After cereals, legumes constitute the second most important family of crops for human and animal consumption. However, in contrast to the former, legumes are capable of growing in arid soils of low fertility, due to their ability to establish symbiotic associations with soil bacteria called rhizobia. These microorganisms form special organs in the roots of legumes called nodules, where atmospheric dinitrogen N 2 is transformed into ammonium that is exported to the plant for growth. Since their discovery in legume nodules until today, knowledge of the bacteria capable of establishing symbiosis with these plants has advanced in many aspects. Especially, advances in molecular techniques for bacterial identification and access to unexplored places have confirmed that the interaction of legumes with rhizobia is older, and that N 2 -fixing bacteria are more abundant and diverse, than considered previously. Here, we attempt to relate the history of an association whose development is key in the history of mankind as we know it now.
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Biological fixation of nitrogen by native isolates of Rhizobium sp. De Wit. Forage legumes such as Leucaena leucocephada, besides being a rich source of protein for animal feed, its inclusion in silvopastoral systems provides fundamental components to improve soil properties. These plants have the ability to establish symbiotic association with the genus Rhizobium sp.
The objective of this research was to evaluate the capacity of native isolates of Rhizobium sp. Two separate bioassays to evaluate the efficiency of the FBN of the native isolates and the commercial strain under greenhouse conditions, followed by a randomized complete block design with 7 x 2 factorial arrangement, seven treatments, two factors: native isolates and commercial strains and bacterial concentrations 10 6 and 10 8 cells.
In the second bioassay with day-old seedlings, the same variables of the first bioassay were determined, with the exception of the percentage of germination. In the first bioassay, a greater stimulation was found in the germination of L. Regarding stem length and thickness, accumulated dry matter, leaf development and nitrogen accumulation, better results were found in the treatments with the native isolates L27, L36 and L38 in a concentration of cells.
The native isolates of Rhizobium sp. Key words: Leucaena leucocephala; biological nitrogen fixation; forage legumes; Rhizobium sp. Los aislados nativos de Rhizobium sp. Livestock, along with commercial crops are the most economically profitable activities after mining in Cesar State Colombia , located at northwest of the Colombian Caribbean; making the region one of the most important in meat and dairy production Fedegan, Portilla et al.
The cattle demand large amounts of grass and forage to maintain a good diet, however the region presents shortages in dry season and even more with the climate effect leading a poor performance in body mass, reproduction and production of milk and meat. To work against forages demand, L. This leaves aside the indiscriminate use 2 of synthetic fertilizers that have generated a negative impact on the soil ecology, what has currently manifested in erosion, desertification and impoverishment of vegetation cover Mahecha, Different research has shown the biopromotor potential of Rhizobium sp.
The isolation of native bacteria of Rhizobium sp. This rhizobacteria, in addition to fixing nitrogen produce phytohormones, participate in the solubilization of phosphorus and antagonistic reaction, allowing a greater productivity of the host legume plant in any type of soil Akhtar and Siddiqui, ; Santillana et al.
The search for native isolates of Rhizobium sp. Therefore, the objective of this research was to evaluate the capacity of native isolates of Rhizobium sp. In the area, the wind speeds reach Seed germination. Three L. The Rhizobium sp. The inoculation was performed aseptically applying 2 ml of the respective bacterial suspensions 10 6 and 10 8 cells. The control treatment was only added 2 mL of sterile distilled water. The Germination Percentage GP was determined daily from day zero until the day on which the last seedling emerged Cubillos- Hinojosa et al.
Evaluation of BNF efficiency of Rhizobium sp. After 2 weeks of germination percentage was determined, the seedlings were thinned, leaving in each pot the most vigorous Mora, ; Matos et al.
After 38 days the stem length SL with a tape measure, stem diameter SD with vernier caliper, the number of true leaves NTL and dry weight of the aerial part WAP were measured based on the methodology proposed by Reyes et al. After 30 days, the inoculation was made carefully removing the soil at the level of the base of the stem and adding 2 mL of the respective bacterial suspensions 10 6 and 10 8 cells. After 18 days, the measurements of the variables evaluated of the first bioassay were made.
Table 1 shows that the native Rhizobium sp. Meanwhile, all the treatments inoculated with the concentrations of 10 8 cells. Similar results were found by Reyes et al. Also were found favorable results in paprika seeds germination after being inoculated with one of the two isolates of Rhizobium sp. Additionally, these results are consistent with those obtained by Dobbelaere et al.
This occurs due to an increase in cell division promoting the formation of radical hair and, consequently, resistance to osmotic stress due to an increase in chlorophyll, K, Ca, soluble sugars and protein content Kennedy et al.
For the stem length SL , analysis of variance showed that treatments L These results were higher than found by Rincon et al. The results were homogeneous among all the treatments to the stem diameter SD and the number of true leaves NTL , except for the control 1. For NTL, only L According to this, it can be affirmed that the SD and NTL did not represent in great magnitude the behavior of each one of the strains; contrasting with the SL in which it was observed, differences between treatments Table 2.
L: native isolate of Rhizobium sp. The dry weight of the aerial part WAP in treatments L 1. According to the concentration, significant differences were found Table 2 between L 1. Only L, presented significant differences with all treatments. The average nodulation for all treatments was For Cc 1, good results were found and do not present significant differences with the best treatments with the exception of L 2, , that gave the highest value.
In addition, L 1, , L 1, , L 1, , L 1, , L 1, and L 1, , did not present significant differences relative to control 1. With the above, it is infer that the bacterial concentration is relate to the levels of nodulation, the greater the concentration the higher the nodulation level, but this variable does not determine the process of biological nitrogen fixation BNF.
For L 1, , L 1, and L 2, nodulation levels were on average with respective values of 6, 10,33 and 9. These results are contrary to those reported by Matos and Zuniga in P. This research found that the ability of the strains to form nodules, not necessarily indicated efficiency BNF; for each legume -rhizobium combination, the optimal level of nodulation was different.
However, abundance, size, distribution and internal coloration of the nodules were important indicators of their effectiveness or ability to fix nitrogen Mora, Analysis of variance for stem length SL , indicated better results for treatments L L: native strain of Rhizobium sp.
In addition, the best treatments also showed significant differences with L Regarding to the stem diameter SD , it was found that the native isolates of Rhizobium sp. The treatments L Regarding CC 0. A L and L in comparison with the control. A Located nodulation for test seedlings, B Nodulation distributed around the root system, for testing seed. Among the best treatments were also found L 0.
It was also found that L 0. These results were better than those reported by Weslermeyer that found that the inoculation of native isolates of Rhizobium sp.
It was observed that, in this analysis, that although the nodulation for L 14,67 and L 16,33 was the best, the results in terms of nitrogen percentage do not corroborate this information.
In the statistical analysis for nitrogen percentage; it was found that the best isolate for this parameter was L 3, showing statistically significant differences with the rest of the treatments regarding this variable. However, this treatment has average levels of nodulation 9,67 Graph 7. The commercial strain CC and CC showed respective values of 4,67 and 10,67 regarding the level of nodulation; and 1, and 1, in terms of nitrogen percentage, presenting no significant differences with respect to the control 0, According to the above, Rincon et al.
This is because the genetic variability of the isolates can be manifested by the diference they exhibit competitive ability for sites nodule formation, which is determined by the interaction of the plant genome, the introduced isolate, population native and environmental factors.
Due to the response to the inoculation and competitive success of each of the isolates is unknown, it is necessary to evaluate their fixation capacity first at the greenhouse level and later in the field Mora, This can be the effect of the competition for nutrients and the root among the same bacterial population, thus slowing down the establishment process between the roots and the rhizobia, thus being able to be noticed in the development of the seedlings.
Additionally, the nodulation results allow to see that the bacterial concentration did not influence notably in the number of nodules with the exception of CC, L and L, which show higher values in relation to the concentration 10 6 of the same native isolate.
This is opposite to that thrown by the percentage of nitrogen, which highest values in the native isolates at a concentration of 10 6 cells. The isolates L27, L36 and L38 were the most efficient, even in concentration 10 6 cells. Ahemad, M. Journal of King Saud University-Science, Akhtar, M. Effects of phosphate solubilizing microorganisms and Rhizobium sp. African J. Bardin, S. Biological control of Pythium damping-off of pea and sugar beet by Rhizobium leguminosarum bv.
Canadian Journal of Botany, 82 3 , En: Sistemas Agroforestales. ISBN Pp Cubillos-Hinojosa, J. Biological nitrogen fixation by Rhizobium sp. Diouf, A. Response of Gliricidia sepium tree to phosphorus application and inoculations with Glomus aggregatum and rhizobial strains in a sub-Saharian sandy soil.
African Journal of Biotechnology, 7 6 Dobereiner, J. Biological nitrogen fixation in the tropics: Social and economic contributions. Soil Biology and Biochemistry, 29 , Dobbelaere, S.
EP0292984A2 - Gène cloné ntrA (rpoN) de rhizobium meliloti - Google Patents
Biological fixation of nitrogen by native isolates of Rhizobium sp. De Wit. Forage legumes such as Leucaena leucocephada, besides being a rich source of protein for animal feed, its inclusion in silvopastoral systems provides fundamental components to improve soil properties. These plants have the ability to establish symbiotic association with the genus Rhizobium sp. The objective of this research was to evaluate the capacity of native isolates of Rhizobium sp.
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Isolation and characterization of rhizobia strains isolated from different legumes in the Cascajal region, Villa Clara. Pastos y Forrajes [online]. ISSN Nineteen rhizobium strains were isolated from the nodules of the legumes Canavalia ensiformis , Stylosanthes guianensis , Centrosema molle , Pueraria phaseoloides and Macroptilium atropurpureum , with the objective of obtaining effective inoculants for such crops in acid soils. For the characterization of the bacterial isolates, their micromorphological, staining and cultural characteristics were studied, as well as some physiologicalbiochemical responses, such as the excretion of acid or base to the culture medium and the cetolactase assay.