Plant Growth-promoting Rhizobacteria Treatments Research Articles

Biochar and Rhizobacteria Amendments Improve Several Soil Properties and Bacterial Diversity.

In the current context, there is a growing interest in reducing the use of chemical fertilizers and pesticides to promote ecological agriculture. The use of biochar and plant growth-promoting rhizobacteria (PGPR) is an environmentally friendly alternative that can improve soil conditions and increase ecosystem productivity. However, the effects of biochar and PGPR amendments on forest plantations are not well known. The aim of this study is to investigate the effects of biochar and PGPR applications on soil nutrients and bacterial community. To achieve this goal, we applied amendments of (i) biochar at 20 t hm−2, (ii) PGPR at 5 × 1010 CFU mL−1, and (iii) biochar at 20 t hm−2 + PGPR at 5 × 1010 CFU mL−1 in a eucalyptus seedling plantation in Guangxi, China. Three months after applying the amendments, we collected six soil samples from each treatment and from control plots. From each soil sample, we analyzed several physicochemical properties (pH, electrical conductivity, total N, inorganic N, NO3−-N, NH4+-N, total P, total K, and soil water content), and we determined the bacterial community composition by sequencing the ribosomal 16S rRNA. Results indicated that co-application of biochar and PGPR amendments significantly decreased concentrations of soil total P and NH4+-N, whereas they increased NO3-N, total K, and soil water content. Biochar and PGPR treatments increased the richness and diversity of soil bacteria and the relative abundance of specific bacterial taxa such as Actinobacteria, Gemmatimonadetes, and Cyanobacteria. In general, the microbial composition was similar in the two treatments with PGPR. We also found that soil physicochemical properties had no significant influence on the soil composition of bacterial phyla, but soil NH4+-N was significantly related to the soil community composition of dominant bacterial genus. Thus, our findings suggest that biochar and PGPR amendments could be useful to maintain soil sustainability in eucalyptus plantations.

Comparing the growth-promoting potential of Paenibacillus lentimorbus and Bacillus amyloliquefaciens in Oryza sativa L. var. Sarju-52 under suboptimal nutrient conditions

An adequate supply of mineral nutrients is crucial to obtain optimum productivity in agriculture. The present investigation was carried to find the inoculation effect of plant growth-promoting rhizobacteria (PGPR), i.e., Paenibacillus lentimorbus B-30488 (B-30488), Bacillus amyloliquefaciens SN13 (SN13) and their consortium for the growth of rice var. Sarju-52, grown under suboptimal nutrient conditions. The study revealed that the individual PGPR treatments showed comparatively better performance than consortia in morphological, physiological, biochemical, and nutrient analysis. Towards understanding the complex mechanism(s), untargeted metabolite profiling was performed using GC-MS, showed alteration of metabolites in rice seedlings facing suboptimal nutrient conditions and inoculated with PGPR. Metabolites such as oleic acid, mannitol, and ethyl iso-allocol were accumulated significantly under starved conditions. Under suboptimal nutrient conditions, sugars such as ribose, glucose, fructose, trehalose, palmitic acid, and myristic acid were accumulated significantly in PGPR inoculated seedlings. The significantly altered pathways due to PGPR inoculation under suboptimal nutrient conditions mainly belongs to carbohydrate and fatty acid metabolism. Interestingly, it was observed that among all the treatments, inoculation with SN13 performed comparatively better than other treatments. Further, in SN13 inoculated samples the qRT-PCR analysis of transcription factors and metabolism-related genes were validated that indicates PGPR deploy metabolic re-programming in rice var. Sarju-52 to enhance its nutrient use efficiency, tolerance, and growth under suboptimum nutrient conditions.

Towards biocontrol of ophiostomatoid fungi by plant growth-promoting rhizobacteria

ABSTRACTOphiostomatoid fungi, Leptographium terebrantis and Grosmannia huntii, are among the most important agents of wood blue stain and root disease of Pinus species. A number of physical, chemical, and cultural strategies adopted to minimise the impact of these fungi are of limited success. Biological control of tree diseases with plant growth-promoting rhizobacteria (PGPR) is attractive given that they provide an alternative and supplement to synthetic chemicals without negative impact on the environment. While a significant number of studies have shown the ability of PGPR to control pathogens of agricultural plants, studies to understand the activity of PGPR against ophiostomatoid fungal pathogens of conifers is still lacking. To understand the utility of PGPR in treating blue stain in woods, twenty-seven Bacillus velezensis strains and single strains of Paenibacillus peoriae and B. altitudinis that had previously shown antibiosis against plant pathogens from six different genera were tested for in vitro antibiosis against L. terebrantis and G. huntii. To understand the efficacy of PGPR in controlling root-disease, Bacillus pumilus SE-34 and INR7, and Serratia marcescens (90–166), previously reported to have efficacy against a root pathogen in conifer, were tested for their capacity to induce resistance of P. taeda to these fungi. All PGPR strains inhibited the growth of L. terebrantis and G. huntii in vitro. In a second experiment, specific PGPR treatment resulted in increased seedling dry matter biomass and reduction of diseased tissue. The results demonstrate tested PGPR strains may have potential as biocontrol agents to the tested ophiostomatoid fungi.

Improved Growth and Nutrition of Sorghum (Sorghum bicolor) Plants in a Low-Fertility Calcareous Soil Treated with Plant Growth–Promoting Rhizobacteria and Fe-EDTA

The low availability of micronutrients such as zinc (Zn) and iron (Fe) and macronutrients (phosphorus (P), in particular) in calcareous soils adversely affects plants such as sorghum (Sorghum bicolor) that are highly sensitive to deficiencies of these elements. This study investigated the potential effects of different Fe chelates and plant growth–promoting rhizobacteria (PGPR) on nutrition and growth of sorghum plants growing in a low-fertility calcareous soil. A glasshouse experiment was carried out in a completely randomized design with four PGPR treatments (Pseudomonas putida P159, Pseudomonas fluorescens T17-24, Bacillus subtilis P96, and an uninoculated control), and three Fe treatments (10 mg Fe kg−1 soil as Fe-EDDHA or Fe-EDTA, and no Fe application). Application of both Fe chelates (Fe-EDDHA and Fe-EDTA) increased plant dry weight, shoot content, and concentration of Zn and Cu (copper) compared with the control treatment; however, Fe-EDTA was found to be more effective than Fe-EDDHA. Fe-EDTA significantly increased the concentration of Cu, Zn, and Mn (manganese) up to 74.7%, 40.3%, and 30.6% in the rhizosphere, respectively. The use of PGPR significantly increased plant growth as well as the content of Mn, Zn, Cu, and K (potassium) compared with the uninoculated plants. Overall, the Fe-EDTA chelate was more effective in increasing nutrient uptake and growth of sorghum plants than Fe-EDDHA because of its low chemical stability at high pH. Combined application of Fe-EDTA and PGPR strains provided the greatest growth and nutritional benefits to sorghum plants growing in the alkaline nutrient-deficient calcareous soil.

Exopolysaccharide producing rhizobacteria and their impact on growth and drought tolerance of wheat grown under rainfed conditions.

The demand for agricultural crops continues to escalate with an increasing population. To meet this demand, marginal land can be used as a sustainable source for increased plant productivity. However, moisture stress not only affects crop growth and productivity but also induces plants’ susceptibility to various diseases. The positive role of plant growth hormone, salicylic acid (SA), on the defence systems of plants has been well documented. With this in mind, a combination of plant growth promoting rhizobacteria (PGPR) and SA was used to evaluate its performance on wheat grown under rainfed conditions (average moisture 10–14%). The selected bacterial strains were characterized for proline production, indole-3-acetic acid (IAA), hydrogen cyanide (HCN), ammonia (NH3), and exopolysaccharides (EPS). Wheat seeds of two genotypes, Inqilab-91 (drought tolerant) and Shahkar-2013 (drought sensitive), which differed in terms of their sensitivity to drought stress, were soaked for three hours prior to sowing in 24-hour old cultures of the bacterial strains Planomicrobium chinense strain P1 (accession no. MF616408) and Bacillus cereus strain P2 (accession no. MF616406). SA was applied (150 mg/L), as a foliar spray on one-month-old wheat seedlings. A significant reduction in the physiological parameters was noted in the plants grown in rainfed conditions but the PGPR and SA treatment effectively ameliorated the adverse effects of moisture stress. The wheat plants treated with PGPR and SA showed significant increases in leaf protein and sugar contents and maintained higher chlorophyll content, chlorophyll fluorescence (fv/fm) and performance index (PI) under rainfed conditions. Leaf proline content, lipid peroxidation, and antioxidant enzyme activity were higher in the non-inoculated plants grown in rainfed conditions but significantly reduced in the inoculated plants of both genotypes. Integrative use of a combination of PGPR strains and SA appears to be a promising and eco-friendly strategy for reducing moisture stress in plants.

The Coupling Effects of Plant Growth Promoting Rhizobacteria and Salicylic Acid on Physiological Modifications, Yield Traits, and Productivity of Wheat under Water Deficient Conditions

Water deficit and soil infertility negatively influence the growth, nutrient uptake, and productivity of wheat. Plant growth promoting rhizobacteria (PGPR) and salicylic acid (SA) were evaluated as possible solutions to mitigate the impacts of water deficit on growth, physiology, productivity, and nutrient uptake of wheat (Triticum aestivum L. cv. Sakha 95). Over two growing seasons (2016/2017 and 2017/2018) field experiments were conducted to examine eight combinations of two water treatments (water deficit and well-watered) with four soil and foliar treatments (control, PGPR, SA, and combination of PGPR + SA). The application of PGPR increased soil microbial activity resulting in increased field capacity and available soil water. Likewise, the application of the combined treatment of PGPR and SA significantly increased chlorophyll content, relative water content, stomatal conductance, soil microbial population, and showed inhibitory impacts on proline content, thus improving yield-related traits, productivity, and nutrient uptake (N, P, K) under water deficit compared to the control treatment. The results show that the integrative use of PGPR in association with SA may achieve an efficacious strategy to attenuate the harmful effects of water deficit as well as the amelioration of productivity and nutrient uptake of wheat under water-deficient conditions.

Effects of PGPR (Pseudomonas sp.) and Ag-nanoparticles on Enzymatic Activity and Physiology of Cucumber.

The present investigation aimed to evaluate the role of Plant Growth- Promoting Rhizobacteria (PGPR) and Ag-nanoparticles on two varieties (American variety, Poinsett 76 and Desi variety, Sialkot selection) of cucumber plants. Cucumber seeds prior to sowing, were inoculated with two strains of PGPR, Pseudomonas putida (KX574857) and Pseudomonas stutzeri (KX574858) at the rate of 106 cells/ml. Agnanoparticles (5ppm) were sprayed on the plant at early vegetative phase 27 d after sowing. The proline, sugar, protein, phenolics, flavonoids, chlorophyll and carotenoids contents of leaves of plants and the activities of Phenylalanine Ammonia-Lyase (PAL), Superoxide Dismutase (SOD) and Catalase (CAT) were determined from leaves of plants at early vegetative phase. After 3 months of seeds sowing, Ag-nanoparticles enhanced the length of root but decreased the length of shoot and fresh weight of root and shoot as compared to control whereas, the leaf protein, proline, phenolics, flavonoids, chlorophyll b, total chlorophyll, sugar and Phenylalanine Ammonia-Lyase (PAL) activity of plants were increased significantly over control. Ag-nanoparticles also suppressed the effect of PGPR for root, shoot length but augmented the protein and phenolics contents of leaves of both the varieties. The combined treatment of Ag-nanoparticles and PGPR enhanced flavonoids content of leaves and the activities of PAL, SOD and CAT in leaves of plants over control. Agnanoparticles effectively increased the Phenylalanine Ammonia-Lyase (PAL), Catalase (CAT) and superoxide dismutase (SOD) activities in leaves of both the varieties. Pseudomonas putida may be used either alone or in combination with Ag-nanoparticles to enhance the antioxidant and defense enzyme activities. Hence, the plant can tolerate the diseases and stresses in a much better way with higher protein and phenolics content.

Integrated Use of Humic Acid and Plant Growth Promoting Rhizobacteria to Ensure Higher Potato Productivity in Sustainable Agriculture

In sustainable agriculture, seeking eco-friendly methods to promote plant growth and improve crop productivity is a priority. Humic acid (HA) and plant growth promoting rhizobacteria (PGPR) are among the most effective methods that utilize natural biologically-active substances. The aim of the present study was to analyze the effect of the presence of HA on potato (Solanum tuberosum L.) inoculation with PGPR (Bacillus megatorium and Bacillus subtilis) when compared to control and recommended doses of NPK. Seed tubers treated by humic acid (200, 400, and 600 kg ha−1) and PGPR, separately or in combination, and NPK (50% and 100%) were planted into soil and untreated soil. Treatments were assessed for plant growth, classified tuber yields, quality, and mineral contents of potato tubers. There were highly significant increases in potato growth, tuber yields, and quality in PGPR and HA inoculated crops. Tuber size, weight, specific gravity, dry matter, starch, protein, and mineral contents (except Cu) were improved with PGPR treatments and further increased when administered with humic acids. Inoculation with PGPR mixed culture and 400 kg ha−1 HA increased total potato tuber yield by about 140% while conventional single treatment of 100% NPK fertilizer only led to an increase in potato production of 111% when compared to the control. The results demonstrated that this integrated approach has the potential to accelerate the transformation from conventional to sustainable potato production.

Variable Influences of Water Availability and Rhizobacteria on the Growth of Schizachyrium scoparium (Little Bluestem) at Different Ages.

There is significant interest in understanding the role of plant growth-promoting rhizobacteria (PGPR) in alleviating different types of plant stress. Schizachyrium scoparium (little bluestem) is a moderately drought tolerant, perennial bunchgrass native to North America. The goal of this experiment was to evaluate whether the addition of a bacterial root isolate in the Pseudomonas genus promoted the growth of S. scoparium with changes in water availability. Pseudomonas are common rhizobacteria and have been shown to improve plant growth. It was hypothesized that plants inoculated with the PGPR strain would have greater growth and health, and would be less affected by shifts in water availability. Pseudomonas strains were isolated from the roots of native S. scoparium plants. After germination, S. scoparium seedlings were subjected to four treatment groups: low water; high water; low water with PGPR; and high water with PGPR. The experiment was run three times with plants at different starting ages; 14-, 28-, and 70-day-old plants. The effects of the water and PGPR treatments were variable between the experimental trials. There were no significant effects of the water treatments on plant growth in Trial 1 (14-day-old plants) or Trial 2 (28-day-old plants), however, there was a significant negative effect of the high watering treatment on the shoot length and biomass in Trial 3. High water availability was significantly associated with greater plant health in Trial 1, but appeared to reduce plant health in Trials 2 and 3. The PGPR treatment appeared to promote root growth and biomass in Trial 2, and was associated with greater plant health in all three trials, especially when paired with the low water treatment. Results from a permutational MANOVA indicate that plant growth was significantly different between the trials due to differences in the starting age of the plants and the duration of the experiments. Thus, methodological choices, such as plant life history stage and experiment duration, may affect the response of plants to PGPR in the rhizosphere. This research provides an insight into the interactions between PGPR and water availability on the growth and health of native plants.

Field Based Assessment of Capsicum annuum Performance with Inoculation of Rhizobacterial Consortia.

Plant growth promoting rhizobacteria (PGPR) are associated with plant roots and augment plant productivity and immunity by reducing fertilizer application rates and nutrient runoff. Studies were conducted to evaluate bell pepper transplants amended with formulation of consortium of two indigenous PGPR isolates (Bacillus subtilis and Bacillus pumilus) in terms of increase in yield and disease resistance under field conditions. Transplants were planted into plots treated by NPK (nitrogen, phosphorus and potassium), fungicides, soil solarization, MeBr fumigation, PGPR and untreated soil. Treatments were assessed for incidence of soil-borne phytopathogens viz. Phytophthora capsici and Colletotrichum sp. Highly significant increases in bell pepper transplant growth occurred in response to formulations of PGPR isolates. Transplant vigor and survival in the field were also improved by PGPR treatments. Consortium of Bacillus subtilis and Bacillus pumilus reduced disease incidence of damping off by 1.81% and anthracnose by 1.75%. Numbers of colony forming units of Phytophthora capsici and Colletotrichum sp. were significantly higher in all plots than those treated with PGPR consortium. Incidence of seed rot and seedling blight on bell pepper was significantly lower in PGPR-treated plots and highest in untreated plots. Total fruit yield of bell pepper increased by 379.36% with PGPR consortium (Bacillus subtilis and Bacillus pumilus).

Control of Fusarium Disease in Onion with Plant Growth Promoting Rhizobacteria (PGPR) and Mycorrhizae and Its Effect on Growth and Yield of Onion

<p>The productivity of onion in Indonesia is generally low due to fusarium wilt disease. Biological controls can be applied using PGPR and Mycorrhizae. The purpose of this research was understand the interaction between PGPR and Mycorrhizal inoculation against fusarium wilt intensity as well as the growth and yield of onions. The isolation of <em>Fusarium oxysporum</em> f.sp <em>cepae</em> and PGPR, followed by the tests of PGPR inhibition ability, phosphate solvent and HCN compound productivity. The method used in the field was a completely randomized design (CRD) with 2 replications. Results showed that the combination of PGPR and mycorrhizae as a whole was unable to suppress <em>Fusarium</em> wilt disease, but had significant effect to postpone the incubation period (26,19 days after inoculation) and increase the growth and yield of onion compared to the onion plants infected with <em>Fusarium</em> but without the combined treatment of PGPR and mycorrhizae and the PGPR treatment and mycorrhizal treatment as single treatments; the application of mycorrhizae as the single factor had a very significant effect on the number of bulbs, but had no significant effect on the inhibition of fusarium wilt intensity as well as the growth and yield of onions.</p>

Metabolic and physiological changes induced by plant growth regulators and plant growth promoting rhizobacteria and their impact on drought tolerance in Cicer arietinum L.

Plant growth regulators (PGRs) and plant growth promoting rhizobacteria (PGPRs) play an important role in mitigating abiotic stresses. However, little is known about the parallel changes in physiological processes coupled with metabolic changes induced by PGRs and PGPRs that help to cope with drought stress in chickpeas. The present investigation was carried out to study the integrative effects of PGRs and PGPRs on the physiological and metabolic changes, and their association with drought tolerance in two chickpea genotypes. Inoculated seeds of two chickpea genotypes, Punjab Noor-2009 (drought sensitive) and 93127 (drought tolerance), were planted in greenhouse condition at the University of Florida. Prior to sowing, seeds of two chickpea varieties were soaked for 3 h in 24 h old cultures of PGPRs (Bacillus subtilis, Bacillus thuringiensis, and Bacillus megaterium), whereas, some of the seeds were soaked in distilled water for the same period of time and were treated as control. Plant growth regulators, salicylic acid (SA) and putrescine (Put), were applied on 25 days old seedlings just prior to the induction of drought stress. Drought stress was imposed by withholding the supply of water on 25-day-old seedlings (at the three-leaf stage) and continued for the next 25 days until the soil water content reached 14%. Ultrahigh-performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS) analysis concomitant with physiological parameters were carried out in chickpea leaves at two-time points i.e. 14 and 25 d after imposition of drought stress. The results showed that both genotypes, treated with PGRs and PGPRs (consortium), performed significantly better under drought condition through enhanced leaf relative water content (RWC), greater biomass of shoot and root, higher Fv/FM ratio and higher accumulation of protein, sugar and phenolic compounds. The sensitive genotype was more responsive than tolerant one. The results revealed that the accumulation of succinate, leucine, disaccharide, saccharic acid and glyceric acid was consistently higher in both genotypes at both time points due to PGRs and PGPRs treatment. Significant accumulation of malonate, 5-oxo-L-proline, and trans-cinnamate occurred at both time points only in the tolerant genotype following the consortium treatment. Aminoacyl-tRNA, primary and secondary metabolite biosynthesis, amino acid metabolism or synthesis pathways, and energy cycle were significantly altered due to PGRs and PGPRs treatment. It is inferred that changes in different physiological and metabolic parameters induced by PGRs and PGPRs treatment could confer drought tolerance in chickpeas.

Comparative Physiological and Metabolic Analysis Reveals a Complex Mechanism Involved in Drought Tolerance in Chickpea (Cicer arietinum L.) Induced by PGPR and PGRs

The plant growth promoting rhizobacteria (PGPR) and plant growth regulators (PGRs) can be applied to improve the growth and productivity of plants, with potential to be used for genetic improvement of drought tolerance. However, for genetic improvement to be achieved, a solid understanding of the physiological and biochemical changes in plants induced by PGPR and PGR is required. The present study was carried out to investigate the role of PGPR and PGRs on the physiology and biochemical changes in chickpea grown under drought stress conditions and their association with drought tolerance. The PGPR, isolated from the rhizosphere of chickpea, were characterized on the basis of colony morphology and biochemical characters. They were also screened for the production of indole-3-acetic acid (IAA), hydrogen cyanide (HCN), ammonia (NH3), and exopolysaccharides (EPS) production. The isolated PGPR strains, named P1, P2, and P3, were identified by 16S-rRNA gene sequencing as Bacillus subtilis, Bacillus thuringiensis, and Bacillus megaterium, respectively. The seeds of two chickpea varieties, Punjab Noor-2009 (drought sensitive) and 93127 (drought tolerant) were soaked for 2–3 h prior to sowing in 24 h old cultures of isolates. The salicylic acid (SA) and putrescine (Put) were sprayed (150 mg/L) on 25 day old chickpea seedlings. The results showed that chickpea plants treated with a consortium of PGPR and PGRs significantly enhanced the chlorophyll, protein, and sugar contents compared to irrigated and drought conditions. Leaf proline content, lipid peroxidation, and activities of antioxidant enzymes (CAT, APOX, POD, and SOD) all increased in response to drought stress but decreased due to the PGPR and PGRs treatment. An ultrahigh performance liquid chromatography-high resolution mass spectrometry (UPLC-HRMS) analysis was carried out for metabolic profiling of chickpea leaves planted under controlled (well-irrigated), drought, and consortium (drought plus PGPR and PGRs) conditions. Proline, L-arginine, L-histidine, L-isoleucine, and tryptophan were accumulated in the leaves of chickpea exposed to drought stress. Consortium of PGPR and PGRs induced significant accumulation of riboflavin, L-asparagine, aspartate, glycerol, nicotinamide, and 3-hydroxy-3-methyglutarate in the leaves of chickpea. The drought sensitive chickpea variety showed significant accumulation of nicotinamide and 4-hydroxy-methylglycine in PGPR and PGR treated plants at both time points (44 and 60 days) as compared to non-inoculated drought plants. Additionally, arginine accumulation was also enhanced in the leaves of the sensitive variety under drought conditions. Metabolic changes as a result of drought and consortium conditions highlighted pools of metabolites that affect the metabolic and physiological adjustments in chickpea that reduce drought impacts.

Effect of rhizobacteria treatments on nutrient content and organic and amino acid composition in raspberry plants

Plant growth-promoting rhizobacteria (PGPR) have been found to be beneficial to plant growth, yield, crop quality, the environment, and sustainable agricultural production. Therefore, six bacterial strains were tested to determine their effects on raspberry's nutrient content and organic and amino acid composition. The experiment was performed from 2015 to 2017. Two-year-old raspberry plants were inoculated with bacterial suspensions by a dipping method and were planted in 30-L pots. The mineral content and organic acid and amino acid composition of the leaf and root were compared in the Alcaligenes 637Ca, Staphylococcus MFDCa1 and MFDCa2, Agrobacterium A18, Pantoea FF1, and Bacillus M3 bacterial strains. Nitrogen (N) content of the leaf was 2.55% in the A18 treatment, while N content of the root was 1.61% in MFDCa2. The leaf's iron (Fe) content was highest in the M3 treatment with 91.76 mg kg-1, while 637Ca gave the highest root's Fe content with 107.80 mg kg-1. The content of malonic acid (16.78 ng µL-1), malic acid (4.59 ng µL-1), citric acid (16.88 ng µL-1), and fumaric acid (4.94 ng µL-1) in leaves was higher in MFDCa2 than in the other treatments. In addition, 637Ca treatment had the highest root organic acid content in tartaric acid (5.94 ng µL-1), butyric acid (15.19 ng µL-1), and maleic acid (5.13 ng µL-1). FF1 treatment was more effective than the other treatments for increasing the leaf?s amino acid content, while the 637Ca, MFDCa1 FF1, and M3 treatments were more effective in increasing the root?s amino acid content. As a result, it was determined that PGPR treatments play a significant role in mineral nutrient uptake and the organic acid and amino acid composition of the raspberry plant.

The effect of plant growth-promoting rhizobacteria on yield, water use efficiency and Brix Degree of processing tomato

Open field experiments were conducted to investigate the effects of plant growth-promoting rhizobacteria (PGPR) (Phylazonit MC®) as a biofertilizer on processing tomato cultivar var. Uno Rosso F<sub>1</sub>, grown under three different regimes of water supply. Field effectiveness of rhizobacteria inoculation on total biomass production, yield and water use efficiency, were examined in 2015 and 2016. Seedlings were inoculated with 1% liquid solution of Phylazonit MC® (Pseudomonas putida, Azotobacter chroococcum, Bacillus circulans, B. megaterium; colony-forming unit: 10<sup>9</sup> CFU/mL) at sowing and planting out by irrigation. There were three different regimes of water supply: rain-fed control (RF); deficit water supply (WS50) and optimum water supply (WS100); the latter was supplied according to the daily evapotranspiration by drip irrigation. Total aboveground biomass (shoot and total yield) and red fruits yield were measured at harvest in August, in both years. Total biomass changed between 32.5 t/ha and 165.7 t/ha, the marketable yield from 14.7 t/ha to 119.8 t/ha and water use efficiency (WUE) between 18.5 kg/m<sup>3</sup> to 32.0 kg/m<sup>3</sup>. The average soluble solids content of the treatment combinations ranged from 3.0 to 8.4°Brix. Seasonal effects were significant between the two years with different precipitation, which manifested in total biomass and marketable yield production. PGPR increased WUE only in WS50 in both years, while under drought stress and higher water supply, the effect was not clear. The effect of PGPR treatment on marketable yield, total biomass and WUE was positive in both years when deficit irrigation was applied and only in the drier season in the case of optimum water supply.

Effects of humic acid and plant growth-promoting rhizobacteria (PGPR) on induced resistance of canola to Brevicoryne brassicae L.

The cabbage aphid, Brevicoryne brassicae L. (Hem: Aphididae), is an important pest of canola that can considerably limit profitable crop production either through direct feeding or via transmission of plant pathogenic viruses. One of the most effective approaches of pest control is the use of biostimulants. In this study, the effects of humic acid, plant growth-promoting rhizobacteria (PGPR), and integrated application of both compounds were investigated on life table parameters of B. brassicae, and the tolerance of canola to this pest. B. brassicae reared on plants treated with these compounds had the lower longevity, fecundity, and reproductive period compared with control treatment. The intrinsic rate of natural increase (r) and finite rate of increase (λ) were lowest on PGPR treatment (0.181 ± 0.004 day-1 and 1.198 ± 0.004 day-1, respectively) and highest on control (0.202 ± 0.005 day-1 and 1.224 ± 0.006 day-1, respectively). The net reproductive rate (R0) under treatments of humic acid, PGPR and humic acid + PGPR was lower than control. There was no significant difference in generation time (T) of B. brassicae among the tested treatments. In the tolerance test, plants treated with PGPR alone or in integrated with humic acid had the highest tolerance against B. brassicae. The highest values of total phenol, flavonoids, and glucosinolates were observed in treatments of PGPR and humic acid + PGPR. Basing on the antibiosis and tolerance analyses in this study, we concluded that canola plants treated with PGPR are more resistant to B. brassicae. These findings could be useful for integrated pest management of B. brassicae in canola fields.

Impact of Salicylic Acid and PGPR on the Drought Tolerance and Phytoremediation Potential of Helianthus annus.

The present study was aimed to isolate and characterize plant growth promoting rhizobacteria (PGPR) from the rhizosphere of rainfed area (Karak) in Pakistan. The influence of isolated rhizobacteria, in association with salicylic acid (SA), physiological attributes, drought tolerance potential, and phytoremediation in drought-stressed sunflower exposed was investigated. The isolated bacteria were named P1 and P2 and characterized on the basis of colony morphology and biochemical traits. Both PGPR P1 and P2 were identified on the basis of 16S-rRNA gene sequencing as Planomicrobium chinense strain P1 (Accession No. MF616408) and Bacillus cereus strain P2 (Accession No. MF616406). The fresh cultures (24 h old) of isolates were used to soak the seeds pre-sowing. SA was foliar applied at three-leaf-stage. Likewise, the 30-days-old seedlings (three leaf stage) were exposed to drought stress. Drought stress was imposed to 30-days-old plants (three-leaf stage) by withholding water supply for the next 15 days until the soil water content reached 10%. The PGPR and/or SA treatment resulted in significant accumulation of Cd (84%), Pb (66%), and Ni (65%) in the rhizosphere. PGPR also induced accumulation of Cd and Ni in plant shoot. Combined treatment of PGPR and SA increased the Cu (21%), Co (11%), and Zn (8%) accumulation but decreased (12%) the Fe accumulation as compared to coinoculation of PGPR P1 and P2. Inoculation of plants with PGPR significantly increased shoot length (60%), root length (68%), root fresh (61%), and dry (63%) biomass under water stress. The inoculated plants had increased chlorophyll (67%), carotenoid (70%), leaf protein (64%), sugar (64%), and phenolic (62%) contents while lower leaf proline (62%) content, malondialdehyde (MDA) (64%), and antioxidant enzymes (67%) which suggest their role in drought tolerance. It is concluded that integrative use of PGPR in combination with SA found to be an efficacious strategy to improve the phytoremediation of heavy metals and plant growth under stressed conditions particularly under water-deficient conditions.

PENGARUH KOMPOS AMPAS SAGU DAN PLANT GROWTH PROMOTION RHIZOBACTERIA (PGPR) TERHADAP PERTUMBUHANDAN HASIL KACANG TANAH (Arachis hypogeal L.)

The aims of this research is to find out the influence of the application of sago waste compost and PGPR on the increase in groundnut growth and yield and to obtain the dose of sago waste compost and PGPR concentration that able to increase the growth and yield of groundnut had been conducted in January to March 2016 in Maba Sangaji Village, Kota Maba Subdistrict, East Halmahera Regency. The research used factorial randomized complete block design consisting of two factors with three replication. Factor I was the dose of sago waste compost consisted of four levels: K0 = without sago waste compost (control), K1 = sago waste compost of 10 t ha-1, K2 = sago waste compost of 15 t ha-1, and K3 = sago waste compost of 20 t ha-1. Factor II was concentration of Plant Growth Promoting Rhizobacteria (PGPR) consisted of 4 levels: P0 = without PGPR (control), P1 = PGPR of 5 ml l-1, P2 = PGPR of 10 ml l-1, and P3 = PGPR of 15 ml l-1. The observation consisted of growth components of plant height, the number of leaves, leaf area, crop dry weight, and crop growth rate, and yield components of the number of pods, filled pods, empty pods, pod weight, grain weight, and weight of 100 grain. Research result shows that there was no interaction between the treatment of sago waste compost and PGPR. However, separately, treatments of sago waste compost and PGPR had the significant influence on the growth and yield of groundnut. The highest groundnut yield was obtained in the treatment of sago waste compost with the dose of 20 t ha-1. Grain weight obtained was 17.51 g or an increase of 52.15% compared to those of treatment without application of sago waste compost and yield of grain weight per hectare was 2.80 t ha-1. The inoculation of PGPR increased the growth and yield of groundnut. The application of PGPR with the concentration of 10 and 15 ml-1 produced better crop growth. The higher result was obtained in the treatment of PGPR with the concentration of 10 and 15 ml l-1with grain weight of 15.46 g and 16.81 g plant-1 or an increase of 31.15% and 42.6%, respectively, compared to control,whereas, grain weight per hectare was 2.47 t ha-1 and 2.69 t ha-1, respectively.

The Effect of Plant Growth Promoting Rhizobacteria on the Water-yield Relationship and Carotenoid Production of Processing Tomatoes

Open field experiments were conducted to investigate the effects of plant growth promoting rhizobacteria (PGPR) biofertilizer on processing tomato, grown under three different irrigation regimes. The field effectiveness of rhizobacteria inoculation on total biomass, yield, water use efficiency (WUE), carotenoid, and ascorbic acid production was examined in 2015 and 2016. The experimental design used was randomized block and the number of replications was four for each treatment. There were three different irrigation regimes: rain-fed control (RF), deficit water supply (WS50), and optimum water supply (WS100), which was delivered by drip irrigation in accordance with daily evapotranspiration (ETc). The test was performed on the Uno Rosso F1 processing tomato hybrid. Red fruit were measured at harvest in August and high-performance liquid chromatography (HPLC) was used for analysis. We evaluated yield quantity and total carotenoids and their composition (lycopene and β-carotene) depending on water supplement in 2 years. The marketable yield varied between 14.7 t·ha−1 and 126.9 t·ha−1 depending on treatment. The average soluble solids content (SSC) of the treatments ranged from 3.0 to 8.4. The total carotenoid yields of the treatments ranged from 0.8 to 40.4 kg·ha−1 and the average lycopene yield of the treatments ranged from 0.6 to 34.1 kg·ha−1. The effect of PGPR treatment was clearly positive for harvested yield, but this effect only prevailed under irrigated conditions.

Plant growth promoting rhizobacteria- Bacillus amyloliquefaciens improves plant growth and induces resistance in chilli against anthracnose disease

The present study was aimed to screen plant growth promoting rhizobacteria (PGPR) for their effect on induction of resistance in chilli (Capsicum annum L.) against anthracnose disease. A total of 59 PGPR were evaluated for their antagonistic activity against Colletotrichum truncatum and only fourteen PGPR were able to inhibit the mycelial growth of the pathogen. The pathogenicity and root colonization of the selected PGPR showed that out of fourteen isolates only eight isolates of Achromobacter, Bacillus, Burkholderia, Enterobacter, Ochrobactrum and Providencia genera were able to be both non-pathogenic and possessed the ability to colonize the host plant. Among the PGPR isolates, seed treatment with Bacillus amyloliquefaciens resulted in maximum enhancement of seed germination (84.75%), seedling vigor (1423.8) along with an increase in vegetative growth parameters. Significant disease protection of 71% against anthracnose disease was observed in plants pretreated with B. amyloliquefaciens followed by B. cepacia and P. rettgeri, under greenhouse conditions. The induced resistance obtained upon PGPR treatment was in line with higher activity of defense enzymes [phenylalanine ammonia lyase (PAL), peroxidase (POX), polyphenol oxidase (PPO) and β-1,3-glucanase]. It was observed that, almost one to two-fold increase in enzyme activities was observed in PGPR treated challenge inoculated seedlings compared to control inoculated seedlings. The results evidenced that the PGPR- B. amyloliquefaciens possesses immense potential to increase the plant growth apart from suppressing anthracnose disease in chilli.