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1.
Despite the importance of the rhizosphere for nutrient turnover, little is known about the spatial patterns of organic phosphorus mineralization by plants and by microorganisms in the rhizosphere. Therefore, the distribution of acid and alkaline phosphatase activity and the abundance of bacteria belonging to various bacterial phyla were investigated in the rhizosphere of barley (Hordeum vulgare L.) as dependent on the availability of inorganic P. For this purpose, we conducted a greenhouse experiment with barley growing in inclined boxes that can be opened to the bottom side (rhizoboxes), and applied soil zymography and fluorescence-in situ-hybridization (FISH). Acid phosphatase activity was strongly associated with the root and was highest at the root tips. Due to P fertilization, acid phosphatase activity decreased in the bulk soil, and less strongly in the rhizosphere. Alkaline phosphatase activity, i.e., microbial phosphatase activity was high throughout the soil in the control treatment and was reduced due to inorganic P fertilization especially in the rhizosphere and less strongly in the bulk soil. P-fertilization slightly increased the total number of bacteria in the rhizosphere. Moreover, P-fertilization decreased the abundance of Firmicutes and increased the abundances of Beta- and Gamma-Proteobacteria. The total number of bacterial cells was significantly higher at the root surface than at the root tip and at a distance of 30 μm from the root surface. Our results show that alkaline phosphatase activity decreased more strongly in the rhizosphere than in the bulk soil due to P fertilization, which might be because of greater C deficiency in the bulk soil compared to the rhizosphere. Furthermore, the results indicate a spatial separation between hotspots of acid phosphatase activity and hotspots of bacteria in the rhizosphere of H. vulgare. Taken together, our study shows that bacteria and phosphatase activity were very heterogeneously distributed in soil, and that the effects of P fertilization on phosphatase activity differed strongly between bulk soil and rhizosphere as well as between various zones of the rhizosphere.  相似文献   

2.
Micropropagated sugarcane plants have been used in Brazil for almost three decades. Besides the improvement in plant health, micropropagated sugarcane carries no endophytic plant growth-promoting bacteria. The Brazilian inoculation technology to reintroduce diazotrophic bacteria in micropropagated sugarcane plantlets revealed a synergistic-like effect in PGP-bacteria mixed inoculations. The infection model of single diazotrophic bacteria species in sugarcane was studied in detail, but still many questions remain open. In this study we used a combined fluorescence in situ hybridization (FISH) and a cultivation based approach (MPN) to evaluate the colonization of sugarcane plantlets by mixed inocula. The highest colonization for three out of the five species studied was obtained with a mixed inoculum, when the Azospirillum amazonense showed an increase by almost 100 times in colonization and Herbaspirillum spp. and Burkholderia tropica was determined at 107 cells per gram root fresh weight. All of the inoculated bacterial species could be detected using the FISH probes 12 h after bacterial inoculation. The FISH results confirmed the MPN counts and showed differences in the population numbers and colonization behavior of particular bacterial inoculum strains in the different mixed inocula. A putative antagonistic effect among the inoculated H. seropedicae and H. rubrisubalbicans strains was observed using FISH, as well as the better competitiveness of B. tropica as compared to the A. amazonense strain. The observed data probably reflect also specific interactions with the sugarcane variety used in this particular inoculation system, and may not be generalized as a rule. This is the first study about the competition for sugarcane colonization in a mixed bacterial inoculum.  相似文献   

3.
Arbuscular mycorrhizal (AM) fungi have been shown to induce the biocontrol of soilborne diseases, to change the composition of root exudates and to modify the bacterial community structure of the rhizosphere, leading to the formation of the mycorrhizosphere. Tomato plants were grown in a compartmentalized soil system and were either submitted to direct mycorrhizal colonization or to enrichment of the soil with exudates collected from mycorrhizal tomato plants, with the corresponding negative controls. Three weeks after planting, the plants were inoculated or not with the soilborne pathogen Phytophthora nicotianae growing through a membrane from an adjacent infected compartment. At harvest, a PCR-Denaturing gradient gel electrophoresis analysis of 16S rRNA gene fragments amplified from the total DNA extracted from each plant rhizosphere was performed. Root colonization with the AM fungi Glomus intraradices or Glomus mosseae induced significant changes in the bacterial community structure of tomato rhizosphere, compared to non-mycorrhizal plants, while enrichment with root exudates collected from mycorrhizal or non-mycorrhizal plants had no effect. Our results support that the effect of AM fungi on rhizosphere bacteria would not be mediated by compounds present in root exudates of mycorrhizal plants but rather by physical or chemical factors associated with the mycelium, volatiles and/or root surface bound substrates. Moreover, infection of mycorrhizal or non-mycorrhizal plants with P. nicotianae did not significantly affect the bacterial community structure suggesting that rhizosphere bacteria would be less sensitive to the pathogen invasion than to mycorrhizal colonization. Of 96 unique sequences detected in the tomato rhizosphere, eight were specific to mycorrhizal fungi, including two Pseudomonas, a Bacillus simplex, an Herbaspirilium and an Acidobacterium. One Verrucomicrobium was common to rhizospheres of mycorrhizal plants and of plants watered with mycorrhizal root exudates.  相似文献   

4.
If mycorrhizal formation could be enhanced by co-inoculation with mycorrhiza helper bacteria (MHB) which promote rapid root colonization by specific ectomycorrhizal fungi, this would be of advantage to the poplar forest industry. A number of poplar rhizobacterial strains were isolated from 11 regions of the eastern China. Four of the isolates, SY15, DZ18, HLJ4, and PY10, were characterized as MHB potential strains based on their positive effect on growth of ectomycorrhizal fungi Pisolithus tinctorius (Pers.) and Lactarius insulsus (Fr.). Under greenhouse conditions, one of the bacterial isolate, DZ18, significantly promoted the poplar trees growth and ectomycorrhizal colonization of P. tinctorius and L. insulsus on Populus deltoides Marsh. In contrast, the other three isolates SY15, HLJ4, and PY10 promoted fungal growth in vitro experiments but did not enhance ectomycorrhizal (ECM) formation in the greenhouse experiment. Therefore, it was concluded that DZ18 can be considered as an MHB strain. DZ18 was identified as Bacillus sp. based on morphological, physiological, and biochemical analyses in combination with analysis of 16S rDNA gene sequences.  相似文献   

5.
Com plants were grown in a non‐sterile soil in a greenhouse or in hydroponic culture in a growth chamber. We studied the influence of chitinolytic, pectinolytic, P‐solubilizing bacterial isolates, and a collection of bacterial strains on the development of native vesicular‐arbuscular mycorrhizal (VAM) populations, colonization of roots by the VAM fungus Glomus fasciculatum and their influence on the phosphorus (P) nutrition and growth of plants. As compared with VAM native control, the most potent stimulants for root colonization of soil‐grown plants by the VAM native population was a strain of Agrobacterium radiobacter and isolate H30. All bacteria used significantly supressed shoot fresh weight of mycorrhizal plants (‐13% up to ‐37%), with the exception of Agrobacterium. Under hydroponic conditions, the P‐solubilizing isolate F27 significantly stimulated the intensity of mycorrhiza, the number of arbuscules in roots, and increased both the P concentration and P content in corn shoots (+30% and +35%), than did the VAM fungus alone. Isolate F27 significantly increased shoot dry weight as compared with the mycorrhizal control. The other bacteria did not influence biomass production of corn.  相似文献   

6.
The aim of this study was to evaluate the effect of plant growth promoting bacteria (PGPB) on emergence, growth, physiology, and mineral content of radish under salinity stress. The study was conducted in pot experiments using a mixture of soil: sand (1:1 v: v) under greenhouse conditions. Bacillus subtilis EY2, Bacillus atrophaeus EY6, and Bacillus spharicus GC subgrup B EY30 were isolated in highly salty soils in Upper Coruh Valley in Turkey. Seeds were soaked in the bacterial suspension incubated at 27°C for 2 h. Emergence percentage (EP) was reduced and mean emergence time (MET) raised with sodium chloride (NaCl) solutions. Inoculated seeds displayed greater EP and less MET compared to the non-inoculated ones. Salinity negatively affected growth of radish; however, plant growth promoting bacteria treatments positively affected growth parameters such as fresh weight (278% for shoot, 371% for root) and dry weights (250% for shoot, 422% for root) compared to non-treated plants that were challenged with salt stress. Furthermore, selected bacteria caused an increase in uptake of minerals except sodium (Na) compared to the non-treated controls in both salt stress and salt stress absence. Sodium concentration of plant leaves was increased by salt stress while bacterial inoculation decreased its concentration. Bacterial treatments increased chlorophyll content and decreased electrolyte leakage of plants in saline conditions. Leaf relative water content (LRWC) of plants in the salt stress condition increased with bacterial application, but reduced without bacterial application. The present study suggests that PGPB seed treatments can ameliorate the deleterious effects of salt stress on radish plants and PGPB could offer an economical and simple application to reduce problems of radish production in an Aridisol caused by high salinity.  相似文献   

7.
We performed a controlled experiment with rice seedlings (Oryza sativa L.) growing in Petri dishes on homogeneous nutrient agar containing a simple rhizosphere food web consisting of a diverse bacterial community and a common soil protozoa, Acanthamoeba castellanii, as bacterial grazer. Presence of amoebae increased bacterial activity and significantly changed the community composition and spatial distribution of bacteria in the rhizosphere. In particular, Betaproteobacteria did benefit from protozoan grazing. We hypothesize that the changes in bacterial community composition affected the root architecture of rice plants. These effects on root architecture affect a fundamental aspect of plant productivity. Root systems in presence of protozoa were characterized by high numbers of elongated (L-type) laterals, those laterals that are a prerequisite for the construction of branched root systems. This was in sharp contrast to root system development in absence of protozoa, where high numbers of lateral root primordia and short (S-type) laterals occurred which did not grow out of the rhizosphere region of the axile root. As a consequence of nutrient release from grazed bacteria and changes in root architecture, the nitrogen content of rice shoots increased by 45% in presence of protozoa. Our study illustrates that interactions over three trophic levels, i.e. between plants, bacteria and protozoa significantly modify root architecture and nutrient uptake by plants.  相似文献   

8.
This study aimed to assess the colonization of thermally treated (i.e. torrefied) grass fibers (TGFs), a new prospective ingredient of potting soil. Eleven bacterial strains and one fungus, Coniochaeta ligniaria F/TGF15, all isolated from TGF or its extract after inoculation with a soil microbial community, were tested for their ability to colonize TGF. Surprisingly, none of these bacteria were able to directly colonize TGF either as single inoculants or as a consortium. Furthermore, bacterial persistence or growth in TGF was not improved by the addition of nutrients or a surfactant. Only extensive washing of the substrate, presumably removing bacteriostatic or bactericidal compounds, allowed bacterial growth on the fibers. Strikingly, the fungal strain consistently colonized TGF up to high densities (up to 1010 CFU per g dry TGF). Given the unique capacity of this fungus to degrade toxic compounds including phenols, TGF was colonized with it for different periods of time, after which a consortium of seven selected bacterial isolates was added. Co-presence of the fungus, or 3 and 24 h pre-colonization with it, was insufficient to create a habitable environment for the bacterial consortium. However, fungal pre-colonization of minimally 3 days allowed the bacterial consortium to colonize the TGF at numbers up to 109 to 1010 CFU per g dry substrate. The resultant bacterial community consisted of at least four strains, i.e. Pseudomonas putida 15/TGE5, Serratia plymuthica 23/TGE5, Pseudomonas corrugata 31/TGE5, and Methylobacterium radiotolerans 56/TGF10, as shown by PCR of colonies on plates and PCR–DGGE profiling. Two persisters, S. plymuthica 23/TGE5 and P. corrugata 31/TGE5, were highly antagonistic towards several phytopathogenic fungi. Thus, a microbial community with plant-beneficial potential was established on TGF, provided that the fungus C. ligniaria F/TGF15 first creates habitable space in the matrix.  相似文献   

9.
Thirty-nine endophytic bacterial strains were isolated from the nodule of Lespedeza sp. grown in two different locations of South Korea. All strains were checked for their plant growth promoting (PGP) abilities under in vitro conditions. Most of the isolates showed multiple PGP activity, i.e., indole acetic acid production, ACC deaminase activity, siderophore production, and phosphate solubilization. The strains were identified by using 16S rRNA gene sequence analysis as belonging to Alphaproteobacteria, Betaproteobacteria, Actinobacteria, and Firmicutes phylum with nine different genera Arthrobacter, Bacillus, Bradyrhizobium, Burkholderia, Dyella, Methylobacterium, Microbacterium, Rhizobium, and Staphylococcus. Gene nodA amplification showed positive results only for strains from Bradyrhizobium and Rhizobium genera. The strains from Bradyrhizobium and Rhizobium genera enhanced plant growth, nodulation, and acetylene reduction activity when inoculated on Vigna unguiculata L. (cowpea), whereas other strains did not induce nodule formation but enhanced plant growth. Herbaceous legume Lespedeza sp. formed root nodules with diverse bacterial group, and probably, these bacteria can be used for stimulating plant growth.  相似文献   

10.
Several Zn-tolerant bacterial strains were isolated from heavy-metal contaminated sludge, and their effects on root elongation, mobility, and accumulation of Zn in Orychophragmus violaceus were studied. The isolated strains included Bacillus subtilis, B. cereus, Flavobacterium sp. and Pseudomonas aeruginosa which were capable of stimulating root elongation in O. violaceus seedlings either in the presence or absence of Zn. The four bacterial strains significantly increased the concentration of water-extractable Zn compared with axenic soil. In addition, the four Zn-tolerant bacteria significantly increased the shoot biomass and Zn accumulation in O. violaceus compared to non-inoculated plants. The bacterial strains displayed different capacities to enhance plant Zn accumulation. Flavobacterium sp. was identified as the best candidate for enhancing Zn accumulation in plants, increasing Zn accumulation up to 1.21- and 1.19-fold in shoots and roots, respectively, compared to non-inoculated plants. It was indicated that Zn-tolerant bacteria played an important role in influencing the availability of water-soluble Zn in soil and Zn accumulation by plants. This study provides insight into the development of plant–microbe systems for phytoremediation.  相似文献   

11.
Two strains of Gluconacetobacter diazotrophicus (Pal 5, UAP5541) and the arbuscular mycorrhizal fungus Glomus intraradices increased both the shoot and root dry weight of sorghum 45 days after inoculation, whereas they had no effect on the shoot and root dry weight of maize. Co-inoculation (Gluconacetobacter diazotrophicus plus Glomus mosseae) did not increase the shoot and root dry weight of either plant. There was a synergistic effect of Gluconacetobacter diazotrophicus on root colonization of maize by Glomus intraradices, whereas an antagonistic interaction was observed in the sorghum root where the number of Gluconacetobacter diazotrophicus and the colonization by Glomus intraradices were reduced. Plant roots inoculated with Gluconacetobacter diazotrophicus and Glomus intraradices, either separately or together, significantly increased root endoglucanase, endopolymethylgalacturonase and endoxyloglucanase activities. The increase varied according to the plant. For example, in comparison with non-inoculated plants, there were higher endoglucanase (+328%), endopolymethylgalacturonase (+180%) and endoxyloglucanase (+125%) activities in 45-day old co-inoculated maize, but not in 45-day old sorghum. The possibility is discussed that hydrolytic enzyme activities were increased as a result of inoculation with Gluconacetobacter diazotrophicus, considering this to be one of the mechanisms by which these bacteria may increase root colonization by AM fungi.  相似文献   

12.
The effect of the plowing of clubbed roots of cracifers on the population of Plasmodiophora brassicae in soil was quantitatively studied by measuring the number of resting spores produced in the diseased plants. Though the mean number of resting spores per diseased plant increased with the increase of the disease severity, it remained almost identical for the disease severity classified into category 3 among host species and cultivars tested. Mean number of resting spores per diseased plant ranged from 9.3 to 10.9 (log) regardless of the value of the disease index. When the number of resting spores in soil was calculated based on these data and plant cultivation methods, the values were equivalent to 4.8-6.4 resting spores g-1soil (log)where clubroot disease occurred severely. The value of the disease index of Chinese cabbage plants grown in the pots where clubbed roots of initially grown plants had been plowed into soil (plowing plot) was higher than that in the pots where no plants had been grown (control plot) and where the clubbed roots of initial plants had been removed (removal plot). Though the number of resting spores of P. brassicae in soil decreased by 14% of the inocoKum concentration immediately after the inoculation, the number of spores after the first cultivation in the removal plot was similar to that in the control plot. On the other hand, the number of resting spores in the plowing plot increased significantly compared with that in the control plot. The plowing of clubbed roots into soil resulted in the increase of the population of P. brassicae and disease severity of clubroot in subsequent cultivation in the field. The results corresponded to the values estimated based on the number of resting spores in soil in relation to each value of the disease index.  相似文献   

13.
《Applied soil ecology》2006,31(1-2):91-100
Field trials were conducted in Florida on bell pepper (Capsicum annuum) to monitor the population dynamics of two plant growth-promoting rhizobacteria (PGPR) strains (Bacillus subtilis strain GBO3 and Bacillus amyloliquefaciens strain IN937a) applied in the potting media at seeding and at various times after transplanting to the field during the growing season. In-field drenches of an aqueous bacterial formulation were used for the mid-season applications. The effects of the applied PGPR and application methods on bacterial survival, rhizosphere colonization, plant growth and yield, and selected indigenous rhizosphere microorganisms were assessed. The Gram-positive PGPR applied to the potting media established stable populations in the rhizosphere that persisted throughout the growing season. Additional aqueous applications of PGPR during the growing season did not increase the population size of applied strains compared to treatments only receiving bacteria in the potting media; however, they did increase plant growth compared to the untreated control to varying degrees in both trials. Most treatments also reduced disease incidence in a detached leaf assay, indicating that systemic resistance was induced by the PGPR treatments. However, treatments did not result in increased yield, which was highly variable. Application of the PGPR strains did not adversely affect populations of beneficial indigenous rhizosphere bacteria including fluorescent pseudomonads and siderophore-producing bacterial strains. Treatment with PGPR increased populations of fungi in the rhizosphere but did not result in increased root disease incidence. This fungal response to the PGPR product was likely due to an increase in nonpathogenic chitinolytic fungal strains resulting from the application of chitosan, which is a component of the PGPR formulation applied to the potting media.  相似文献   

14.
Abstract

Seedlings of Brassica oleracea were infected by the pathogenic fungus Plasmodiophora brassicae. causing clubroot formation. Proteins from healthy roots and clubroots were extracted by two different methods and analysed by two-dimensional gel electrophoresis. Host-proteins induced during clubroot infection were not analysed, since the fungus was always present in the infected roots. This work showed that several proteins present in non-infected roots were lost or strongly reduced in the infected roots.  相似文献   

15.
This study was conducted with sugar beet in greenhouse and field at two soil type with different organic matter (containing 2.4 and 15.9% OM, referred as the low- and high-OM soil) conditions in order to investigate seed inoculation of sugar beet, with five N2-fixing and two phosphate solubilizing bacteria in comparison to control and mineral fertilizers (N and P) application. Three bacterial strains dissolved P; all bacterial strains fixed N2 and significantly increased growth of sugar beet. In the greenhouse, inoculations with PGPR increased sugar beet root weight by 2.8-46.7% depending on the species. Leaf, root and sugar yield were increased by the bacterial inoculation by 15.5-20.8, 12.3-16.1, and 9.8-14.7%, respectively, in the experiment of low- and high-OM soil. Plant growth responses were variable and dependent on the inoculants strain, soil organic matter content, growing stage, harvest date and growth parameter evaluated. The effect of PGPR was greater at early growth stages than at the later. Effective Bacillus species, such as OSU-142, RC07 and M-13, Paenibacillus polymyxa RC05, Pseudomonas putida RC06 and Rhodobacter capsulatus RC04 may be used in organic and sustainable agriculture.  相似文献   

16.
A total of 45 cyanobacterial strains isolated from rice fields near Loktak Lake in Manipur, India were tested for their rice root colonization capacity under light and under darkness. Twenty-one of these strains showed significant colonization of rice roots. The average colonization values were 637 and 381?μg chl a g?1 root dry wt in N2 medium and 792 and 451?μg chl a g?1 root dry wt in NO 3 ? medium under light and darkness, respectively. Thus, while the colonization was higher under light and in NO 3 ? medium, there was significant level of colonization under darkness in N2 medium (381?μg chl a g?1 root dry wt). A 16S rRNA gene fragment-based denaturing gradient gel electrophoresis analysis revealed difference in the competence of individual strains to colonize rice roots exposed to individual or mixed population. The colonization pattern of seven strains used in competition experiments was found to be biphasic. A 16S rRNA gene-based phylogenetic analysis revealed high level of molecular similarity among strains of Nostoc and Anabaena.  相似文献   

17.
Paenibacillus polymyxa P2b-2R is a bacterium that originated from internal lodgepole pine (Pinus contorta var. latifolia (Dougl.) Engelm.) seedling stem tissue and fixes nitrogen (N) in association with pine and western red cedar (Thuja plicata Donn.). To evaluate endophytic colonization by this microorganism, we generated P. polymyxa P2b-2Rgfp, a green fluorescent protein (GFP)-labeled derivative of P2b-2R, and grew pine seedlings that were inoculated with the marked strain in a N-limited soil. Tissue disintegration during sample preparation precluded examination of needles for the GFP-labeled endophyte but GFP was detected on roots and in stems of 2- to 14-week-old pine seedlings using confocal laser scanning microscopy. Due to excessive autofluorescence of seedling tissues, labeled bacteria were clearly discernible only in stem tissues of 4- and 6-week-old seedlings. P2b-2Rgfp colonized the root surface extensively and was detected inside the stem cortex, primarily intracellularly. Some labeled bacteria appeared to contain endospores and none were detected in vascular tissues. We conclude that P. polymyxa P2b-2R is capable of endophytic colonization of pine seedlings with specific colonization sites that include the stem cortex but that GFP labeling is of limited value for localization of endophytic bacteria in pine seedling tissues.  相似文献   

18.
恶臭假单胞菌P861(Gus)在油菜根部定殖的生态研究   总被引：3，自引：0，他引：3  
本研究采用Gus 基因标记技术和常规方法跟踪考察了恶臭假单胞菌P861(Gus) 在缩影系统油菜根圈的定殖情况,以及缩影系统内土壤类型、土壤含水量对根部定殖的影响。土壤含水量分别为60% FC和75% FC时,P861(Gus) 在砂姜黑土中的定殖水平高于50% FC的,不但能散布至种子下8cm 以内的根段部位,且定殖水平分别为7.5×102和2.8×103cfu·g-1。在灰潮土缩影中,P861(Gus) 在油菜根圈的定殖动态表现为在油菜播种后3 ～6 天,定殖密度可达最高水平(5.5×106cfu·g-1) ,然后急速下降,最后保持在一个相对稳定的较低水平(7.6×102cfu·g-1) 。P861(Gus) 在不同根段部位的定殖密度并无从上到下逐渐递减的规律。  相似文献   

19.
Two indole-producing Paenibacillus species, known to be associated with propagules of arbuscular mycorrhizal (AM) fungi, were examined for their mycorrhization helper bacteria activity at pre-symbiotic and symbiotic stages of the AM association. The effects were tested under in vitro and in vivo conditions using an axenically propagated strain of the AM fungus Glomus intraradices and Glycine max (soybean) as the plant host. The rates of spore germination and re-growth of intraradical mycelium were not affected by inoculation with Paenibacillus strains in spite of the variation of indole production measured in the bacterial supernatants. However, a significant promotion in pre-symbiotic mycelium development occurred after inoculation of both bacteria under in vitro conditions. The Paenibacillus rhizosphaerae strain TGX5E significantly increased the extraradical mycelium network, the rates of sporulation, and root colonization in the in vitro symbiotic association. These results were also observed in the rhizosphere of soybean plants grown under greenhouse conditions, when P. rhizosphaerae was co-inoculated with G. intraradices. However, soybean dry biomass production was not associated with the increased development and infectivity values of G. intraradices. Paenibacillus favisporus strain TG1R2 caused suppression of the parameters evaluated for G. intraradices during in vitro symbiotic stages, but not under in vivo conditions. The extraradical mycelium network produced and the colonization of soybean roots by G. intraradices were promoted compared to the control treatments. In addition, dual inoculation had a promoting effect on soybean biomass production. In summary, species of Paenibacillus associated with AM fungus structures in the soil, may have a promoting effect on short term pre-symbiotic mycelium development, and little impact on AM propagule germination. These findings could explain the associations found between some bacterial strains and AM fungus propagules.  相似文献   

20.
Colonization behaviour of two enterobacterial strains on cereals   总被引：4，自引：0，他引：4  
 Two diazotrophic enterobacterial strains, Pantoea agglomerans D5/23 and Klebsiella pneumoniae CC12/12, were observed in sterile and non-sterile hydroponic and soil experiments in order to determine, by means of an immunological detection method (double antibody sandwich enzyme linked immunosorbent assay), their colonization sites, their migration within individuals of different plant species, and their ability to compete with indigenous organisms. To investigate the interaction between bacteria and plants, root and shoot samples were analysed using electron microscopy. Field experiments were performed to determine the growth-promoting abilities of the bacterial strains. In field experiments, inoculation with P. agglomerans led to an increase in the grain yield of different wheat (Triticum aestivum) cultivars. The same strain was also able to colonize the rhizosphere and the phyllosphere of different cereals due to its ability to migrate within the plant. Roots and media were colonized 10–100 times more intensively than shoots, with about 106 cells g–1 root and 104 cells g–1 shoot. We found that P. agglomerans colonized the root and plant-growth medium of wheat to a greater extent than those of rye (Secale cereale) and barley (Hordeum vulgare), whereas the colonization of shoots was higher in rye and barley compared to wheat. Furthermore, while cell numbers of K. pneumoniae in media and roots were 10 times higher than cell numbers of P. agglomerans, only the latter markedly increased root growth. We were able to detect significant differences in colonization numbers between treatments even if the data were not normally or log-normally distributed or the variances were not homogenous. Received: 14 June 1999  相似文献   

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