Plant Growth-promoting Abilities Research Articles

Actinobacteria Associated with Vineyard Soils of Algeria: Classification, Antifungal Potential Against Grapevine Trunk Pathogens and Plant Growth-Promoting Features

Grapevine trunk diseases(GTDs) are among the most destructive diseases of vineyards worldwide, including Algeria. In the fungal complex involved in GTD symptoms, referred as grapevine trunk-pathogens, Paeomoniella chlamydospora and Phaeoacremonium minimum have a determining infecting role as pioneer fungi. Due to the lack of efficiency of conventional disease management practices, a search for alternative strategies, such as biocontrol, is needed. Taking the approach of looking for biocontrol candidates in the environment surrounding the plant, the present study explored actinobacteria diversity within vineyard soils of six grape-producing regions in Algeria. Based on their 16S rRNA gene sequence, identification and phylogenic analysis were performed on the 40 isolates of actinobacteria obtained. Forty percent of strains were attached to Streptomyces, including two evidenced new species, and 32.5% were affiliated to Saccharothrix. The other less represented genera were Actinoplanes, Nocardia, Nocardiopsis, Lentzea, Nonomuraea, Promicromonospora, Saccharopolyspora and Streptosporangium. Screening based on antagonistic and plant growth promotion (PGP) abilities of the strains showed that 47.5% of the isolates exhibited appreciable antagonistic activities against both Pa. chlamydospora and Pm. minimum, with the two best strains being Streptomyces sp. Ms18 and Streptomyces sp. Sb11. Screening for plant growth promoting properties demonstrated that majority of the strains were able to produce indole acetic acid, siderophores, ammonia, ACC deaminase, cellulase and amylase, and fix N2. Through a PGP-traits-based cluster analysis, the most interesting strains were highlighted. Taking into account both antagonistic and PGP properties, Streptomyces sp Sb11 was selected as the most promising candidate for further evaluations of its efficiency in a GTDs context.

Bacterial endophytes from Lycoris radiata promote the accumulation of Amaryllidaceae alkaloids

Lycoris radiata is the major source of Amaryllidaceae alkaloids, having various medicinal activities. However, the low content of these alkaloids in planta limits their pharmaceutical development and utilization. In this study, the ability of bacterial endophytes to enhance the accumulation of five important Amaryllidaceae alkaloids was investigated. A total of 188 bacterial endophytes were isolated from L. radiata and their composition and diversity were analyzed. Fourteen ones were demonstrated to significantly increase the concentration of the alkaloids of interest in different organs, up to 11.1-fold over the control level, with no adverse influence on the plant growth. An additional 3 bacterial endophytes were found to significantly increase the dry weight of L. radiata with no adverse influence on the concentration of the alkaloids in planta, so the total yield of alkaloids in planta was increased up to 2.4-fold over the control level. Considering the plant growth-promoting abilities of these bacterial endophytes, it is speculated that the indole-3-acetic acid and siderophore secreted by them, combined with their nitrogen fixation ability, may contribute to the enhanced plant growth and the increased alkaloid accumulation in L. radiata. To our knowledge, this work is firstly defining the diversity of culturable bacterial endophytes in L. radiata and determining which species promoted the accumulation of Amaryllidaceae alkaloids. It provides several valuable bacterial inoculants that can be further applied to improve alkaloid production in L. radiata and broadens our understanding of the interactions between a medicinal plant and the bacterial endophytes.

Characterization of the Plant Growth-Promoting Activities of Endophytic Fungi Isolated from Sophora flavescens.

Endophytic fungi in symbiotic association with their host plant are well known to improve plant growth and reduce the adverse effects of both biotic and abiotic stresses. Therefore, fungal endophytes are beginning to receive increased attention in an effort to find growth-promoting strains that could be applied to enhance crop yield and quality. In our study, the plant growth-promoting activities of endophytic fungi isolated from various parts of Sophora flavescens (a medicinally important plant in Mongolia and China) have been revealed and investigated. Fungal isolates were identified using molecular taxonomical methods, while their plant growth-promoting abilities were evaluated in plate assays. Altogether, 15 strains were isolated, representing the genera Alternaria, Didymella, Fusarium and Xylogone. Five of the isolates possessed phosphate solubilization activities and twelve secreted siderophores, while all of them were able to produce indoleacetic acid (IAA) in the presence or absence of tryptophan. The endogenous and exogenous accumulation of IAA were also monitored in liquid cultures using the HPLC-MS/MS technique to refine the plate assay results. Furthermore, for the highest IAA producer fungi, the effects of their extracts were also examined in plant bioassays. In these tests, the primary root lengths of the model Arabidopsis thaliana were increased in several cases, while the biomasses were significantly lower than the control IAA treatment. Significant alterations have also been detected in the photosynthetic pigment (chlorophyll-a, -b and carotenoids) content due to the fungal extract treatments, but these changes did not show any specific trends.

Isolation and Characterization of Bacillus spp. Endowed with Multifarious Plant Growth-Promoting Traits and Their Potential Effect on Tomato (Lycopersicon esculentum) Seedlings

In agriculture, Bacillus species are widely used to stimulate plant growth and act as an efficient and ecologically sound tool for protecting the plant from pathogens and other environmental stresses. This study reveals the plant growth-promoting (PGP) ability of bacteria isolated from the rhizosphere soil of the tomato (Lycopersicon esculentum). The isolates were identified as Bacillus species based on a 16S rRNA gene sequence analysis. Among the PGP attributes, the isolates were found to be positive for indole acetic acid (IAA) production, phosphate solubilization, siderophore production, ammonia production, and nitrogen fixation. The isolates were found negative for zinc and potassium solubilization. The quantitative estimation of IAA production ranged from 10.28 to 25.81 µg/ml, solubilization of inorganic phosphorous ranged from 0.12 to 13.83 μg/ml, and siderophore production ranged from 1.39 to 78.79%. The isolates also had the ability to produce lytic enzymes such as amylase, cellulase, lipase, protease, and pectinase and biocontrol activity against Fusarium oxysporum. The inoculation PGP Bacillus improved germination rate, seedling vigor index, and a range of growth parameters in the tomato (L. esculentum) compared to uninoculated control plants. These findings give an insight into the ways to use PGP bacteria as an alternative to chemicals and pesticides.

Enhancing artemisinin yields through an ecologically functional community of endophytes in Artemisia annua

Studying the role of endophytic microbial diversity in plant growth is helpful to understand plant-microbe interaction. The present experiment was aimed to investigate the effect of seed endophytes of Artemisia annua on plant biomass and artemisinin content. All the ten bacterial endophytes were found to express a varying degree of plant growth-promoting ability in pots, and of these six better performing were inoculated in A. annua in monocultures and all possible combinations thereof for analyzing the contribution of species identity and species richness on plant growth and artemisinin yield. The significant effect of species identities was found on plant biomass and artemisinin yields by inoculated endophytes. Community identity was found to be a more important factor than species richness in predicting biomass and artemisinin content. Most of the microbial combinations could not enhance plant growth over their monocultures. In this way, it has been demonstrated that there is a significant role of ecological interactions in bacterial mixtures, which are directly linked with the net performance of the community. In the presence of a combination of four endophytes comprising of Bacillus subtilis, Bacillus licheniformis, Burkholderia sp. and Acinetobacter pittii, artemisinin yield was found exceeding all of these microbes as in monocultures. This microbial consortium was able to increase the artemisinin yield of about 658 % over uninoculated control. Application of endophytic microbial consortium, similar to that found in this study, may prove an effective alternative to chemical fertilizers for enhancing artemisinin yield in an economically and eco-friendly manner with the reduced cost of its production.

Plant Growth Promotion Abilities of Phylogenetically Diverse Mesorhizobium Strains: Effect in the Root Colonization and Development of Tomato Seedlings.

Mesorhizobium contains species widely known as nitrogen-fixing bacteria with legumes, but their ability to promote the growth of non-legumes has been poorly studied. Here, we analyzed the production of indole acetic acid (IAA), siderophores and the solubilization of phosphate and potassium in a collection of 24 strains belonging to different Mesorhizobium species. All these strains produce IAA, 46% solubilized potassium, 33% solubilize phosphate and 17% produce siderophores. The highest production of IAA was found in the strains Mesorhizobium ciceri CCANP14 and Mesorhizobium tamadayense CCANP122, which were also able to solubilize potassium. Moreover, the strain CCANP14 showed the maximum phosphate solubilization index, and the strain CCANP122 was able to produce siderophores. These two strains were able to produce cellulases and cellulose and to originate biofilms in abiotic surfaces and tomato root surface. Tomato seedlings responded positively to the inoculation with these two strains, showing significantly higher plant growth traits than uninoculated seedlings. This is the first report about the potential of different Mesorhizobium species to promote the growth of a vegetable. Considering their use as safe for humans, animals and plants, they are an environmentally friendly alternative to chemical fertilizers for non-legume crops in the framework of sustainable agriculture.

Bacterial endophytes of rice (Oryza sativa L.) and their potential for plant growth promotion and antagonistic activities

Bacterial endophytes live inside the plant tissues and known to play a crucial role in the functioning of host plants through influencing their physiology and development. In present study, a total of 32 bacterial endophytes were isolated from four plant tissues (root, stem, leaf and grain) of six rice varieties cultivated in central-eastern and northeastern states of India. Microbial composition varied among the plant tissues studied, they were predominant in the root and leaf tissues. Biochemical and molecular characterization identified these bacterial isolates belonging to phyla Proteobacteria and Firmicutes representing 5 genera. Out of 32 isolates, (19) 59.3% Gram's stain-positive, (17) 53.1% were able to produce indole acetic acid, (9) 28.1% siderophore development and (18) 56.2% phosphate solubilization activities indicating the plant growth-promoting (PGP) ability. The antagonistic activity of identified bacterial endophytes was determined against bacterial leaf blight disease-causing pathogen, Xanthomonas oryzae pv. oryzae (8 isolates) and soilborne fungal pathogens viz, Rhizoctonia solani (17 isolates), Fusarium verticillioides (15 isolates) and Sclerotium rolfsii (9 isolates) were exhibiting antagonistic activities against tested pathogens. Further, to confirm the probable role of lipopeptides in antagonism, PCR based detection of lipopeptide genes in the genome of bacterial endophytes showed the presence of antibacterial (surfactin) and antifungal (iturin D and bacillomycin D) genes in Bacillus subtilis (NIBSM_OsR10). This Bacillus subtilis isolate showed potential antibacterial activities against Xanthomonas oryzae pv. oryzae and strong antagonistic activities against fungal pathogens Rhizoctonia solani, Fusarium verticelloides and Sclerotium rolfsii. Potential isolates exhibiting antibacterial and antifungal activities in the present study may be used for the development of biocontrol formulations for controlling multiple biotic stresses.

Assessment and selection of multi-trait plant growth promoting bacteria associated with rice rhizosphere

The application of plant growth promoting bacteria is the need of present day for sustainable agriculture. The present study was carried out to assess and select of multi-trait plant growth promoting bacteria associated with rice. Seventeen rhizospheric samples from different rice varieties were collected from different locations of South Gujarat. Total of 98 isolates obtained from different rhizospheric samples were screened out for PGPR activities. Primary screening revealed 15 isolates having potential PGPR activities. These isolates were further evaluated for their ability to produce IAA, phosphate solubilization, siderophore production, protease, cellulase and chitinase enzyme production quantitatively. The result showed that isolate M2 found to produce maximum of 48.4 mg/L IAA, 80 % siderophore and solubilizing 11 mg/L phosphate. Besides these growth promotion traits, M2 also found to produce 14 IU protease, 0.98 IU cellulase and 0.24 IU chitinase. Considering the multi-trait plant growth promotion abilities of M2 isolate it was further characterized and identified tentatively as Pseudomonas species.

ACC deaminase-producing rhizosphere competent Bacillus spp. mitigate salt stress and promote Zea mays growth by modulating ethylene metabolism

Plant growth-promoting rhizobacteria (PGPR) are known for growth promotion and mitigating environmental stresses. Here, we examined the propitiousness of three indigenous salt-tolerant PGPR, i.e., Bacillus subtilis (NBRI 28B), B. subtilis (NBRI 33N), and B. safensis (NBRI 12M) for plant growth promotion and salt stress amelioration in Zea mays. Results of the in vitro plant growth-promoting attribute revealed NBRI 12M demonstrated the highest values at 1M salt (NaCl) concentration. Furthermore, the greenhouse experiment using three Bacillus strains confirmed plant growth-promoting and salt stress-ameliorating ability, through colonizing successfully and mitigating the adverse effects of ethylene by modulating 1-aminocyclopropane-1-carboxylic acid (ACC) accumulation, ACC-oxidase (ACO), and ACC-synthase (ACS) activities under salt stress. Bacillus sp. inoculation has also induced plant response for defense enzymes, chlorophyll, proline and soluble sugar under salt stress. Among three Bacillus strains, NBRI 12M not only demonstrated higher values for plant growth-promoting (PGP) attributes but also the same was observed in the greenhouse experiment. Thus, the outcomes of this comparative study represent for the first time that salt-tolerant Bacillus strains exhibiting multiple PGP attributes under salt stress along with high rhizosphere competence can alleviate salt stress by reducing the stress ethylene level in the host plant.

A preliminary study on L-asparaginase from mangrove detritus-derived fungi and its application in plant growth promotion

L-asparaginase enzyme has wide applications in medicine, food industry and developing biosensors. The present study was carried out to investigate the plant growth-promoting characteristics of L-asparaginase, an aspect that is poorly studied. Two filamentous fungi, Peroneutypa sp. GU-S and Lecanicillium sp. GU-G, derived from mangrove detritus in Goa, India, produced L-asparaginase enzyme in laboratory conditions which was active at room temperature, and 37 °C. A higher amount of enzyme was produced under aeration than without aeration. The optimum pH for asparaginase activity was 8. The enzyme isolated from Peroneutypa sp. GU-S was more stable at lower pH 4, and thus further processed. The enzyme was produced using economical sources, i.e., powdered soya and grass by solid-state fermentation. Germinating seeds of pea, Pisum sativum inoculated with crude enzyme extract produced a better quality of seedlings than the seedlings from un-inoculated seeds. The shoot and the root length were 1.2 and 2.2 times greater in the test than in control plants, within twenty days of incubation. This study demonstrates plant growth-promoting ability of the L-asparaginase, which can be further studied on other plants.

The effect of substrate composition on the activity of amylase and cellulase by Trichoderma harzianum strains under solid state fermentation

Trichoderma harzianum is a filamentous fungus that has been known to have biocontrol and plant growth-promoting ability. However, the propagation of this fungus particularly through solid state fermentation (SSF) and characterization of its enzyme activity as one the indicator of quality of fermentation process are still needed to be explored further. Rice grain and its derivative products have economically as well as nutrient composition features beneficial as substrates of fungal propagation through SSF. Therefore, the aim of this study was to investigate the effect of white rice, rice bran, and combination of white rice and rice bran on the activity of amylase and cellulase by Trichoderma harzianum strains under SSF. Two strains of the fungus, InaCC F116 and InaCC F89, as well as their consortium were employed as fungal inoculants. After closed fermentation in dark chamber at 30 ± 1°C for 7 days, the activity of amylolytic as well as cellulolytic enzyme was assayed. The result showed that the presence of rice bran as a substrate increased the activity of crude amylase and crude cellulase. In all substrates, the strain F116 has low activity of both enzymes. The fungal consortium improves the activity of crude enzymes in all substrates. Therefore, the amylase and cellulase activity by T. harzianum in SSF condition were strain- as well as substrate-dependent.

Interactions between putatively endophytic bacteria and tall fescue (Festuca arundinacea): plant growth promotion and colonization in host and non-host cultivars

Tall fescue (Festuca arundinacea) is a forage grass highly used in prairies. Cultivar SFRO Don Tomas has excellent drought and cold resistance, characteristics which are influenced by the native endophytic bacterial community. The aims of this work were to deepen the characterization of a selected group of putatively endophytic strains with different plant growth promoting (PGP) traits and to analyze the relationship between colonization and PGP abilities. PGP with single inoculations in pots containing a mixture of sterile sand and field soil and with paired inoculations in field soil cores were carried out. Colonization of plants inoculated singly or co-inoculated under gnotobiotic conditions was quantified. Confocal laser microscopy was used to visualize the colonization and infection processes of strain Streptomyces sp. UYFA156 in cultivars SFRO Don Tomas and Tacuabe. Tall fescue cultivars displayed different responses to single bacterial inoculation. Inoculation with two strain pairs which included UYFA156 were successful in promoting growth in soil cores. Higher bacterial densities did not correspond to higher PGP. Strain UYFA156 was observed colonizing both fescue cultivars. UYFA156 is a true endophyte of tall fescue. Its PGP activity is cultivar-specific and may be related to the modulation of other endophytes.

Phylogenetic analysis of halophyte-associated rhizobacteria and effect of halotolerant and halophilic phosphate-solubilizing biofertilizers on maize growth under salinity stress conditions.

The main objective of the present work was to evaluate plant growth-promoting abilities of bacterial strains from the rhizosphere of halophytes and their effect on maize growth under salinity stress. Halophilic bacteria were identified using 16S rRNA sequence analysis and their plant growth-promoting abilities were characterized. Phylogenetic analysis showed that bacterial strains belonging to Bacillus, Halobacillus and Pseudomonas were dominant in the rhizosphere of halophytes. More than 93% strains showed P-solubilization activity and IAA production. About 54% strains were able to produce ACC deaminase, 29% strains showed positive results for nitrogen fixation, 41 and 21% strains showed siderophores and HCN production ability respectively. More than 90% strains showed antifungal activity against more than two fungal pathogens and production of different hydrolytic enzymes. To study the plant growth-promoting effect on maize, five bacterial strains Bacillus safensis HL1HP11 and Bacillus pumilus HL3RS14, Kocuria rosea HL1RP8, Enterobacter aerogenes AT1HP4 and Aeromonas veronii AT1RP10 were used as inoculants; in the form of seed coat and enriched soil-based phosphate biofertilizers. All bacterial strains positively affected the maize growth as compared to non-inoculated control+NaCl plants. Plants inoculated with Bacillus HL3RS14-based soil biofertilizers showed maximum increase in dry weights of root (48-124%) and shoot (52-131%) as compared to control+NaCl (soil+rock phosphate, no inoculum). PGPR inoculations under salinity stress conditions showed high concentrations of proline, glycine betaine and malondialdehyde. These results indicated that under saline soil conditions, halophilic PGPR strains combined with carrier materials are promising candidates as biofertilizers.

Alleviation of Drought Stress and Plant Growth Promotion by Pseudomonas libanensis EU-LWNA-33, a Drought-Adaptive Phosphorus-Solubilizing Bacterium

Drought is a very common abiotic stress worldwide in arid and semiarid areas. It decreases the growth and yield of the crops. Due to drought stress, there is insufficient intake of the nutrients, the low rate of photosynthesis and limited supply of water in plants. Inoculating crops with plant growth-promoting rhizobacteria (PGPR) mitigates the deleterious effects of stress by promoting beneficial effects such as helping them in the acquisition of less available nutrients, increasing the levels of plant growth regulators, improving the physiological health of the plants. In the present study, drought-tolerant phosphorus-solubilizing rhizobacteria with multifunctional plant growth-promoting attributes were isolated from different cereal crops grown in the Divine Valley of Baru Sahib, Himachal Pradesh, using a different nutrient combination. A total of 86 bacteria were isolated from different growth media. All 86 could tolerate 5% PEG, and 19, 6 and 6 isolates could tolerate 6%, 7% and 8% PEG-8000, respectively. Among 86, 48 drought-adapted and P-solubilizing strains were selected and screened for diverse PGP attributes such as solubilization of potassium and zinc, production of siderophores, hydrogen cyanide, ammonia and 1-aminocyclopropane-1-carboxylate deaminase. The efficient drought-adaptive P-solubilizing strain was used for seed germination and plant growth-promoting ability in different pot assays under laboratory and greenhouse conditions at different water regimes. The strain EU-LWNA-33 positively influencing the growth parameters and physiological parameters was identified using 16 S rRNA gene sequencing as Pseudomonas libanensis. To our knowledge, this is the first report for P. libanensis EU-LWNA-33 to solubilize a considerable amount of P under the water-deficient conditions. The use of stress-adaptive and P-solubilizing PGPR provides significant promise to overcome the challenges of sustainable agriculture in stressed environmental conditions.

Promoting Effects on Watermelon and Fermentation Optimization of Plantibacter sp. WZW03

Plantibacter sp. WZW03 can effectively improve the utilization efficiency of soil potassium by plants. However, high production cost of Plantibacter sp. WZW03 has limited its utilization. The study assessed the plant growth-promoting ability of Plantibacter sp. WZW03 on watermelon (Citrullus lanatus L. cv. Jingxin No. 1) by pot experiment and investigated the fermentation process using different substrate by response surface analysis. The results showed Plantibacter sp. WZW03 exhibited the maximum indole-3-acetic acid (IAA) secretion of 89.41 mg/L at 96 h and siderophore activity of 30.68% at 48 h in Medium-K basalt medium. Application of Plantibacter sp. WZW03 to watermelon effectively promoted root growth and increased root weight, length, and volume. The optimal fermentation substrate of Plantibacter sp. WZW03 was 65.7% chicken manure, 32.9% straw, 0.9% starch, and 0.5% Fe(OH)3. The optimal conditions included the culture time on 20.36 h, culture temperature at 29.87 °C and C/N at 19:1. The maximum biomass was 1.47 × 109 cfu/mL based on the optimum conditions, in agreement with the predicted value of the response surface. Compared with the silicate bacteria medium, the culture time was shortened by 12 h, the biomass was improved by 95.52%, and the cost of the fermentation process was lowered by 89.04%. Plantibacter sp. WZW03 could promote root growth and optimize root structure in watermelon and present the strong capacity to secrete IAA and produce siderophores. The developed fermentation process significantly enhanced the bacterial biomass, shortened the fermentation period, and lowered the production cost, thus providing theoretical and technical support for applying Plantibacter sp. WZW03 to promote the growth of watermelon.

Olea europaea L. Root Endophyte Bacillus velezensis OEE1 Counteracts Oomycete and Fungal Harmful Pathogens and Harbours a Large Repertoire of Secreted and Volatile Metabolites and Beneficial Functional Genes.

Oomycete and fungal pathogens, mainly Phytophthora and Fusarium species, are notorious causal agents of huge economic losses and environmental damages. For instance, Phytophthora ramorum, Phytophthora cryptogea, Phytophthora plurivora and Fusarium solani cause significant losses in nurseries and in forest ecosystems. Chemical treatments, while harmful to the environment and human health, have been proved to have little or no impact on these species. Recently, biocontrol bacterial species were used to cope with these pathogens and have shown promising prospects towards sustainable and eco-friendly agricultural practices. Olive trees prone to Phytophthora and Fusarium disease outbreaks are suitable for habitat-adapted symbiotic strategies, to recover oomycetes and fungal pathogen biocontrol agents. Using this strategy, we showed that olive trees-associated microbiome represents a valuable source for microorganisms, promoting plant growth and healthy benefits in addition to being biocontrol agents against oomycete and fungal diseases. Isolation, characterization and screening of root microbiome of olive trees against numerous Phytophthora and other fungal pathogens have led to the identification of the Bacillus velezensis OEE1, with plant growth promotion (PGP) abilities and strong activity against major oomycete and fungal pathogens. Phylogenomic analysis of the strain OEE1 showed that B. velezensis suffers taxonomic imprecision that blurs species delimitation, impacting their biofertilizers’ practical use. Genome mining of several B. velezensis strains available in the GenBank have highlighted a wide array of plant growth promoting rhizobacteria (PGPR) features, metals and antibiotics resistance and the degradation ability of phytotoxic aromatic compounds. Strain OEE1 harbours a large repertoire of secreted and volatile secondary metabolites. Rarefaction analysis of secondary metabolites richness in the B. velezenis genomes, unambiguously documented new secondary metabolites from ongoing genome sequencing efforts that warrants more efforts in order to assess the huge diversity in the species. Comparative genomics indicated that B. velezensis harbours a core genome endowed with PGP features and accessory genome encoding diverse secondary metabolites. Gas Chromatography-Mass Spectrometry (GC-MS) analysis of OEE1 Volatile Organic Compounds (VOCs) and Liquid Chromatography High Resolution Mass Spectrometry (LC-HRMS) analysis of secondary metabolites identified numerous molecules with PGP abilities that are known to interfere with pathogen development. Moreover, B. velezensis OEE1 proved effective in protecting olive trees against F. solani in greenhouse experiments and are able to inhabit olive tree roots. Our strategy provides an effective means for isolation of biocontrol agents against recalcitrant pathogens. Their genomic analysis provides necessary clues towards their efficient implementation as biofertilizers.

Biocontrol and plant growth-promoting ability of plant-associated bacteria from tomato (Lycopersicum esculentum) under field condition

Forty-five bacterial isolates recovered from surface-sterilized root, stem and leaf tissues of tomato were studied for their antifungal activity against phytopathogens, and plant growth-promoting (PGP) and biocontrol traits. Six plant-associated bacteria suppressed all the pathogens tested under in vitro plate assay and also shown PGP and biocontrol traits. The six isolates showing PGP and biocontrol properties were identified as Bacillus spp., based on the microbial identification system (Biolog) and partial sequence analysis of 16S rDNA. Two independent field trials were conducted with biocontrol bacteria along with chemical control (Thiram+Fytolan) and control (Without treatment). The averaged results of two field trails revealed that tomato plants inoculated with BETS11 (11.73 t/ha) and BETR11 (11.24 t/ha) strains showed significantly higher yield and disease reduction on par with chemical control (11.81 t/ha). However, there was an increase in the yield with respect to uninoculated control except the isolate BETS5 (9.09 t/ha). Therefore, the isolates BETS11 and BETR11 may be used as efficient biofertilizer and bio-control agent for tomato production in the Island agricultural ecosystem.

Isolation and characterization of novel soil- and plant-associated bacteria with multiple phytohormone-degrading activities using a targeted methodology.

Ethylene (ET), salicylic acid (SA) and indole-3-acetic acid (IAA) are important phytohormones regulating plant growth and development, as well as plant-microbe interactions. Plant growth-promoting bacteria (PGPB) naturally associate with plants and facilitate plant growth through a variety of mechanisms, including the ability to modulate the concentrations of these phytohormones in planta. Importantly, the wide presence of phytohormone degradation mechanisms amongst symbiotic and other soil- and plant-associated bacteria indicates that the ability to modulate phytohormone concentrations plays an important role in bacterial colonization and plant-growth promotion abilities. Obtaining phytohormone-degrading bacteria is therefore key for the development of novel solutions aiming to increase plant growth and protection. In this paper, we report an optimized targeted methodology and the consequent isolation of novel soil- and plant-associated bacteria, including rhizospheric, endophytic and phyllospheric strains, with the ability to degrade the phytohormones, SA and IAA, as well as the ET precursor, 1-aminocyclopropane-1-carboxylic acid (ACC). By using an optimized targeted methodology, we rapidly isolated diverse soil- and plant-associated bacteria presenting phytohormone-degrading abilities from several plants, plant tissues and environments, without the need for prior extensive and laborious isolation and maintenance of large numbers of isolates. The developed methodology facilitates PGPB research, especially in developing countries. Here, we also report, for the first time, the isolation of bacterial strains able to concomitantly catabolize three phytohormones (SA, IAA and ACC). Ultimately, the described targeted methodology and the novel phytohormone-degrading bacteria obtained in this work may be useful tools for future plant-microbe interaction studies, and in the development of new inoculant formulations for agriculture and biotechnology.

Acetobacter sacchari sp. nov., for a plant growth-promoting acetic acid bacterium isolated in Vietnam

Two bacterial strains, designated as isolates VTH-Ai14T and VTH-Ai15, that have plant growth-promoting ability were isolated during the study on acetic acid bacteria diversity in Vietnam. The phylogenetic analysis based on 16S rRNA gene sequences showed that the two isolates were located closely to Acetobacter nitrogenifigens RG1T but formed an independent cluster. The phylogenetic analysis based on 16S rRNA gene and three housekeeping genes’ (dnaK, groEL, and rpoB) sequences were analyzed. The genomic DNA of the two isolates, VTH-Ai14T and VTH-Ai15, Acetobacter nitrogenifigens RG1T, the closest phylogenetic species, and Acetobacter aceti NBRC 14818T were hybridized and calculated the %similarity. Then, phenotypic and chemotaxonomic characteristics were determined for species’ description using the conventional method. The 16S rRNA gene and concatenated of the three housekeeping genes phylogenetic analysis suggests that the two isolates were constituted in a species separated from Acetobacter nitrogenifigens, Acetobacter aceti, and Acetobacter sicerae. The two isolates VTH-Ai14T and VTH-Ai15 showed 99.65% and 98.65% similarity of 16S rRNA gene when compared with Acetobacter nitrogenifigens and Acetobacter aceti and they were so different from Acetobacter nitrogenifigens RG1T with 56.99 ± 3.6 and 68.15 ± 1.8% in DNA-DNA hybridization, when isolates VTH-Ai14T and VTH-Ai15 were respectively labeled. Moreover, the two isolates were phenotypically distinguished from Acetobacter nitrogenifigens in growth in the presence of 0.35% acetic acid (v/v), on nitrogen-free LGI medium and D-mannitol, and in no ability to solubilize phosphate. Therefore, the two isolates, VTH-Ai14T(= VTCC 910031T= BCC 67843T= TBRC 11175T= NRIC 0977T) and VTH-Ai15 (= VTCC 910032 = BCC 67844 = TBRC 11176 = NRIC 0978), can be assigned to an independent species within the genus Acetobacter, and the name of Acetobacter sacchari sp. nov. is proposed for the two isolates.

Isolation, identification and plant growth promotion ability of endophytic bacteria associated with lupine root nodule grown in Tunisian soil.

The present study aims to characterize nodule endophytic bacteria of spontaneous lupine plants regarding their diversity and their plant growth promoting (PGP) traits. The potential of PGPR inoculation was investigated to improve white lupine growth across controlled, semi-natural and field conditions. Lupinus luteus and Lupinus angustifolius nodules were shown inhabited by a large diversity of endophytes. Several endophytes harbor numerous plant growth promotion traits such as phosphates solubilization, siderophores production and 1-aminocyclopropane-1-carboxylate deaminase activity. In vivo analysis confirmed the plant growth promotion ability of two strains (Paenibacillus glycanilyticus LJ121 and Pseudomonas brenneri LJ215) in both sterilized and semi-natural conditions. Under field conditions, the co-inoculation of lupine by these strains increased shoot N content and grain yield by 25% and 36%, respectively. These two strains Paenibacillus glycanilyticus LJ121 and Pseudomonas brenneri LJ215 are effective plant growth-promoting bacteria and they may be used to develop an eco-friendly biofertilizer to boost white lupine productivity.