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1.
In acid soil, low pH, reduced availability of nutrients, and toxicity of Al and Mn limit plant growth and the survival and effectiveness of rhizobia. The symbiosis between legumes and rhizobia is particularly sensitive to acid soil stress. A pot experiment evaluated whether Bradyrhizobium japonicum strain growth on acidic agar media would predict ability to colonize the rhizosphere and form effective nodules in acidic soils. Three Indonesian strains of B. japonicum with similar effectiveness at neutral pH in sand culture but with different tolerance of acid soil stress factors in agar media, and an acid-tolerant commercial strain (CB1809) of comparable effectiveness, were tested in three acid soils using the Al tolerant soybean (Glycine max cv PI 416937). At 7 days after inoculation all strains had achieved large rhizosphere populations, but by day 14 the rhizosphere population of the acid-sensitive strain had decreased, while the more acid-tolerant strains increased. The acid-tolerant strains had significantly greater nodulation and symbiotic effectiveness than plants inoculated with the acid-sensitive strain. Laboratory prescreening of B. japonicum for acid, Al and Mn tolerance in acid media successfully identified strains which were symbiotically competent in low pH soils.  相似文献   

2.
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   

3.
In previous work, Variovorax paradoxus strain HB44, next to Burkholderia terrae BS001 and Dyella japonica BS003, were found to be selected in the mycosphere of the tricholomataceous fungi Laccaria proxima and Lyophyllum sp. strain Karsten in an acid soil denoted G. V. paradoxus HB44 showed poor survival in G bulk soil, irrespective of prior soil sterilization, and this poor survival also occurred for B. terrae BS001 and D. japonica BS003. In contrast, the survival rate of strain HB44 in two other soils, with pH values > 5.5, was significantly raised. Also, significantly enhanced strain HB44 survival in G soil was found if the pH was raised to 5.5 or 6.5, and it was even shown to grow (in the presence of the exogenous carbon source glycerol) at such pH values in the sterile G soil. This behaviour was similar to that of the V. paradoxus type strain. Strikingly, Lyophyllum sp. strain Karsten, when colonizing the sterilized G soil, significantly raised the soil pH from about 4.6 to ≥5.0. The pH raise was dependent on time, hyphal development, as well as on initial soil pH, but was consistent throughout. The modulated soil pH conditions were shown to be permissive for the survival and growth of strain HB44, and this was extended to strains BS001 and BS003. These findings corroborate the hypothesis that L. sp. strain Karsten provides a suitable habitat for acid-sensitive strains like HB44, BS001 and BS003 in its mycosphere in acid soil, which is strongly defined by the establishment of a growth-permissive pH.  相似文献   

4.
In Ethiopia, inoculation of soybean with rhizobial inoculants is not common practice, but could provide an option to increase grain yields in low nitrogen (N) acidic soils. In these acid soils, the selection of acid tolerant rhizobia is one strategy that may increase the performance of soybean. In this study, rhizobial strains isolated from Ethiopian soils were evaluated for their acid tolerance and symbiotic N fixation efficiency with soybean, in controlled environments. Following this, four isolated rhizobial strains were evaluated in six field experiments in major soybean growing areas of Ethiopia. Inoculation with the commercial strain or with one of two locally sourced isolates, that were developed as inoculants, improved soybean yield. The yield increase due to inoculation with the commercial strain was consistent and greater than other treatments, while the increase due to the two locally sourced strains was comparable to, or greater than, application of 46 kg N/ha in soils, where the resident rhizobial population was ≤1.4 × 103 cfu/g soil. For soils with high background rhizobial populations, there was no response to inoculation. In one of the experimental sites (Bako), the percentage of N fixed (%Ndfa) was 55 for the commercial strain and 35 for the local strain, ES3. This study demonstrated that field validation is a necessary step in the selection of acid-tolerant strains of rhizobia to increase soybean production for Ethiopia.  相似文献   

5.
《Applied soil ecology》2007,35(2):441-448
The size of the background rhizobial population can often determine the success of field nodulation and persistence of inoculant rhizobia. Field experiments were conducted to determine the nodulation response of annual medics (Medicago spp.) in a pasture-wheat-pasture rotation when grown in soils of contrasting pH and rhizobial populations. Medicago truncatula Gaertn. and M. polymorpha L. were inoculated with one of three different strains of Sinorhizobium medicae (WSM540, WSM688) or S. meliloti (NA39) or left uninoculated and sown in two fields of pH (CaCl2) 5.9 and 7.2 of differing soil rhizobial backgrounds (11 and 7.1 × 104 cells/g soil, respectively). Nodulation was assessed in years 1 and 3 of the rotation. At the site with a small rhizobial background, M. polymorpha nodulated poorly when inoculated with the acid-sensitive strain NA39 but nodulated well when inoculated with acid-tolerant strains WSM688 and WSM540. M. truncatula had a similar extent of nodulation with each of the rhizobial inoculants. At the site with a large rhizobial background all treatments had greater than 85% of plants nodulated. Nodule occupancies, assessed by PCR, provided further insight: at the site with a small rhizobial background both medic species successfully nodulated with the acid-tolerant strains WSM540 and WSM688 and these strains persisted to year 3. However, at the site with large rhizobial background, only one strain, WSM688, was identified from M. truncatula nodules in year 3. This study highlights the importance of edaphic constraints and plant–rhizobia interactions to the successful development of nodulation in a field environment.  相似文献   

6.
Physiological responses to acid stress in two strains of Rhizobium leguminosarum bv trifolii of differing acid-soil tolerance were compared. Acidity affected the size and morphology of the acid-tolerant strain, WSM409, but not of the acid-sensitive strain, TA1. Acid grown cells of WSM409 and TA1 had less cell-associated Ca and Mg and more P than cells grown at pH 7.0. Potassium content was lower in acid grown cells; WSM409 was less affected by pH than that in TA1. WSM409 was more tolerant of pH shock at pH 3.5 when grown at pH 4.8 than when grown at pH 7.0. TA1 was more sensitive to pH shock when grown at pH 4.8 than when grown at pH 7.0. WSM409 shows a characteristic adaptive acid tolerance response, whereas TA1 shows an acid sensitive response.  相似文献   

7.
The nodulation of Lotus pedunculatus and the multiplication of three Rhizobium loti (fast-growing, acid-producing) and two Bradyrhizobium (slow-growing, alkali-producing) strains was investigated in acidified rooting solution. R. loti strains multiplied at pH 4.5 but Bradyrhizobium strains failed to multiply. No difference in growth rate between R. loti and Bradyrhizobium strains was apparent in rooting solution at pH 6.7. Similar responses to pH were observed in yeast extract-mannitol broth except that Bradyrhizobium strains multiplied more slowly than R. loti at pH 6.7. All strains nodulated L. pedunculatus growing in acid (pH 4.5) rooting solution when presented as single cultures. Following inoculation with 1:1 mixtures of R. loti and Bradyrhizobium strains, R. loti formed 93% of nodules at pH 4.5 and significantly fewer nodules (66%) at pH 6.7. These results demonstrate a competitive advantage for acid-tolerant strains over acid-sensitive strains in nodulation of their lost legume at pH 4.5.  相似文献   

8.
Clover rhizobia (55 strains) were screened for tolerance of acidity and Al, using the technique of Keyser and Munns (1979). Assessment of visible turbidity after 14 days indicated three strains tolerant of pH 4.5 (although growth rate was reduced), 25 strains tolerant of 5μm Al and no strains tolerant of 50 μ m Al at pH 5.5.50 μmAl caused a decrease in the numbers of acid-tolerant strains at pH 4.5. Tolerance of acidity or Al was not associated with the pH or Al status of the soil from which a strain was isolated.Screening of eight strains of clover rhizobia and nine strains of Lotus rhizobia using turbidity assessment and viable counts indicated seven strains of clover rhizobia with different degrees of tolerance of 20 μm Al but none tolerant of 50 μm Al at pH 5.5. All Lotus rhizobia (both slow- and fast-growers) were tolerant of 20 and 50 μm Al at pH 5.5, with 50 μm Al causing a reduction in growth rate.Subculturing of strains in non-stressed and stressed media had no effect on the response to 50 μmAl at pH 5.5.  相似文献   

9.
Experiments were conducted to estimate the saprophytic competence of four Rhizobium japonicum strains (110, 123, 532c, and 586) in a Rossmoyne silt loam (almost free of R. japonicum) and a Miamian silt loam (containing indigenous R. japonicum strains).All strains increased about 100-fold in sterilized Rossmoyne or Miamian soil during the first 2 weeks, and the population remained constant for 26 and 6 weeks respectively. Such results indicated that abiotic factors were not limiting Rhizobium populations in these soils under laboratory conditions. There was no inter-strain competition when strains were mixed and applied to either sterilized soil.All R. japonicum strains decreased about ten-fold but survived well in non-sterile Rossmoyne soil during 26 weeks incubation. But, all strains died at varying rates in non-sterile Miamian soil during a 6 week incubation. The most rapid decline occurred with strain 123, which decreased about 1000-fold during the first 5 days, while strain 586, decreased about 1000-fold during the first 10 days. The die-back of strain 123 was found to coincide with an increase in numbers of a parasitic microorganism which passed through a 0.45 μm pore-sized filter. A bacteriophage has been implicated, although Bdellovibrio cannot be ruled out completely. This parasitic microorganism is strain specific but does not lyse a field isolate of serogroup 123.  相似文献   

10.
From acidic tea soils in Kagoshima Prefecture in Japan, 38 strains of acid-tolerant microorganisms were isolated and some soil properties were determined. Different Al concentrations were applied to YG media to estimate the Al resistance. Selected microbial strains were able to grow actively in liquid media in the presence of 100 mM Al and to survive even in 300 mM Al at pH 3.0. The base sequences of 28S rDNA-D1/D2 were determined and sequence data were searched using the Basic Local Alignment Search Tool (BLAST) system. The results of sequencing revealed that the isolates belonged to two different species, Cryptococcus sp. and Candida palmioleophila . Subsequently, Neighbor-Joining molecular phylogenetic trees were constructed. When the yeasts were cultured at various Al concentrations, the growth was inhibited at a concentration of 200 mM. Pre-culture of these strains with 0–30 mM Al did not promote the growth response induced by Al. Inductively coupled plasma-mass spectrometry (ICP-MS) was used to assess the elimination of Al from YG media. The amount of Al remaining in the culture media decreased considerably after culture. Due to a capacity for resistance to significant Al concentrations as well as high Al elimination, these acid-tolerant and Al-resistant yeasts may offer potential applications for the bio- and phyto-remediation of acid soils with a high level of Al.  相似文献   

11.
Studies were conducted to evaluate the survival and persistence of Sinorhizobium meliloti 104A14 and two acid phosphatase-negative mutants in Kirkland (fine, mixed, thermic Udertic Paleustolls) silt loam soils with various fertility levels, and to assess the impact of inoculation on nodule occupancy and soil microbial community structure in the inoculated alfalfa (Medicago sativa L.) rhizosphere. Recovery of the inoculated strains was 100% (in the order of 108 cells g−1 soil) immediately following inoculation to soils, but decreased from 108 cells g−1 soil to undetectable levels in a nutrient-poor soil within 32 days. In a nutrient-rich soil, approximately 2–3% (4.7–7.43×106 cells g−1 soil) of the mutants and 23% (5.84×107 cells g−1 soil) of the wild-type inocula persisted for more than 64 days. Survivability and persistence of the wild-type S. meliloti were significantly greater than that of the genetically modified acid phosphatase negative mutants in all the soils tested. The persistence and nodule occupancy of the introduced S. meliloti in sterile and non-sterile soils were also tested for two repeated alfalfa growth periods in the same plant growth units, with a 1 month interval in between and no additional inoculation for the second period. Nodule occupancy of the introduced S. meliloti in non-sterile soils ranged from 30 to 60% for the first period and 85 to 100% for the second period. Our results suggest that survival and persistence of S. meliloti was enhanced by alfalfa cultivation and increased soil fertility, but impaired by mutation of acid phosphatase genes regardless of phosphorus nutritional levels. Moreover, inoculation with genetically modified S. meliloti strain 104A14 promoted indigenous bacterial growth in soil (increased bacterial population from 1.4×106 to 4.3×106 cells g−1 soil), but not the growth of fungi and yeast. However, inoculation of the wild-type S. meliloti or genetically modified mutants did not result in significant changes in microbial community structure as indicated by EP indices and ratios of r/K strategists.  相似文献   

12.
Growth interference in culture was shown by 57 strains of Rhizobium belonging to different inoculation groups. The assays were conducted in vitro by spot tests on agar plates and using 1007 paired combinations, 240 cases of interference were observed.A frequency of interference of about 30% was found among strains of R. meliloti and R. meliloti, R. lupini, R. trifolii and R. leguminosarum. Only one case out of 168 showed interference between R. meliloti and R. japonicum.  相似文献   

13.
Recently, two strains related to Burkholderia terrae, denoted BS001 and BS110, were shown to be strongly interactive with the soil fungus Lyophyllum sp. strain Karsten, forming a biofilm around the L. sp. strain Karsten hyphae and migrating along growing hyphae in soil. Here, we extend the findings obtained with strains BS001 and BS110 and show that the migratory ability with extending fungal hyphae is actually distributed among four Burkholderia phylotypes obtained from a range of soils with different characteristics. The majority of the migrating strains fell into a rather narrow group related to the original strain B. terrae BS001, but others fell in groups related to B. terricola, B. xenovorans and B. phytofirmans. To obtain these novel strains, bacterial inocula were obtained as cell extracts from eight soils and subsequently introduced into four (sandy acidic) pre-sterilized soils in microcosms which were then colonized by L. sp. strain Karsten or kept without this fungus. After 2 weeks of incubation, the soil microcosms were sampled at the migration front and samples were plated on semi-selective PCAT agar medium next to R2A medium. A total of 19 strains that had revealed the capability to comigrate with the fungus were obtained from this set-up, whereas four other strains were found in previous field work. Strains were analysed by BOX-PCR, pulsed-field gel electrophoresis, partial 16S rRNA gene similarity, metabolic profiling using BIOLOG and for the presence of a type three secretion system (TTSS). All strains belonged to the genus Burkholderia. Following this, selected strains were shown to be capable of single-strain comigration with the L. sp. strain Karsten hyphae through different soils. However, their avidity to do so differed across soils. For their ecological competence, the four different comigrating phylotypes may rely on their capacities to migrate as well as consume fungal-released compounds.  相似文献   

14.
Summary The existence of a balance survival rate of different B. japonicum strains in soils has been well established. Balance levels (M) were shown to be independent of inoculum size but differences between strains in a soil could not be discussed partly because of the instability of the recovery's efficiency in the area of the plateau. In this paper, a dynamic model, the Gompertz equation, is fitted to the data, to estimate the rate (A) at which equilibrium is reached. For the three strains in the three soils previously studied, this rate is also independent of inoculum size and the soil-strain interaction is highly significant. Some data from the literature are also well fitted by the model. We propose to characterize the saprophytic potential of a strain with the pair of parameters A-M. An optimal experimental procedure is proposed to obtain the most precise estimates for these parameters. Their biological significance is discussed, but the fact that they are not dependent upon inoculation level is of basic importance for agronomic practice.  相似文献   

15.
Sixty-seven strains of Bradyrhizobium isolated from soybean plants growing on acid soils in West Java and Sumatra, Indonesia, were examined for the effect of the pH and aluminum concentration on their growth in nutrient media, compared with 61 strains of Bradyrhizobium from soils in Japan. The results in this study indicated that the indigenous population of Bradyrhizobium in the soils of Indonesia showed a large difference in acid- and Al-tolerance from that of Japan. Eighty-five and 48% of the isolates from Japanese soils and Indonesian soils, respectively, were unable to grow in YEM broth at pH below 4.5. The acid-tolerance was correlated with AI-tolerance of the isolates on YEM agar plates at pH 4.4. Seventy-five percent of the isolates that grew in YEM broth at pH 4.5 were also resistant to 400 µM Al on the YEM plates. Acetylene reduction assay of the root nodules revealed that 3 of the acid- and Al-tolerant isolates from Indonesian soils showed a significantly high nitrogen fixation activity.  相似文献   

16.
Twenty-seven strains of Lotus rhizobia were tested for acid tolerance in yeast-extract mannitol broth (pH 4.6) by multiplication from low initial cell densities. Acid production on unbuffered yeast-extract mannitol agar slopes incorporating bromothymol blue indicator was also determined. All slow-growing, alkali-producing strains were acid sensitive and four of the six fast-growing, acid-producing strains were acid tolerant as was one fast-growing, alkali-producing strain. The method of testing for acid tolerance proved suitable for fast-growing strains and results are discussed in relation to the ecological implications of acid and alkali production by rhizobia.  相似文献   

17.
This study tested the competitive ability of three locally isolated Cyclopia rhizobia and strain PPRICI3, the strain currently recommended for the cultivation of Cyclopia, a tea-producing legume. Under sterile glasshouse conditions, the three locally isolated strains were equally competitive with strain PPRICI3. In field soils, the inoculant strains were largely outcompeted by native rhizobia present in the soil, although nodule occupancy was higher in nodules growing close to the root crown (the original inoculation area). In glasshouse experiments using field soil, the test strains again performed poorly, gaining less than 6% nodule occupancy in the one soil type. The presence of Cyclopia-compatible rhizobia in field soils, together with the poor competitive ability of inoculant strains, resulted in inoculation having no effect on Cyclopia yield, nodule number or nodule mass. The native rhizobial population did not only effectively nodulate uninoculated control plants, they also out-competed introduced strains for nodule occupancy in inoculated plants. Nonetheless, the Cyclopia produced high crop yields, possibly due to an adequate supply of soil N.  相似文献   

18.
Two hypotheses that antibiotic-resistant nodule isolates from uninoculated soybeans grown in a strongly acidic soil were naturally occurring rhizobia which had acquired resistance to spectinomycin and streptomycin or were contaminants from adjacent, inoculated treatments, were tested in laboratory experiments. Soybean nodule isolates (166) as well as 48 cowpea and 89 Rhizobium japonicum strains were used in tests of resistance to six concentrations (0–500 μg ml?1) of kanamycin, spectinomycin and streptomycin, tolerance of stresses of pH 4.6, with or without 50 μm Al, and serological cross-reactivity.More strains from the strongly acidic soil were resistant to the antibiotics than from slightly acidic soils, but resistance to antibiotics did not necessarily entail resistance to pH 4.6 or to 50 μm Al. Twenty-three nodule isolates which were resistant to spectinomycin or streptomycin cross-reacted with antisera of the inoculum strains, indicating that they were contaminants. None of 59 antibiotic-sensitive nodule isolates from uninoculated plants and none of 31 from inoculated plants cross-reacted with the antisera. All 53 antibiotic-resistant isolates from nodules of plants in inoculated plots cross-reacted with test antisera, indicating stability of the antibiotic markers.Cowpea rhizobia were generally more resistant to the antibiotics and more tolerant of pH 4.6 and 50 μm Al than were R. japonicum. Among strains of R. japonicum, slow growers were more resistant to antibiotics than moderately fast growers.  相似文献   

19.
The largest numbers of the Brazilian traditional upland rice varieties are found in the Maranhão state, Northeast region of Brazil. However, no information is available on the diazotrophic bacterial population associated as well as the plant growth promoting potential when these traditional genotypes are inoculated with native strains. Here, we evaluated the response of ten traditional rice varieties to inoculation with ten diazotrophic strains, previously isolated from rice soil of this region and screened for their ability to produce indole-3-acetic acid (IAA) in vitro. The procedure for selection of the best diazotrophic strain/rice variety interaction involved three steps: gnotobiotic conditions, soil pot and field experiments. The gnotobiotic experiment showed that the Azospirillum amazonense strain AR3122 increased the biomass of the traditional varieties Cana Roxa and Cana Forte (28 and 48%, respectively) while this effect was less evident for the other combination of strains/rice varieties. The soil pot experiment showed that the combination of Burkholderia vietnamiensis strain AR 1122 and traditional variety Arroz 70 was superior to the other strains/varieties and the treatment fertilized with 100 kg N ha−1. The best performance of the Burkholderia vietnamiensis strain AR1122/variety Arroz 70 was confirmed in the field experiment. There was an increase of up 10 and 29% in the grain yield in comparison to both the N fertilization and Herbaspirillum seropedicae ZAE 94 strain treatments, respectively. In contrast, the response of the commercial variety Bonança to inoculation with strain AR1122 was much lower, suggesting that a biofertilizer inoculation program for traditional rice varieties should consider the genetic interaction between strain and rice variety. The diazotrophic B. vietmaniensis strain AR1122 was a good biofertilizer candidate for inoculation of traditional rice varieties and therefore should be used for further studies to confirm the strain-genotype effect envisaging a sustainable rice crop system mainly in the Northeast region of Brazil.  相似文献   

20.
The survival of different strains of Rhizobium japonicum was evaluated in three soils with two matric- and three osmotic-induced moisture potentials. Both drying and added NaCl significantly decreased populations. Strains CC 709 and USDA 110 were less affected by the matric- or osmotic-induced desiccation than strains CB 1809 and USDA 123. The survival of CC 709 and USDA 110 at 2 weeks with 0.7% added NaCI was 33 and 46% of initial counts in soils undergoing drying, and 70 and 69% in soils maintained at the 30kPa (0.3 bar) potential. Comparable survivals of CB 1809 and USDA 123 were 15 and 18% and 56 and 59%, respectively. The soil with the greatest clay and organic C contents maintained the highest populations during desiccation. Turbidity measurements indicated similar rates of growth of the four strains at a water activity (Aw) of 0.999 in yeast mannitol broth (YMB). When the YMB was adjusted with glycerol to lower water activities, strains CC 709 and USDA 110 consistently showed greater growth than did strains CB 1809 and USDA 123. No growth of CB 1809 and USDA 123 was observed at an (Aw) of 0.975. Water adsorption isotherms of freeze-dried cells showed that the more desiccation-susceptible strains (CC 709 and USDA 110) retained greater amounts of water at a given relative vapor pressure than did the two more tolerant strains.  相似文献   

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