evaluate the effect of inoculation on rice seedlings growth and arsenic uptake. The bacterization with ACCD-induced cells significantly improved seed germination and seedling heights if compared with the seeds inoculated with non-induced cells and non-primed seeds. Enhanced arsenic uptake was evidenced in the presence of ACCD-induced cells, suggesting a role of ACCD activity on the mitigation of the toxicity of arsenic accumulated by the plant. This kind of responses should be taken into account when proposing PGP strains for improving plant growth in arsenic-rich soils.     

Use of chitinolytic Bacillus atrophaeus strain S2BC-2 antagonistic to Fusarium spp. for control of rhizome rot of ginger

An antagonistic bacillus S2BC-2 isolated from apple rhizosphere soil was identified to be highly chitinolytic on chitinase detection agar. Standard bacteriological tests and sequencing of 16S rRNA, and gyrA and rpoB genes, indicated a taxonomic affiliation of the strain to Bacillus atrophaeus. The strain was studied for its ability to grow and produce chitinase on different substrates. Bacterial cells grown on chitin-containing media showed enhanced growth and chitinase production with increased anti-fungal activity against vascular wilt pathogens. Extracellular proteins of cell-free extracts of media amended with chitin and fungal cell wall contained 4–10 novel polypeptides. In polyhouse (bamboo structures that provide protective shade made of polyvinyl sheet) studies, a chitin-supplemented talc-based formulation of the S2BC-2 challenge inoculated with Fusarium oxysporum f. sp. zingiberi recorded low percent disease indices of 84.9 % and 79.2 % for yellows and rhizome rot, respectively, over the non-bacterised pathogen control. The low disease incidences correlated with 113.3 % maximum rhizome production and 2-fold higher chitinase induction over the pathogen control. In native gel activity assays, upon challenge-inoculation, S2BC-2 expressed more chitinase isoforms than the pathogen control. The results suggest that chitinolytic B. atrophaeus can be used in the biocontrol of rhizome rot of ginger.     

Rhizosphere colonization and arsenic translocation in sunflower (Helianthus annuus L.) by arsenate reducing Alcaligenes sp. strain Dhal-L

In the present study, six arsenic-resistant strains previously isolated were tested for their plant growth promoting characteristics and heavy metal resistance, in order to choose one model strain as an inoculum for sunflower plants in pot experiments. The aim was to investigate the effect of arsenic-resistant strain on sunflower growth and on arsenic uptake from arsenic contaminated soil. Based on plant growth promoting characteristics and heavy metal resistance, Alcaligenes sp. strain Dhal-L was chosen as an inoculum. Beside the ability to reduce arsenate to arsenite via an Ars operon, the strain exhibited 1-amino-cyclopropane-1-carboxylic acid deaminase activity and it was also able to produce siderophore and indole acetic acid. Pot experiments were conducted with an agricultural soil contaminated with arsenic (214 mg kg^?1). A real time PCR method was set up based on the quantification of ACR3(2) type of arsenite efflux pump carried by Alcaligenes sp. strain Dhal-L, in order to monitor presence and colonisation of the strain in the bulk and rhizospheric soil. As a result of strain inoculation, arsenic uptake by plants was increased by 53 %, whereas ACR3(2) gene copy number in rhizospheric soil was 100 times higher in inoculated than in control pots, indicating the colonisation of strain. The results indicated that the presence of arsenate reducing strains in the rhizosphere of sunflower influences arsenic mobilization and promotes arsenic uptake by plant.     

Molecular Inversion Probe: A New Tool for Highly Specific Detection of Plant Pathogens

Highly specific detection methods, capable of reliably identifying plant pathogens are crucial in plant disease management strategies to reduce losses in agriculture by preventing the spread of diseases. We describe a novel molecular inversion probe (MIP) assay that can be potentially developed into a robust multiplex platform to detect and identify plant pathogens. A MIP has been designed for the plant pathogenic fungus Fusarium oxysporum f.sp. conglutinans and the proof of concept for the efficiency of this technology is provided. We demonstrate that this methodology can detect as little as 2.5 ng of pathogen DNA and is highly specific, being able to accurately differentiate Fusarium oxysporum f.sp. conglutinans from other fungal pathogens such as Botrytis cinerea and even pathogens of the same species such as Fusarium oxysporum f.sp. lycopersici. The MIP assay was able to detect the presence of the pathogen in infected Arabidopsis thaliana plants as soon as the tissues contained minimal amounts of pathogen. MIP methods are intrinsically highly multiplexable and future development of specific MIPs could lead to the establishment of a diagnostic method that could potentially screen infected plants for hundreds of pathogens in a single assay.     

Application of Pantoea agglomerans strain Z01 to control Fusarium wilt and its effect on the quality parameters of rockets

An antagonistic bacterium, denoted as strain Z01, was isolated from suppressive soils and identified using fatty acid profile analysis and molecular tools. Its efficacy to control Fusarium oxysporum f. sp. conglutinans on rockets (cv. Eruca sativa) was investigated in the presence of the pathogen, and its effects on the growth and pigment contents of rockets, including the plant biomass and chlorophyll and carotenoid contents, were evaluated in the absence of the pathogen. Z01 was identified as Pantoea agglomerans (GenBank accession number is JX257179). Rockets were grown under greenhouse conditions for 21 days at 25 °C and 95 % relative humidity. When the antagonist suspension was applied at 10⁸, 10⁷ and 10⁶ cells/ml by root-dipping for 20 min before transplanting, the disease incidence was 23.5 %, 28.5 % and 60.0 %, respectively. The disease incidence of rockets treated with carbendazim was 22.5 %, and in the inoculated control, the disease incidence was 82.0 %. In the absence of the pathogen, compared with the average plant biomass (10.7 g/4 plants) of the uninoculated control, application of the antagonist at 10⁸ or 10⁷ cells/ml significantly increased the biomass of the rockets by 40.9 % and 39.1 %, respectively, suggesting that Z01 had an additional ability to promote plant growth beyond its role in Fusarium wilt control. This study indicated that P. agglomerans Z01 has a potential to control Fusarium wilt in rockets. This report is the first to describe the application of P. agglomerans to control Fusarium wilt.     

1-Aminocyclopropane-1-carboxylate (ACC) Deaminase-Producing Endophytic Diazotrophic <Emphasis Type="Italic">Enterobacter</Emphasis> sp. EN-21 Modulates Salt–Stress Response in Sugarcane

Soil salinity is a wide-reaching environmental problem that lowers the yield of commercial crops such as maize, rice, and sugarcane. In this study, we examined the effect of 1-aminocyclopropane-1-carboxylate (ACC) deaminase-producing endophytic diazotrophic Enterobacter sp. EN-21 on growth promotion, salt tolerance, and root colonization of sugarcane. Enterobacter sp. EN-21 inoculated and uninoculated sugarcane plants were grown in a greenhouse with and without 200 mM NaCl for 7 days. Sugarcane inoculated with Enterobacter sp. EN-21 substantially increased in total plant length, dry, and fresh weights in both non-salt and salt treatments. Under the salt–stress condition, Enterobacter sp. EN-21 significantly reduced proline, malondialdehyde, ethylene emission, and Na⁺ accumulation in sugarcane but markedly increased total chlorophyll content and K⁺ accumulation. The gfp-tagged Enterobacter sp. EN-21 was observed to colonize early at the root cap, root hairs, and lateral root junctions of sugarcane and later localized in intercellular spaces. Altogether the results of this study indicated that ACC deaminase-producing Enterobacter sp. EN-21 is a true endophyte and able to promote growth and enhance salt tolerance in sugarcane.     

Microbial Consortium-Induced Changes in Oxidative Stress Markers in Pea Plants Challenged with Sclerotinia sclerotiorum

The ability for rhizobacteria and fungus to act as bioprotectants via induced systemic resistance has been demonstrated, and considerable progress has been made in elucidating the mechanisms of plant–biocontrol agent–pathogen interactions. Pseudomonas aeruginosa PJHU15, Trichoderma harzianum TNHU27, and Bacillus subtilis BHHU100 from rhizospheric soils were used singly and in consortium and assessed on the basis of their ability to provide disease protection by relating changes in ascorbic acid and hydrogen peroxide (H₂O₂) production, lipid peroxidation, and antioxidant enzymes in pea under the challenge of Sclerotinia sclerotiorum. Increased production of H₂O₂ 24 h after pathogen challenge was observed and was 254.4 and 231.7–287.7 % higher in the triple consortium and singly treated plants, respectively, when compared to untreated challenged control plants. A similar increase in ascorbic acid content and ascorbate peroxidase activity was observed 24 and 48 h after pathogen challenge, respectively, whereas increased activities of catalase, guaiacol peroxidase, and glutathione peroxidase were observed 72 h after pathogen challenge. Similarly, lipid peroxidation reached a maximum at 72 h of pathogen challenge and was 61.2 and 11.2–32.1 % less in the triple consortium and singly treated plants, respectively, when compared to untreated challenged control plants. These findings suggest that the interaction of microorganisms in the rhizosphere enhanced protection from oxidative stress generated by pathogen attack through induction of antioxidant enzymes and improved reactive oxygen species management.     

Post-infection development of Meloidogyne incognita on tomato treated with the endophytes Fusarium oxysporum strain Fo162 and Rhizobium etli strain G12

The endophytic fungus Fusarium oxysporum strain Fo162 and the endophytic bacterium Rhizobium etli strain G12 have been shown to enhance plant resistance toward the root-knot nematode Meloidogyne incognita. The individual inoculation of tomato seedlings with these antagonists lead to significant reductions in the number of juveniles that penetrated the root and ultimately the number of galls and egg-masses produced. The present study determined the influence of Fo162 and G12 root colonization on juvenile development inside the root system over time after a synchronized nematode infection. The results showed that 14 and 21 days after nematode inoculation, the development into the third-stage juvenile as well as into the adult-stage was significantly lower in endophyte-treated plants when compared to the untreated control, respectively. In addition, Fo162 and G12 treatment led to a significant reduction in the number of eggs per female 35 days after nematode inoculation. The results demonstrated that both Fo162 and G12 not only reduce M. incognita root penetration, but also reduce their development and reproduction.