摘要:

Extensive cross testing on a relatively few legume hosts led initially to a taxonomic characterization of rhizobia based on bacteria–plant cross–inoculation groups. This has gradually become less acceptable, and has been replaced by taxonomic groupings derived from numerical taxonomy, carbohydrate metabolism, antibiotic susceptiblities, serology, and various molecular techniques. It has long been recognized that there are two distinct groups of rhizobia based on growth rate. The fast-growing genusRhizobiumincludesR.leguminosarum,R.meliloti,R.loti,R.galegae,R.tropici, andR.huakuii. The slow-growing genusBradyrhizobiumcontains only one recognized species,B.japonicum. Two new genera have been recognized:Azorhizobium, with one recognized species (A.caulinadans), andSinorhizobium, with two species (S.frediiandS.xinjiangensis). Genetic studies of both the fast- and slow-growing groups show unacceptably wide intrageneric and intergeneric diversity. Although there have been some elegant studies of some of the genetic relationships among rhizobia, overall there has (have) not been the comprehensive study(ies) needed to allow a conclusive taxonomic scheme. Because proposals for revision are accelerating, minimum standards have been proposed by the International Subcommittee for the Taxonomy ofRhizobiumandAgrobacterium.Key words:Rhizobiumtaxonomy, classification of rhizobia, interrelationships of rhizobia.

ISSN:0008-4166    

DOI:10.1139/m92-075

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Rhizobial specificity, defined in terms of nodulation and nitrogen-fixing effectiveness characteristics of a group of rhizobia on a host legume, serves as a basis for predicting the need to inoculate, selecting species for most probable number plant-infection assays, and preparing rhizobial inoculants suitable for a range of legume species. A series of inoculation experiments were performed under growth room and greenhouse conditions to delineate rhizobial specificity of a variety of tree legumes.Gliricidia sepium,Calliandra calothyrsus, andLeucaena leucocephalanodulated effectively with rhizobia isolated from each of the three genera. With a few exceptions,Sesbania grandifloraandRobinia pseudoacacianodulated effectively only with rhizobial strains isolated from each genus respectively. A range of specificity was found among species that nodulate withBradyrhizobium. WhereasAcacia mearnsiinodulated with most strains but fixed N2effectively with relatively few,Acacia mangiumandLysiloma latisiliquawere specific for both nodulation and effectiveness.Key words: nitrogen fixation, effectiveness, nodulation, rhizobia, tree legumes.

ISSN:0008-4166    

DOI:10.1139/m92-076

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Genes and cDNAs encoding several enzymes in the nitrogen assimilatory pathway have been cloned and characterised from a number of legume species. Molecular studies using these clones have revealed how these genes are regulated to effect changes in the activity of the enzymes in the different cells of the nodule. Current work is addressing the mechanism of the cell-specific expression and metabolic regulation of these genes and is investigating the role of the nitrogen assimilatory enzymes in regulating flux through the nitrogen fixation and assimilation pathways.Key words: legume root nodules, nitrogen assimilatory enzymes, nitrogen metabolism, plant gene expression.

ISSN:0008-4166    

DOI:10.1139/m92-077

出版商:NRC Research Press    

年代:1992

数据来源: NRC

ISSN:0008-4166    

DOI:10.1139/m92-078

出版商:NRC Research Press    

年代:1992

数据来源: NRC

ISSN:0008-4166    

DOI:10.1139/m92-079

出版商:NRC Research Press    

年代:1992

数据来源: NRC

ISSN:0008-4166    

DOI:10.1139/m92-080

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Understanding the impact of environmental variables on interstrain competition is important to ensure the successful use of rhizobial inoculant. In eight inoculation trials conducted at five diverse sites on Maui, Hawaii, equal numbers of three serologically distinct strains of effective, homologous rhizobia in a peat-based inoculant were applied to seeds of soybean, bush bean, cowpea, lima bean, peanut, leucaena, clover, and tinga pea. We studied the influence of environmental variables on interstrain competition between applied and indigenous rhizobia and among the three strains comprising the inoculum. Although temperature and soil fertility were correlated with nodule occupancy by inoculant strains in a few cases, the most significant environmental variable controlling their competitive success was the size of the indigenous rhizobial population. Nodule occupancy was best described (r2 = 0.51,p < 0.001) by the equationy = 97.88 − 15.03(log10(x + 1)), whereyis percent nodule occupancy by inoculant rhizobia andxis the most probable number of indigenous rhizobia per gram soil. For each legume, one of the three inoculant strains was a poor competitor across sites. Competition between the other two strains varied between sites, but was infrequently related to environmental variables. Results indicated that competitive strains could be selected that perform well across a range of environments.Key words: competition, rhizobial ecology, inoculation response, competitiveness index.

ISSN:0008-4166    

DOI:10.1139/m92-081

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Fourteen randomly selected clones from cosmid libraries ofBradyrhizobiumwere used as hybridization probes in Southern blot analysis. Seven of the probes used were from strain USDA 83, a group II strain, and the other seven were from strain I-110, a group Ia strain. The 30 strains examined included 9 strains ofRj4-incompatible soybean bradyrhizobia. Considerable polynucleotide sequence dissimilarity between DNA homology groups was evidenced by striking differences in the number of hybridizing bands, except where the probe carried repetitive DNA. Predictable, simple restriction fragment length polymorphism differences were observed only within DNA homology groups. The previous description that 8 of 9Rj4-incompatible strains belonged to DNA homology group II was verified. The new data, together with many previously documented differences, make it clear that the DNA homology group II organisms should be classified as a new species, for which the nameBradyrhizobium elkaniiis proposed, and strain USDA 76 is designated the type strain. The ATCC number for the type strain is 49852.Key words: DNA:DNA hybridization, soybean, nodulation, bacteria, symbiosis, nitrogen fixation, host compatibility.

ISSN:0008-4166    

DOI:10.1139/m92-082

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

The results of fluorescent antibody staining of threeRhizobium melilotistrains using three "strain-cross-reactive" and three "strain-specific" monoclonal antibodies indicated that strain-specific antigens present on surfaces of laboratory-cultured vegetative cells were diminished or absent on surfaces of bacteroid cells extracted from alfalfa nodules formed by the respective strains. In contrast, the monoclonal antibody cross-reactive antigens appeared to be generally conserved during the transition from vegetative cells to bacteroids. These results offer a basis for observed reductions or complete loss of capability of some "strain-specific" monoclonal antibodies developed against vegetativeRhizobiumcells to detect the strains in nodule squash material by enzyme-linked immunosorbent assay.Key words:Rhizobium, monoclonal antibody, bacteroid, surface antigen, fluorescent antibody.

ISSN:0008-4166    

DOI:10.1139/m92-083

出版商:NRC Research Press    

年代:1992

数据来源: NRC

摘要:

Particulate enzyme preparations fromRhizobiumandBradyrhizobiumsynthesize β-glucans when incubated with uridine diphosphate glucose (UDP-glucose) and a divalent cation. Synthesis of β-1,2-linked glucans inRhizobium frediiinvolves the product of thendvBgene, a 319-kDa membrane protein, which is labeled with [14C]glucose from UDP-[14C]glucose as previously demonstrated inRhizobium melilotiandAgrobacteriumsp.Bradyrhizobium japonicumsynthesize β-1,3- and β-1,6-linked glucans of a lower molecular weight than those synthesized byR.meliloti. In comparative experiments, no evidence was found for a protein-bound intermediate inB.japonicum. ThendvBgene ofR.frediiwas mobilized toB.japonicumand the gene was expressed, as evidenced by appearance of a large membrane protein (ca. 319 kDa) which was labeled with UDP-[14C]glucosein vitro.Key words: soybean, nitrogen fixation, β-glucan,Bradyrhizobium,Rhizobium.

ISSN:0008-4166    

DOI:10.1139/m92-084

出版商:NRC Research Press    

年代:1992

数据来源: NRC