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1.
The antimicrobial metabolites 2,4-diacetylphloroglucinol (2,4-DAPG) and pyoluteorin contribute to the ability of Pseudomonas fluorescens strain CHA0 to control plant diseases caused by soil-borne pathogens. P. fluorescens strain CHA0 and its derivatives CHA89 (antibiotics-deficient) and CHA0/pME3424 (antibiotics overproducing) were investigated as potential biocontrol agents against Meloidogyne javanica the root-knot nematode. Exposure of root-knot nematode to culture filtrates of P. fluorescens under in vitro conditions significantly reduced egg hatch and caused substantial mortality of M. javanica juveniles. Nutrient broth yeast extract (NBY) medium amended with 2% (w/v) glucose or 1 mM EDTA markedly repressed hatch inhibition activity of the strain CHA0 but not that of CHA0/pME3424 or CHA89. On the other hand, NBY medium amended with glucose significantly enhanced nematicidal activity of the strain CHA0/pME3424. Neither glucose nor EDTA had an influence on the nematicidal activity of the strains CHA0 and CHA89. Under in vitro conditions, antibiotic overproducing strain CHA0/pME3424 and CHA0 expressed phl‘-’lacZ reporter gene but strain CHA89 did not. Expression of the reporter gene reflects actual production of DAPG. In general, CHA0/pME3424 expressed reporter gene to a greater extent compared to its wild type counterpart CHA0. Regardless of the bacterial strains, reporter gene expression was markedly enhanced when NBY medium was amended with glucose but EDTA had no such effect. A positive correlation between the degree of juvenile mortality and extent of phl‘-’lacZ reporter gene expression was also observed in vitro. Strain CHA0 produced zones of 4-6 mm on MM medium containing gelatin while strain CHA0/pME3424 and CHA89 did not. When MM medium containing gelatin was amended with 2% glucose of 1 mM EDTA size of haloes produced by the strain CHA0 reduced to 2 mm. Under glasshouse conditions aqueous cell suspension of the strains CHA0 or CHA0/pME3424 at various inoculum levels (107, 108 or 109 cfu ml−1) significantly reduced root-knot development. CHA89 caused significant reduction in galling when applied at 109 cfu ml−1. To better understand the mechanism of nematode suppression, split root bioassay was performed. Split-root experiments, that guarantee a spatial separation of inducing agent and a challenging pathogen, showed that soil treatment of one half of the root system with cell suspension of CHA0 or CHA0/pME3424 resulted in a significant systemic induced resistance leading to reduction of M. javanica infection of tomato roots in the non-baterized nematode treated half. The results clearly suggest that the antibiotic 2,4-DAPG from P. fluorescens CHA0 act as the inducing agents of systemic resistance in tomato roots. Populations of CHA0 and its derivatives declined progressively by 10-fold between first and fourth harvests (0-21 days after inoculation). However, bacterial populations increased at final harvest (28 days after application).  相似文献   

2.
Although often neglected, variability in cell lysis efficiency and DNA extraction yield represents the major hurdles of any polymerase chain reaction (PCR)-based quantification protocol in soil and other natural environments. In this study we developed a technique that minimizes the effects of these constraints, providing at the same time a reliable internal control to distinguish between PCR-inhibition and negative results. We used Pseudomonas fluorescens Pf153, a root-colonizing bacterium that shows biocontrol activity against tobacco and cucumber black root rot, as the target organism for PCR quantification. Prior to DNA extraction, the genetically engineered, cognate reference strain P. fluorescens CHA0/c2 was inoculated in a reference soil. CHA0/c2 in the reference soil and Pf153 in the soil sample were lysed in parallel and afterward the lysates were mixed in known proportions. CHA0/c2 carries the plasmid pME6031-cmp2 that contains an allelic variant (competitor) of the Pf153 specific sequence Pf153_2. In a quantitative competitive PCR (QC-PCR) assay the competitor allows the quantification of the target strain down to 0.66 Pf153 CFU/mg soil. Processing the reference strain in the same way as Pf153 enables the exact quantification of the target strain in biocontrol assays performed in natural soil, overcoming differences in DNA extraction efficiency and PCR amplification from different soil environments. This technique is easily adaptable to other Pseudomonas strains simply by replacing the competitor used here with one derived from a SCAR-marker which is specific for the strain of choice.  相似文献   

3.
Pseudomonas strains may be used as alternatives to fungicides as some of them produce secondary metabolites, which can inhibit growth of plant pathogenic fungi. Increased knowledge of non-target effects of the antagonistic bacteria on other soil organisms as well as of the survival and predation resistance of the antagonistic bacteria is necessary for risk assessment and increased performance of antagonistic bacteria as biological control agents. In the present study, we aimed to investigate the difference between Pseudomonas spp. with respect to their predation resistance to and effects on the three different and common soil flagellates Bodo caudatus, Cercomonas longicauda, and Neocercomonas jutlandica. Two antagonistic Pseudomonas: Pseudomonas fluorescens CHA0 and P. fluorescens DR54 and two positive control strains: P. fluorescens DSM 50090T and Pseudomonas chlororaphis ATCC 43928 were studied. CHA0, which is reported to produce a range of different antibiotic substances, was inhibitory to all the tested flagellates whereas DR54, which produces viscosinamide, only inhibited the growth rate of B. caudatus. Removal of spent medium from a CHA0 culture reduced the growth inhibition of C. longicauda, although the growth rate was still lowered compared with DSM 50090T. In contrast, removal of spent medium from a DR54 culture had minor effect on C. longicauda. The flagellate B. caudatus was far more sensitive towards the antagonistic Pseudomonas strains of the tested flagellates.  相似文献   

4.
The acid tolerance of Sinorhizobium meliloti in culture media and in soils is considered a useful criteria to select for strains with improved survival in agricultural acidic soils. Using a glass tube system with gamma-irradiated soil at different pH values, we analysed the survival of two different alfalfa-nodulating rhizobia: S. meliloti (pHlimit for growth 5.6–6.0) and the acid-tolerant Rhizobium sp. LPU83, closely related to the strain Rhizobium sp. Or191 (pHlimit for growth below 5.0). Although the acid-tolerant rhizobia showed a slightly better survival during the first months in acid soil (pH=5.6), none of the strains could be detected 2 months after inoculation (bacterial counts were below 103 colony-forming units (cfu)/30 g of soil). The inclusion of two alfalfa plants/glass tube with soil, however, supported the persistence of both types of rhizobia at pH 5.6 for over 2 months with counts higher than 9×106 cfu/30 g of soil. Remarkably, in the presence of alfalfa the cell densities reached by S. meliloti were higher than those reached by strain LPU83, which started to decline 1 week after inoculation. Although more acid-sensitive in the culture medium than the Or191-like rhizobia, in the presence of the host plant the S. meliloti strains showed to be better adapted to the free-living condition, irrespective of the pH of the soil.  相似文献   

5.
Plant growth-promoting rhizobacteria (PGPR) strains CHA0 (Pseudomonas fluorescens), IE-6 S+ (Pseudomonas aeruginosa) and 569Smr (Bradyrhizobium japonicum) were tested singly and in combinations for biological control against multiple tomato pathogens (root-infecting fungi and root-knot nematodes). Strains CHA0 and IE-6S+ inhibited in vitro growth of 569Smr while IE-6S+ suppressed CHA0. The bacterial species not only inhibited the radial growth of three root-infecting fungi, Macrophomina phaseolina, Fusarium solani and Rhizoctonia solani (AG 8), but also caused substantial mortality of Meloidogyne javanica juveniles. Used as a soil drench the three bacteria not only suppressed root-infecting fungi and root-knot nematodes but also enhanced growth of tomato plants both under glasshouse and field conditions. The suppressive effect was generally more pronounced when the bacteria were employed together. Strain IE-6S+ exhibited better rhizosphere colonization than CHA0 and 569Smr. Populations of CHA0 in the rhizosphere declined when the bacterium was used with either IE-6S+ and/or 569Smr, while populations of IE-6S+ in the rhizosphere were enhanced when used in combination with CHA0 and/or 569Smr. IE-6S+ was the only bacterium that colonized inner root tissues of tomato plants. When using an iron chelator to create iron deficiency in the soil, the biocontrol efficacy of the bacteria against F. solani and R. solani was enhanced while against M. phaseolina and M. javanica this activity remained unchanged. Only strain 569Smr gave significant suppression of M. phaseolina in both iron-deficient and iron-sufficient soils.  相似文献   

6.
Survival of inoculated rhizosphere bacteria and their influence on native bacterial populations in the rhizosphere of alfalfa The survival of inoculated bacteria and their influence on native bacterial populations in the rhizosphere of alfalfa were investigated in a greenhouse experiment. The plant growth promoting strains Rhizobium meliloti me18 and Pseudomonas fluorescens PsIA12 were reisolated from the rhizosphere about 7 weeks after single and mixed strain inoculation. They did not induce lasting changes in the diversity of the native bacterial communities of the rhizosphere. Only within the first week after inoculation was an increase in total bacterial abundance observed. In general, the diversity of bacterial communities increased with plant age and with proximity to the root tip.  相似文献   

7.
The symbiotic nitrogen-fixing soil bacterium, Sinorhizobium meliloti, is well known for its ability to interact with the leguminous plant Medicago sativa L. It has, however, not been reported that this species possesses the capability to degrade toxic nitroaromatic compounds, such as 2,4-dinitrotoluene (DNT) which is commonly associated with the degradation of the explosive trinitrotoluene (TNT). In this study, the pJS1 DNT-biodegradative plasmid was genetically transferred to S. meliloti strain USDA 1936, which was confirmed by plasmid profile analysis. Several standard analytical and chemical tests including high performance liquid chromatography (HPLC), nitrite (NO2) release assays, rhizosphere population and plant greenhouse studies were conducted to test the ability of S. meliloti to degrade 2,4-DNT. The possible presence of 2,4-DNT remaining in the treated soil was tested, and no 2,4-DNT had been absorbed by the soil. The pJS1-carrying recombinant strain DHK1 produced ‘ARC’ alfalfa plants that were almost 2-fold higher in shoot dry weight than that produced by the parent strain on soil containing 0.14 mM 2,4-DNT. The transconjugant strain DHK1 reduced significantly one-third more 2,4-DNT in both 0.14 and 0.28 mM contaminated soil, and in 0.55 mM contaminated soil it degraded 94% of the 2,4-DNT present. In liquid cultures, however, only about 4% reduction in 2,4-DNT concentrations was obtained in 10 days. We interpret the results as clearly establishing that genetic modification was successfully used, for the first time, to improve the capability of the symbiotic nitrogen-fixing soil bacterium S. meliloti DHK1 to bioremediate in situ 2,4-DNT-contaminated soil in the presence of alfalfa plants.  相似文献   

8.
Repetitive extragenic palindromic (REP)-PCR and enterobacterial repetitive intergenic consensus (ERIC)-PCR analysis was applied to the identification and classification of local isolates of 44 Bradyrhizobium japonicum, 7 Sinorhizobium meliloti, 10 Rhizobium leguminosarum strains from Japan and Thai. Using genomic DNA of the 61 strains, both REP and ERIC primers induced reproducible PCR band patterns, although REP-PCR generated more bands and appeared to be more useful for distinguishing the isolates from each other. Using mixed matrix data from both REP- and ERIC-PCR data, it become possible to distinguish all the isolates analyzed in this experiment from each other. When cluster analysis was applied to both PCR matrix data of 44 B. japonicum isolates, only the REP-PCR dendrogram showed a grouping profile corresponding to the exo-polysaccharide phenotype with a exceptions. When the matrix data of R. leguminosarum and S. meliloti were subjected to cluster analysis, S. meliloti appeared to form a different subgroup from R. leguminosarum in the dendrogram of REP-PCR data except for one strain. In the case of ERIC-PCR, isolates of R. leguminosarum from northern Thailand formed a separate subgroup from other R. leguminosarum and S. meliloti which were dispersed in the dendrogram. These data suggest that REP-PCR and ERIC-PCR were effective for the identification of individual isolates even though the isolates showed a wide genetic diversity and the same phenotype. When the data of the local isolates from Japan and Thailand were subjected to cluster analysis, REP- and ERIC-PCR analysis revealed different grouping characteristics.  相似文献   

9.
 Rhizobium "hedysari" HCNT1 and Sinorhizobium meliloti 41 were investigated and compared for their ability to shift from a typical aerobic, growth-supporting metabolism to O2–limiting, low-energy-expending, basal activities. Such metabolic conversion leads bacteria to stop reproduction although allows them to survive. Once anaerobic, both rhizobia started to consume their internal energy budget and most of the cells remained metabolically active for a long time, as revealed by microscope-based analyses. However, although R. "hedysari" HCNT1 also maintained the same number of culturable cells, S. meliloti 41 started to reduce this number almost immediately when anaerobic incubation took place. In the presence of NO2 – the ability of R. "hedysari" HCNT1 to restore normal growth reduced drastically. A mutant strain, previously obtained by inactivation of the gene encoding nitrite reductase (nirK), did not burn up internal adenosine triphosphate when exposed to the same O2–limiting conditions in the presence of NO2 –. This finding indicated that NO2 –-reduction activity in the wild type strain, HCNT1, results in a decrease in cell energy content and culturability. Therefore, R. "hedysari" HCNT1 and S. meliloti 41 follow different paths to reduce the internal energy pool towards the so-called viable-not-culturable state that can be reached within a relatively large interval of internal energy charge, depending upon the bacterial strain. Received: 25 May 1999  相似文献   

10.
We have evaluated the genetic diversity and phylogeny of alfalfa rhizobia, originating from different types of soils in Serbia and their ability to establish an effective symbiosis with alfalfa (Medicago sativa L.). A collection of 65 strains isolated from root nodules of alfalfa were characterized by rep-PCR analysis, partial and complete 16S rDNA gene and recA gene sequencing, as well as atpD gene sequencing and DNA–DNA hybridizations. The results of the sequence analyses revealed that Sinorhizobium meliloti is the dominant species in alfalfa nodules. Only one strain was identified as Sinorhizobium medicae, two strains as Rhizobium tibeticum and one strain as Rhizobium sp. Despite the fact that the majority of strains were identified as S. meliloti, a high genetic diversity at strain level was detected. Almost all isolates shared the ability to nodulate and fix nitrogen with M. sativa, except 11 of them, which were incapable of fixing nitrogen with this species. About 50% of the isolates showed values of symbiotic effectiveness (SE) above 50%, while 10% of the strains were highly effective with SE values above 70%. Some of the strains which were highly effective in nitrogen fixation at the same time could intensively solubilize phosphates, offering a possibility for multipurpose inoculum development. This was the first genetic study of rhizobia isolated from this region and also the first report of natural presence of R. tibeticum in root nodules of M. sativa.  相似文献   

11.
The impact of ectomycorrhizal fungi or rhizosphere bacteria on tree seedling growth and nutrient uptake is well known. However, few studies have combined those microorganisms in one experiment to clarify their relative contribution and interactions in nutrient acquisition. Here, we monitored the respective contributions of pine roots, two ubiquitous forest ectomycorrhizal fungi Scleroderma citrinum and Laccaria bicolor, and two S. citrinum-mycorrhizosphere bacterial strains of Burkholderia glathei and Collimonas sp., on mineral weathering, nutrient uptake, and plant growth. Pinus sylvestris plants were grown on quartz–biotite substrate and inoculated or not with combinations of mycorrhizal fungi and/or bacterial strains. Magnesium and potassium fluxes were measured and nutrient budgets were calculated. Both ectomycorrhizal fungi significantly increased Mg plant uptake. No significant effects of the two bacterial strains were detected on the K and Mg budgets, but co-inoculating the mycorrhizal fungus S. citrinum and the efficient mineral-weathering B. glathei bacterial strain significantly improved the Mg budget. Similarly, co-inoculating S. citrinum with the Collimonas sp. bacterial strain significantly improved the pine biomass compared to non-inoculated pine plants. In order to better understand this process, we monitored the survival of the inoculated bacterial strains in the quartz–biotite substrate, the pine rhizosphere, and the mycorrhizal niche. The results showed that the two bacterial strains harboured different colonization behaviours both of which depended on the presence of the ectomycorrhizal partner. The populations of the Burkholderia strain were maintained in all these environments with a significantly higher density in the mycorrhizal niche, especially of S. citrinum. In contrast the population of the Collimonas strain reached the detection level except in the treatment inoculated with S. citrinum. These results highlight the need for taking into account the ecology of the microorganisms, and more specifically the fungal–bacterial interactions, when studying mineral weathering and plant nutrition.  相似文献   

12.
Two strains of Rhizobium meliloti and one of R. japonicum were grown in broth adjusted to selected water activities (aw) using KCl, NaCl, LiCl or glycerol. The optimum doubling time for R. meliloti RCR 2011 of 2.5 h (at aw 0.999) was not affected but the yield at the stationary phase was decreased by a reduction of the aw to 0.99. Regardless of the solute used, as the aw was reduced below 0.99 growth rates and yields decreased and lag times were lengthened. The extent to which these responses changed depended on the solute used to lower the aw. Lag times were affected most when LiCl, NaCl and KCl were used to lower aw below 0.9866. No growth occurred at aw 0.969 when NaCl or KCl were used but consistent growth did occur at this aw when glycerol or LiCl were employed. In contrast with these results, LiCl was more toxic than NaCl for the slow-growing R. japonicum 5. This strain was susceptible to aw 0.9840 (glycerol).Prior growth of R. meliloti RCR 2011 and 1.5 in media of lowered aw improved the tolerance of strain RCR 2011 but not of strain 1.5 to desiccation (0% relative humidity).The growth stage of R. meliloti RCR 2011 affected the survival of this strain during storage at different r.h. values. When subjected to drought stress, stationary phase cells survived better than cells collected at three different times during the exponential growth phase.The optimum r.h. value for storage of R. meliloti strain RCR 2011 was within the range 22–43%.Extracellular polysaccharides provided protection against storage at 0% r.h. but their presence was detrimental during storage in semi-dried states.  相似文献   

13.
 The effect of cucumber roots on survival patterns of the biocontrol soil inoculant Pseudomonas fluorescens CHA0-Rif was assessed for 22 days in two non-sterile soils, using a combination of total immunofluorescence cell counts, Kogure's direct viable counts and colony counts on plates containing rifampicin. In Eschikon soil (high fertility status for cucumber), CHA0-Rif persisted as culturable cells in bulk soil and in the rhizosphere, but colony counts were lower than viable counts and total cell counts inside root tissues. The occurrence of viable but non-culturable (VBNC) cells inside root tissues (5 log cells g–1 root) was unlikely to have resulted from the hydrogen peroxide treatment used to disinfect the root surface, as hydrogen peroxide caused the death of CHA0-Rif cells in vitro. In Siglistorf soil (low fertility status for cucumber), the inoculant was found mostly as non-culturable cells. Colony counts and viable counts of CHA0-Rif were similar, both in bulk soil and inside root tissues, whereas in the rhizosphere viable counts exceeded colony counts at the last two samplings (giving about 7 log VBNC cells g–1). In conclusion, soil type had a significant influence on the occurrence of VBNC cells of CHA0-Rif, although these cells were found in root-associated habitats (i.e. rhizosphere and root tissues) and not in bulk soil. Received: 12 November 1999  相似文献   

14.
《Applied soil ecology》2003,22(1):55-66
The ability of antibiotic-producing streptomycetes to colonize alfalfa (Medicago sativa L.) plants and influence the activities of a fungal plant pathogen (Phoma medicaginis var. medicaginis) and a mutualistic symbiont (Sinorhizobium meliloti) was investigated. Streptomyces strains were introduced around seeds at the time of planting. Hyphal filaments and spore chains were observed by scanning electron microscopy on roots of alfalfa seedlings receiving the streptomycete amendment. Streptomyces strain densities on leaves decreased 10–100-fold over an 8-week period, while densities on roots remained constant over time. The Streptomyces strains also colonized alfalfa root nodules. We then tested the ability of 15 antibiotic-producing strains of Streptomyces to inhibit in vitro growth of Phoma medicaginis var. medicaginis Malbr. & Roum., the causal agent of spring blackstem and leaf spot of alfalfa. The majority of the Streptomyces strains inhibited growth of three diverse strains of P. medicaginis. In a detached leaf assay, one Streptomyces strain decreased leaf spot symptoms caused by P. medicaginis when inoculated onto leaves 24 h before the pathogen. Two Streptomyces strains decreased defoliation caused by P. medicaginis when the streptomycetes were introduced around seeds at the time of planting. We also examined inhibitory activity of Streptomyces strains against 11 strains of S. meliloti. Eight of the 15 Streptomyces strains inhibited in vitro growth of five or more of the S. meliloti strains, while four Streptomyces strains had no effect on growth of any test strains. In a growth chamber assay, two of six Streptomyces strains, when inoculated into the planting mix, significantly reduced plant dry weight compared to the treatment with S. meliloti alone, but did not significantly reduce the number of nodules. These results suggest that careful selection of Streptomyces isolates for use in biological control of plant diseases will limit the potential negative impacts on rhizobia.  相似文献   

15.
《Journal of plant nutrition》2013,36(9):1367-1375
A study was conducted to compare the responses to acid pH of Medicago sativa and Lotus glaber, two forage legumes with different environmental requirements, either supplied with inorganic nitrogen (N) or inoculated with different strains of their nodule bacteria. Medicago sativa showed, in both treatments, a significant reduction in total dry weight at pH below 6.0. In contrast, Lotus glaber grew equally well at all the pHs assayed in the presence of adequate N. Under inoculated conditions, in the absence of N supply, plant growth was dependent on the bacterial strain used. When the ability of each strain to multiply in culture medium was examined, it was observed that Sinorhizobium meliloti strains showed a pH-sensitive response that inhibited growth at pH 4.0, whereas Mesorhizobium loti strains showed normal growth at this pH. These results suggest that for the effectiveness of Mesorhizobium loti–Lotus glaber symbiosis in acid soils the major factor to be considered is the tolerance of the bacterial strain to acid conditions, while the limiting factors for the Sinorhizobium meliloti–Medicago sativa symbiosis are the sensitivity to low pH of both the plant and its bacteria.  相似文献   

16.
In this paper the interactive effects of different Sinorhizobium meliloti strains and alfalfa cultivars on the host plant growth and nodulation were evaluated. In the experiments, six alfalfa cultivars (Giza-1, Ismailia-94, Kometa, Radius, Luzella and Legend) as well as five S. meliloti strains (ARC-1, ARC-2, A2, TAL and L5-30) were included. The alfalfa cultivars, Giza-1 and Ismailia-94, exhibited the highest average dry forage weight with all studied strains. Generally, plants inoculated with the S. meliliti ARC-2 strain produced significantly higher shoot and root dry weights over all evaluated cultivars. The strain L5-30 of S. meliloti produced the highest nodule number with all the studied alfalfa cultivars whereas, among tested cultivars, N2-fixing Luzella showed the highest nodulation with the majority of rhizobial strains. Analysis of correlation coefficients for the studied alfalfa-rhizobium associations revealed positive and significant relationships of shoot dry weight with root dry weight. In contrast, nodule number per plant correlated negatively with forage dry weight of plants. It was also found that nodule number per plant is not a promising trait with which to select the most effective N2-fixing rhizobium-legume systems; selection of such symbiotic associations should be done on the basis of shoot and root dry weights.  相似文献   

17.
Using Tn5 mutagenesis of lysogenic Sinorhizobium meliloti strain L5–30 (L54), three neomycin-resistant transconjugants differing in phage-resistance profiles were isolated. Two of them increased the dry weight of plants and were capable of establishing root nodules, whereas the third one was ineffective. The bacterium-phage interaction did not have observable consequences in the Medicago sativa - S. meliloti symbiosis because it did not affect the number of nodules on M. sativa or plant dry weight.  相似文献   

18.
The organic matter supply can promote the dispersal and activity of applied plant growth–promoting rhizobacteria (PGPR), but the complementary effect of organic fertilization and PGPR application on the turnover of P is scarcely known. The effects of the application of two PGPR strains (Pseudomonas fluorescens strain DR54 and Enterobacter radicincitans sp. nov. strain DSM 16656) alone and in combination with organic fertilization (cattle manure and biowaste compost) on growth and P uptake of maize (Zea mays L.) and oilseed rape (Brassica napus L.) were investigated under semi–field conditions. Furthermore, P pools and phosphatase activities in soil and the arbuscular mycorrhizal colonization of maize were examined. The organic‐fertilizer amendments increased the growth and P uptake of both plant species and the soil P pools. The application of the E. radicincitans strain increased P uptake of oilseed rape when no organic fertilizer was added. Furthermore, the application of both bacterial strains increased the activities of phosphatases under both plant species. Here, the effect of the PGPR application even exceeded the effect of organic fertilization. The magnitude of this effect varied between the different fertilizing treatments and between the two bacterial strains. Phosphatase activities were increased to the greatest extent after application of P. fluorescens in the unfertilized soil. Under rape increases of 52% for acid phosphatase activities (ACP), 103% for alkaline phosphatase activities (ALP), and 133% for phosphodiesterase (PDE) were observed therewith. In the unfertilized soil, the application of P. fluorescens also resulted in a strong increase of the arbuscular mycorrhizal colonization of maize. We conclude that application of PGPR can promote the P mobilization and supply of crops in P‐deficient soils, however, in combination with organic fertilization these effects might be masked by a general improved P supply of the crops. Interactive effects of applied bacterial strains and organic fertilization depend on the sort of organic fertilizer and crop species used.  相似文献   

19.
Summary A method was developed to improve the colonizing ability of inoculated strains of root-nodule bacteria using aliette (aluminum tris-O-ethyl phosphonate), a basipetally translocated fungicide. Aliette applied to seeds of alfalfa inoculated with an aliette-resistant strain of Rhizobium meliloti increased the numbers of R. meliloti in the rhizosphere after 3 but not 37 days, increased the number of nodules, and with some seed treatments, increased the growth of alfalfa. The enhanced colonization by R. meliloti as a result of seed treatment with aliette lasted for at least 31 days for alfalfa, although plant weights did not increase, Colonization by R. meliloti was further enhanced if seeds and foliage were treated with the fungicide. Coating seeds or sparaying the foliage with aliette also increased the number and weight of nodules and nitrogenase activity in soybeans inoculated with an aliette-resistant strain of Bradyrhizobium japonicum. The stimulation of B. japonicum in the rhizosphere and of nodulation was evident with successive plantings of soybeans if the seeds for each planting were treated with the chemical, but aliette did not increase the yield of inoculated soybeans in the subsequent plantings. With only the seeds of the first planting of inoculated soybeans treated with aliette, the numbers of B. japonicum in the rhizosphere of subsequent plantings were only occasionally greater and the numbers of nodules on the later plantings were not increased. We suggest that root colonization, nodulation, and N2 fixation by Rhizobium and Bradyrhizobium may be enhanced by the use of basipetally translocated antimicrobial compounds together with root-nodule bacteria that are resistant to those compounds.  相似文献   

20.
Bunchy top is one of the most important viral diseases affecting banana production worldwide. Several approaches have been made to control or combat the bunchy top virus disease in banana, transmitted by the banana aphid, Pentalonia nigronervosa Coq. No tactic is able to completely protect the plants against this viral infection. To ameliorate this problem, an attempt was made to use different bacterial strains, which could be inoculated to the roots of micropropagated plantlets to avoid the post transplanting problems. Virus indexed micropropagated plantlets of banana cv. Virupakshi (AAB) were subjected to root colonization followed by foliar spraying with three bacterial strains viz., Pseudomonas fluorescens strains Pf1, CHA0 and Bacillus subtilis strain EPB22 along with an un-inoculated control during primary and secondary hardening stage in the nursery and at the time of transplanting, 3rd, 5th and 7th month after planting in the field. Microbe inoculated plantlets showed improved vegetative growth, physiological attributes, PR—proteins and phenol contents besides reducing banana bunchy top disease (BBTD) incidence in the field. These results indicate that, transplant mixes amended with beneficial bacterial strains can enhance growth of banana plants, besides reducing the damage caused by banana bunchy top virus.  相似文献   

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