Characterization of rhizobia fromLeucaena

Seventy-six rhizobia were isolated from the nodules ofLeucaena plants of various genotypes growing in a wide range of soil types and climatic regions. The isolates were fast-growing and acid-producing. In establishing a serological grouping for the isolates, the intrinsic antibiotic resistance (IAR) patterns to low concentrations of eight antibiotics was helpful for selecting the strains for immunization purposes. Eight distinct somatic serogroups ofLeucaena rhizobia were identified by using strain-specific fluorescent antibodies. The results indicated that use of serological markers is a more specific technique than IAR pattern for strain identification. Strains from some different serogroups had the same IAR patterns. The immunofluorescence cross-reactions ofLeucaena rhizobia serogroups among themselves and with other species of fast- and slow-growing rhizobia were very low. Sero-grouping is ideal for use in further ecological studies in field inoculation trials.     

Genetic diversity of rhizobia isolated from Caragana intermedia in Maowusu sandland,north of China

AIMS: Thirty-three rhizobial strains isolated from nodules of Caragana intermedia in Maowusu sandland were examined for their genetic diversity and putative phylogenetic position. METHODS AND RESULTS: Isolates from Caragana intermedia were classified into 12 genotypes by 16S rDNA polymerase chain reaction-restriction fragment length polymorphism (RFLP), which showed no distinct relationships with those of the reference strains. The genotypes of rhizobia were not related to geographical location. Thr 16S rDNA sequence of representative strain GH2001 from dominant genotype 2 shared high homologuey with some Rhizobium species: Rh. giardinii (96.4%), Rh. huautlense (95.3%), Rh. galegae (95.7%), Rh. yanglingense (95.2%), Rh. mongolense (95.6%), Rh. radiobacter (99%) and Rh. rubi (98.3%). CONCLUSIONS: A high degree of genetic diversity existed among rhizobia nodulating Caragana intermedia in Maowusu sandland. Most of the new isolates might belong to Rhizobium. SIGNIFICANCE AND IMPACT OF THE STUDY: The results suggest that the rich diversity of rhizobia might have contributed to the adaptation of the arid region. These strains could be valuable at the economic and ecosystem level.     

Phenotypic and genotypic diversity of rhizobia nodulating Pterocarpus erinaceus and P. lucens in Senegal

A total of fifty root nodules isolates of fast-growing and slow growing rhizobia from Pterocarpus ennaceus and Pterocarpus lucens respectively native of sudanean and sahelian regions of Senegal were characterized. These isolates were compared to representative strains of known rhizobial species. Twenty-two new isolates were slow growers and twenty-eight were fast growers. A polyphasic approach was performed including comparative total protein sodium dodecyl sulphate polyacrylamide gel (SDS-PAGE) profile analysis; 16S rDNA and 16S-23S rDNA intergenic spacer (IGS) sequence analysis. By SDS-PAGE the slow growing isolates grouped in one major cluster containing reference strains of Bradyrhizobium sp. including strains isolated in Africa, in Brazil and in New Zealand. Most of the fast-growing rhizobia grouped in four different clusters or were separate strains related to Rhizobium and Mesorhizobium strains. The 16S rDNA and 16S-23S rDNA IGS sequences analysis showed accurately the differentiation of fast growing rhizobia among the Rhizobium and Mesorbizobium genospecies. The representative strains of slow growing rhizobia were identified as closely related to Bradyrbizobium elkanii and Bradyrhizobium japonicum. Based on 16S rDNA sequence analysis, one slow growing strain (ORS199) was phylogenetically related to Bradyrbizobium sp. (Lupinus) and Blastobacter denitrificans. This position of ORS 199 was not confirmed by IGS sequence divergence. We found no clear relation between the diversity of strains, the host plants and the ecogeographical origins.     

Endophytic occupation of peanut root nodules by opportunistic Gammaproteobacteria

Several bacterial isolates were recovered from surface-sterilized root nodules of Arachis hypogaea L. (peanut) plants growing in soils from Córdoba, Argentina. The 16S rDNA sequences of seven fast-growing strains were obtained and the phylogenetic analysis showed that these isolates belonged to the Phylum Proteobacteria, Class Gammaproteobacteria, and included Pseudomonas spp., Enterobacter spp., and Klebsiella spp. After storage, these strains became unable to induce nodule formation in Arachis hypogaea L. plants, but they enhanced plant yield. When the isolates were co-inoculated with an infective Bradyrhizobium strain, they were even found colonizing pre-formed nodules. Analysis of symbiotic genes showed that the nifH gene was only detected for the Klebsiella-like isolates and the nodC gene could not be amplified by PCR or be detected by Southern blotting in any of the isolates. The results obtained support the idea that these isolates are opportunistic bacteria able to colonize nodules induced by rhizobia.     

Zur Transformierbarkeit der Knöllchenbakterien

Summary We did not succeed in transforming the host specificity of rhizobia reliably, in spite of the use of DNA preparations from 3 different rhizobia species (Rh. meliloti, Rh. trifolii, Rh. leguminosarum) and of 35 acceptor strains representative for 7 rhizobia species. Very few positive results could not be repeated. Rhizobia from ineffective nodules on alfalfa plants of the first inoculation test following the transformation procedure formed effective nodules during a second plant passage. Reisolates from these nodules exhibiting a rough type of growth differ from the smooth colonies of the donator strain as well as of the acceptor strains. These rough growing rhizobia agree with the donator strain but not with the acceptor strains as to the base composition of their deoxyribonucleic acids. Therefore we assume that some cells of the donator have survived the DNA preparation and the 24 h sterilization by ethanol, and being only weakened have formed at first ineffective but secondly—by way of regeneration—effective nodules.Pseudonodules of unknown origin on alfalfa roots may be very similar to ineffective bacteria root nodules. They consist mainly of parenchymatic tissue partly with one or several vascular bundles. Because these exuberances were found also on the roots of uninoculated control plants, they did not result from a transformation process.     

Genetic diversity of <Emphasis Type="Italic">Sinorhizobium meliloti</Emphasis> associated with alfalfa in Chilean volcanic soils and their symbiotic effectiveness under acidic conditions

A study was conducted with the aim of evaluating the genetic diversity of alfalfa rhizobia isolated from volcanic soils in southern Chile and their ability to establish an effective symbiosis with alfalfa. Rhizobial strains isolated from nodules were identified and selected based on PCR analyses and acid tolerance. Symbiotic effectiveness (nodulation and shoot dry weight) of acid-tolerant rhizobia was evaluated in glasshouse experiments under acidic conditions. The results revealed that Sinorhizobium meliloti is the dominant species in alfalfa nodules with a high genetic diversity at strain level grouped in three major clusters. There was a close relationship (r ² = 0.895, P ≤ 0.001, n = 40) between soil pH and the size of rhizobial populations. Representative isolates from major cluster groups showed wide variation in acid tolerance expressed on buffered agar plates (pH 4.5–7.0) and symbiotic effectiveness with alfalfa. One isolate (NS11) appears to be suitable as an inoculant for alfalfa according to its acid tolerance and symbiotic effectiveness at low pH (5.5). The isolation and selection of naturalized S. meliloti strains with high symbiotic effectiveness under acidic conditions is an alternative approach to improving the productivity of alfalfa and for reducing the application of synthetic fertilizers in Chile.     

Genotypic Characterization of Phage-Typed Indigenous Soybean Bradyrhizobia and Their Host Range Symbiotic Effectiveness

Analysis of genetic diversity among indigenous rhizobia and its symbiotic effectiveness with soybean cultivar is important for development of knowledge about rhizobial ecology. In India, little is known about the genetic resources and diversity of rhizobia nodulating soybean. Indigenous bradyrhizobia isolated from root nodules of soybean plants, collected from traditional cultivating regions of two states (Madhya Pradesh and Uttar Pradesh) of India, were screened for bacteriophage sensitivity to identify successful broad host range symbiotic effectivity. Of 172 rhizobial isolates, 91 showed sensitivities to eight lytic phages and form ten groups on the basis of sensitivity patterns. The genetic diversity of 23 isolates belonging to different phage groups was assessed along with that of strains USDA123 and USDA94 by the restriction fragment length polymorphism (RFLP) analysis of 16S rDNA, intergenic spacer (IGS) (16S–23S rDNA), and DnaK regions. RFLP analysis of 16S rDNA formed 5 groups, whereas 19 and 9 groups were revealed by IGS and the DnaK genes, respectively. The IGS regions showed many amplified polymorphic bands. Nine isolates which revealed high RFLP polymorphism in the abovementioned regions (16S rRNA, IGS, DnaK) were used for 16S rRNA sequence analyses. The results indicate that taxonomically, all isolates were related to Rhizobium etli, Bradyrhizobium spp., and Bradyrhizobium yuanmingense. The doubling time of isolates varied from 9 h (MPSR155) to 16.2 h (MPSR068) in YM broth. Five isolates which did not show cross infectivity with isolated phage strains were studied for symbiotic efficiency. All isolates showed broad host range symbiotic effectiveness forming effective nodules on Vigna mungo, Vigna radiata, Vigna unguiculata, and Cajanus cajan. The present study provides information on genetic diversity and host range symbiosis of indigenous soybean rhizobia typed by different phages.     

Long-term monoculture reduces the symbiotic rhizobial biodiversity of peanut

Long-term monoculture (LTM) decreases the yield and quality of peanut, even resulting in changes in the microbial community. However, the effect of LTM on peanut rhizobial communities has still not been elucidated. In this study, we isolated and characterized peanut rhizobia from 6 sampling plots with different monoculture cropping durations. The community structure and diversity index for each sampling site were analyzed, and the correlations between a peanut rhizobium and soil characteristics were evaluated to clarify the effects on peanut rhizobial communities. The competitive abilities among representative strains were also analyzed. A total of 283 isolates were obtained from 6 sampling plots. Nineteen recA haplotypes were defined and were grouped into 8 genospecies of Bradyrhizobium, with B. liaoningense and B. ottawaense as the dominant groups in each sample. The diversity indexes of the rhizobial community decreased, and the dominant groups of B. liaoningense and B. ottawaense were enriched significantly with extended culture duration. Available potassium (AK), available phosphorus (AP), available nitrogen (AN), total nitrogen (TN) and organic carbon (OC) gradually increased with increasing monoculture duration. OC, TN, AP and AK were the main soil characteristics affecting the distribution of rhizobial genospecies in the samples. A competitive nodulation test indicated that B. liaoningense presented an excellent competitive ability, which was congruent with its high isolation frequency. This study revealed that soil characteristics and the competitive ability of rhizobia shape the symbiotic rhizobial community and provides information on community formation and the biogeographic properties of rhizobia.     

Performance of phaseolus bean rhizobia in soils from the major production sites in the Nile Delta

The symbiotic and competitive performances of two highly effective rhizobia nodulating French bean P. vulgaris were studied in silty loam and clayey soils. The experiments were carried out to address the performance of two rhizobia strains (CE3 and Ph. 163] and the mixture thereof with the two major cultivated bean cultivars in two soil types from major growing French bean areas in Egypt. Clay and silty loam soils from Menoufia and Ismailia respectively were planted with Bronco and Giza 6 phaseolus bean cultivars. The data obtained from this study indicated that rhizobial inoculation of Giza 6 cultivar in clayey soil showed a positive response to inoculation in terms of nodule numbers and dry weight. This response was also positive in dry matter and biomass accumulation by the plants. The inoculant of strain CE3 enhanced plant growth and N-uptake relative to Ph. 163. However, the mixed inoculant strains were not always as good as single strain inoculants. The competition for nodulation was assessed using two techniques namely fluorescent antibody testing (FA) and REP-PCR fingerprinting. The nodule occupancy by inoculant strain Ph. 163 in both soils occupied 30-40% and 38-50 of nodules of cultivar Bronco. The mixed inocula resulted in higher proportions of nodules containing CE3 in silty loam soil and Ph. 163 in clayey soil. The native rhizobia occupied at least 50% of the nodules on the Bronco cultivar. For cultivar Giza 6, the native rhizobia were more competitive with the inoculant strains. Therefore, we suggest using the studied strains as commercial inocula for phaseolus bean.     

Diversity of a Soybean Bradyrhizobial Population Adapted to an Indian Soil

Soybean (Glycine max) is an introduced crop in India. Over the years it has been regularly inoculated with indigenous rhizobia. In this study genetic diversity has been studied at a site where soybean has been regularly grown with inoculation. Rhizobia were plant trapped using soybean varieties as host, and fingerprinted using BOX-PCR. BOX-PCR genomic fingerprints of 69 isolates from the nodules of 4 soybean varieties Pusa22, Bragg, PK1041 and PK1142 showed a high level of genetic diversity. The population profiles of the 69 isolates clustered them into 10 groups. Root nodule isolates from the four varieties were Bradyrhizobium japonicum types, growing in 4–7 days with typical colonies which were found to be genetically distinct from the USDA and SEMIA strains of B. japonicum and B. elkanii. Also the genotype of the host plant seemed to be one of the factors determining the diversity. The high diversity could be attributed both to lateral transfer of genetic material between inoculant and indigenous strains and to genomic rearrangements during the adaptation to the Indian soils.     

Genetic diversity of rhizobia nodulating Trifolium ambiguum in North America

Kura clover (Trifolium ambiguum M.B.) is a persistent rhizomatous forage legume, whose use in the U.S.A. is limited by establishment difficulties in part attributable to nodulation problems. In this study, soil was collected from established stands of Kura clover growing in 9 diverse North American environments. Rhizobia were plant-trapped using Kura clover cv. Endura as host, then rhizobia from nodules fingerprinted using BOX-PCR. The diversity of isolates from North America was then contrasted to that of rhizobia from a single Caucasian environment (Russia), the center of origin for this species. Populations were characterized using clustering methods, and genetic diversity estimated using the Shannon-Weaver diversity index. The genetic diversity of the North American populations was extremely limited, all isolates being closely related to two of the strains found in a locally available commercial inoculant. In contrast, Russian isolates formed a distinct cluster with significant internal genetic diversity. Genetic diversity indices for the North American and Russian populations were 3.5 and 10.76, respectively. The implication of this and other studies is that Kura clover is highly specific in Rhizobium requirement. If the performance of this legume in the U.S.A. is to be improved, either by modifying current establishment practices or plant breeding, it is essential that these studies be paralleled by more collections and evaluation of rhizobia from its center of origin, given the extremely limited diversity of rhizobia found in North America.     

Improvement of biological nitrogen fixation in Egyptian winter legumes through better management of Rhizobium

The diversity of rhizobia nodulating common bean ( Phaseolus vulgaris), berseem clover (Trifolium alexanderinum) and lentil (Lens culinaris) was assessed using several characterization techniques, including nitrogen fixation efficiency, intrinsic antibiotic-resistance patterns (IAR), plasmid profiles, serological markers and rep-PCR fingerprinting. Wide diversity among indigenous rhizobial populations of the isolates from lentil, bean and clover was found. Strikingly, a large percentage of the indigenous rhizobial population was extremely poor at fixing nitrogen. This emphasizes the need to increase the balance of highly efficient strains within the rhizobial population. Use of high-quality inocula strains that survive and compete with other less-desired and less-efficient N2-fixing rhizobia represents the best approach to increase biological nitrogen fixation of the target legume. In field-grown lentils, the inoculant strains were not able to outcompete the indigenous rhizobia and the native lentil rhizobia occupied 76–88% of the total nodules formed on inoculated plants. Nitrogen fixation by lentils, estimated using the ¹⁵N isotope dilution technique, ranged between 127 to 139 kg ha-1 in both inoculated and un-inoculated plants. With berseem clover, the inoculant strains were highly competitive against indigenous rhizobia and occupied 52–79% of all nodules. Inoculation with selected inocula improved N2 fixation by clover from 162 to 205 kg ha-1 in the three cuts as compared with 118 kg ha-1 in the un-inoculated treatment. The results also indicated the potential for improvement of N2 fixation by beans through the application of efficient N2-fixing rhizobia.     

Genetic diversity of rhizobia associated with Desmodium species grown in China

AIMS: Desmodia are leguminous plants used as important forage and herbal medicine in China. Little information is available about the nodule bacteria of Desmodium species. To understand the genetic diversity of rhizobia associated with Desmodium species grown in China, isolates from temperate and subtropical regions were obtained and analysed. METHODS AND RESULTS: A total of 39 rhizobial strains isolated from 9 Desmodium species grown in China were characterized by PCR-based 16S rDNA gene and 16S-23S rDNA intergenic spacer gene restriction fragment length polymorphism (RFLP) and 16S rRNA gene sequencing. The results showed high diversity among rhizobia symbiotic with Desmodium species. Most microsymbionts of Desmodium species belonged to Bradyrhizobium closely related to Bradyrhizobium elkanii, Bradyrhizobium japonicum and Bradyrhizobium yuanmingense. Several small groups or single strain were related to Rhizobium, Sinorhizobium or Mesorhizobium. CONCLUSIONS: Desmodium species formed nodules with diverse rhizobia in Chinese soils. SIGNIFICANCE AND IMPACT OF THE STUDY: These results offered the first systematic information about the microsymbionts of desmodia grown in the temperate and subtropical regions of China.     

Phylogenetic relationship of Lotus uliginosus symbionts with bradyrhizobia nodulating genistoid legumes

Lotus species are legumes with potential for pastures in soils with low-fertility and environmental constraints. The aim of this work was to characterize bacteria that establish efficient nitrogen-fixing symbiosis with the forage species Lotus uliginosus. A total of 39 isolates were obtained from nodules of L. uliginosus naturally growing in two different locations of Portugal. Molecular identification of the isolates plus the commercial inoculant strain NZP2039 was performed by REP-PCR, 16S rRNA RFLP, and 16S rRNA, glnII and recA sequence analyses. Limited genetic diversity was found among the L. uliginosus symbionts, which showed a close phylogenetic relationship with the species Bradyrhizobium japonicum. The symbiotic nifH, nodA and nodC gene sequences were closely related with the corresponding genes of various Bradyrhizobium strains isolated from Lupinus and other genistoid legumes and therefore were phylogenetically separated from other Lotus spp. rhizobia. The L. uliginosus bradyrhizobia were able to nodulate and fix nitrogen in association with L. uliginosus, could nodulate Lotus corniculatus with generally poor nitrogen-fixing efficiency, formed nonfixing nodules in Lotus tenuis and Lupinus luteus roots and were unable to nodulate Glycine soja or Glycine max. Thus, L. uliginosus rhizobia seem closely related to B. japonicum biovar genistearum strains.     

Symbiotic effectiveness and plant growh promoting traits in some Rhizobium strains isolated from Phaseolus vulgaris L.

The ability of Rhizobia to colonize roots of certain legumes and promote their growth has been proven previously. In this study the symbiotic efficiency of 47 Rhizobium strains with 6 common bean cultivars was evaluated under greenhouse condition. Fourteen strains showed the best symbiotic efficiency, whereas some isolates could not induce nodules on host plants. The ability of fourteen superior strains to solubilize phosphorus and zinc and to produce auxin, HCN and siderohores was evaluated in the laboratory assays. Rhizobium strain Rb102 produced the highest amount of auxin (14.2?mg?l^?1) in the medium containing l-tryptophan. None of the isolates were able to solubilize ZnO and ZnCO₃ on solid medium but in liquid medium some of them had negligible solubilization. The highest P solubility in liquid and solid medium was observed in strains Rb113 and Rb130, respectively. Strain Rb102 produced the highest amount of siderophores. None of the isolates were able to produce HCN. This study showed that there was a great diversity between the strains of Rhizobium in terms of their plant growth promoting traits symbiotic efficiency which supports the importance of screening rhizobia for selecting the most efficient strains. The genetic diversity of the isolates was analyzed by PCR–RFLP of the 16S rDNA. Our rhizobia were clustered into 10 groups showing high levels of diversity.     

Phylogeny of bradyrhizobia from Chinese cowpea miscellany inferred from 16S rRNA, atpD, glnII, and 16S-23S intergenic spacer sequences

The cowpea (Vigna unguiculata L.), peanut (Arachis hypogaea L.), and mung bean (Vigna radiata L.) belong to a group of plants known as the "cowpea miscellany" plants, which are widely cultivated throughout the tropic and subtropical zones of Africa and Asia. However, the phylogeny of the rhizobial strains that nodulate these plants is poorly understood. Previous studies have isolated a diversity of rhizobial strains from cowpea miscellany hosts and have suggested that, phylogenetically, they are from different species. In this work, the phylogeny of 42 slow-growing rhizobial strains, isolated from root nodules of cowpea, peanut, and mung bean from different geographical regions of China, was investigated using sequences from the 16S rRNA, atpD and glnII genes, and the 16S-23S rRNA intergenic spacer. The indigenous rhizobial strains from the cowpea miscellany could all be placed in the genus Bradyrhizobium , and Bradyrhizobium liaoningense and Bradyrhizobium yuanmingense were the main species. Phylogenies derived from housekeeping genes were consistent with phylogenies generated from the ribosomal gene. Mung bean rhizobia clustered only into B. liaoningense and B. yuanmingense and were phylogenetically less diverse than cowpea and peanut rhizobia. Geographical origin was significantly reflected in the phylogeny of mung bean rhizobia. Most cowpea rhizobia were more closely related to the 3 major groups B. liaoningense, B. yuanmingense, and Bradyrhizobium elkanii than to the minor groups Bradyrhizobium japonicum or Bradyrhizobium canariense . However, most peanut rhizobia were more closely related to the 2 major groups B. liaoningense and B. yuanmingense than to the minor group B. elkanii.     

Characterization of high temperature-tolerant rhizobia isolated from Prosopis juliflora grown in alkaline soil

A method was developed for the fast screening and selection of high-temperature tolerant rhizobial strains from root nodules of Prosopis juliflora growing in alkaline soils. The high-temperature tolerant rhizobia were selected from 2,500 Rhizobium isolates with similar growth patterns on yeast mannitol agar plates after 72 h incubation at 30 and 45 degrees C, followed by a second screening at 47.5 degrees C. Seventeen high-temperature tolerant rhizobial strains having distinguishable protein band patterns were finally selected for further screening by subjecting them to temperature stress up to 60 degrees C in yeast mannitol broth for 6 h. The high-temperature tolerant strains were NBRI12, NBRI329, NBRI330, NBRI332, and NBRI133. Using this procedure, a large number of rhizobia from root nodules of P. juliflora were screened for high-temperature tolerance. The assimilation of several carbon sources, tolerance to high pH and salt stress, and ability to nodulate P. juliflora growing in a glasshouse and nursery of the strains were studied. All five isolates had higher plant dry weight in the range of 29.9 to 88.6% in comparison with uninoculated nursery-grown plants. It was demonstrated that it is possible to screen in nature for superior rhizobia exemplified by the isolation of temperature-tolerant strains, which established effective symbiosis with nursery-grown P. juliflora. These findings indicate a correlation between strain performance under in vitro stress in pure culture and strain behavior under symbiotic conditions. Pure culture evaluation may be a useful tool in search for Rhizobium strains better suited for soil environments where high temperature, pH, and salt stress constitutes a limitation for symbiotic biological nitrogen fixation.     

<Emphasis Type="Italic">Rhizobium etli</Emphasis> maize populations and their competitiveness for root colonization

Rhizobium etli, which normally forms nitrogen-fixing nodules on Phaseolus vulgaris (common bean), is a natural maize endophyte. The genetic diversity of R. etli strains from bulk soil, bean nodules, the maize rhizosphere, the maize root, and inside stem tissue in traditional fields where maize is intercropped with P. vulgaris-beans was analyzed. Based on plasmid profiles and alloenzymes, it was determined that several R. etli types were preferentially encountered as putative maize endophytes. Some of these strains from maize were more competitive maize-root colonizers than other R. etli strains from the rhizosphere or from bean nodules. The dominant and highly competitive strain Ch24-10 was the most tolerant to 6-methoxy-2-benzoxazolinone (MBOA), a maize antimicrobial compound that is inhibitory to some bacteria and fungi. The R. tropici strain CIAT899, successfully used as inoculant of P. vulgaris, was also found to be a competitive maize endophyte in inoculation experiments.     

用rep—PCR技术研究中国花生根瘤菌的多样性

采用细菌基因组重复序列ＰＣＲ技术（简称ｒｅｐＰＣＲ）中常用的ＲＥＰＰＣＲ和ＥＲＩＣＰＣＲ,对从中国１１个省、市的２３个点、２４个花生品种采集的根瘤中分离的５９株花生根瘤菌Ｂｒａｄｙｒｈｉｚｏｂｉｕｍｓｐ．（Ａｒａｃｈｉｓ）进行多样性研究,同时对来自国外的６株花生根瘤菌及１４株参比慢生根瘤菌也进行了比较。得到的低相似性结果表明中国花生根瘤菌基因组存在显著的多样性。ＲＥＰＰＣＲ揭示,在相似性５０％上分为１１个群,而ＥＲＩＣＰＣＲ却得到２４个分群。这两种结果对菌株的分群有差异,暗示这两种短重复序列在慢生根瘤菌基因组中的分布的不同。没有发现菌株间基因组的多样性分布与花生品种、地理来源之间的必然联系。将两者电泳图谱结合并分析,得到介于上述两者间的结果。此结果进一步反映了菌株基因组间存在的多样性。同时还表明ｒｅｐＰＣＲ不仅是研究生物多样性的快速简便方法,还可应用于菌株的鉴别和生态学研究。     

Genetic Diversity of Rhizobia Nodulating Arachis hypogaea L. in Central Argentinean Soils

The diversity of thirty-nine isolates from peanut plants growing at fourteen different sites in the Argentinean province of Córdoba was examined by rep-PCR, RFLP of PCR amplified 16S rRNA gene and complete sequencing of ribosomal genes. The genomic analysis of the peanut isolates indicated that each group encompasses heterogeneity among their members, having distinct rep fingerprints and 16S rRNA alleles. Complete sequencing of 16S rRNA demonstrated that native peanut rhizobia from Córdoba soils representative of the slow and fast growers are phylogenetically related to Bradyrhizobium japonicum and Bradyrhizobium sp. and Rhizobium giardinii and R. tropici species, respectively. The nodC gene sequence analysis showed phylogenetic similarity between fast grower peanut symbionts and Rhizobium tropici.