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1.
The use of the GUS reporter gene was found to be very suitable for studying the competitiveness of the Rhizobium strain NGR234 and Bradyrhizobium strain CP283 for nodulation in siratro. However, the expression from the transposon mTn5SSgusA20 declined in the nodules of old plants, particularly the nodules at 35 d after inoculation and onward. Siratro inoculated with both gusA-marked NGR234 and CP283 strains showed a similar nodulation and acetylene reduction activity (ARA) to those of their parental strains. No major changes in nodulation and symbiotic properties in these marked strains were observed. When the Rhizobium strain NGR234 and Bradyrhizobium strain CP283 were inoculated separately to siratro, both of them were found equally effective for nodulation in the plant. But when the Rhizobium strain NGR234, and gusAmarked Bradyrhizobium strain CP283 were co-inoculated to the plants in a ratio of 1:1, the strain NGR234 occupied 75% of the nodules, while, the strain CP283 occupied only 25%, irrespective of the growth stages and inoculum concentrations. Similar results were also observed in the plants in which the Bradyrhizobium strain CP283 and gusA-marked Rhizobium strain NGR234 had been co-inoculated. Thus, the Rhizobium strain NGR234 was more competitive for nodulation in siratro.  相似文献   

2.
Summary We investigated the reliability of antibiotic resistance and colony morphology of clones of a Bradyrhizobium sp. (Lotus) strain for strain identification in nodulation competitiveness experiments in soil. There was no difference in nodulation competitiveness between the wild type strain and each of five mutants resistant to streptomycin and spectinomycin at the time of their isolation from antibiotic-containing media. However, these mutants were significantly less competitive when tested 4 months later. The apparent instability of the newly isolated mutants and their subsequently decreased nodulation competitiveness show that mutants must be examined carefully after being allowed time to stabilize. Two clones of the Bradyrhizobium sp. (Lotus) strain that differed in colony morphology on yeast mannitol medium did not differ in antigenic properties, whole cell protein electrophoresis profiles, mean cell generation times in yeast mannitol medium, N2-fixing ability, nodulation of Lotus pedunculatus in growth pouches, or in nodulation competitiveness. Both clones retained their colony morphology after numerous transfers on yeast mannitol agar over 3 years and after at least 6 months in soil. A limiting factor, which may restrict the use of colony morphology as a marker for strain identification in competition experiments, is the problem of detecting double-infected nodules when the small colony type comprises a relatively small portion of the total nodule population.  相似文献   

3.
Rhizobium trifolii were isolated from soils along a transect covering a range of soil pH (3.6–5.6) using two varieties of white clover by either growing seedlings directly in soil or in nutrient solution in tubes inoculated with soil. Rhizobia were present at pH 4.5 but absent at pH 3.9. Neither nodule number nor effectiveness were influenced by the method of isolation and the clover variety on which the strain was isolated. There was no relationship between the pH of the soils and either the number of nodules or the effectiveness of the isolates from those soils. Screening the isolates for tolerance of acidity and Al showed that multiplication was unaffected at pH 5.0 but was slowed for all strains at pH 4.5. Multiplication at pH 5.5 was unaffected by 10 μM Al but was inhibited by 50 μM Al. At pH 4.5 all but 16% of the isolates were inhibited by 10 μM Al; none multiplied with 50 μM Al. The strains which multiplied at pH 4.5 with and without Al were isolated equally from soils in the range pH 4.5–5.6. They were also isolated in almost equal proportions from the two varieties of clover and by the two isolation methods. Overall there was little variation in the effectiveness and acid- and Al-tolerance of isolates from these soils of different pH.  相似文献   

4.
《Soil biology & biochemistry》2001,33(4-5):457-463
The potential enhancement of root growth and nodulation in vegetable soybean (AGS190) was studied with application of Azospirillum brasilense (Sp7) and A. lipoferum (CCM3863) co-inoculated with two Bradyrhizobium japonicum strains (TAL102 and UPMR48). Significant root growth stimulation and nodulation were observed in Azospirillum as well as during its co-inoculation with Bradyrhizobium. Nodule formation is linked with the initiation of new roots; nodules were almost absent even in Bradyrhizobium inoculated plant due to the absence of new roots development in clipped rooted seedlings. Total root length, root number, specific root length, root dry matter, root hair development and shoot dry matter were significantly increased by Azospirillum alone and its co-inoculum. Co-inoculated plants significantly influenced the number of nodules and its fresh weight. A. brasilense seemed to perform better in root growth and nodule development compared to A. lipoferum.  相似文献   

5.
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   

6.
In 1993 and 1994, 12 bacterial isolates were isolated from root nodules of cicer milkvetch (Astragalus cicer). In the tests for nodulation of A. cicer by these bacterial isolates, five were found to form hypertrophic structures, while only two formed true nodules. These true nodules were formed in a sterilized soil system. This system might be able to act as a DNA donor to provide residual DNA to other microbes in the soil. The rhizobial isolates were thought to have lost genetic material crucial to nodulation during the isolation process. This hypothesis was supported by an experiment in which isolate B2 was able to nodulate A. cicer in vermiculite culture after being mixed with heat-killed rhizobia, Rhizobium leguminosarum bv. trifolii and R. loti. The nodulation would not occur in vermiculite culture system without the heat-killed rhizobia. Based on the biochemical data, the B2 and 9462L, which formed true nodules with A. cicer, were closely related. The rhizobia type cultures that nodulate A. cicer include Bradyrhizobium japonicum, Rhizobium leguminosarum bv. trifolii, R. leguminosarum bv. viceae, and R. loti. All of these rhizobia were from different cross-inoculation groups. The B2 and 9462L isolates could only nodulate Medicago sativa, Phaseolus vulgaris, and Melilotus officinalis, but not these species within the genus from which they were isolated: Astragalus. The traditional cross-inoculation group concept obviously does not fit well in the classification of rhizobia associated with Astragalus. The rhizobia isolated from A. cicer can be quite different, and the rhizobia able to renodulate A. cicer also quite diverse. Received: 27 June 1996  相似文献   

7.
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   

8.
 The effect of six Bradyrhizobium sp. (lupin) strains (WPBS 3201D, WPBS 3211D, USDA 3040, USDA 3041, USDA 3042 and CB 2272) and Fe supply on nodulation, N2-fixation and growth of three lupin species (Lupinus termis, L. albus and L. triticale) grown under Fe deficiency in an alkaline soil, were examined in sterilized and non-sterilized pot experiments. When inoculated with USDA 3040, 3041, 3042 and CB2272 without Fe addition, the three lupin species had a very low nodule number and mass, low shoot and root dry matter accumulation and lower N yield. However, inoculation with WPBS 3201D and 3211D without Fe treatments increased all these parameters substantially. The ability of WPBS 3201D and 3211D to form nodules on the three lupin species under conditions of Fe stress could be attributed to their ability to scavenge Fe from Fe-deficient environments through their siderophore production. Addition of Fe to the other four strains significantly increased nodulation and N2-fixation of the three lupin species, indicating that the poorer nodulation and N2-fixation of these strains in the absence of Fe, resulted from a low ability to obtain Fe from alkaline soils. Bradyrhizobium strains WPBS 3201D and 3211D were superior to the other four strains in terms of promoting greater nodulation, N2-fixation, plant growth and N accumulation of L. termis and L. albus. However, the other four strains were more efficient in symbiotic association with L. triticale. The greater variations in nodule efficiencies (specific nitrogenase activity) under different levels of Fe supply could be attributed to the quantities of bacteroid protein and leghaemoglobin in the nodules. The results suggested that Bradyrhizobium (lupin) strains differ greatly in their ability to obtain Fe from alkaline soils, and that the selection of bradyrhizobial strains which are tolerant of Fe deficient soils could complement plant breeding for the selection of legume crops for Fe-deficient soils. Received: 5 January 1998  相似文献   

9.
Biserrula pelecinus is a pasture legume species new to Australian agriculture. The potential N benefit from B. pelecinus pastures in agricultural systems may not be realised if its symbiotic interactions with Mesorhizobium spp. are not well understood. This study evaluated the symbiotic interactions of four strains of Biserrula root-nodule bacteria (WSM1271, WSM1283, WSM1284, WSM1497) with four genotypes of B. pelecinus (cv. Casbah, 93GRC4, 93ITA33, IFBI1) and with a range of related legumes, including species known to be nodulated by strains of Mesorhizobium loti and other Mesorhizobium spp. Structures of root nodules were studied using light and electron microscopy enabling the ultrastructure of effective and ineffective nodules to be compared. B. pelecinus always formed typical indeterminate, finger-like nodules. The number of bacteroids inside symbiosomes varied between host×strain combinations, however, nodules formed by ineffective associations had well developed peribacteroid membranes and abundant bacteroids. Considerable variation was found in N2-fixing effectiveness of strains isolated from B. pelecinus on the four B. pelecinus genotypes. Strains WSM1271, WSM1284 and WSM1497 nodulated Astragalus membranaceus, only strains WSM1284 and WSM1497 nodulated Astragalus adsurgens. Strain WSM1284 also nodulated Dorycnium rectum, Dorycnium hirsutum, Glycyrrhiza uralensis, Leucaena leucocephala, Lotus edulis, Lotus glaber, Lotus maroccanus, Lotus ornithopodioides, Lotus pedunculatus, Lotus peregrinus, Lotus subbiflorus and Ornithopus sativus. The four strains from B. pelecinus did not nodulate Amorpha fruticosa, Astragalus sinicus, Cicer arietinum, Hedysarum spinosissimum, Lotus parviflorus, Macroptilium atropurpureum or Trifolium lupinaster. M. loti strain SU343 nodulated all four genotypes of B. pelecinus. However, M. loti strain CC829 only nodulated B. pelecinus genotypes 93ITA33 and IFBI1 and the nodules were ineffective. The root nodule isolates from H. spinosissimum (E13 and H4) nodulated B. pelecinus cv. Casbah whereas the commercial inoculant strain for Cicer (CC1192) could not nodulate any genotype of B. pelecinus. These results indicate that strains WSM1271, WSM1283 and WSM1497 isolated originally from B. pelecinus have a specific host range while strain WSM1284 is promiscuous in its capacity to nodulate with a broad range of related species. As B. pelecinus can be nodulated by Mesorhizobium spp. from other agricultural legumes, particularly Lotus, there is an opportunity to utilise this trait in cultivar development.  相似文献   

10.
Summary The nodulation competitiveness of 17 Rhizobium leguminosarum bv. phaseoli and 3 R. tropici strains was analysed in growth pouches, at pH 5.2 and 6.4. All 20 strains were coinoculated with a gus + strain of R. leguminosarum bv. phaseoli strain KIM5s. The gus+ phenotype, carrying the glucuronidase gene, was used to type nodules directly in the growth pouches. Nodule occupancy ranged from 4% for the least competitive to 96% for the most competitive R. leguminosarum bv. phaseoli strain. The R. tropici strains showed low rates of nodule occupancy at pH 6.4 but their competitiveness improved significantly under acid conditions. CIAT 895 was the only R. leguminosarum bv. phaseoli strain that was less competitive (P<0.05) at the lower pH. The competitiveness of all the other R. leguminosarum bv. phaseoli strains was unaffected by pH. Various physiological and genetic properties of the strains were analysed in search of correlations with nodulation competitiveness. Hybridisation patterns with three different DNA probes (nif KDH, common nod genes, and hup genes) and the metabolism of 53 different C sources were compared. No general correlations were found between hybridisation or growth pattern and competitiveness. The less competitive R. tropici strains had a unique DNA hybridisation pattern and were not able to use shikimate, ferulate, coumarate, or asparagine as C sources. Most of the less competitive R. leguminosarum bv. phaseoli strains could not metabolize either ferulate or coumarate. This might indicate a relationship between nodulation competitiveness and the ability to degrade aromatic compounds.  相似文献   

11.
Summary Bacteria isolated from the root zones of field-grown soybean plants [Glycine max (L.) Merr.] were examined in a series of glasshouse experiments for an ability to affect nodulation competition among three strains of Bradyrhizobium japonicum (USDA 31, USDA 110, and USDA 123). Inocula applied at planting contained competing strains of B. japonicum with or without one of eleven isolates of rhizosphere bacteria. Tap-root nodules were harvested 28 days after planting, and nodule occupancies were determined for the bradyrhizobia strains originally applied. Under conditions of low iron availability, five isolates (four Pseudomonas spp. plus one Serratia sp.) caused significant changes in nodule occupancy relative to the corresponding control which was not inoculated with rhizosphere bacteria. During subsequent glasshouse experiments designed to verify and further characterize these effects, three fluorescent Pseudomonas spp. consistently altered nodulation competition among certain combinations of bradyrhizobia strains when the rooting medium did not contain added iron. This alteration typically reflected enhanced nodulation by USDA 110. Two of these isolates produced similar, although less pronounced, effects when ferric hydroxide was added to the rooting medium. The results suggest that certain rhizosphere bacteria, particularly fluorescent Pseudomonas spp., can affect nodulation competition among strains of R. japonicum. An additional implication is that iron availability may be an important factor modifying interactions involving the soybean plant, B. japonicum, and associated microorganisms in the host rhizosphere.Paper No. 10648 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601, USA  相似文献   

12.
The Medicago sativa-Sinorhizobium symbiosis is challenged by acidity, resulting in generally poor nodulation and production. Medicago murex, however, can nodulate and grow at low pH. The effect of low pH on signal exchange in the Sinorhizobium-Medicago symbiosis was studied to gain a greater understanding of the basis for poor nodulation of M. sativa compared to M. murex. Root exudates from M. sativa and M. murex grown in buffered nutrient solution at pH 4.5, 5.8 and 7.0, were collected to measure the expression of nodB induction in Sinorhizobium. A nodB-gusA fusion was constructed and inserted into Sinorhizobium medicae strains WSM419 (acid tolerant) and CC169 (acid sensitive). We identified greater induction by root exudates from both Medicago spp. collected at pH 4.5 than at pH 5.8 and 7.0, less induction by M. murex than M. sativa and less induction of WSM419 than CC169. The same major inducing compounds, 4′,7-dihydroxyflavanone (liquiritigenin), 4′,7-dihydroxyflavone, and 2′,4′,4-trihydroxychalcone (isoliquiritigenin), were identified in exudates of M. murex and M. sativa at all pH values, although in increasing amounts at lower pH. Poor nodulation of M. sativa relative to M. murex under acid conditions is not the consequence of decreased induction of Sinorhizobium nodB by chemical inducers present in the root exudates of both species at low pH.  相似文献   

13.
Effects of acidic minesoil on sericea lespedeza [Lespedeza juncea (L.F.) var. sericea (Mig.)] and its nitrogen (N2)‐fixing symbiotic relationship with Bradyrhizobium spp. were examined. Sericea lespedeza was grown in pots with N fertilization, without N fertilization, or with commercial Bradyrhizobium as a seed inoculant. Minesoil (pH 5.2) was fertilized with calcium (Ca), phosphorus (P), molybdenum (Mo), and potassium (K), and the pH level was adjusted to 4.8 or 4.5 with aluminum or iron sulfate [Al2(SO4)3; Fe2(SO4)3]. Minesoil was also limed to pH 6.1. Shoot dry weights, shoot N concentrations, nodule dry weights, and nodule numbers were significantly lower (P < 0.05) when inoculated plants were grown in soil at pH 4.5 and 4.8 compared to limed soil. Thus, the N2 fixation process was adversely affected below pH 5.0. Nitrogen‐fertilized plants grew well in acidified soil, and there were no significant differences in shoot dry weights of such plants among the soil acidification treatments including limed soil. Thus, the N2‐fixing symbiosis appeared to be more sensitive to acidified soil than the plant host. The effects of Al toxicity versus other factors could not be determined because Al2(SO4)3‐ and Fe2(SO4)3‐amended soils contained similar levels of toxic Al at the highest pH (4.8) that prevented N2 fixation.

Time periods required for cells of Bradyrhizobium strains to multiply by a factor of 104 were significantly longer (P ≤ 0.05) in extracts of Al2(SO4)3‐amended soil (pH 4.8 and 4.5) than in extracts of calcium carbonate [CaCO3]‐amended soil (pH 6.1). These increases suggested that reduced multiplication of Bradyrhizobium in acidified minesoils may have been at least partially responsible for the large decreases in nodulation and N2 fixation observed in these soils. It was also reasoned that the inability of existing bacteria to infect and nodulate plant roots may also have been a factor, based on the high inoculation rates used and the abilities of Bradyrhizobium cells to survive and multiply (albeit at a reduced rate) in extracts of acidified soil. Sericea lespedeza is known to tolerate soils of pH 4.5. However, results of this study suggested sericea lespedeza may not fix appreciable N2 in acidic soil below pH 5 when inoculated with commercial Bradyrhizobium, even after the establishment of lespedeza plants tolerant of such conditions.  相似文献   

14.
Communities of resident rhizobia capable of effective nodulation of pulse crops were found to vary considerably over a range of soil environments. These populations from soils at 50 sites in Southern Australia were evaluated for nitrogen fixing effectiveness in association with Pisum sativum, Vicia faba, Lens culinaris, Vicia sativa, Cicer arietinum and Lupinus angustifolius. The values for nitrogen fixing effectiveness could be related to soil pH as determined by soil type and location. It was found that 33% of paddocks had sufficient resident populations of Rhizobium leguminosarum bv viciae for effective nodulation of faba bean, 54% for lentils, 55% for field pea and 66% for the effective nodulation of the vetch host plant. Mesorhizobium cicer populations were very low with only 7% of paddocks surveyed having sufficient resident populations for effective nodulation. Low resident rhizobial populations (<10 rhizobia g−1 soil) of R. leguminosarum bv viciae and M. cicer were found in acid soil conditions. In contrast, Bradyrhizobium populations increased as soil pH decreased. Inoculation increased faba bean yields from 0.34 to 4.4 t ha−1 and from 0.47 to 2.37 t ha−1 for chickpeas on acid soils. On alkaline soils, where resident populations were large there was no consistent response to inoculation. Observations at experimental field sites confirmed the findings from the survey data, stressing the importance of rhizobial inoculation, especially on the acid soils in south-eastern Australia.  相似文献   

15.
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   

16.
The symbiosis between the soil bacteria Rhizobium, Sinorhizobium, Azorhizobium, Mesorhizobium or Bradyrhizobium and leguminous plants is characterised by a specific multistep signal exchange. Only when a compatible rhizobial strain encounters its leguminous host, nodules will be formed on the roots of the host. During infection of this nodule, the microsymbiont evolves into a bacteroid form which, when provided with plant-derived carbon sources, is able to convert atmospheric nitrogen to ammonia that subsequently is supplied to the plant. The developmental programme underlying nodule organogenesis and functioning has been studied intensively for several decades. In this review, several observed plant phenotypes resulting from an ineffective symbiosis between plants and mutant rhizobial strains are represented. Besides the influence of the bacterial nodulation, nitrogen fixation and surface polysaccharide genes on symbiosis, the role of other genes important for the formation of effective nitrogen fixing nodules will be explained.  相似文献   

17.
以缺铁的石灰性紫色土为供试土壤进行盆栽实验,选用三株慢生型花生根瘤菌Spr3 5、Spr3 7、Spr4 5及gusA和celB标记的菌株gusA3 5、gusA3 7、gusA4 5、celB3 5、celB3 7、celB4 5接种天府9号花生。通过标记根瘤菌形成的根瘤能与检测试剂产生颜色反应的特征,检测施铁肥及施不同浓度的铁肥对花生 根瘤菌有效性和竞争性的影响。结果发现:缺铁的石灰性紫色土上单施铁肥、单接种根瘤菌、接种根瘤菌配施铁肥均能促进花生与根瘤菌的共生固氮效应和竞争结瘤能力,但接种根瘤菌配施铁肥的效果最好,单接种根瘤菌的效果次之,单施铁肥的效果差。喷施0 .2 %硫酸亚铁溶液的效果比0 .3%的好。植株全氮含量和叶绿素含量都是指示共生固氮效应的重要指标,与花生产量间存在极显著的相关性,相关系数分别为0 .76 3和0 .795。gusA和celB两种标记方法检测的结果基本一致,两种标记根瘤菌的平均占瘤率分别为79.6 4 %、75 .6 2 %、74 .4 1%。供试菌株中Spr4 5的有效性和竞争性最强,Spr3 7次之,Spr3 5最差  相似文献   

18.
《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   

19.
Soil samples taken from 28 sites following varying periods of cropping in a crop-pasture rotation contained very low populations of Rhizobium trifolii. Populations were less than 103g?1R. trifolii of soil for 89% of the sites and were significantly correlated with soil pH. Application of lime resulted in a build-up of R. trifolii in the absence of the host legume, subterranean clover, but when inoculated clover seed was sown the populations built up to satisfactory levels after the first season's growth, regardless of soil pH.The number of nodules per plant was increased by the application of lime, but the plants growing in unlimed soil had fewer, larger nodules. The increase in nodulation with lime on these low-calcium acid soils persisted to the third growing season.  相似文献   

20.
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   

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