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.
Mukhtar S
，Zareen M
，Khaliq Z
，Mehnaz S
，Malik KA
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Assessment of two carrier materials for phosphate solubilizing biofertilizers and their effect on growth of wheat (Triticum aestivum L.).
Biofertilizers are usually carrier-based inoculants containing beneficial microorganisms. Incorporation of microorganisms in carrier material enables easy-handling, long-term storage and high effectiveness of biofertilizers. Objective of the present study was to assess enriched biogas sludge and soil as biofertilizer carriers on growth and yield of wheat. Six phosphate solubilizing strains were used in this study. Three phosphate solubilizing strains, 77-NS2 (Bacillus endophyticus), 77-CS-S1 (Bacillus sphaericus) and 77-NS5 (Enterobacter aerogenes) were isolated from the rhizosphere of sugarcane, two strains, PSB5 (Bacillus safensis) and PSB12 (Bacillus megaterium) from the rhizosphere of wheat and one halophilic phosphate solubilizing strain AT2RP3 (Virgibacillus sp.) from the rhizosphere of Atriplex amnicola, were used as bioinoculants. Phosphate solubilization ability of these strains was checked in vitro in Pikovskaya medium, containing rock phosphate (RP) as insoluble P source, individually supplemented with three different carbon sources, i.e., glucose, sucrose and maltose. Maximum phosphate solubilization; 305.6μg/ml, 217.2μg/ml and 148.1μg/ml was observed in Bacillus strain PSB12 in Pikovskaya medium containing sucrose, maltose and glucose respectively. A field experiment and pot experiments in climate control room were conducted to study the effects of biogas sludge and enriched soil based phosphorous biofertilizers on growth of wheat. Bacillus strain PSB12 significantly increased root and shoot dry weights and lengths using biogas sludge as carrier material in climate control room experiments. While in field conditions, significant increase in root and shoot dry weights, lengths and seed weights was seen by PSB12 and PSB5 (Bacillus) and Enterobacter strain 77-NS5 using biogas sludge as carrier. PSB12 also significantly increased both root and shoot dry weights and lengths in field conditions when used as enriched soil based inoculum. These results indicated that bacterial isolates having plant beneficial traits such as P solubilization are more promising candidates as biofertilizer when used with carrier materials.
Mukhtar S
，Shahid I
，Mehnaz S
，Malik KA
... -
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Diversity analysis of ACC deaminase producing bacteria associated with rhizosphere of coconut tree (Cocos nucifera L.) grown in Lakshadweep islands of India and their ability to promote plant growth under saline conditions.
ACC deaminase producing Plant growth promoting rhizobacteria (PGPR) offers a great promise for ameliorating the negative impacts of salinity stress manifested on plants. In this context, 28 rhizospheric bacteria associated with ACC deaminase potential (198-1069 nmol α-ketobutyrate mg protein-1 h-1) were isolated from 5 different islands of Lakshadweep, union territory, India- Agatti, Kavaratti, Bangaram, Kadmat, and Thinnakara islands using DF-minimal medium. The diversity of cultivable ACC deaminase producing bacteria was analysed by PCR-RFLP (Restriction Fragment Length Polymorphism) method using three endonucleases AluI, MspI and HaeIII which led to the grouping of these isolates into six clusters at 80 % similarity index. Subsequently, isolates were functionally characterized for various PGP traits such that indole-3-acetic acid (IAA) production (∼10-80 μg mL-1); 16 isolates had phosphate solubilizing potential ranging from ∼19 to 88 P mg L-1 ; siderophore and ammonia production abilities were observed in 5 and 24 isolates, respectively while two strains tolerated up to 8% NaCl. Phylogenetic analysis of 16S rRNA gene sequences of representative strain from each cluster revealed that twenty-eight ACC deaminase producing PGPR belong to eight distinct genera: Pseudomonas, Bacillus, Azospirillum, Azotobacter, Escherichia, Paenibacillus, Burkholderia, and Klebsiella. Two isolates, CO1 (Pseudomonas putida) and CO8 (Bacillus paramycoides) were evaluated for plant growth promoting effects on French bean (Phaseolus vulgaris) under salinity (100 mM NaCl) stress. Both the selected isolates in consortium form significantly increased the root length, shoot length, root fresh and dry weight, shoot fresh and dry weight of French bean seedlings exposed to salinity stress, compared to non-inoculated control plants. The co-inoculation with selected strains CO1 and CO8 has significantly improved chlorophyll concentration, relative water content, membrane stability index, gas exchange parameters including net photosynthesis rate (PN), stomatal conductance (gs), transpiration rate (E) and water use efficiency of French bean plants by ∼100 %, ∼85 %, ∼40 %, ∼198 %, ∼80 %, ∼70 % and ∼75 %, respectively under saline conditions in comparison with non-inoculated plants. Moreover, the consortium treated French bean plants showed lower levels of stress-induced ethylene by 38 %, electrolyte leakage and Malondialdehyde (MDA) content by ∼15 % under salt stress compared to non-inoculated ones. This study unveiled the potential of halotolerant strains, Pseudomonas putida and Bacillus paramycoides as French bean biofertilizers in mitigating the adverse effects of salinity in plant growth in sustainable agriculture.
Pandey S
，Gupta S
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