Screening of Multi-Trait Rhizobacteria for Improving the Growth,Enzyme Activities,and Nutrient Uptake of Tea (Camellia sinensis)

The use of plant growth-promoting rhizobacteria (PGPR) as agricultural inputs for increasing crop production needs the selection of efficient bacteria with plant growth-promoting (PGP) attributes. Therefore, the purpose of this study was to evaluate the effects of 20 multi-traits bacteria on tea growth, nutrient uptake, chlorophyll contents, and enzyme activities under field conditions for over 3 years. These isolates were screened in vitro for their PGP traits such as the production of indole acetic acid (IAA), nitrogenase activity, phosphorus (P) solubilization, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. Screening of rhizobacteria that show multiple PGP traits suggests that they stimulated overall plant growth, including shoot development and leaf yield, improving macro- and micro-nutrient uptake, chlorophyll contents, and activities of enzymes of tea plant. Use of strains with multiple PGP traits could be a more effective approach and have great potential for the environmentally-friendly tea production.     

在受控条件下植物促生菌对扁豆的生长，结瘤和养分积累的效应

Application of plant growth-promoting rhizobacteria (PGPR) has been shown to increase legume growth and development under field and controlled environmental conditions. The present study was conducted to isolate plant growth-promoting rhizobacteria (PGPR) from the root nodules of lentil (Lens culinaris Medik.) grown in arid/semi-arid region of Punjab, Pakistan and examined their plant growth-promoting abilities. Five bacterial isolates were isolated, screened in vitro for plant growth-promoting (PGP) characteristics and their effects on the growth of lentil were assessed under in vitro, hydroponic and greenhouse (pot experiment) conditions. All the isolates were Gram negative, rod-shaped and circular in form and exhibited the plant growth-promoting attributes of phosphate solubilization and auxin (indole acetic acid, IAA) production. The IAA production capacity ranged in 0.5-11.0 μg mL-1 and P solubilization ranged in 3-16 mg L-1 . When tested for their effects on plant growth, the isolated strains had a stimulatory effect on growth, nodulation and nitrogen (N) and phosphorus (P) uptake in plants on nutrient-deficient soil. In the greenhouse pot experiment, application of PGPR significantly increased shoot length, fresh weight and dry weight by 65%, 43% and 63% and the increases in root length, fresh weight and dry weight were 74%, 54% and 92%, respectively, as compared with the uninoculated control. The relative increases in growth characteristics under in vitro and hydroponic conditions were even higher. PGPR also increased the number of pods per plant, 1 000-grain weight, dry matter yield and grain yield by 50%, 13%, 28% and 29%, respectively, over the control. The number of nodules and nodule dry mass increased by 170% and 136%, respectively. After inoculation with effective bacterial strains, the shoot, root and seed N and P contents increased, thereby increasing both N and P uptake in plants. The root elongation showed a positive correlation (R2 = 0.67) with the IAA production and seed yield exhibited a positive correlation (R2 = 0.82) with root nodulation. These indicated that the isolated PGPR rhizobial strains can be best utilized as potential agents or biofertilizers for stimulating the growth and nutrient accumulation of lentil.     

Alleviation of drought stress in maize (Zea mays L.) by using endogenous endophyte Bacillus subtilis in North West Himalayas

ABSTRACT

In the present study, we reported the isolation and molecular characterisation of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-producing endophyte and its effect on alleviating drought stress in maize. Ten morphologically distinct indigenous plant growth-promoting rhizobacteria (PGPR) from maize roots and rhizosphere were screened for multiple plant growth-promoting (PGP) traits, and of ten, two strains (DHK and B1N1) possessing maximum PGP traits were evaluated at three water stress regimes in maize: (i) 80% field capacity (FC), (ii) 60% FC, and (iii) 40% FC for 45 days, starting 15 days after sowing to the maturity. Inoculation of DHK strain with maize at 80% FC induced a significant increase in plant biomass (root biomass, 86.67%; shoot biomass, 111.63%) together with decreased reactive oxygen species and increased activity of antioxidant enzymes (superoxide dismutase, 14.11?U/g fresh weight; peroxidase, 1.14?U/g fresh weight and catalase; 14.91?U/g fresh weight) compared to uninoculated control at same water regime (80% FC). The derivative strain also significantly accrued nutrients in maize and enhanced total chlorophyll and amino acid content in comparison with non-inoculated plants. 16S rDNA analysis of DHK strain revealed its lineage to Bacillus subtilis. Present investigations demonstrated the potential of the bacterial partner in alleviating drought stress in maize.     

Rhizobacteria: Influence of cultivar and soil type on plant growth and yield of potato

The influence of potato cultivar and soil type on effectiveness of plant growth-promoting rhizobacteria (PGPR) was examined. Rhizobacteria were isolated from potato roots and tubers obtained from fields with a history of high potato yields. Fluorescent pigment-producing rhizobacteria. identified as strains of Pseudomonas putida and P. fluorescens, were selected for their antibiosis against Erwinia carovotora ssp. carotovora and growth-promoting activity on potatoes. In greenhouse tests, treatments of potato seedpieces and stem cuttings increased shoot dry weight from 1.23- to 2.00-fold and root dry weight from 1.27- to 2.78-fold. Survival of PGPR in the rhizosphere was monitored using antibioticresistant strains. Populations of these strains decreased from 3.6 × 10⁹ cgu g^?1 dry root weight to 4.5 × 10⁵ cfu g^?1 dry root weight 4 weeks after treatment. In field trials, PGPR strains were applied to seedpieces of cultivars Kennebec, Pungo, Red Pontiac and Superior and planted in Cape Fear loam. Plymouth loamy sand or Delanco sandy loam. Significant yield increases of 1.17–1.37-fold over controls were observed in two of three field trials. Variability in plant growth-promoting activity was observed between greenhouse and field trials, and no given treatment combination of PGPR strain, potato cultivar and soil type was consistently better than another.     

抗重金属植物根际细菌的植物促生长特征以及它们对黑芥种子萌发的影响

Phytoremediation is an emerging technology that uses plants and their associated microbes to clean up pollutants from the soil, water, and air. In order to select the plant growth-promoting rhizobacteria(PGPR) for phytoremediation of heavy metal contamination, 60 bacterial strains were isolated from the rhizosphere of two endemic plants, Prosopis laevigata and Spharealcea angustifolia, in a heavy metal-contaminated zone in Mexico. These rhizobacterial strains were characterized for the growth at different pH and salinity, extracellular enzyme production, solubilization of phosphate, heavy metal resistance, and plant growth-promoting(PGP) traits, including production of siderophores and indol-3-acetic acid(IAA). Overall, the obtained rhizobacteria presented multiple PGP traits. These rhizobacteria were also resistant to high levels of heavy metals(including As as a metalloid)(up to 480 mmol L(-1)As(V), 24 mmol L(-1)Pb(Ⅱ), 21 mmol L(-1)Cu(Ⅱ), and 4.5 mmol L(-1)Zn(Ⅱ)). Seven rhizobacterial strains with the best PGP traits were identified as members of Alcaligenes, Bacillus, Curtobacterium, and Microbacterium, and were selected for further bioassay.The inoculation of Brassica nigra seeds with Microbacterium sp. CE3R2, Microbacterium sp. NE1R5, Curtobacterium sp. NM1R1,and Microbacterium sp. NM3E9 facilitated the root development; they significantly improved the B. nigra seed germination and root growth in the presence of heavy metals such as 2.2 mmol L(-1)Zn(Ⅱ). The rhizobacterial strains isolated in the present study had the potential to be used as efficient bioinoculants in phytorremediation of soils contaminated with multiple heavy metals.     

盐条件下产胞外多糖植物促生细菌研究

Salt-tolerant plant growth-promoting rhizobacteria (PGPR) can play an important role in alleviating soil salinity stress during plant growth and bacterial exopolysaccharide (EPS) can also help to mitigate salinity stress by reducing the content of Na + available for plant uptake.In this study,native bacterial strains of wheat rhizosphere in soils of Varanasi,India,were screened to identify the EPS-producing salt-tolerant rhizobacteria with plant growth-promoting traits.The various rhizobacteria strains were isolated and identified using 16S rDNA sequencing.The plant growth-promoting effect of inoculation of seedlings with these bacterial strains was evaluated under soil salinity conditions in a pot experiment.Eleven bacterial strains which initially showed tolerance up to 80 g L -1 NaCl also exhibited an EPS-producing potential.The results suggested that the isolated bacterial strains demonstrated some of the plant growth-promoting traits such as phosphate solubilizing ability and production of auxin,proline,reducing sugars,and total soluble sugars.Furthermore,the inoculated wheat plants had an increased biomass compared to the un-inoculated plants.     

Performance of Pseudomonas spp. containing ACC-deaminase for improving growth and yield of maize (Zea mays L.) in the presence of nitrogenous fertilizer

Some plant-growth-promoting rhizobacteria (PGPR) promote plant growth by lowering the endogenous ethylene synthesis in the roots through their 1-aminocylopropane-1-carboxylate (ACC)-deaminase activity. However, in the vicinity of the roots may decrease the efficiency of these PGPR by stimulating ACC-oxidase activity resulting in greater ethylene production by the roots. This study was designed to assess the performance of PGPR containing ACC-deaminase for improving growth and yield of maize grown in N-amended soil. Several strains of rhizobacteria containing ACC-deaminase were screened for their growth-promoting activity in maize roots under gnotobiotic conditions. Six strains were selected and their effectiveness in soil amended with N at a concentration of 175 kg ha⁻¹ (1050 mg pot⁻¹) was investigated by conducting a pot trial on maize. Significant increases in plant height, root weight and total biomass were observed in response to inoculation. Based upon the results of pot trials, the three most efficient strains were selected and tested in the field for their effectiveness in the presence and absence of N fertilizer. Results of the field trial revealed that the inoculum performed relatively better in the absence of N-fertilizer application. Pseudomonas fluorescens biotype G (N₃) was the most effective strain both in the presence and absence of N fertilizer. Results may imply that even in the presence of optimum levels of nitrogenous fertilizers, inoculation with rhizobacteria containing ACC-deaminase activity could be effective to improve the growth and yield of inoculated plants.     

Diversity and plant growth promoting evaluation abilities of bacteria isolated from sugarcane cultivated in the South of Brazil

Plant growth promoting (PGP) bacteria associated with sugarcane are a promising alternative for the expansion of this crop in Southern Brazil. In this study bacterial strains from different sugarcane fields were isolated to estimate their diversity, to evaluate some of their PGP activities and to use them as inoculant strains in field experiment. Samples of rhizospheric soil, roots, and stems of sugarcane were collected in six Rio Grande do Sul localities. The isolation of bacteria was made in three different N-free media. DNA from each isolate was subjected to nifH or 16S rDNA PCR-RFLP, and to the 16S rDNA partial sequencing. Five hundred and sixteen strains were isolated and several PGP characteristics were analyzed. Shannon index was used to evaluate the bacterial diversity. Indexes varying from 0.94 to 2.46 were obtained. Soil pH and clay were the characteristics most closely related to bacterial diversity. Achromobacter, Agrobacterium, Burkholderia, Gluconacetobacter, and Stenotrophomonas were the most abundant genera. Concerning the PGP activities, indolic compounds production was detected in 368 isolates; 138 isolates were able to solubilize phosphate; and 390 were siderophores producers. The inoculation of sugarcane with Gluconacetobacter diazotrophicus VI27 strain showed a significant increase in the number of sets germinated, in the amount of soluble solids, and in the yield of sugarcane juice compared with the control. As a conclusion, a diverse population of PGP bacteria was found in the sugarcane samples. These bacteria, especially G. diazotrophicus strain VI27, could be used as biofertilizers of sugarcane as well as other cereal crops under controlled conditions to avoid or reduce the use of standard N fertilizers.     

Autochthonous halotolerant plant growth-promoting rhizobacteria promote bacoside A yield of Bacopa monnieri (L.) Nash and phytoextraction of salt-affected soil

Phytoremediation is a promising approach for reclamation of salt-affected soil. Phytoextraction is the most commonly used process, which exploits plants to absorb, immobilize, and accumulate salt in their shoots. In this study, halotolerant plant growth-promoting rhizobacteria (PGPR) were isolated from the rhizosphere of wild grasses growing naturally in salt-affected areas of Lucknow, Uttar Pradesh (India) and were tested for their efficacies of salt-tolerance and plant growth-promoting (PGP) abilities. Based on 16S rRNA sequences, the most efficient halotolerant isolates possessing PGP traits were identified as Pseudomonas plecoglossicida (KM233646), Acinetobacter calcoaceticus (KM233647), Bacillus flexus (KM233648), and Bacillus safensis (KM233652). Application of these isolates as bio-inoculants significantly (P < 0.05) increased the growth and bacoside A yield of a medicinal plant, Bacopa monnieri (L.) Nash, grown on natural salt-affected soil. The phytoremediation of salt-affected soil was evident by the substantial increase in shoot Na⁺:K⁺ ratio of bio-inoculant-treated plants. When compared to un-inoculated control plants, the soil physico-chemical properties of bio-inoculant-treated plants were improved. The shoot and root biomass (fresh and dry weights), soil enzymes, and soil nutrient parameters showed significant positive correlations with the shoot Na⁺:K⁺ ratio. Consequently, the halotolerant PGPR screened in this study could be useful for the reclamation of saline soils concomitant with improved plant growth and bacoside A yield.     

Effect of conjoint application of indigenous PGPR and chemical fertilizers on productivity of maize (Zea mays L.) under mid hills of Himachal Pradesh

The present study was conducted to work out the conjoint application of indigenous PGPR (plant growth promoting rhizobacteria) and chemical fertilizers levels on the productivity of maize (Zea mays L.). Three best PGPR isolates (B1N1, MAT1 and DHK) having maximum PGP (plant growth promoting) traits were screened at different recommended doses (80%, 60% and 40%) of NP (Nitrogen and Phosphorous) under net house conditions, and finally two isolates (B1N1 and MAT1) along with optimum dose i.e. 80% of NP were selected for field experimentation, which was performed for two years consecutively i.e. 2013–2015 under random block design (RBD). Conjoint application of 80% recommended doses of NP with PGPR (B1N1) significantly increased maize yield (11.7%), plant height (12.9%) and biomass (17.9%), over control (100% recommend dose of fertilizer (RDF) of chemical fertilizer). Therefore, the results revealed the potential of indigenous PGPR isolates to supplement about 20% NP fertilizers without hampering the productivity of maize.     

Improvement of yield,yield components and oil quality in sesame (Sesamum indicum L.) by N-fixing bacteria fertilizers and urea

Experiments were conducted in 2009–2010 at the Agricultural and Natural Resources Research Center of Yazd, Iran, to study the effect of nitrogen levels and plant growth-promoting rhizobacteria (PGPR) containing Azotobacter sp. and Azospirillum sp. on seed yield, its components and quality traits of sesame cultivars. Treatments were arranged in a factorial experiment based on randomized complete block design with nitrogen rates (0 (control), 25 and 50 kg N ha^?1), cultivars (Darab-14, GL-13 and local) and N-fixing bacteria levels (non-inoculation and inoculation) were applied with three replications. Nitrogen fertilizer significantly increased yield and yield components, but reduced oil content in 2010. Inoculating seeds with PGPR increased yield and yield components of sesame cultivars compared to the control treatment. Seed yield in PGPR inoculation with half a rate of N fertilizer treatment was more than seed yield in the full rate of N fertilizer without a PGPR inoculation treatment. N fertilizer and PGPR application significantly decreased saturated fatty acids (palmitic and stearic acid) while it significantly increased unsaturated fatty acids (oleic and linoleic acid). Oleic acid had a significant negative correlation with linoleic acid (r = ?0.79). The result showed that an application of PGPR could be usefully applied to reduce use of chemical fertilizer.     

Influence of nitrogen fertilisation on pasture culturable rhizobacteria occurrence and the role of environmental factors on their potential PGPR activities

Plant growth-promoting rhizobacteria (PGPR) naturally occur in the rhizospheres of pasture, but still little is understood regarding how soil agricultural practices affect them. Here, we examined the effects of long-term nitrogen (N) fertilisation on the occurrence of potential culturable PGPR in rhizosphere soils from pastures grown in Chilean Andisols. We also evaluated in vitro the effects of organic acids (citric, malic and oxalic acids), metals (Al and Mn) and N supply (urea and ammonium sulphate) on indole acetic acid (IAA) production and phosphorus (P) liberation by selected strains. Compared with non-N-fertilised pasture, N fertilisation significantly increased (30%) the occurrence of culturable phosphobacteria but decreased (7%) the occurrence of IAA-producing rhizobacteria. Most efficient IAA-producing phosphobacteria were identified as Bacillus, Enterobacter, Pseudomonas and Serratia. At low pH (4.8), the assays showed that the IAA production by Serratia sp. N0-10LB was increased (31–74%) by organic acids. On the other hand, the IAA production by Pseudomonas sp. N1-55PA was increased two- to fivefold by metals. In all strains, the growth and IAA production were significant decreased by 500 μM of Al, except Serratia sp. N0-10LB, suggesting its potential as PGPR for Chilean Andisols. When urea was added as main N source, the bacterial growth and P utilisation significantly increased compared with ammonium sulphate. The influence of environmental factors that are typical of Chilean Andisols on rhizobacterial communities will provide better management practices to enhance their PGPR functions as well as a better selection biofertilisers to be used in Chilean Andisols.     

Study the Effects of Siderophore-Producing Bacteria on Zinc and Phosphorous Nutrition of Canola and Maize Plants

Plant growth-promoting rhizobacteria (PGPR) are soil bacteria that are able to colonize rhizosphere and to enhance plant growth by means of a wide variety of mechanisms. In the present study, Myristica yunnanensis and Stenotrophomonas chelatiphaga strains were recognized as new records in Iran flora. According to the results, these strains significantly affected plants’ zinc and phosphorous contents which could be due to the production of phytosiderophore. Siderophore-producing bacteria increased canola zinc (Zn) content as strategy-I plant, while in maize, it can be said that probably the effect of phytosiderophore produced by plant on increasing root and shoot Zn content was more than siderophore produced by bacteria. These isolates could be used as bio-input for improving the plant productivity as a substitute to chemical fertilizers and also to correct the nutrient deficiencies in canola and maize for sustainable agriculture.     

The endophyte Enterobacter sp. FD17: a maize growth enhancer selected based on rigorous testing of plant beneficial traits and colonization characteristics

With the aim to select powerful microbial strains to be used for the enhancement of maize yield and resistance to abiotic and biotic stresses, we tested five endophytic bacterial strains previously isolated from maize roots. A range of different laboratory assays in regard to potential plant growth promotion was performed and strains were further evaluated for improving growth of five maize cultivars under axenic and natural soil conditions. Endophytic colonization was an additional component in our selection process as it is of high importance for an inoculant strain to efficiently colonize the plant environment. All strains had the potential to improve maize seedling growth under axenic conditions. Enterobacter sp. strain FD17 showed both the highest growth-promoting activity under axenic conditions as well as colonization capacity. FD17 was therefore selected for further plant tests in a net house, in which two different maize cultivars were grown in large pots until ripening and subjected to outdoor climatic conditions. Results showed that inoculation significantly increased plant biomass, number of leaves plant^?1, leaf area, and grain yield up to 39 %, 14 %, 20 %, and 42 %, respectively, as compared to the un-inoculated control. Similarly, inoculation also improved the photochemical efficiency of photosystem II (PSII) of maize plant and reduced the time needed for flowering. We also confirmed that strain FD17 is able to colonize the rhizosphere, roots and stems. Based on rigorous testing, Enterobacter sp. strain FD17 showed the highest potential to promote growth and health of maize grown under natural conditions. This study suggested that in vitro plant growth-promoting traits and potential of maize seedling growth promotion by bacterial endophytes could be used for the selection of potential inoculant strains subjected for further testing as bio-inoculant under field conditions.     

Assessment of the plant growth promotion abilities of six bacterial isolates using Zea mays as indicator plant

Zea mays, one of the most important cereals worldwide, is a plant not only with food and energy value, but also with phytoremediation potential. The use of plant growth promoting (PGP) rhizobacteria may constitute a biological alternative to increase crop yield and plant resistance to degraded environments. In search for PGP rhizobacteria strains, 6 bacterial isolates were isolated from a metal contaminated site, screened in vitro for their PGP characteristics and their effects on the growth of Z. mays were assessed. Isolates were identified as 3A10^T, ECP37^T, corresponding to Chryseobacterium palustre and Chryseobacterium humi, and 1ZP4, EC15, EC30 and 1C2, corresponding to strains within the genera Sphingobacterium, Bacillus, Achromobacter, and Ralstonia, respectively. All the bacterial isolates were shown to produce indole acetic acid, hydrogen cyanide and ammonia when tested in vitro for their plant growth promoting abilities, but only isolates 1C2, 1ZP4 and ECP37^T have shown siderophore production. Their further application in a greenhouse experiment using Z. mays indicated that plant traits such as root and shoot elongation and biomass production, and nutrient status, namely N and P levels, were influenced by the inoculation, with plants inoculated with 1C2 generally outperforming the other treatments. Two other bacterial isolates, 1ZP4 and ECP37^T also led to increased plant growth in the greenhouse. These 3 species, corresponding to strains within the genera Ralstonia (1C2), Sphingobacterium (1ZP4), and to a strain identified as C. humi (ECP37^T) can thus be potential agents to increase crop yield in maize plants.     

Antifungal and Plant Growth Promoting Activities of Indigenous Rhizobacteria Isolated from Maize (Zea mays L.) Rhizosphere

Plant growth promoting rhizobacteria (PGPR) enhance the plant growth directly by assisting in nutrient acquisition and modulating plant hormone levels, or indirectly by decreasing the inhibitory effects of various pathogens. The aim of this study was to select effective PGPR from a series of indigenous bacterial isolates by plant growth promotion and antifungal activity assays. This study confirmed that most of the isolates from maize rhizosphere were positive for PGPR properties by in vitro tests. Azotobacter and Bacillus isolates were better phosphate solubilizers and producers of lytic enzymes, hydrocyanic acid (HCN), and siderophores than Pseudomonas. Production of indole-3-acetic acid (IAA) and antifungal activity were the highest in Azotobacter, followed by Bacillus and Pseudomonas. The most effective Azotobacter isolates (Azt₃, Azt₆, Azt₁₂) and Bacillus isolates (Bac_10, Bac₁₆) could be used as PGPR agents for improving maize productivity. Further selection of isolates will be necessary to determine their efficiency in different soils.     

Enhanced root uptake of acibenzolar-S-methyl (ASM) by tomato plants inoculated with selected Bacillus plant growth-promoting rhizobacteria (PGPR)

The combination of plant growth-promoting rhizobacteria (PGPR) and plant resistance inducers is an alternative crop protection approach in modern agricultural systems. Despite the numerous reports regarding the improved suppression of plant pathogens by their combined application, little is known about the interactions among these components. In the present study, the persistence behavior of the plant activator acibenzolar-S-methyl (ASM) in the rhizosphere of tomato plants and its root uptake as well as systemic translocation ability in aboveground parts after combined use with certain Bacillus PGPR strains (B. amyloliquefaciens IN937a, B. pumilus SE34, B. subtilis FZB24 and GB03) were investigated. Additionally, the population dynamics of the PGPR strain B. subtilis GB03 at the tomato root system and rhizosphere soil applied with or without the pesticide were studied. The results showed that the addition of PGPR inocula did not affect the dissipation rate of ASM in rhizosphere soil. Also, the formation of its major metabolite CGA 210007 in soil was rapid, since it was detected one hour after root drench and it was maintained at high levels during the sampling period without considerable variations among the bacterial treatments compared to the control. The uptake and systemic translocation of ASM and its metabolite CGA 210007 from root to shoot was rapid and maximum concentrations were observed at 48–96 h after its application. It was revealed that in plants treated with the PGPR strains B. subtilis GB03 and B. pumilus SE34 the uptake and systemic translocation of ASM and CGA 210007 in the aerial parts of the tomato plants was significantly higher compared to the control receiving no bacterial treatment. Also, the populations of the strain B. subtilis GB03 showed high colonizing ability in the root system and the rhizosphere soil. PGPR strains that lead to enhanced pesticide uptake by plants should be further evaluated as components in integrated management systems.     

Effect of Indigenous Plant Growth-Promoting Rhizobacteria on Wheat (Triticum Aestivum L.) Productivity and Soil Nutrients

The present study aimed at selection of efficient bacterial isolates with multiple plant growth-promoting (PGP) traits at variable doses of chemical fertilizers for enhanced wheat productivity and sustenance of soil health. Ten bacterial isolates from wheat (rhizosphere soil and root endosphere) were screened for PGP traits (indole acetic acid, phosphate solubilization, siderophore production, and ammonia production). Only three isolates (B2, SIR1, and BIS2) possessed all PGP traits. Net house evaluation of these isolates at graded doses of chemical fertilizers revealed that the potential of B2 isolate is significantly superior for enhancing wheat yield and soil properties. On the basis of 16S rDNA analysis, the potential isolate (B2) was identified as Serratia marcescens. Conjoint use of the B2 isolate at 80% recommended doses of fertilizers (RDF) significantly increased wheat growth and saved 18 kg nitrogen and 10 kg phosphorous on per hectare basis. The developed module not only increases profitability but also protects the environment and sustains soil health.     

Changes in agricultural management drive the diversity of Burkholderia species isolated from soil on PCAT medium

In order to assess the diversity of culturable Burkholderia populations in rhizosphere and bulk soil and to evaluate how different agricultural management regimes and land use history affect this diversity, four treatments were evaluated: permanent grassland; grassland converted into maize monoculture; arable land and arable land converted into grassland. Burkholderia isolates obtained on PCAT medium were grouped in 47 clusters using 16S ribosomal RNA gene based PCR-DGGE combined with BOX genomic fingerprinting (DGGE-BOX). The distribution of the isolates in the DGGE-BOX clusters was used to calculate the Shannon diversity index per treatment. Interestingly, we observed that the Burkholderia diversity was affected by changes in the agricultural management, since the highest diversity was observed in permanent grassland and in continuous arable land. In addition, the diversity tended to be higher in the rhizosphere than in the corresponding bulk soil. The use of species abundance models indicated that rhizosphere communities had more even distributions than communities collected from the bulk soil. Identification of isolates revealed that only 2% of these belonged to the B. cepacia complex and that the majority was assigned to either (1) new Burkholderia species or (2) Burkholderia species that had originally been isolated from soil. Isolates classified as B. hospita, B. caledonica and Burkholderia sp. ‘LMG 22934’ and ‘LMG 22936’ were found mainly in the arable land, while isolates belonging to Burkholderia sp. ‘LMG 22929’ and B. phytofirmans were associated with the grassland area. Another potentially new Burkholderia species, ‘LMG 22932’, was found in both areas, in close association with the maize rhizosphere.     

Phosphate-solubilizing rhizobacteria enhance the growth and yield but not phosphorus uptake of canola (Brassica napus L.)

The ability of phosphate-solubilizing rhizobacteria to enhance the growth and phosphorus uptake of canola (Brassica napus L., cv. Legend) was studied in potted soil experiments in the growth chamber. One hundred and eleven bacteria isolated from the rhizosphere of field-grown plants, and a collection of nine bacteria known to be effective plant growth-promoting rhizobacteria (PGPR), were screened for P-solubilization in vitro. All rhizobacteria were identified using whole-cell fatty acids methyl ester (FAME) profiles. The best P-solubilizing isolates were two Bacillus brevis strains, B. megaterium, B. polymyxa, B. sphaericus, B. thuringiensis, and Xanthomonas maltophilia (PGPR strain R85). The P-solubilizers were tested for their effects on growth and P-uptake of canola plants in a P-deficient soil amended with rock phosphate. Although some of the P-solubilizing rhizobacteria significantly increased plant height or pod yield, none increased P-uptake. The most effective inoculant was a B. thuringiensis isolate which significantly increased the number and weight of pods and seed yield without rock phosphate. Xanthomonas maltophilia increased plant height, whereas the other bacilli increased the number on weight of pods. These results demonstrate the potential use of these P-solubilizing rhizobacteria as inoculants for canola, but indicate that P-solubilization was not the main mechanism responsible for positive growth response. Received: 8 February 1996