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1.
We investigated the taxonomic position and symbiotic capabilities of two root-nodule bacterial strains isolated from the South African herbaceous, papilionoid legume Rhynchosia ferulifolia. The 16S rRNA gene sequence of the two strains was determined along with intragenic sequences of nodA and nifH, together with their symbiotic capabilities when inoculated onto the papilionoid legumes R. ferulifolia, Rhynchosia caribaea, Rhynchosia minima and Macroptilium atropurpureum (Siratro). Burkholderia phymatum STM815T, Cupriavidus taiwanensis LMG 19424T and root-nodule bacteria isolated from R. minima and Rhynchosia totta were included in the study. Root-nodule bacteria isolated from R. ferulifolia, WSM3937 and WSM3930, belong to the genus Burkholderia and are most closely related to Burkholderia terricola (98.8% similarity). The phylogenetic analysis of nodA and nifH revealed substantial similarity of the novel strains with Burkholderia tuberum STM678T, a β-rhizobium also originated from South Africa, and only a distant relationship with South American Mimosa-nodulating β-rhizobia. R. ferulifolia was effectively nodulated only by Burkholderia sp. WSM3937 and WSM3930 and not by bradyrhizobia isolated from Rhynchosia minima and Rhynchosia totta or STM815 and LMG 19924. Nodules induced by the novel strains were determinate and hosted well organized symbiosomes within infected cells. In this study we describe a new symbiotic N-fixing relationship between Burkholderia sp. and the South African legume R. ferulifolia. This is the first report of N-fixation between β-rhizobia and an herbaceous, papilionoid legume from which the strains were originally isolated. The level of N-fixation in this symbiosis approached that achieved by effectively nodulated Medicago sativa and suggests that the β-rhizobia may have a role in N-fixation in agricultural systems.  相似文献   

2.
Nitrogen is a critical nutrient in plant-based primary production systems, therefore measurements of N cycling by microorganisms may add value to agricultural soil monitoring programs. Bacterial-mediated nitrogen cycling was investigated in soils from two broad land-uses (managed and remnant vegetation) across different Soil Orders from three geomorphic zones in Victoria, Australia, by examining the abundance of the genes amoA and nifH using quantitative polymerase chain reaction (qPCR). The aim of the study was to identify parameters influencing bacterial populations possessing the genes nifH and amoA, and examine their distribution at a regional scale across different management treatments. The gene amoA was most abundant in the neutral to slightly alkaline surface soils from Calcarosols in North-West Victoria. There was a highly significant (P < 0.001) interaction between land-use and geomorphic zones in terms of the abundance of amoA. Detection of the gene nifH was site specific with low copy number (less than 100 copies per nanogram of DNA) observed for some strongly acidic surface soil sites in North-East Victoria (Dermosols) and South-West Victoria (Sodosols/Chromosols), while nifH was more abundant in selected Calcarosols of North-West Victoria. The gene amoA was detected across more sites than nifH and was strongly influenced by land-use, with almost consistently greater abundance in managed compared to remnant sites, particularly for North-West and South-West Victoria. The abundance of nifH was not related to land-use, with similar copy numbers observed for both managed and remnant sites at some locations. For the gene nifH, there was no significant interaction between land-use and geomorphic zones, between managed and remnant sites or between the three geomorphic zones. Regression tree analysis revealed a number of likely soil chemical and microbial variables which may act as drivers of gene abundance of amoA and nifH. Variables identified as drivers for amoA included pH, Olsen P, microbial biomass carbon, nitrate and total nitrogen while for nifH the variables were microbial biomass carbon, electrical conductivity, microbial biomass nitrogen, total nitrogen and total potassium. Measures of N cycling genes could be used as an additional indicator of soil health to assess potential ecosystem functions. The spatial scale of the current study demonstrates that a landscape approach may assist soil health monitoring programs by evaluating N cycle gene abundance in the context of the different microbial and chemical conditions related to Soil Order and land-use management.  相似文献   

3.
Root-nodule bacteria that nodulate the legume genus Lotononis are being investigated to develop new forage species for agriculture. Bacteria isolated from nodules of Lotononis angolensis were fast-growing, highly mucoid and pink-pigmented, and on the basis of 16S rRNA phylogeny <94% related to other genera in the Alphaproteobacteria. Root-nodule bacteria isolated from other Lotononis species (L. bainesii, L. solitudinis and L. listii) resembled the more common dry, slow-growing, pink-pigmented rhizobia previously described for L. bainesii. These isolates could be attributed to the Methylobacterium genus, although not to the type species Methylobacterium nodulans. Further differences were uncovered with nodulation studies revealing that nodule isolates from L. angolensis were effective at nitrogen fixation on their host plant, but could nodulate neither L. bainesii nor L. listii. Reciprocal tests showed isolates from L. bainesii, L. listii and L. solitudinis were incapable of nodulating L. angolensis effectively. Nodule morphology for L. bainesii, L. angolensis and L. listii was characteristically lupinoid, with little structural divergence between the species, and with nodules eventually enclosing the entire root.  相似文献   

4.
Two root-colonizing Fusarium strains, Ls-F-in-4-1 and Rs-F-in-11, isolated from roots of Brassicaceae plants, induced the resistance in Lepidium sativum seedlings against Pythium ultimum. These strains caused an increase in the content of benzyl isothiocyanate, and of its precursor glucotropaeolin, in the roots of the host plants. The increased isothiocyanate content is one of the factors contributing to the resistance of L. sativum against P. ultimum. To be transformed into the fungitoxic compound benzyl isothiocyanate, glucotropaeolin has to be hydrolyzed by myrosinase, which can be produced either by plants or microorganisms. The Fusarium strain Ls-F-in-4-1 has a myrosinase activity but the strain Rs-F-in-11 has not. These results suggest that both strains are able to trigger the metabolic pathway leading to benzyl isothiocyanate production in the plant. In the case of the myrosinase-negative strain Rs-F-in-11, hydrolyzation into isothiocyanate is only due to the myrosinase activity of the plant, and in the other case, the myrosinase produced by the strain Ls-F-in-11 also would contribute to the production of isothiocyanate. This paper reports a new mode of action of non-pathogenic Fusarium strains in controlling P. ultimum.  相似文献   

5.
The possible transfer of genes from Bacillus thuringiensis subsp. kurstaki (Btk) to indigenous Bacillus spp. was investigated in soil samples from stands of cork oak in Orotelli (Sardinia, Italy) collected 5 years after spraying of the stands with a commercial insecticidal preparation (FORAY 48B) of Btk. Two colonies with a morphology different from that of Btk were isolated and identified as Bacillus mycoides by morphological and physiological characteristics and by 16S rDNA analysis. Amplification by the polymerase chain reaction (PCR) of the DNA of the two isolated B. mycoides colonies with primers used for the identification of the Btk cry genes showed the presence of a fragment of 238 bp of the cry1Ab9 gene that had a similarity of 100% with the sequence of the cry1Ab9 gene present in GenBank, indicating that the isolates of B. mycoides acquired part of the sequence of this gene from Btk. No cells of Btk or B. mycoides carrying the 238-bp fragment of the cry1Ab9 gene were isolated from samples of unsprayed control soil. However, the isolates of B. mycoides were not able to express the partial Cry1Ab protein. Hybridization with probes for IS231 and the cry1Ab9 gene suggested that the inverted repeated sequence, IS231, was probably involved in the transfer of the 238-bp fragment from Btk to B. mycoides. These results indicate that transfer of genes between introduced Btk and indigenous Bacillus spp. can occur in soil under field conditions.  相似文献   

6.
New Caledonia is characterized by an exceptional concentration of endemic Casuarinaceae species including eight Gymnostoma species and Casuarina collina. Frankia strains isolated from nodules from C. collina have been studied through a range of techniques including molecular typing, infectivity/effectivity and host spectrum. All these isolates had characteristics similar to those of atypical Frankia from Casuarina previously described. This work evidenced several original features within these 26 isolates: (i) they are localized inside the nodule; (ii) they fit into the Elaeagnus-infective Frankia group; (iii) they belonged to four ITS groups already described for Frankia from Gymnostoma. In fact, it is highly probable that atypical Frankia from C. collina and Frankia from Gymnostoma are the same. We can formulate the hypothesis that the Frankia from Gymnostoma could use C. collina as an alternative host in absence of Gymnostoma spp. or when the ecological conditions are favourable to C. collina.  相似文献   

7.
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   

8.
It is generally accepted that there are two major centers of genetic diversification of common beans (Phaseolus vulgaris L.): the Mesoamerican (Mexico, Colombia, Ecuador and north of Peru, probably the primary center), and the Andean (southern Peru to north of Argentina) centers. Wild common bean is not found in Brazil, but it has been grown in the country throughout recorded history. Common bean establishes symbiotic associations with a wide range of rhizobial strains and Rhizobium etli is the dominant microsymbiont at both centers of genetic diversification. In contrast, R. tropici, originally recovered from common bean in Colombia, has been found to be the dominant species nodulating field-grown common-bean plants in Brazil. However, a recent study using soil dilutions as inocula has shown surprisingly high counts of R. etli in two Brazilian ecosystems. In the present study, RFLP-PCR analyses of nodABC and nifH genes of 43 of those Brazilian R. etli strains revealed unexpected homogeneity in their banding patterns. The Brazilian R. etli strains were closely similar in 16S rRNA sequences and in nodABC and nifH RFLP-PCR profiles to the Mexican strain CFN 42T, and were quite distinct from R. etli and R. leguminosarum strains of European origin, supporting the hypothesis that Brazilian common bean and their rhizobia are of Mesoamerican origin, and could have arrived in Brazil in pre-colonial times. R. tropici may have been introduced to Brazilian soils later, or it may be a symbiont of other indigenous legume species and, due to its tolerance to acidic soils and high temperature conditions became the predominant microsymbiont of common bean.  相似文献   

9.
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   

10.
Phaseolus vulgaris is a legume extensively cultivated in Spain, León province being the most important producer. This province produces selected varieties of common bean highly appreciated by their quality that warrants a Protected Geographic Indication (PGI). In this work we analysed the rhizobia present in nodules of the variety “Riñón” in several soils from León province in order to select native rhizobial strains to be used as biofertilizers. The analysis of rrs and housekeeping genes of these strains showed that they belong to two phylogenetic groups within Rhizobium leguminosarum (I and II). Although the group II strains were most abundant in nodules, very effective strains were also found in group I. Strains LCS0306 from group I and LBM1123 from group II were the best nitrogen fixers among all strains isolated and were selected for field experiments. The field research showed that the biofertilization of common bean with native and selected rhizobial strains can completely replace the fertilization with chemical N fertilizers. The biofertiliser designed in such way, was valid for the whole agroecological area, regardless the specific properties of each soil and microclimatic conditions. This conclusion can be generalised as a strategy for the development of biofertilisers in different agroecological conditions worldwide.  相似文献   

11.
Common bean (Phaseolus vulgaris) is native to the Americas, and Rhizobium etli is the dominant microsymbiont in both the Mesoamerican and the Andean centers of genetic diversification. Wild common beans are not found in Brazil, although the legume has been cropped in the country throughout time and all but one of the rhizobial species that nodulate it (Rhizobium gallicum) have been broadly detected in Brazilian soils. However, the majority of the effective rhizobial strains isolated so far from field-grown plants belong to R. tropici. This study describes the analysis of symbiotic and non-symbiotic genes of 15 effective R. tropici strains, isolated from four geographically distant regions in Brazil. With RFLP-PCR of the 16S and 23S rRNA genes and sequence analysis of 16S rRNA, two clusters were observed, one related to R. tropici type A and another to type B strains. Diversity in ribosomal genes was high, indicating that type A strains might represent a new species. High intraspecies diversity was also observed in the rep-PCR analysis with BOX, ERIC and REP primers. However, in the RFLP-PCR analysis of nifH and nodC genes, all R. tropici showed unique combinations of profiles, which might reflect an evolutionary strategy to maximize N2 fixation.  相似文献   

12.
Soil populations of Rhizobium leguminosarum bv. viciae (Rlv) that are infective and symbiotically effective on pea (Pisum sativum L.) have recently been shown to be quite widespread in agricultural soils of the eastern Canadian prairie. Here we report on studies carried out to assess the genetic diversity amongst these endemic Rlv strains and to attempt to determine if the endemic strains arose from previously used commercial rhizobial inoculants. Isolates of Rlv were collected from nodules of uninoculated pea plants from 20 sites across southern Manitoba and analyzed by plasmid profiling and PCR-RFLP of the 16S-23S rDNA internally transcribed spacer (ITS) region. Of 214 field isolates analyzed, 67 different plasmid profiles were identified, indicating a relatively high degree of variability among the isolates. Plasmid profiling of isolates from proximal nodules (near the base of the stem) and distal nodules (on lateral roots further from the root crown) from individual plants from one site suggested that the endemic strains were quite competitive relative to a commercial inoculant, occupying 78% of the proximal nodules and 96% of the distal nodules. PCR-RFLP of the 16S-23S rDNA ITS also suggested a relatively high degree of genetic variability among the field isolates. Analysis of the PCR-RFLP patterns of 15 selected isolates by UPGMA indicated two clusters of three field isolates each, with simple matching coefficients (SMCs) ≥0.95. However, to group all field isolates together, the SMC has to be reduced to 0.70. Regarding the origin of the endemic Rlv strains, there were few occurrences of the plasmid profiles of field isolates being identical to the profiles of inoculant Rlv strains commonly used in the region. Likewise, the plasmid profiles of isolates from nodules of wild Lathyrus plants located near some of the sites were all different from those of the field isolates. However, comparison of PCR-RFLP patterns suggested an influence of some inoculant strains on the chromosomal composition of some of the field isolates with SMCs of ≥0.92. Overall, plasmid profiles and PCR-RFLP patterns of the isolates from endemic Rlv populations from across southern Manitoba indicate a relatively high degree of genetic diversity among both plasmid and chromosomal components of endemic strains, but also suggest some influence of chromosomal information from previously used inoculant strains on the endemic soil strains.  相似文献   

13.
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   

14.
Clianthus is an acutely threatened, bird-pollinated genus endemic to New Zealand, represented in the wild by only one population of C. puniceus and 11 populations of C. maximus, each with very few individuals (typically <10 per population). A limited number of named Clianthus cultivars of indeterminate origin are commonly grown as ornamentals. Genomic DNA from individual Clianthus plants was extracted for genetic diversity analysis using a range of molecular markers, including amplified fragment length polymorphism (AFLP). Data were analysed by the unweighted pair-group method with arithmetic averaging (UPGMA), the generation of Neighbor-Joining trees, and analyses of molecular variance (AMOVA). Genetic distance between wild populations of C. maximus was highly correlated with geographical distance between populations. Sequencing of intron 2 of a putative partial homologue of the floral meristem identity gene LEAFY (CmLFY) revealed a 7 bp deletion that was exhibited homozygously in the more northern populations of C. maximus, and in all individuals tested from the sole population of C. puniceus. This deletion was not exhibited in more southern populations of C. maximus. Further, one geographically intermediate population contained some plants that were heterozygous for the deletion. Parallel analyses of cultivated Clianthus genotypes, more than half of which were also homozygous for the 7 bp deletion, showed that these were not representative of the broad, but threatened, diversity remaining in the wild. It is argued that wild populations of C. maximus are unlikely to have arisen from the escape of plants from cultivation. Conservation effort should focus on the protection and study of the extant plants in these wild populations, rather than on the introduction of disturbance regimes to uncover potential seed banks.  相似文献   

15.
We previously reported that commercial Rhizobium leguminosarum bv. trifolii inoculants failed to outcompete naturalized strains for nodule occupation of clover sown into an alkaline soil [Aust. J. Agric. Res. 53 (2002) 1019]. Two field isolates that dominated nodule occupancy at the field site were labeled with a PnifH-gusA marker. Marked strains were chosen on the basis that they were equally competitive and fixed similar amounts of nitrogen in comparison to their parental strain. The minitransposon insertions were cloned and sequence analysis revealed that neither lesion disrupted the integrity of any known gene. The marked strains were then used to follow nodule occupancy of Trifolium alexandrinum in competition against the commercial inoculant TA1 under a range of experimental conditions. In co-inoculation experiments in sand-vermiculite, TA1 outcompeted each marked field isolate for nodule occupancy. However, using TA1-inoculated seed sown into alkaline soil containing a marked field strain, it was demonstrated that by increasing the cell number of marked rhizobia in the soil and reducing the cell number of the commercial inoculant, the proportion of nodules occupied by TA1 was reduced. These studies indicate that the ability of the field isolates to dominate nodule occupancy in the alkaline field soils was most likely caused by poor commercial inoculant survival providing the advantage for naturalized soil rhizobia to initiate nodulation.  相似文献   

16.
《Applied soil ecology》2000,14(3):249-255
In the absence of available symbiotic nitrogen-fixing Frankia strains associated with Casuarina trees in Mexico for reforestation purposes, isolation was undertaken using root nodules from trees growing in different habitats in Mexico, from the coast of the Gulf of Mexico up to 2550 m above the sea level. A total of 24 strains were isolated and clonal cultures were obtained from one filament of each strain. The use of acetate as the sole carbon source was essential for the isolation of the endosymbiont from the nodules due to the fact that other contaminant actinomycetes utilize propionate. Clonal cultures were obtained, and cultural and symbiotic characteristics of pure cultures were assessed. All strains grew well in stirred DPM (defined propionate medium) with no mineral nitrogen. Isolates showed hyphae, multilocular sporangia and characteristic vesicles. The presence of the gene nifH was also demonstrated, with all strains being able to nodulate Casuarina equisetifolia. Nitrogenase activity (acetylene reduction) of the formed root nodules varied among the different associations depending on the isolate used to inoculate the plants. Several of the isolates can be used as inoculants for the propagation of Casuarina trees.  相似文献   

17.
To achieve stable expression of the heterologous and reporter genes in the Bradyrhizobium genome, we constructed suicide plasmids capable of site-directed genomic integration of the gusA, gfp and nifA genes by homologous recombination into non-essential repeated sequences (RS-α), isolated from B. japonicum strain CPAC7 (SEMIA5080). In this report, we describe the strategies to construct the vectors and their use to obtain mutants with site-specific insertions.  相似文献   

18.
Our previous study indicated that the diversity of the major capsid gene (g23) of T4-type bacteriophages (phages) of Novosphingobium and Sphingomonas strains isolated from the floodwater of a Japanese paddy field is comparable to those of the clones obtained from other Japanese paddy fields. For more strict comparison of the diversity, this study examined g23 sequences between Novosphingobium and Sphingomonas phages and phage communities in the identical floodwater of a Japanese paddy field. The clones were obtained by applying g23-specific primers to DNA extracted from the floodwaters. Many 23 clones in the floodwater were grouped into the same clusters of Paddy Groups I-VI with g23 genes of Novosphingobium/Sphingomonas phages with some clones belonging to an additional cluster. In addition, the remaining clones belonged to the clusters of marine clones and T4-type enterophages. These findings indicate that the g23 genes in the floodwater are more diversified than those of Novosphingobium/Sphingomonas phages including g23 genes closely related to the genes of enterophages and marine origins.  相似文献   

19.
The capacity of different soils of New Caledonia to induce nodulation in Gymnostoma poissonianum was studied. The soils were sampled under five Gymnostoma species, Alphitonia neocaledonica (a non-nodulated endemic Rhamnaceae) and Pinus caribea (an introduced species) growing in various ecological conditions. Using G. poissonianum as trap-host, we observed a higher abundance of Frankia from Gymnostoma spp. in the rhizosphere of A. neocaledonica as compared with bare soils and P. caribea rhizosphere. The nodulating capacity of A. neocaledonica rhizosphere was almost similar to that of the five Gymnostoma species (symbiotic host) studied in the same stations. In comparison, bare soils or rhizosphere of P. caribea had poor nodulating capacities. We isolated fourteen Frankia strains from nodules of G. poissonianum after baiting with the rhizospheric soils of five Gymnostoma and A. neocaledonica. Using the PCR/RFLP method, we confirmed the similarity with those already described. Frankia was abundant in the rhizosphere of A. neocaledonica in all the sites studied. One explanation could be a positive tropism of Frankia towards species belonging to families having nodulated species, which is the case of A. neocaledonica endemic in New Caledonia. We can suppose that the non-nodulated plants belonging to these families can excrete some chemical substances able to attract Frankia and to induce its proliferation.  相似文献   

20.
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   

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