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1.
 Most soils sown with field beans (Phaseolus vulgaris L.) contain indigenous rhizobia which might interfere with the establishment of inoculated strains. As a consequence, the benefits of bean inoculation are usually questioned, and the use of N fertilizer is gradually becoming a common practice. The present study had the objective of evaluating the effectiveness of inoculation and N fertilization in field soil with (site 1) and without (site 2) a previous bean-cropping history. At site 1, which had a rhizobial population of 7×102 cells g–1 soil, inoculation had no effect on nodulation or yield, whereas at site 2 (<10 cells g–1 soil) inoculation increased nodulation, nodule occupancy by the inoculated strain and grain yield. N fertilizer decreased nodulation at both sites, but increased grain yield at site 1 but not at site 2, indicating that the response to inoculation and N fertilization depends on the cropping history. When bean was cultivated for the first time, indigenous populations of rhizobia were low and high yields were accomplished solely with seed inoculation, with no further response to N fertilizer. In contrast, previous cultivation of bean increases soil rhizobia, preventing nodule formation by inoculated strains, and N fertilizer may be necessary for maximum yields. A significant interaction effect between N fertilizer and inoculation was detected for serogroup distribution only at site 2, with N fertilizer decreasing nodule occupancy by the inoculated strain and increasing the occurrence of indigenous strains. Consequently, although no benefits were obtained by the combination of inoculation and N fertilizer, this practice may be feasible with the selection of appropriate N-tolerant strains from the indigenous rhizobial population. Received: 26 May 1999  相似文献   

2.
The competition with established soil populations of Bradyrhizobium able to nodulate soybean has been one of the major constraints to the introduction of more efficient strains in Cerrados soils. The effects of nodulation establishment and persistence of four serologically distinct strains of Bradyrhizobium japonicum (CPAC 15 and CPAC 7, belonging to serogroups USDA 123 and CB 1,809) and B. elkanii (29 W and SEMIA 587, belonging to serogroups 29 W and 587) were examined. These strains were introduced in a dark-red oxisol, without indigenous populations of soybean bradyrhizobia, and were evaluated for 6 years. The experimental design was a completely randomized block with four replicates. In the first year, besides the inoculation treatments, there was also an uninoculated control. In the second year, the main plots were split into three sub-plots and treatments consisted of an uninoculated control, CPAC 7 and CPAC 15. In the third year, the entire area was inoculated with CPAC 7. In the fourth and sixth years, the plots were planted with soybean without inoculation, and in the fifth year the plots were left fallow. The strains introduced in the first year influenced nodule occupancy by strain CPAC 7 until the third successive growing season. By the fourth and sixth years, as a consequence of the dispersal of strains serologically related to serocluster 123 in the entire experimental area, this serogroup dominated the nodulation, occurring, on average, in more than 50% of the nodules of the treatments where it had never been inoculated.  相似文献   

3.
The present study was conducted to isolate and characterize rhizobial strains from root nodules of cultivated legumes, i.e. chickpea, mungbean, pea and siratro. Preliminary characterization of these isolates was done on the basis of plant infectivity test, acetylene reduction assay, C-source utilization, phosphate solubilization, phytohormones and polysaccharide production. The plant infectivity test and acetylene reduction assay showed effective root nodule formation by all the isolates on their respective hosts, except for chickpea isolate Ca-18 that failed to infect its original host. All strains showed homology to a typical Rhizobium strain on the basis of growth pattern, C-source utilization and polysaccharide production. The strain Ca-18 was characterized by its phosphate solubilization and indole acetic acid (IAA) production. The genetic relationship of the six rhizobial strains was carried out by random amplified polymorphic DNA (RAPD) including a reference strain of Bradyrhizobium japonicum TAL-102. Analysis conducted with 60 primers discriminated between the strains of Rhizobium and Bradyrhizobium in two different clusters. One of the primers, OPB-5, yielded a unique RAPD pattern for the six strains and well discriminated the non-nodulating chickpea isolate Ca-18 from all the other nodulating rhizobial strains. Isolate Ca-18 showed the least homology of 15% and 18% with Rhizobium and Bradyrhizobium, respectively, and was probably not a (Brady)rhizobium strain. Partial 16S rRNA gene sequence analysis for MN-S, TAL-102 and Ca-18 strains showed 97% homology between MN-S and TAL-102 strains, supporting the view that they were strains of B. japonicum species. The non-infective isolate Ca-18 was 67% different from the other two strains and probably was an Agrobacterium strain.  相似文献   

4.
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   

5.
This study reports for the first time the presence of diazotrophic bacteria belonging to the genera Achromobacter and Zoogloea associated with wheat plants. These bacterial strains were identified by the analysis of 16S rDNA sequences. The bacterium IAC-AT-8 was identified as Azospirillum brasiliense, whereas isolates IAC-HT-11 and IAC-HT-12 were identified as Achromobacter insolitus and Zoogloea ramigera, respectively. A greenhouse experiment involving a non-sterilized soil was carried out with the aim to study the endophytic feature of these strains. After 40 days from inoculation, all the strains were in the inner of roots, but they were not detected in soil. In order to assess the location inside wheat plants, an experiment was conducted under axenic conditions. Fifteen days after inoculation, preparations of inoculated plants were observed by the scanning electron microscope, using the cryofracture technique, and by the transmission electron microscope. It was observed that all isolates were present on the external part of the roots and in the inner part at the elongation region, in cortex cells, but not in the endodermis or in the vascular bundle region. No colonizing bacterial cells were observed in wheat leaves.  相似文献   

6.
Naturally growing Sesbania species with tolerance to unfavourable habitats are widely distributed in non-cultivated seasonally wetland areas in Uruguay. We investigated the relative abundance, diversity and symbiotic efficiency of Sesbania punicea and S. virgata rhizobia in three ecologically different undisturbed and water-logged sites in Uruguay. Numbers of native-soil rhizobia infective on S. punicea or S. virgata were low, with higher numbers associated with the presence of S. virgata. Plants of S. virgata inoculated with soil suspension showed aerial and nodule biomass greater than that obtained with S. punicea. The rhizobia nodulating Sesbania species in water-logged lands in different regions of Uruguay were diverse differing in growth rates, acid production, growth at 39°C and in LB medium, host range and symbiotic efficiency. Seventeen representative strains clustered into four groups on the basis of phenotypic characteristics, ARDRA and DNA fingerprinting (GTG5-PCR). Partial sequence of 16S rRNA from eight of these strains classified them into at least two genera with four species: Azorhizobium doebereinerae, Rhizobium sp. related to R. etli and two different Rhizobium sp.-Agrobacterium. Our results confirm the presence of the specie Azorhizobium doebereinerae as microsymbionts of S. virgata in South America. No strain of Rhizobium etli has previously been reported as a microsymbiont of Sesbania, though R. etli like organisms have also been recovered from Dalea purpurea and Desmanthus illinoensis. Significant increases in dry matter production were obtained with S. virgata plants inoculated with selected rhizobial strains under growth chamber conditions.  相似文献   

7.
This research reports the effect of Bradyrhizobium spp strains on dry matter yield, nodulation and seed yield of soybean varieties grown in N-deficient soil in Uzbekistan in pot and field experiments, in 2001 and 2002. The results of experiments revealed that significant positive effects on growth, nodule number and yield of soybean were obtained after inoculation with Bradyrhizobium spp strains; and, generally, strains S62 and S63 were more effective than strain S61. The protein content of seeds also increased after inoculation. Both Orzu and Uzb2 soybean varieties gave a higher response than the Uzb6 variety.  相似文献   

8.
This study evaluated the response of pea (Pisum sativum cv. Trapper) to arbuscular mycorrhizal fungi (AMF) and Rhizobium leguminosarum bv. viceae strains varying in their effectiveness on pea. Plants were inoculated with the AMF species Glomus clarum NT4 or G. mosseae NT6 and/or ten Rhizobium strains, and grown for 90 days in soil containing indigenous AMF and rhizobia. The effectiveness of the Rhizobium strains on the growth (P <0.046; r =0.64) and N nutrition (P <0.04; r =0.65) of 6-week-old pea grown under gnotobiotic conditions was correlated with the growth and N nutrition of 90-day-old pea grown in natural soil for all strains except LX48. The growth and yield response of pea to co-inoculation with AMF and Rhizobium strains depended on the particular AMF-Rhizobium strain combination. In some cases, the yield and N nutrition of pea inoculated with a superior Rhizobium strain was significantly (P <0.05) enhanced by an apparently compatible AMF species compared to the Rhizobium treatment. On the other hand, an apparently incompatible AMF species significantly (P <0.05) reduced the performance of an effective Rhizobium strain. In general, treatments with effective Rhizobium strains or co-inoculation treatments with effective Rhizobium strains and a compatible AMF species produced the best results. Changes in total shoot dry matter production was significantly (P <0.05) correlated with the total shoot N (P <0.0001; r =0.95) and P content (P <0.0001; r =0.87), indicating that this response was mediated by enhanced N and P nutrition. Growth, yield and nutrition of pea were not related to AMF colonization of roots. Our results suggest that careful co-selection of AMF species and Rhizobium strains can enhance pea yield and nutrition.  相似文献   

9.
Laboratory tests and greenhouse experiments were carried out to investigate the abilities of Bacillus subtilis Y-IVI to promote plant growth and to colonize the rhizosphere and interior tissues of muskmelon. Laboratory tests showed that B. subtilis Y-IVI can produce indole acetic acid, siderophores, and ammonia. The inoculation of soil with green fluorescent protein-tagged Y-IVI (GY-IVI) significantly increased plant shoot and root dry weights as compared with the non-inoculated soils. The inoculation of soil with B. subtilis GY-IVI maintained approximately 108 colony-forming units (cfu) of GY-IVI per gram of dry rhizosphere soil for 1 month. The GY-IVI recovered from the interior of crowns and roots in the inoculated soil were 106 and 107 cfu g−1 dry weight, respectively, suggesting that GY-IVI acted as an endophyte. In the present study, we combined the two important growth promotion ingredients, colonization ability and growth promotion metabolites produced by biological agents, to investigate B. subtilis Y-IVI’s promotion effects on muskmelon growth.  相似文献   

10.
Nitrogen fixing potential in terms of acetylene reducing activity (ARA) and biomass accumulation (in terms of chlorophyll) were investigated using surface and below-surface soil cores, collected from rice fields 45 and 90 days after transplanting (DAT). Treatments included different levels of urea (30, 60, 90 and 120 kg N ha–1) in combination with inoculation using blue green algae (BGA) and Azolla biofertilizers. Application of biofertilizers brought about a significant enhancement in chlorophyll accumulation and nitrogenase activity, when measured 45 DAT. Positive effects in below-surface soil cores, on both these parameters as a result of application of biofertilizers further emphasized their contribution to the N economy of rice fields. Plots treated with 30 and 60 kg N ha–1 along with biofertilizers exhibited the highest percentage increase in terms of algal biomass and ARA, both in surface and below-surface soil cores at 45 DAT. A definite need to examine critically the nature and metabolic activities of below-surface microflora is highlighted through our investigation.  相似文献   

11.
Summary The competitive ability of inoculated and indigenous Rhizobium/Bradyrhizobium spp. to nodulate and fix N2 in grain legumes (Glycine max, Vigna unguiculata, Phaseolus vulgaris) and fodder legumes (Vicia sativa, Medicago sativa, and Trifolium subterraneum) was studied in pots with two local soils collected from two different fields on the basis of cropping history. The native population was estimated by a most-probable-number plant infectivity test in growth pouches and culture tubes. The indigenous rhizobial/bradyrhizobial population ranged from 3 to 2×104 and 0 to 4.4×103 cells g-1 in the two soils (the first with, the second without a history of legume cropping). Inoculated G. max, P. vulgaris, and T. subterraneum plants had significantly more nodules with a greater nodule mass than uninoculated plants, but N2 fixation was increased only in G. max and P. vulgaris. A significant response to inoculation was observed in the grain legume P. vulgaris in the soil not previously used to grow legumes, even in the presence of higher indigenous population (>103 cells g-1 soil of Rhizobium leguminosarum bv phaseoli). No difference in yield was observed with the fodder legumes in response to inoculation, even with the indigenous Rhizobium sp. as low as <14 cells g-1 soil and although the number and weight of nodules were significantly increased by the inoculation in T. subterraneum. Overall recovery of the inoculated strains was 38–100%, as determined by a fluorescent antibody technique. In general, the inoculation increased N2 fixation only in 3 out of 12 legume species-soil combinations in the presence of an indigenous population of rhizobial/bradyrhizobial strains.  相似文献   

12.
Ten leguminous trees, four exotic species (Australian Acacia) and six indigenous species (three Sahelian Acacia spp. and three Sesbania spp.), were grown for 4 months in a natural Sahelian soil inoculated with or without the endomycorrhizal fungus, Glomus intraradices. In control trials, the determinant factor structuring the soil nematode fauna was the plant species, related plants having a similar influence on the nematode community in the soil. Soil nematode abundance increased from exotic acacias (3.3 g-1 dry soil) to native acacias (11.5 g-1 dry soil) and Sesbania species (17.6 g-1 dry soil). Plant feeding nematodes (mainly Scutellonema and Tylenchorhynchus) were significantly less abundant under exotic acacias (1.4 g-1 dry soil) than under native acacias (7.2 g-1 dry soil) or Sesbania species (7.3 g-1 dry soil). Bacterial feeding nematode density increased from exotic acacias (1.2 g-1 dry soil) to native acacias (3.0 g-1 dry soil) and Sesbania species (7.7 g-1 dry soil) as total densities. However, the differences in the structure of the nematode communities between plant groups were suppressed in the presence of the mycorrhizal fungus. In fact, no difference in nematode densities remained between plant groups when G. intraradices developed in several dominant taxa belonging to different trophic groups, particularly: Tylenchorhynchus, Apelenchina, Cephalobus and Dorylaimoidea. This study clearly indicated that inoculation with the arbuscular mycorrhizal fungus G. intraradices diminished the plant-specific effect on the structure of the soil nematode community.  相似文献   

13.
Crops grown in the first or second year after Medicago sativa L. (lucerne or alfalfa) in southern Australia have sometimes yielded less than crops grown after Trifolium subterraneum L. (subterranean clover), despite the greater annual accumulation of legume nitrogen (N) and enhanced N2 fixation in lucerne-based pastures. To understand why, we studied the N mineralisation patterns of root residues collected from 16- or 20-week-old plants using incubation assays, in two separate experiments with contrasting soil types (a red loam and a grey clay loam). Fine roots of both species added to soil produced more mineral N than the control soil with no root residues added. In contrast, less mineral N accumulated in the presence of coarse roots than in the control soil. These patterns were not explained by differences in physical size or surface-area, but appeared to be more related to the carbon to nitrogen ratio (C:N) of fine and coarse roots. Fine roots of both species had a C:N of about 11, while the C:N of coarse roots ranged from 28 to 37. Subterranean clover had a high proportion of fine roots giving a weighted average C:N of 19 for the whole root system, and could be expected to result in a rapid net mineralisation of N. The root systems of lucerne on the other hand, consisted mainly of coarse roots giving an average C:N of 26, and would be likely to induce a transient net immobilisation of N and a delay in net mineralisation. The same general patterns of N mineralisation/immobilisation were observed in the second experiment. Tissue chemical analyses suggested that even where the total C:N of subterranean clover and lucerne residues were similar, the amounts of C and N in the soluble fraction of the residues and the C:N of that soluble fraction could largely account for the observed differences in N mineralisation/immobilisation.  相似文献   

14.
The genetic diversity and symbiotic efficiency among indigenous rhizobia isolates obtained from native field with or without organic fertilization and superficial mineral fertilization were investigated. Eighty-six indigenous rhizobia were isolated from these fields using four common bean varieties as trap-host. The common bean varieties Mexico 309 and Rio Tibagi selected the most efficient rhizobia strains because they showed the best yields and N contents results. The genetic characterization of 36 rhizobia isolates was evaluated by using electrophoretic profiles of amplification products using primers ERIC1-R and ERIC-2. Our results demonstrated that besides the large diversity in the indigenous rhizobial community, the genotype of the trap-host probably influences the selection of the most efficient strains.  相似文献   

15.
The interactions between Phaseolus vulgaris, Rhizobium spp. strains nodulating P. vulgaris, and arbuscular mycorrhizal (AM) fungi were assessed under greenhouse conditions in a nonsterilized Typic Haplustalf soil from Cauca, Colombia. Our results indicate a specific involvement of AM fungal species in nitrogen acquisition by the legume plants from symbiotic nitrogen fixation and from soil. A significant specific influence of inoculation with Glomus spp. on the 15N/14N ratio in plant shoots was dependent on the inoculated rhizobial strain, but AM fungal inoculation had no significant effect on shoot dry weight or nodule occupancy in the two different rhizobial strain treatments. The results imply that in low P soils the effects of an improved mycorrhizal symbiosis may include improved symbiotic N2 fixation efficiency and/or improved soil N uptake. Received: 11 May 1996  相似文献   

16.
Benefits from the application of plant growth-promoting bacteria in agriculture largely depend on the complex interactions between several factors including the nature of fertilizers selected. This study was designed to determine the fine tuning between the inoculated bacteria and different fertilizers and their effect on the growth of lettuce plants (Lactuca sativa L.). Plant growth promotion by a novel species of the genus Azospirillum, namely A. rugosum IMMIB AFH-6, was tested by biochemical, bioassay, and greenhouse studies. The treatments used in the greenhouse study were; unfertilized control (Blank), half recommended dose of chemical fertilizer (1/2CF), full recommended dose of chemical fertilizer (1CF), pig manure fertilizer (PMF), pig manure fertilizer + half recommended dose of chemical fertilizer (PMF + 1/2CF), and pig manure fertilizer + full recommended dose of chemical fertilizer (PMF + 1CF). All these treatments when inoculated with A. rugosum IMMIB AFH-6 inoculation were, respectively, In-Blank, In-1/2CF, In-1CF, In-PMF, In-PMF + 1/2CF, and In-PMF + 1CF. Significant increase in plant biomass and shoot N, P, Ca, and Fe was shown in the In-Blank treatment. Plant growth in soil amended with PMF and A. rugosum IMMIB AFH-6 was significantly lower than in soil treated with the chemical fertilizer, but inoculation combined with chemical fertilizer significantly elevated the plant biomass. The In-PMF + 1/2CF treatment showed the highest yield. A. rugosum IMMIB AFH-6 facilitated the accumulation of trace minerals in higher concentrations when PMF was combined with 1CF. To examine the benefits of inoculation by A. rugosum IMMIB AFH-6, we have proposed a new type of data analysis which considers both biomass and nutrient content of plants. This new type of analysis has shown the importance of the mineral content of plant.  相似文献   

17.
The response of faba bean to the application of four rates of gypsum (0, 2.5, 5.0, 10.0 t ha−1) to a non-saline, alkaline sodic soil was measured in terms of grain yield, dry matter (DM) production, N accumulation and the proportional dependence of the legume on symbiotic N2 fixation (P atm). A yield-independent, time-integrated 15N-dilution model was used to estimate symbiotic dependence. A significant decrease in the exchangeable sodium percentage and significant increases in exchangeable Ca++ and the Ca++:Mg++ ratio in the 0–10-cm soil layer were measured 30 months after application of 10 t ha−1 gypsum. Despite low and erratic rainfall during crop growth, faba bean DM and N uptake responded positively to gypsum application. The symbiotic dependence of the legume at physiological maturity was little affected by sodicity (P atm = 0.74 at zero gypsum and 0.81–0.82 at 2.5–10 t ha−1 gypsum). The increase in fixed N due to gypsum application was mainly due to increases in legume DM and total N uptake. At 10 t ha−1 of gypsum, faba bean fixed more than 200 kg N ha−1 in above-ground biomass.  相似文献   

18.
Summary Six Rhizobium leguminosarum bv. phaseoli strains (Ciat 151, Ciat 895, Ciat 899, CE3, H2C, Kim5s) were tested for nodule occupancy in different bean cultivars at two field sites (one fertile, one acid tropical soil) and in the greenhouse. The effects of several environmental factors such as low pH, high temperature, Al and Mn toxicity, iron deficiency, bean tannins, and bean phytoalexins were tested in vitro. Strain Kim5s was competitive under all tested conditions while strains CE3 and H2C had consistently low nodule occupancy levels. Strain Ciat 151 was superior to the other inoculant strains in the acid soil but competed poorly in the fertile soil. Strain Ciat 895 was more competitive in the fertile soil. There was a decline in nodule occupancy for all strains tested from the first trifoliate leaf stage to the pod-filling stage. No plant genotype effect on nodule occupancy was observed. There were significant (P<0.05) plant genotype and location effects, but no significant strain effect on acetylene reduction activity, plant dry weight, and nodule number. The greenhouse experiments confirmed, at least partially, the results from the field trials. In Leonard jars with an acid soil, strains Ciat 151 and Kim5s were amongst the most competitive strains. In coinoculation experiments, Kim5s was the most competitive strain, followed by Ciat 899 and Ciat 895. The competitiveness of a given strain was affected by the coinoculant strain. Tolerance in vitro to low pH, high growth temperature, Al or Mn toxicity, or Fe limitation was not related to competitiveness of the inoculum strains. The sensitivity of the strains towards bean tannins or bean phytoalexins also was not correlated with their competitiveness.  相似文献   

19.
Improved fallows with leguminous trees have been developed in Southern Africa as a viable alternative to inorganic fertilizers but the changes in soil properties that are responsible for crop productivity improvement and implications of mixing litter and fresh leaves from the same tree species on soil fertility are not fully understood. Our objectives were to quantify (1) some changes in soil properties that are responsible for crop production improvement under improved fallow systems; (2) the N mineralization patterns of mixtures of litter and fresh leaves from the same tree species. The treatments used in the study were 2-year planted Sesbania sesban (sesbania) and Cajanus cajan (cajanus) and controls of natural fallow, continuous fertilized and unfertilized maize. At fallow clearing sesbania contributed 56 kg N ha–1 through litter and fresh leaves. Sesbania (fresh leaves + litter) showed high N mineralization after 10 weeks compared to the mixture of cajanus fresh leaves with litter. Maize yields were significantly correlated with preseason NO3–-N and total inorganic-N content of the top 20-cm soil layer. Soil penetrometer resistance at 4 weeks after planting was lowest in the sesbania land-use system (2.2 Mpa), whereas the highest percentage of water-stable aggregates at fallow clearing and crop harvest was in sesbania (83%) and cajanus (77%), respectively. The improved soil conditions and N contribution of sesbania and cajanus fallows to the subsequent maize crop was evidenced by increased maize yields of between 170–200% over maize without fertilizer.  相似文献   

20.
This study aimed to investigate the effect of inoculation with plant growth-promoting Rhizobium and Pseudomonas species on NaCl-affected maize. Two cultivars of maize (cv. Agaiti 2002 and cv. Av 4001) selected on the basis of their yield potential were grown in pots outdoors under natural conditions during July. Microorganisms were applied at seedling stage and salt stress was induced 21 days after sowing and maintained up to 50% flowering after 120 days of stress. The salt treatment caused a detrimental effect on growth and development of plants. Co-inoculation resulted in some positive adaptative responses of maize plants under salinity. The salt tolerance from inoculation was generally mediated by decreases in electrolyte leakage and in osmotic potential, an increase in osmoregulant (proline) production, maintenance of relative water content of leaves, and selective uptake of K ions. Generally, the microbial strain acted synergistically. However, under unstressed conditions, Rhizobium was more effective than Pseudomonas but under salt stress the favorable effect was observed even if some exceptions were also observed. The maize cv. Agaiti 2002 appeared to be more responsive to inoculation and was relatively less tolerant to salt compared to that of cv. Av 4001.  相似文献   

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