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1.
When subjected to desiccation with Ca(NO3)2 at 27°C, strains of the fast growing Rhizobium meliloti and R. trifolii, survived better than slow-growing strains of R. japonicum and of the “cowpea miscellany”. At lower vapour pressures in a forced-draught oven, the pattern of survival changed and strains of slow-glowing Rhizobium withstood desiccation better than those of fast-growing species. The results are considered to be consistent with the interpretation that a lower internal water-retaining ability at any relative vapour pressure, renders strains of slow-growing Rhizobium more resistant to severe desiccation than strains of fast-growing species. It is suggested that under conditions of milder desiccation, this property is disadvantageous to the slow-growing Rhizobium because insufficient moisture is available to allow for the functioning of vital enzymes. 相似文献
2.
Several Rhizobium spp were tested for chemotaxis using a soft agar assay. Bacteria migrated in chemotactic bands in response to substances present in the agar medium. R. japonicum S-110 formed chemotactic bands in response to l-arabinose, l-canavanine, and yeast extract but not to several other common compounds, including several amino acids and sugars. These results suggested that simple compounds present in legume root exudates may attract these bacteria and aid in their rhizosphere accumulation and, thus, in the nodulation process. A slow-migrating mutant of R. japonicum S-110 was isolated. Microscopic examination showed that mutant populations had a much lower proportion of motile cells than did wild-type populations. Greenhouse nodulation tests, in which mutant and wild-type cells were mixed and used as inoculum, indicated that the mutant had less nodulation potential. 相似文献
3.
When a bacteriocin-sensitive and a bacteriocin-resistant strain of Rhizobium were added together to plant-tubes, containing Trifolium subterraneum cv. Dwalganup seedlings, the bacteriocinresistant strain occupied less than 10% of the nodules sites. But when a bacteriocin-producer was added with the inoculum, the bacteriocin-resistant strain occupied 75% of the nodule sites. In a replicate experiment, using a different bacteriocin-sensitive strain, the proportion of the nodules formed by the bacteriocin-resistant strain was increased from 17%, in the absence of the bacteriocin-producer, to 100% in its presence.Similar experiments were set up in non-sterile soil that contained ineffective, bacteriocin-sensitive rhizobia. When an effective bacteriocin-resistant strain was inoculated with a bacteriocin-producing strain, the proportion of nodules formed by the effective strain was greater than in the absence of the bacteriocin-producer. This was because nodulation by the indigenous rhizobia was reduced in the presence of the bacteriocin-producer.Such experiments suggest that bacteriocin-producing strains of R. trifolii that reduce the nodulation success of competing bacteriocin-sensitive strains could be used to increase the proportion of nodules formed by a desired bacteriocin-resistant strain. 相似文献
4.
Establishment of vesicular-arbuscular mycorrhizal fungi in plant roots involves a pre-infection phase of propagule germination, hyphal growth and appressorium formation, followed by growth of the fungus within the root. The effect of soil temperature on the pre-infection stage was examined by counting the numbers of fungal “entry-points” on the main roots of Medicago truncatula and Trifolium subterraneum, grown at soil temperatures of 12°, 16°, 20° and 25°C for periods up to 12 days. Increased root temperature was positively associated with increased numbers of “entry-points”. This effect was more marked between 12° and 16°C than at higher temperatures, as shown by comparing plants at the same stage of development (emergence of spade leaf) and by calculating the results as entry points per cm root.The first root nodules appeared sooner at higher temperatures (20° and 25°), but subsequent development of nodules (measured as nodule number and aggregate volume of nodules per plant, up to 21 days) was best at 16°C for both host Rhizobium combinations in non-sterile and autoclaved soil. There was no evidence that competition between mycorrhizal fungi and Rhizobium for infection sites occurred.A method of obtaining numbers of infective propagules of vesicular-arbuscular mycorrhizal fungi in soil is described. 相似文献
5.
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
6.
The ability of fluorescein isothiocyanate (FITC) labelled lectins extracted from the legumes Aspalathus linearis, Glycine max, Lotononis bainesii, Phaseolus vulgaris and Pisum sativum, respectively, to react with strains of various Rhizobium spp. was studied. With the exception of six out of ten strains of R. phaseoli and two out of ten strains of R. japonicum, none of the Rhizobium strains tested were able to bind lectin from their normal host plants. Many strains of R. leguminosarum, R. trifolii and R. phaseoli bound each of the plant lectins studied with the exception of the P. sativum lectin. This lectin was only bound by two strains of R. meliloti and a slow-growing strain isolated from Macroptilium atropurpureum. These results do not support suggestions by other workers that plant lectins play an important role in Rhizobium specificity. 相似文献
7.
Success in introducing Rhizobium japonicum strains into soil is related to their interaction with native microorganisms including some that are antagonistic. Actinomycetes, bacteria, fungi and rhizobiophages antagonistic towards strains of R. japonicum were counted directly using soil samples from field plots under different crop and soil management systems. The antagonistic actinomycete population varied from 1.3 × 103 to 4.5 × 105 g?1 dry soil and ranged up to 90% of total actinomycetes. Soybean rhizosphere soil samples included antagonistic actinomycetes ranging up to 70% of total actinomycetes. The antagonistic bacterial population was less than 10% of total bacteria and the proportion did not vary significantly with crop or soil management practices. Antagonistic fungi were observed for many of the soils examined but they could not be counted. There were few rhizobiophages and they were found most frequently in soybean rhizospheres. Occasional bacterial and actinomycete colonies that stimulated growth of R. japonicum were randomly observed among the soil samples tested. 相似文献
8.
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
9.
Four strains of Rhizobium phaseoli were examined for N2 fixation effectiveness and for competitiveness for nodule occupancy by utilizing strain-specific fluorescent antibodies. Competition studies in Leonard jars held in a growth chamber showed strain KIM-5 (a cool season isolate from Kimberly, Idaho) consistently occupied the majority of nodules on bean plants (Phaseolus vulgaris L.) cv. Kentucky Wonder, when applied as a mixed inoculant with desert strains (K-1, 36 or 90). Competitiveness of KIM-5 was relatively independent of cell numbers as shown by the high recovery of KIM-5 from nodules, even when extensively outnumbered in the inoculant. KIM-5 out-competed the desert strains regardless of whether they were ineffective (strains 36 and 90) or highly effective (K-1). Although KIM-5 was more competitive than K-l, no difference in infectiveness (as shown by nodule mass) or effectiveness (as shown by % N, total plant N, C2H2 reduction and total plant weight) was observed.In YEM broth, strain K-l showed increasing growth rates when the temperature was increased from 27° to 35°C, and was viable at 40°C. These data indicate K-1 to be an unusually heat-tolerant strain. Growth rates of KIM-5 were constant from 27° to 35°C and the organism was not viable at 40°C. Both strains produced acid in a defined broth medium.The effectiveness of KIM-5 and K-l was also evaluated under field conditions using single strain inoculants with two cultivars of pinto beans (P. vulgaris L.) ev. Mexicali 80 and Delicias 71. Inoculation with K-1 resulted in yield increases with both cultivars over uninoculated plants, whereas there was little difference between KIM-5 inoculated and uninoculated plants. 相似文献
10.
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
11.
Non-protein nitrogen accumulated in nodules formed on Trifolium subterraneum cv. Tallarook by Rhizobium trifolii strain NA30, but not in nodules formed by strain TA1. Studies with six R. trifolii strains and four T. subterraneum cultivars indicated that the accumulation of non-protein nitrogen was a characteristic of certain strains and that it was accompanied by a greater development of nodule tissue. With normal symbiotic associations, approximately 6 per cent of the total plant nitrogen was located in the nodule system whereas nodules accumulating non-protein nitrogen contained, on average, 12 per cent of the total nitrogen in the plant.The principal component of the accumulating non-protein nitrogen was identified as “bound” γ-aminobutyric acid. Moderate to high concentrations of γ-aminobutyric acid (0.3–1.7 mmoles/g nodule dry weight) were found in nodules formed by 10 strains (of 36 examined) on Tallarook. With two “accumulating” strains, higher concentrations of γ-aminobutyric acid were found in nodules formed on the cultivar Clare (2.0 mmoles/g nodule dry weight) than in nodules formed on Tallarook or Yarloop (1 1.4 mmoles). No γ-aminobutyric acid was found in cultured cells of either an accumulating strain (NA30) or a nonaccumulating strain (TA1) of R. trifolii.The accumulation of non-protein nitrogen as γ-aminobutyric acid, and the accompanying increase in nodule tissue, each resulting in the export of a lower proportion of the nitrogen fixed to the host, is considered to be a factor causing a lower degree of symbiotic effectiveness. 相似文献
12.
Peanuts (Arachis hypogaea L.) were introduced to China about 500 years ago. However, the diversity of Rhizobial strains in China that can nodulate peanut was poorly understand. Diversity and phylogeny of 50 slow-growing strains, isolated from root nodules of peanut in different geographical regions of China, were studied using polyphasic techniques. All stains were clustered by phenotypic tests into two distinct groups: Group I: 16S rRNA RFLP genotype 3, and Group II, which divided into 16S rRNA RFLP genotypes 1 and 2. Genotype 1 shares the same genotype with USDA110, USDA122 and USDA127 of Bradyrhizobium japonicum, and genotype 2 solely consisted of extra-slow growing bradyrhizobia isolated from Hongan, China. Results of 16S rRNA sequencing revealed that peanut bradyrhizobia were phylogenetically related to B. japonicum and their sequence divergence was less than 1.1%. Based upon the size of the internally transcribed spacer (ITS) between the16S and 23S RNA genes, strains were classified into ITS-I, ITS-II and ITS-III genotypes. Strains could be further divided into sub-clusters IA, IB, IIa, IIb and IIc five sub-clusters through ITS PCR-RFLP and repetitive extragenic palindromic PCR (REP-PCR) analysis. Host specificity test revealed that all peanut bradyrhizobia tested nodulated Phaseolus vulgaris and strains of clusters IIb and IIc nodulated Glycine soja efficiently. Bradyrhizobia isolated from peanut were related, but still exhibited phylogenetical divergence with B. japonicum. 相似文献
13.
The usage of sewage sludge on agricultural lands is an effective and inexpensive practice that provides nutrients for crops. A successful legume crop also depends on the survival of Rhizobium in the soil environment. The number of R. japonicum (USDA 110) in treatment groups containing various soil-to-sludge ratios (control, 13:1, 9:1 and 5:1) during incubation for 1, 21 and 42 days was investigated. The control group contained soil without sludge. Mecklenburg clay and Enon sandy loam soils (both are fine, mixed, thermic, ultic Hapludalfs) were used. All treatments were adjusted to pH 6.7 and brought to 75% of field capacity with 1 ml inoculum (9 × 108 cells ml? 1) and distilled water. Samples were incubated at 25 C and monitored periodically for the number of surviving R. japonicum (USDA 110) organism by the plant infcction-MPN method. Strains were identified by gel-immunodiffusion. Recovery of rhizobia from both soils was < 1% in all treatment groups after 42 days. However, for control, 13:1, 9:1 and 5:1 groups, the percentage recovery was higher in Enon sandy loams (7.9, 2.3, 2.3 and 2.3%, respectively) at 21 days. Recovery of rhizobia in the 5:1 group from both soils was 7.9% after 1 day, whereas control values were 92%. A decline in rhizobial populations in higher sludge soils may be due to the heavy metals present and available during mineralization of sludge in soils. However, the number of R. japonicum that survived to 21 days was 1.7 × 105g?1 and 1.7 x 106g?1 for Mecklenburg clay and Enon sandy loam soils with highest sludge, respectively. 相似文献
14.
F. M. Hashem D. M. Swelim L. D. Kuykendall A. I. Mohamed S. M. Abdel-Wahab N. I. Hegazi 《Biology and Fertility of Soils》1998,27(4):335-341
Rhizobium-legume symbioses are important for their nitrogen input, but salinity and elevated temperature in arid and semi-arid areas
limit their effectiveness, and therefore plant growth and productivity. Sixteen Rhizobium strains isolated from root nodules of Leucaena trees grown in different geographical areas of Egypt varied in their degree of tolerance to salinity and in their symbiotic
effectiveness with Leucaena
leucocephala under saline conditions. Three strains were tolerant to >3% NaCl. L.
leucocephala grown in the greenhouse at concentrations of NaCl up to 1.0% and inoculated either with strain DS 78 or strain DS 158 displayed
significantly better growth than those plants grown at the same levels of salinity and inoculated with reference strain TAL
583. Although nine of the Rhizobium strains grew at 42 °C, their mean generation times were lengthened two- to fourfold. When daylight growth temperatures were
elevated from 30 °C to 42 °C, nodule number and mass, nitrogenase activities and shoot top dry weight of plants inoculated
with strains DS 78, DS 157 and DS 158 significantly increased, whereas these parameters decreased in plants inoculated with
strain TAL 583. Rhizobium strains that effectively nodulate Leucaena under adverse saline conditions and at high temperatures were thus isolated, identified and characterized.
Received: 12 September 1997 相似文献
15.
Twenty-eight Rhizobium strains were isolated from the root nodules of faba bean (Vicia faba L.) collected from 11 governorates in Egypt. A majority of these strains (57%) were identified as Rhizobium leguminosarum bv. viciae (Rlv) based on analysis of a nodC gene fragment amplified using specific primers for these faba bean symbionts. The strains were characterized using a polyphasic approach, including nodulation pattern, tolerance to environmental stresses, and genetic diversity based on amplified ribosomal DNA-restriction analysis (ARDRA) of both 16S and 23S rDNA. Analysis of tolerance to environmental stresses revealed that some of these strains can survive in the presence of 1% NaCl and a majority of them survived well at 37 °C. ARDRA indicated that the strains could be divided into six 16S rDNA genotypes and five 23S rDNA genotypes. Sequence analysis of 16S rDNA indicated that 57% were Rlv, two strains were Rhizobium etli, one strain was taxonomically related to Rhizobium rubi, and a group of strains were most closely related to Sinorhizobium meliloti. Results of these studies indicate that genetically diverse rhizobial strains are capable of forming N2-fixing symbiotic associations with faba bean and PCR done using nodC primers allows for the rapid identification of V. faba symbionts. 相似文献
16.
Sudan is the fourth largest exporter of groundnuts in the world, yet little is known concerning the plant-rhizobial symbiosis. A study was made on the abundance of groundnut-nodulating rhizobia in the soils of Sudan as related to soil properties and the duration since groundnuts were last planted. Also, physiological, serological and nitrogen-fixing characteristics of Sudanese rhizobia are reported. All but one of 32 sites contained more than 300 rhizobia g?1 soil capable of forming nodules on siratro (Macroptilium atropurpureum). Several of these soils had never been planted to groundnut. A correlation matrix indicated no relationship was present between soil rhizobial populations and any of the measured soil properties, or between soil rhizobial populations and the time since groundnuts were last planted in the rotation. Individual isolates of Rhizobium from six legumes: groundnut (Arachis hypogaea), mung bean (Vigna radiata), lubia (Dolichos lablab), cowpea (Vigna unguiculata), pigeonpea (Cajanus cajan) and bambara groundnut (Voandzeia subterranea) were obtained from four locations in Sudan. All isolates were able to nodulate each of the six legumes when grown in sterile vermiculite. The isolates grew in 0.1% NaCl-amended media, but growth was variable in 2.0% amended media. Most isolates grew after exposure to moist heat for 15 min at 50°C. Optimum pH for growth was, in general, between pH 6 and 8. Agglutination reactions indicated isolates from groundnuts, as well as isolates from other legumes, belonged to several serological groupings. Some isolates formed a large number of nodules on a Sudanese groundnut cultivar, whereas other isolates formed only few nodules. 相似文献
17.
An examination of 85 strains of bacteria from five species of rhizobia (Rhizobium sp., R. japonicum, R. lupini, R. meliloti and R. trifolii), using a new semi-quantitative assay procedure, disclosed wide diversity among the strains in their requirement for, and response to, vitamins, carbon sources, and nitrogen sources. Approximately half of the strains in the first four species grew as well without vitamins as they did when supplied with a vitamin mixture or with yeast extract, but the other strains showed considerable variation in their requirements. Some strains were inhibited by yeast extract, or showed best growth in basic media supplemented with only one vitamin. The strains within the species differed widely in their utilization of gluconate, mannitol and arabinose as C-sources; there was less diversity in their use of glutamine, histidine, NH4+-N and NO3?-N as N-sources. The significance of these observations in the culture of rhizobia in the laboratory, in their ecological adaptation to particular environments, and in their ability to form an effective symbiosis with particular host legumes, is discussed. 相似文献
18.
The ability of 4 strains of Rhizobium trifolii to compete with naturalized strains in nodulating Trifolium subterruneum cv. Mt Barker and cv. Woogenellup was assessed at 5 sites in New South Wales. The populations of naturalized rhizobia at these sites ranged from 4 × 106 rhizobia/g to one where no rhizobia were detected. The introduced strains were inoculated singly or as mixed strain inocula onto seed of the host at 2 × 106 rhizobia/seed. There were marked differences in competitive ability between the strains but these differences were modified by the host cultivar and the site.At the R. trifolii-free site the inoculum strain formed 100% of the nodules in the 1st yr; by the second year serologically unrelated strains had invaded the plots and these formed almost all of the nodules in the 3rd yr. At the site where competition was greatest (4 × 106 naturalized rhizobia/g), there were no differences in the competitive abilities of the strains in the first year but at all other sites WU95 was superior whether used as a single strain or in a mixed strain inoculum. In these sites also the proportion of nodules formed by the inoculum strains declined markedly by the 2nd yr. 相似文献
19.
Hyperparasites of oospores of Phytophthora megasperma Drechs. var. sojae Hildb. were present in each of 15 field soils tested. Maximum numbers of oospores parasitized ranged from 42.5 to 87.5% for flooded soils, and from 25.5 to 73.0% for soils adjusted to 50% water holding capacity; the mean for all soils was 51.5%. The frequency of hyperparasitism was not correlated with the disease potential soils for Phytophthora root-rot of soybean as determined in seedling tests on flooded soil samples. Of eight isolated hyperparasitic fungi tested in steamed soil, the most efficient parasites were Hyphochytrium catenoides, Humicola fuscoatra, and Pythium monospermum, each of which parasitized at least 76% of oospores during 3 weeks. Hyphae were not parasitized by any of the eight fungi. Parasitism by H. catenoides in sterilized soil increased as soil temperature increased from 16° to 28°C. Parasitism by P. monospermum was maximum at 20°–24°C. Oospores of P. meyasperma var. sojae race 7 were more resistant to infection by hyperparasites than were oospores of races 1 and 3. Oospores produced in culture were slightly more susceptible to hyperparasitism in soils than were oospores produced in soybean seedlings. 相似文献
20.
Summary Variation in nodulation and N2 fixation by the Gliricidia sepium/Rhizobium spp. symbiosis was studied in two greenhouse experiments. The first included 25 provenances of G. sepium inoculated with a mixture of three strains of Rhizobium spp. N2 fixation was measured using the 15N isotope dilution method 12 weeks after planting. On average, G. sepium derived 45% of its total N from atmospheric N2. Significant differences in fixation were observed between provenances. The percentage of N derived from atmospheric N2 ranged from 26 to 68% (equivalent to 18–62 mg N plant-1) and was correlated with total N in the plant (r=0.70; P=0.05). The second experiment included six strains of Rhizobium spp. and two methods of inoculation and the plants were harvested 14,35 and 53 weeks after planting. In the first harvest significant differences were found between the number of nodules and the percentage and amount of N2 fixed. There was also a significant correlation between the number of nodules and the amount of N2 fixed (r=0.92; P=0.05). In the final harvest no correlation was observed, although there were significant differences between the number of nodules and the percentage of N derived from the atmosphere. The amount of N2 fixed increased with time (from an average of 27% at the first harvest to 58% at the final harvest) and was influenced by the Rhizobium spp. strain and the method of inoculation. It ranged from 36% for Rhizobium sp. strain SP 14 to 71% for Rhizobium SP 44 at the last harvest. Values for the percentage of atmosphere derived N2 obtained by soil inoculation were slightly higher than those obtained by seed inoculation. 相似文献