[Show abstract][Hide abstract] ABSTRACT: Legume trees are symbiotically associated with rhizobia and mycorrhizal fungi, microorganisms that improve their growth. The objective of this work was to characterize 61 rhizobial isolates from eight species of native legume trees: Acacia caven, Inga urugüensis, Lonchocarpus nitidus, Prosopis nigra, Sesbania virgata, Peltophorum dubium, Enterolobium contortisiliquum and Erythrina crista-galli. The strains were isolated from nodules with high nitrogenase activity and their growth rate, antibiotic, salinity and acidity resistances were determined. Their relationships were analyzed building a matrix with the resistance characteristics. Most of the isolates were fast growers and acid-producing with high level of exopolysaccharides. In general, isolates were erythromycin resistant but sensitive to rifampicin. All the isolates grew well at pH 5.5 while 75% did so at pH 4.4. More than 60% of the isolates grew in 2% of NaCl but this declined to 21% of the isolates in 3% NaCl. This population showed high antibiotic, salinity and pH resistance, suggesting adaptability to major ecological environment stresses, and great saprohytic competence within soil environments. Isolates from the same host showed high homology between them.
[Show abstract][Hide abstract] ABSTRACT: The level of colonization by ectomycorrhizae (ECM) and arbuscular endomycorrhizae (AM) of 23 species of native trees and shrub legumes was studied. Root samples were obtained from different regions of Uruguay. Colonization level was determined by observing AM fungal structures (hyphae, arbuscules, vesicules) in stained root segments. The number and morphological type of spores were determined in 100g of rhizosphere soil. Ectomycorrhizal colonization was evaluated by direct and microscopic observation of root tips. All species had a high level of AM colonization. In Papilionoideae colonization varied between 62% and 78%, in the Mimosoideae between 18% and 69% and in the Caesalpinioideae the variation was larger (6–74%). These results show a significant presence of fungi that form arbuscular mycorrhizae in our soils. The number of spores forming AM in rhizosphere soil (280–l.620 spores/100g of dry soil) was also highly relative to references for other leguminous trees. Spores were grouped in three principal morphological types Acaulospora, Glomus and Sclerocystis. Presence of ECM fungi was evident only when observed under the microscope. 26% of the plant species exhibited this type of mycorrhizae, reaching a maximal value of 36% in Mimosoideae. Only six plant species exhibited both types of mycorrhizae. Dual colonization could help in the colonization of poor soils and for their use in agroforestry systems.
[Show abstract][Hide abstract] ABSTRACT: The leguminous Acacia caven, Erythrina crista-galli, Enterolobium contortisiliquum, Prosopis affinis and P. nigra nodulated with rhizobial strains isolated from other legume trees; therefore they were considered to be promiscuous (poorly specific) for nodulation. Sesbania punicea and Parapiptadenia rigida did not nodulate with the different strains, indicating a significant specificity for nodulation. A. caven was promiscuous for nodulation and nodulated with both fast- and slow-growing strains of rhizobia and our data suggest that the most efficient strains would be fast-growing rhizobia. A. caven was specific for effectivity since the amount of N2 which was fixed markedly depended on the strain. The relative efficiency (RE) of 6 out of the 11 strains used was higher than 0.80, suggesting they had an active uptake hydrogenase. Ac5, a strain isolated from A. caven, exhibited the highest N2-fixing ability and highest NE (nodule efficiency) when inoculated on its host and also had the highest RE. Shoot dry weight and acetylene reducing activity (ARA) were significantly correlated with the amount of N2 fixed (determined by the total nitrogen difference method), indicating that any of these methods could be used for screening the strains according to their ability to fix N2. The relative efficiency was not correlated with any of these parameters.
[Show abstract][Hide abstract] ABSTRACT: A survey of the nodulating ability of 17 Uruguayan native and subspontaneous tree legumes has added Inga uragüensis to the list of legumes known to fix N2. Nodulation and N2 fixation capability of the following species were confirmed: Acacia caven, Calliandra tweediei, Parapiptadenia rigida, Lonchocarpus nitidus, Erythrina crista-galli. Whereas A. caven bore many nodules in all soil types observed, Prosopis nigra and P. affinis were always poorly nodulated. Seedlings of E. crista-galli bore aerial nodules at the base of their stem when grown in waterlogged conditions. The morphology, structure and nitrogenase activity (ARA) of the aerial nodules were similar to root nodules. Nodulation ability of Geoffroea decorticans was not confirmed. The species belonging to the Caesalpinoideae sub-family did not nodulate and were unable to do so even when they were inoculated with a mixture of rhizobia strains, thus confirming previous observations. Nodule morphology was described according to Corby's classification. Anatomical studies showed the presence of spaces in the inner zone of A. caven nodules. E. crista-galli and Enterolobium contortisiliquum nodules exhibited several infected zones, probably related to the coralloid morphology of the nodules. The acetylene-reducing activity of the nodules of the different species was generally low. Rhizobial strains were isolated from the most active nodules for future investigations.
[Show abstract][Hide abstract] ABSTRACT: This report describes some biochemical and genetic characteristics of seven rhizobial isolates that nodulate legume trees Inga uragüensis, Prosopis nigra, Acacia caven, Erythrina crista-galli and Enterolobium contortisiliquum, native to Uruguay. Based on specific growth rates, carbon source utilization and acid production the isolates could be assigned to the fast-growing group of rhizobia. The analysis of plasmid content showed that from seven isolates examined, three contained a single plasmid of approximately 220 Mda, two harboured two plasmids with molecular weight < 220 Mda and no plasmid was detected in the remaining isolates. All the isolates examined showed a distinguishable protein profile using one-dimensional SDS-PAGE. This technique could distinguish one isolate from another. Hybridization studies using R. leguminosarum hup probe did not indicate hup genes in any of the isolates examined.
[Show abstract][Hide abstract] ABSTRACT: The growth of Frankia cells within alginate beads was inhibited when the amount encapsulated exceeded 0.5 to 2.5 µg protein/ml of beads. Frankia growth was observed not only in the beads incubated in nutrient media (with of without combined N), but also in those incubated in air provided they retained enough nutrients. The results allow some recommendations to be made for the preparation of Frankia inoculants.
World Journal of Microbiology and Biotechnology 01/1994; 10(1):118-121. DOI:10.1007/BF00357578 · 1.78 Impact Factor