PLANT GROWTH PROMOTING AND ANTAGONISTIC TRAITS OF INDIGENOUS FLUORESCENT PSEUDOMONAS SPP. ISOLATED FROM WHEAT RHIZOSPHERE AND A. HALIMUS ENDOSPHERE

Fluorescent Pseudomonas spp. are an important group of plant growth promoting rhizobacteria (PGPR). They increase the growth of their host plant directly or indirectly. In this study, 3 Fluorescent pseudomonads were isolated from the wheat rhizosphere and one from the endophyte of the halophyte Atriplex halimus. Based on biochemical, physiological reactions and 16S rRNA gene sequences, the isolates were identified as Pseudomonas putida AF2, P. aeruginosa RB5, P. fluorescens RB13 and P. aeruginosa EH4. These strains and P. fluorescens CHA0 were screened for their PGPR activities. All the strains solubilized phosphate with a maximum of 187.9 μg / ml. P. fluorescens CHA0 produced a significant amount (88.37μg/ml) of IAA. The siderophores production by all the strains was proved and the percent of production varied from 38 to 46. The strains produced HCN, protease and amylase. Mycelial growth of F. oxysporum and A. alternata was strongly reduced in the presence of antagonistic fluorescent Pseudomonas spp., with the inhibition rate varying between 25 to 38% and 17 to 27%, respectively. On the basis of excellent growth promoter, biocontrol activities, the fluorescent Pseudomonas spp. tested could be applied as inoculants of wheat for sustainable agriculture in salty soils

PLANT GROWTH PROMOTING AND ANTAGONISTIC TRAITS OF INDIGENOUS FLUORESCENT PSEUDOMONAS SPP. ISOLATED FROM WHEAT RHIZOSPHERE AND A. HALIMUS ENDOSPHERE

Fluorescent Pseudomonas spp. are an important group of plant growth promoting rhizobacteria (PGPR). They increase the growth of their host plant directly or indirectly. In this study, 3 Fluorescent pseudomonads were isolated from the wheat rhizosphere and one from the endophyte of the halophyte Atriplex halimus. Based on biochemical, physiological reactions and 16S rRNA gene sequences, the isolates were identified as Pseudomonas putida AF2, P. aeruginosa RB5, P. fluorescens RB13 and P. aeruginosa EH4. These strains and P. fluorescens CHA0 were screened for their PGPR activities. All the strains solubilized phosphate with a maximum of 187.9 μg / ml. P. fluorescens CHA0 produced a significant amount (88.37μg/ml) of IAA. The siderophores production by all the strains was proved and the percent of production varied from 38 to 46. The strains produced HCN, protease and amylase. Mycelial growth of F. oxysporum and A. alternata was strongly reduced in the presence of antagonistic fluorescent Pseudomonas spp., with the inhibition rate varying between 25 to 38% and 17 to 27%, respectively. On the basis of excellent growth promoter, biocontrol activities, the fluorescent Pseudomonas spp. tested could be applied as inoculants of wheat for sustainable agriculture in salty soils

Loss of Gramicidin Biosynthesis in Gram-Positive Biocontrol Bacterium Aneurinibacillus migulanus (Takagi et al., 1993) Shida et al. 1996 Emend Heyndrickx et al., 1997 Nagano Impairs Its Biological Control Ability of Phytophthora

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Durum wheat stress tolerance induced by endophyte <i>pantoea agglomerans</i> with genes contributing to plant functions and secondary metabolite arsenal

In the arid region Bou-Sa&acirc;da at the South of Algeria, durum wheat Triticum durum L. cv Waha production is severely threatened by abiotic stresses, mainly drought and salinity. Plant growth-promoting rhizobacteria (PGPR) hold promising prospects towards sustainable and environmentally-friendly agriculture. Using habitat-adapted symbiosis strategy, the PGPR Pantoea agglomerans strain Pa was recovered from wheat roots sampled in Bou-Sa&acirc;da, conferred alleviation of salt stress in durum wheat plants and allowed considerable growth in this unhostile environment. Strain Pa showed growth up to 35 &deg;C temperature, 5&ndash;10 pH range, and up to 30% polyethylene glycol (PEG), as well as 1 M salt concentration tolerance. Pa strain displayed pertinent plant growth promotion (PGP) features (direct and indirect) such as hormone auxin biosynthesis, production of 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and ammonia and phosphate solubilization. PGPR features were stable over wide salt concentrations (0&ndash;400 mM). Pa strain was also able to survive in seeds, in the non-sterile and sterile wheat rhizosphere, and was shown to have an endophytic life style. Phylogenomic analysis of strain Pa indicated that Pantoea genus suffers taxonomic imprecision which blurs species delimitation and may have impacted their practical use as biofertilizers. When applied to plants, strain Pa promoted considerable growth of wheat seedlings, high chlorophyll content, lower accumulation of proline, and favored K+ accumulation in the inoculated plants when compared to Na+ in control non-inoculated plants. Metabolomic profiling of strain Pa under one strain many compounds (OSMAC) conditions revealed a wide diversity of secondary metabolites (SM) with interesting salt stress alleviation and PGP activities. All these findings strongly promote the implementation of Pantoea agglomerans strain Pa as an efficient biofertilizer in wheat plants culture in arid and salinity-impacted regions

Screening for Fusarium Antagonistic Bacteria From Contrasting Niches Designated the Endophyte Bacillus halotolerans as Plant Warden Against Fusarium

Date palm (Phoenix dactylifera L.) plantations in North Africa are nowadays threatened with the spread of the Bayoud disease caused by Fusarium oxysporum f. sp. albedinis, already responsible for destroying date production in other infected areas, mainly in Morocco. Biological control holds great promise for sustainable and environmental-friendly management of the disease. In this study, the additional benefits to agricultural ecosystems of using plant growth promoting rhizobacteria (PGPR) or endophytes are addressed. First, PGPR or endophytes can offer an interesting bio-fertilization, meaning that it can add another layer to the sustainability of the approach. Additionally, screening of contrasting niches can yield bacterial actors that could represent wardens against whole genera or groups of plant pathogenic agents thriving in semi-arid to arid ecosystems. Using this strategy, we recovered four bacterial isolates, designated BFOA1, BFOA2, BFOA3 and BFOA4, that proved very active against F. oxysporum f. sp. albedinis. BFOA1–BFOA4 proved also active against 16 Fusarium isolates belonging to four species: F. oxysporum (with strains phytopathogenic of Olea europaea and tomato), F. solani (with different strains attacking O. europaea and potato), F. acuminatum (pathogenic on O. europaea) and F. chlamydosporum (phytopathogenic of O. europaea). BFOA1–BFOA4 bacterial isolates exhibited strong activities against another four major phytopathogens: Botrytis cinerea, Alternaria alternata, Phytophthora infestans, and Rhizoctonia bataticola. Isolates BFOA1–BFOA4 had the ability to grow at temperatures up to 35°C, pH range of 5–10, and tolerate high concentrations of NaCl and up to 30% PEG. The isolates also showed relevant direct and indirect PGP features, including growth on nitrogen-free medium, phosphate solubilization and auxin biosynthesis, as well as resistance to metal and xenobiotic stress. Phylogenomic analysis of BFOA1–BFOA4 isolates indicated that they all belong to Bacillus halotolerans, which could therefore considered as a warden against Fusarium infection in plants. Comparative genomics allowed us to functionally describe the open pan genome of B. halotolerans and LC-HRMS and GCMS analyses, enabling the description of diverse secondary metabolites including pulegone, 2-undecanone, and germacrene D, with important antimicrobial and insecticidal properties. In conclusion, B. halotolerans could be used as an efficient bio-fertilizer and bio-control agent in semi-arid and arid ecosystems

Recent Advances in Encapsulation Techniques of Plant Growth-Promoting Microorganisms and Their Prospects in the Sustainable Agriculture

In addition to changing global demography and global warming, agricultural production systems around the world are threatened by intensive agricultural practices (overuse of land and excessive use of chemical fertilizers and pesticides) that deplete soils by affecting their dynamics and their fertility, pollute the environment, lower production, and alter biodiversity on a large scale. The use of bioformulations based on PGPMs (plant growth-promoting microorganisms) seems to be a promising and sustainable strategy to overcome these threats, thanks to their tolerance to various biotic and abiotic stresses and via their beneficial effects in promising plant growth, pest protection, bioremediation, and restoration of degraded lands. In recent years, particular attention has been paid to encapsulated formulations because they offer several advantages over conventional bioformulation (liquid and solid) related to shelf life, problems of survival and viability in the environment, and the efficiency of rhizospheric colonization. This review focuses on the types of encapsulations and the different technologies used in this process as well as the most commonly used substrates and additives. It also provides an overview on the application of encapsulated bioformulations as biofertilizers, biopesticides, or other biostimulators and summarizes the knowledge of the scientific literature on the development of nanoencapsulation in this sector

Biocontrol Efficiency of Rhizospheric <i>Bacillus</i> against the Plant Pathogen <i>Fusarium oxysporum</i>: A Promising Approach for Sustainable Agriculture

Among plant disease management strategies, biological control is a sustainable alternative to the use of chemicals for the control of vascular wilt caused by Fusarium oxysporum. Fusarium wilt is the most devastating disease affecting a wide variety of plants. Bacillus species are the most widely used biological control candidates for the control of these fungal diseases. This review describes the pathogenicity of F. oxysporum, its virulence mechanisms, and host plant–pathogen interactions. The control means deployed by Bacillus species inhibit or kill these phytopathogens. Bacillus spp. produce a wide range of secondary metabolites, including volatile and non-volatile organic compounds. Biocontrol potential is achieved through direct antimicrobial activity, the induction of the host plant’s immune response (Induced Systemic Resistance), and competition for nutrients and space. In addition, parameters governing the selection of effective biocontrol agents and their survival in plant microbial communities are discussed. The influence of the microbiota on the establishment and development of biocontrol agents can assess the potential of these treatments and facilitate the development of effective biopesticides during their field application

Loss of Gramicidin Biosynthesis in Gram-Positive Biocontrol Bacterium Aneurinibacillus migulanus (Takagi et al., 1993) Shida et al. 1996 Emend Heyndrickx et al., 1997 Nagano Impairs Its Biological Control Ability of Phytophthora

The soil-borne species Aneurinibacillus migulanus (A. migulanus) strains Nagano and NCTC 7096 were shown to be potent biocontrol agents active against several plant diseases in agricultural and forest ecosystems. Both strains produce the cyclic peptide gramicidin S (GS) that was described as the main weapon inhibiting some gram-negative and gram-positive bacteria and fungus-like organisms along with the production of biosurfactant and hemolysis activities. However, the contribution of the cyclic peptide gramicidin S (GS) to the biocontrol ability of A. migulanus has never been studied experimentally. In this paper, using a mutant of the A. migulanus Nagano strain (E1 mutant) impaired in GS biosynthesis we evaluated the contribution of GS in the biocontrol potential of A. migulanus against Phytophthora spp. The two strains of A. migulanus, Nagano and NCTC 7096, were tested in a pilot study for the inhibition of the growth of 13 Phytophthora species in dual culture assays. A. migulanus Nagano was significantly more inhibitory than NCTC 7096 to all species. Additionally, using apple infection assays, P. rosacearum MKDF-148 and P. cryptogea E2 were shown to be the most aggressive on apple fruits displaying clear infection halos. Therefore, the three A. migulanus strains, Nagano, NCTC 7096, and E1, were used in apple infection experiments to check their effect on infection ability of these two Phytophthora species. Treatment with A. migulanus Nagano significantly reduced the severity of symptoms in apple fruits compared with NCTC 7096. A. migulanus E1 mutant showed total loss of biocontrol ability suggesting that GS is a major actor in the biocontrol ability of A. migulanus Nagano strain

Mitigation of NaCl Stress in Wheat by Rhizosphere Engineering Using Salt Habitat Adapted PGPR Halotolerant Bacteria

There is a great interest in mitigating soil salinity that limits plant growth and productivity. In this study, eighty-nine strains were isolated from the rhizosphere and endosphere of two halophyte species (Suaeda mollis and Salsola tetrandra) collected from three chotts in Algeria. They were screened for diverse plant growth-promoting traits, antifungal activity and tolerance to different physico-chemical conditions (pH, PEG, and NaCl) to evaluate their efficiency in mitigating salt stress and enhancing the growth of Arabidopsis thaliana and durum wheat under NaCl–stress conditions. Three bacterial strains BR5, OR15, and RB13 were finally selected and identified as Bacillus atropheus. The Bacterial strains (separately and combined) were then used for inoculating Arabidopsis thaliana and durum wheat during the seed germination stage under NaCl stress conditions. Results indicated that inoculation of both plant spp. with the bacterial strains separately or combined considerably improved the growth parameters. Three soils with different salinity levels (S1 = 0.48, S2 = 3.81, and S3 = 2.80 mS/cm) were used to investigate the effects of selected strains (BR5, OR15, and RB13; separately and combined) on several growth parameters of wheat plants. The inoculation (notably the multi-strain consortium) proved a better approach to increase the chlorophyll and carotenoid contents as compared to control plants. However, proline content, lipid peroxidation, and activities of antioxidant enzymes decreased after inoculation with the plant growth-promoting rhizobacteria (PGPR) that can attenuate the adverse effects of salt stress by reducing the reactive oxygen species (ROS) production. These results indicated that under saline soil conditions, halotolerant PGPR strains are promising candidates as biofertilizers under salt stress conditions