Native Rhizobium Strains Research Articles

Enhance of tomato production and induction of changes on the organic profile mediated by Rhizobium biofortification.

The extensive use of chemical fertilizers has served as a response to the increasing need for crop production in recent decades. While it addresses the demand for food, it has resulted in a decline in crop productivity and a heightened negative environmental impact. In contrast, plant probiotic bacteria (PPB) offer a promising alternative to mitigate the negative consequences of chemical fertilizers. PPB can enhance nutrient availability, promote plant growth, and improve nutrient uptake efficiency, thereby reducing the reliance on chemical fertilizers. This study aimed to evaluate the impact of native Rhizobium strains, specifically Rhizobium calliandrae LBP2-1, Rhizobium mayense NSJP1-1, and Rhizobium jaguaris SJP1- 2, on the growth, quality, and rhizobacterial community of tomato crops. Various mechanisms promoting plant growth were investigated, including phosphate solubilization, siderophore production, indole acetic acid synthesis, and cellulose and cellulase production. Additionally, the study involved the assessment of biofilm formation and root colonization by GFP-tagged strains, conducted a microcosm experiment, and analyzed the microbial community using metagenomics of rhizospheric soil. The results showed that the rhizobial strains LBP2-1, NSJP1-1 and SJP1-2 had the ability to solubilize dicalcium phosphate, produce siderophores, synthesize indole acetic acid, cellulose production, biofilm production, and root colonization. Inoculation of tomato plants with native Rhizobium strains influenced growth, fruit quality, and plant microbiome composition. Metagenomic analysis showed increased Proteobacteria abundance and altered alpha diversity indices, indicating changes in rhizospheric bacterial community. Our findings demonstrate the potential that native Rhizobium strains have to be used as a plant probiotic in agricultural crops for the generation of safe food and high nutritional value.

Efficient native strains of rhizobia improved nodulation and productivity of French bean (Phaseolus vulgaris L.) under rainfed condition.

Biological nitrogen fixation is the most important eco-friendly approach to nitrogenous fertilizer management in the rhizosphere. Rhizobium is considered the most important symbiotic N-fixing microorganism. Native strains of Rhizobium perform better than the non-native strains by getting ambient conditions for growth and proliferation. Native strains enhance the soil fertility and productivity of pulses. The study was carried out in three phases, i.e., pot experiment, field experiment, and farmers' field demonstrations. In a pot experiment, two isolated rhizobia were inoculated to seeds of French bean (Phaseolus vulgaris) and applied with and without lime to evaluate crop growth, photosynthetic activity, and nodule characteristics of the target crop. In the field, strains were inoculated to seeds of French bean, which received different combinations of inputs- inorganic fertilizers, lime, and boron- to study the influence of native stains on crop productivity and agronomic efficiency. In comparison to non-limed packaging, the amounts of chlorophyll a, chlorophyll b, total chlorophyll, and chlorophyll a:b were, respectively, 13% to 30%, 1% to 15%, 10% to 27%, and 1% to 20% greater in limed packages. In limed packages compared to non-limed packages, the root length, biomass, density, and growth rate were increased by 16% to 17%, 36% to 52%, 38% to 49%, and 36% to 52%, respectively. In contrast to non-limed packages, limed packages had nodule attributes like the number of nodules per plant and nodular weight, which were 28% to 41% and 33% to 37% greater, respectively. Inoculation of native rhizobia strains with liming to acid soil increased 46% to 72% of leaf nitrogen content over non-limed rhizobia inoculated packages. In a field experiment, the adoption of soil test-based fertilizer application had an advantage of 25% in pod yield over farmers' practice. Acid soil amelioration with lime improved pod yield from 14% to 39% over non-limed packages. Farmers' field demonstration recorded the highest pod yield in the package where seeds were inoculated with S2 (RBHR-21) strain added with soil test-based fertilizers (STD) followed by STD + S1 (RBHR-15) with 98% and 84% increase over farmers' practice. However, experimental evidence favored using both strains for bio-inoculation of the French bean crop.

Effect of Rhizobium Inoculation on Growth of Common Bean in Low-Fertility Tropical Soil Amended with Phosphorus and Lime

The cultivation of grain legumes (e.g., common bean) in sub-Saharan Africa contributes to the provision of food for a growing population and delivers environmental benefits such as inputs of nitrogen (N) to crops and soil via symbiotic nitrogen fixation (SNF). However, the success of SNF is constrained by several factors such as the poor efficiency of native rhizobial strains to fix N, the low availability of phosphorus (P) and the acidity of soils. Two trials have been conducted in low-fertility tropical soils at the smallholder farm scale in Madagascar to assess the effects of Rhizobium inoculation together with inputs of P and lime on the growth of the common bean. We showed that inoculation with native strains of Rhizobium had significant effects on bean root nodulation, which was increased by up to 15-fold on plant growth, which increased by 78% and on bean yield, which increased by 126%. Moreover, we observed positive and significant relationships between inoculation with Rhizobium and P fertilization on nodulation, plant growth and yield. However, the addition of dolomite lime did not show any effect in our study. The addition of P decreased the mycorrhization rate of roots. Additional research is still needed to improve our understanding of soil fertility conditions (mainly on nutrient availability, including micronutrients) allowing better efficiency of legume symbionts (rhizobium and mycorrhiza) in such low-fertility soils.

Abundance and Symbiotic Rhizobia Colonizing Soybean (Glycine max) in Soils of Kakamega County, Western Kenya

Identification of effective indigenous rhizobia strain nodulating soybean (Glycine max) was conducted in Kakamega County, Western Kenya. This study was carried out to establish the abundance and symbiotic efficiency of native rhizobia strains in soil samples collected from 12 sites in four agroecological zones within the region. The MPN enumeration technique was used to estimate the indigenous rhizobia numbers and showed that 54% of the sampled sites had high abundance. Rhizobia number in the soil collected from the six regions varied from 2.5 × 102 to 3.12 × 103 cells·g− soil. Thirty isolates from the soil collected in the four regions were tested for efficiency using soybean as the trap plant in Leonard jars containing sterilized vermiculite irrigated with nitrogen-free media. Determination of the relationship between rhizobial abundance and symbiotic efficiency with respect to the soil chemical conditions was performed using ANOVA, and the means were compared using Tukey’s honest significant difference test. Inoculation with bacterial isolates significantly ( P < 0.05 ) increased the nodule number and shoot dry weight, while weight of the seeds showed variations across the groups. The soil pH across the 4 regions ranged between 5.41 and 6.52.

Native Rhizobia Strains Enhance Seed Yield of Groundnut Varieties in Northern Ghana

Rhizobia inoculation with effective strains is an environmentally friendly approach for enhancing nodulation and yield of legumes. To obtain an ideal strain for inoculant production, the strain's performance must be matched to the environmental conditions. A 2 × 9 cross-factorial experiment laid in a randomized complete block design with three replications on farmers' fields in the northern part of Ghana was set up to evaluate the rhizobia's performance. The factors were groundnut varieties (Chinese and Samnut 22) and nine strains consisting of five native rhizobia (KNUST 1001, 1002, 1003, 1032, and 1031), two commercial strains (Biofix and BR3267), and a positive (N+) and absolute control (N–). In addition, the population of the strains was assessed after a cropping season. The strains' performance on groundnut was location and variety dependent. At Cheshegu, KNUST 1031 and 1002 significantly increased seed yield of the Chinese variety compared to other strains; however, KNUST 1031 elicited a 24% yield increase while KNUST 1002 caused a 16% yield increase over the control. Strain KNUST 1031 increased the seed yield of the Chinese variety by 24% while KNUST 1002 increased the seed yield of Samnut by 16%. Only KNUST 1002 elicited a significant seed yield increase in Samnut 22 at Cheshegu. At Binduri, strain KNUST 1003 significantly increased the seed yield of the Chinese variety by 35% relative to the control. Samnut 22 did not show a clear preference for any of the strains. The Chinese variety did not show a clear response to the strains at Tanina. However, Samnut 22 responded to KNUST 1002 as it increased seed yield by 45% relative to the control. On average, the seed yield at Tanina (846.15 kg ha−1) was less than the seed yield recorded at Binduri (1,077.66 kg ha−1) and Cheshegu (1,502.78 kg ha−1). Inoculation with strains KNUST 1002, 1003, and 1031 was all profitable under the current experimental conditions as they recorded value cost ratios (VCRs) above the threshold of 3–4. The study has shown that strains KNUST 1002, 1003, and 1031 have the potential to be used in inoculant formulation to increase groundnut production and enhance the income of smallholder groundnut farmers in northern Ghana.

Isolation and Characterization of Native Rhizobium Strains Nodulating Some Legumes Species in South Brazzaville in Republic of Congo

Actually, in Republic of Congo, rhizobia have poorly phenotypically and biochemically characterized. This study aimed to characterize native rhizobia. Rhizobia strains were isolated using nodule roots collected on Milletia laurentii, Acacia spp., Albizia lebbeck, and Vigna unguiculata. The strains isolated were characterized microbiologically, biochemically, physiologically, and molecularly identified using 16S rRNA method. The results reported in this study are only for six strains of all 77 isolated: RhA1, RhAc4, RhAc15, RhAc13, RhW1, and RhV3. All native strains were positive to urease activity, negative to cellulase and pectinase activity except for one isolate that showed a positive cellulase activity. Moreover, isolates have grown at 12% of NaCl. On different effects of temperatures, isolates were able to grow up to 44°C and showed good growth at pH from 7 to 9 and the ability to use ten different carbon hydrates sources. The strains were identified as Rhizobium tropici, Rhizobium sp., Mesorhizobium sp. Bradyrhizobium yuanmingense and Bradyrhizobium elkanii. The phylogenetically analysis of the 16S rRNA genes, using a clustering method, allowed us to have a history that is both ancient and stable of four clades among genes with similar patterns. Expanding our awareness of the new legume-rhizobia will be a valuable resource for incorporating an alternative nitrogen fixation approach to consolidate the growth of legumes. These germs can be used in Congolese agriculture to improve yield of crops.

ЭФФЕКТИВНОСТЬ ПРИМЕНЕНИЯ КОМПЛЕКСНЫХ МИНЕРАЛЬНЫХ УДОБРЕНИЙ В АГРОЦЕНОЗЕ СОИ

Soybean is one of the most valuable protein crops on the modern market of agricultural producers and its production has been constantly growing in recent decades. The level of its productivity, as well as any other crop, depends on the biological productivity potential of the cultivated variety and the degree of implementation of its cultivation techniques. The aim of the research was to study the responses of soybean Glycine max (L.) Merr. Zusha varieties for various mineral nutrition in the conditions of agrocenosis. The research was conducted on the basis of the research and educational production center "Integration" of the Orel State Agrarian University named after N.V. Parakhin. We determined the biological efficiency of fertilizer systems, the productivity and quality of grain under different mineral nutrition conditions .Testing of liquid complex fertilizers on soy has shown high biological and economic efficiency of mineral fertilizers. In conditions of dark gray forest soils with average agrochemical indicators of the soil, as well as with spontaneous inoculation of soybean by native rhizobia strains, the maximum economic effect was demonstrated with the pre-sowing application of complex mineral fertilizer NPK (S)+Ca 5:15:30(5)+7 in a dose of 150 kg/ha and 20 kg/ha of urea, as well as diammofoski NPK(S) 10:26:26 (2) in conjunction with the ZhCU. The use of mineral fertilizers contributed to an increase in the growth of biomass by an average of 23%, and the area of leaves-by 8.5% compared to the control. Changes in mineral nutrition led to an increase in the content of raw protein in soy grains. Additionally, 4.4-4.6 C/ha of grain was obtained from 1 ha, respectively 4.7 and 5.4 thousand rubles of income due to an increase in soybean productivity by 22-23% compared to the control.

Influence of Rhizobium Inoculation on Nodulation, Biomass Production and Yield of Some Indigenous Legumes in the Rainforest Agro-Ecological Zone of Nigeria

A field study was conducted during the late cropping seasons of 2015 and 2016 at Akamkpa (latitude 5°15' N and longitude 8°22'E), southern Nigeria, to evaluate the response of some legume genotypes to seed inoculation with NoduMax, a Rhizobium inoculant developed by the International Institute of Tropical Agriculture (IITA). Treatments were factorial combinations of inoculated and non-inoculated seeds of Cowpea, Groundnut, Bambara groundnut, Bebi (Viny Lima) bean, Mucuna bean, and African yam bean, laid out in randomized complete block design replicated thrice. The response of the test crops to inoculation varied with growth stage. At the seedling stage, effective nodule number was not significantly affected in all but Mucuna bean in which there was a 42.7% reduction. At pre-an thesis, Bambara groundnut, Bebi bean, Groundnut, and Cowpea recorded a statistically similar number of nodules(p=0.05) under inoculated and non-inoculated conditions, but inoculation reduced nodule formation in Mucuna bean and African yam bean by 22.4 and 20.4%, respectively. Nodule dry weight of Bebi bean, Bambara groundnut, Mucuna bean and Cowpea was unaffected by inoculation when assessed at the seedling and pre-anthesis growth stages, but that of Groundnut was reduced by 35, and African yam bean increased by 60%, respectively. Inoculation increased the nodule dry weight of African yam bean and Mucuna bean by 56.5 and 60.6% at seed initiation stage, and reduced that of Bambara groundnut and Groundnut by 25.6 and 50.0%, respectively. The effect of genotype í— inoculation interaction on plant biomass and fresh grain yield was significant; whereas inoculation significantly increased the yield of Cowpea from 2,471 to 2,794 kg/ha and 2,995 to 3504 kg/ha in 2015 and 2016, respectively, it did not significantly affect that of Bebi bean, African yam bean and Bambara groundnut. On the contrary, the yield of groundnut was reduced from 884 to 560 kg/ha and 963 to 678 kg/ha in 2015 and 2016, respectively. Inoculation with NoduMax was beneficial to cowpea, but did not significantly improve the performance of Bebi bean, and Groundnut. It could be that Bebi bean is promiscuous and better adapted to the native strains of Rhizobium, while the Rhizobium in Groundnut is antagonistic and incompatible with the introduced inoculants. Binang et al.; JALSI, 11(4): 1-9, 2017; Articleno.JALSI.32624 2 recorded a statistically similar number of nodules (p=0.05) under inoculated and non-inoculated conditions, but inoculation reduced nodule formation in Mucuna bean and African yam bean by 22.4 and 20.4%, respectively. Nodule dry weight of Bebi bean, Bambara groundnut, Mucuna bean and Cowpea was unaffected by inoculation when assessed at the seedling and pre-anthesis growth stages, but that of Groundnut was reduced by 35, and African yam bean increased by 60%, respectively. Inoculation increased the nodule dry weight of African yam bean and Mucuna bean by 56.5 and 60.6% at seed initiation stage, and reduced that of Bambara groundnut and Groundnut by 25.6 and 50.0%, respectively. The effect of genotype í— inoculation interaction on plant biomass and fresh grain yield was significant; whereas inoculation significantly increased the yield of Cowpea from 2,471 to 2,794 kg/ha and 2,995 to 3504 kg/ha in 2015 and 2016, respectively, it did not significantly affect that of Bebi bean, African yam bean and Bambara groundnut. On the contrary, the yield of groundnut was reduced from 884 to 560 kg/ha and 963 to 678 kg/ha in 2015 and 2016, respectively. Inoculation with NoduMax was beneficial to cowpea, but did not significantly improve the performance of Bebi bean, and Groundnut. It could be that Bebi bean is promiscuous and better adapted to the native strains of Rhizobium, while the Rhizobium in Groundnut is antagonistic and incompatible with the introduced inoculants.

Evaluation of native Rhizobium leguminosarum bv. viceae of pea plants (Pisum sativum L.) for nodulation efficiency and yield promotion in lentil crop (Lens culnaris Medik.) under acid soil

Most leguminous crops including lentil require neutral to slightly acidic range of soil pH for favourable nodulation and nitrogen fixation. The quest for acid soil compatible Rhizobium leguminosarum bv. viceae strain is important for promotion of lentil crop under rice-lentil rotation in acid soil regions. In this investigation, native R. leguminosarum strains were isolated from the nodules of pea plants grown in pots using acid soil and isolated native Rhizobium strains were confirmed on CRYEMA (congo red Yeast Extract Mannitol Agar) media. Four native R. leguminosarum strains (NR1, NR2, NR3 and NR4) obtained from four acid soil types were further screened for nodulation efficiency and yield attributes of lentil crop against a reference exotic strain R. leguminosarum CK1 (ER). The results indicated that the performance of native Rhizobium strain (NR2) was the best among native isolates and performed on par with the reference strain (CK1) in acid soils of Meghalaya.

Densidade, caracterização e eficiência de bactérias fixadoras de Nitrogênio em áreas de caatinga degradada

A degradação do solo resultante de práticas não conservacionistas pode acarretar prejuízos irreparáveis às propriedades químicas e biológicas do sistema edáfico de regiões Semiáridas do Nordeste brasileiro. O objetivo do trabalho foi avaliar os atributos químicos do solo, estimando a densidade populacional de rizóbios nativos e isolando estirpes eficientes na fixação simbiótica do N2 no feijão-caupi em áreas de exclusão e de superpastejo. O estudo foi realizado na Fazenda Formigueiro, pertencente ao município de Irauçuba Ceará. As coletas do solo foram realizadas em duas áreas caracterizadas por diferentes níveis de degradação, sendo: área de exclusão e área de superpastejo. O delineamento experimental adotado foi inteiramente casualizado com oito tratamentos e quatro repetições, sendo um controle com adição de nitrogênio mineral C (+N-R); e um com omissão de nitrogênio mineral e ausência de inoculação C (-N-R), totalizando 32 unidades experimentais. O uso intensivo do solo e o histórico de manejo das áreas estudadas contribuíram de forma negativa para as propriedades químicas e densidade de células rizobianas. O estudo da eficiência fixadora de N2 das estirpes nativas nas áreas de exclusão e superpastejo evidenciaram a ocorrência de estirpes com eficiência variável, apresentando uma eficácia simbiótica em torno de 22 a 41% para a cultura do feijão-caupi.

Genetic and phenotypic diversity of Rhizobium isolates from Southern Ecuador

ABSTRACT Rhizobium-legume symbioses play relevant roles in agriculture but have not been well studied in Ecuador. The aim of this study was to characterize the genetic and phenotypic diversity of Rhizobium isolates associated with Phaseolus vulgaris from southern Ecuador. Morpho-cultural characterization, biochemical tests and physiological analyses were conducted to authenticate and determine the diversity of bacteria Rhizobium-like isolates. The genetic diversity of the isolates was determined by molecular techniques, which consisted of bacteria DNA extraction and amplification and sequencing of the 16S rRNA gene. The nodulation parameters and nitrogen fixation for P. vulgaris under greenhouse conditions were also assessed to determine the phenotypic diversity among isolates. Furthermore, bacteria indole-acetic-acid production was evaluated by the colorimetric method. Morpho-cultural and biochemical characteristic assessments demonstrated that Rhizobium-like bacteria was associated with the P. vulgaris nodules. The diversity among the isolates, as determined by physiological analyses, revealed the potential of several isolates to grow at different pH values, salinity conditions and temperatures. Partial sequencing of the 16S rRNA gene identified the Rhizobium genus in every sampling site. From a total of 20 aligned sequences, nine species of Rhizobium were identified. Nodule formation and biomass, as well as nitrogen fixation, showed an increase in plant phenotypic parameters, which could be influenced by IAA production, especially for the strains R. mesoamericanum NAM1 and R. leguminosarum bv. viciae COL6. These results demonstrated the efficiency of native symbiotic diazotrophic strains inoculants for legume production. This work can serve as the basis for additional studies of native Rhizobium strains and to help spread the use of biofertilizers in Ecuadorian fields.

Inoculation of Schizolobium parahyba with Mycorrhizal Fungi and Plant Growth-Promoting Rhizobacteria Increases Wood Yield under Field Conditions.

Schizolobium parahyba var. amazonicum (Huber ex Ducke) occurs naturally in the Brazilian Amazon. Currently, it is being planted extensively because of its fast growth and excellent use in forestry. Consequently, there is great interest in new strategies to increase wood production. The interaction between soil microorganisms and plants, specifically in the roots, provides essential nutrients for plant growth. These interactions can have growth-promoting effects. In this way, this study assessed the effect of the inoculation with arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) on growth of S. parahyba var. amazonicum under field conditions. We used two native species of arbuscular mycorrhizal fungi, Claroideoglomus etunicatum (Ce), and Acaulospora sp. (Ac); two native strains of Rhizobium sp. (Rh1 and Rh2); and a non-native strain of Burkholderia sp. Different combinations of microorganisms were supplemented with chemical fertilizers (doses D1 and D2) in two planting methods, seed sowing and seedling planting. In seed sowing, the results showed that treatments with Ce/Rh1/Fertilizer D2 and Ac/No PGPR/Fertilizer D2 increased wood yield. In seedling planting, two combinations (Ac/Rh2/Fertilizer D1 and Ac/Rh1/Fertilizer D1) were more effective in increasing seedling growth. In these experiments, inoculation with AMF and PGPR increased wood yield by about 20% compared to the application of fertilizer alone.

Common Bean Seed Complements Molybdenum Uptake by Plants from Soil

Molybdenum (Mo) reserve in large seeds can complement Mo uptake by plants from soil, but the content of Mo in common bean (Phaseolus vulgaris L.) seed for this purpose is unknown. We hypothesized that 3.639 ± 0.751 μg Mo seed−1 would be sufficient to complement Mo uptake by irrigated common bean plants from a Mo‐poor soil. Three field experiments were performed in a clayey Ultisol naturally infested by native strains of Rhizobium in Zona da Mata, Minas Gerais, Brazil. Treatments were arranged as 4 × 2 factorial combination of Mo contents in seeds [small (0.007 ± 0.007 or 0.248 ± 0.057 μg Mo seed−1) or large (3.639 ± 0.751 or 6.961 ± 1.844 μg Mo seed−1)] and Mo spraying treatments (90 g ha−1 or unsprayed) with six replications. Phosphorus, N (25 kg ha−1), and K were applied together in the furrow during planting time. No topdressing N was applied. Final plant population and seed yield were evaluated in two experiments. Molybdenum contents in the seeds did not affect plant population. On average, unsprayed plants from seeds with small Mo contents yielded 1785 kg ha−1, while those from seeds with large Mo content yielded 2109 kg ha−1. Foliar application of Mo increased plant N status, plant growth, and yield in plants originated from seeds with small Mo content, but not in plants grown from seeds with large Mo content. We conclude that 3.639 ± 0.751 μg Mo seed−1 sufficiently complement the Mo uptake by common bean plants from soil.

GROWTH OF Inga vera WILLD. SUBSP. Affinis UNDER RIZOBIA INOCULATION

Nitrogen, in general, is the largest limiting plant growth nutrient in the tropics and is required as a synthetic fertilizer to improve plants productivity. Therefore, studies aiming in understanding and using nitrogen fixation by leguminous trees have been done as a low-cost alternative for chemical fertilizer. Native legume trees such as Inga vera have been recommended in the rehabilitation of degraded areas due their ability to establish symbiosis with nitrogen fixation organisms replacing nitrogen fertilization. These species are able to increase soil organic matter, nitrogen and phosphorus availability. Thus, the present study aims to assess the inoculation effects of native rhizobia strains on nodulation, dry matter production, nitrogen and phosphorus leaf incorporation in I. vera seedlings. With this purpose, four strains were obtained from inga nodules and tested in a greenhouse. The inoculation of I. vera seedlings with native rhizobium strains promoted an increase in shoot dry mass as well as in leaf nitrogen content. According to symbiotic efficiency equation, this approach ranged from 50 to 80% indicating that the nitrogen fertilization for this species can be partially replaced by rhizobia inoculation.

Colonization and Nitrogenase Activity of Triticum aestivum (cv. Baccross and Mahdavi) to the Dual Inoculation with Azospirillum brasilense and Rhizobium meliloti plus 2,4-D

The potential enhancement of root colonization and nitrogenase activity of wheat cultivars (Baccross and Mahdavi) was studied with application of two Azospirillum brasilense strains (native and Sp7) co-inoculated with two Rhizobium meliloti strains (native and DSMZ 30135). The results indicated that the colonization was different due to the strains and cultivars of wheat were used. Native A. brasilense colonized wheat root better than Sp7 strain. However, Baccross cv. reacted better with native Azospirillum compared to Mahdavi cv. which reacted better with Sp7. When plants inoculated with dual inoculants (SP7 with standard Rhizobium), the colonization of Azospirillum were increased significantly (from 1.67 x 10(5) to 22 x 10(5) cfu g(-1) FW for Baccras cv. and 3.67 x 10(5) to 26 x 10(5) cfu g(-1) FW for Mahdavi cultivar). When the standard Rhizobium as co-inoculants changed to the native Rhizobium, the colonization of Azospirillum was higher when compared to the single inoculants but was almost the same when compared to the standard Rhizobium. When the standard or native strains of Rhizobium used as single inoculation of wheat roots, the number of Rhizobium in the wheat roots were not changed significantly. However, when plants co-inoculated with Rhizobium and Azospirillum, the colonization of Rhizobium was increased. Co-inoculation of standard strain of R. melilot with A. brasilense Sp7 showed that the colonization of Rhizobium were increased from 0.67 x 10(5) to 21 x 10(5) cfu g(-1) FW for Baccross cv. and 0.33 x 10(5) to 18 x 10(5) cfu g(-1) FW for Mahdavi cv. This behavior was the same when inoculation of Rhizobium was happened with the native one. In dual inoculation, the highest nitrogenase activity was measured in combination of the local strains (native A. brasilense with the native R. meliloti) and the lower one belongs to the combination of standard strains (Sp7 with standard R. meliloti). The difference in nirtogenase activity for different cultivars of wheat with Sp7 and standard Rhizobium is not significant but the difference for Sp7 strain plus native Rhizobium is significant (p > 0.05). However, the differences were not significant (p < 0.05) for nitrogenase activity in bacterial tubes, the difference for nitrogenase activity of co-inoculated plants with combination of Sp7 and Rhizobium either standard or native were significantly different.

Rhizobium strains competitiveness on bean nodulation in Cerrado soils

The objective of this work was to identify the most competitive and effective Rhizobium strains in order to increase common bean yield by nitrogen fixation as alternative or complementation to the nitrogen fertilization. Competitiveness tests were lead in axenic conditions, in Cerrado soil pots and in three field experiments, with native Rhizobium strains that were previously identified, according to their effectiveness and genetic variability. The identification of strains in nodules was performed using serological tests (axenic conditions) - agglutination and enzyme linked immunosorbent (Elisa) assays - and random amplified polymorfic DNA (RAPD) (Cerrado soil). Plant yield was determined using the dry weight (greenhouse conditions), total N and grain yield (field experiments). Among the analyzed Rhizobium strains, native strain SLA 2.2 and commercial strain CIAT 899 were the dominant nodules in plants of the most productive plots, presenting yield productivity similar or higher to those obtained in treatments where 20 kg ha-1 of N were applied.

Adubação nitrogenada e molíbdica da cultura do feijão na Zona da Mata de Minas Gerais

Três séries de experimentos foram realizadas. Na primeira, estudaram-se, em dois municípios, os efeitos de N, Mo e rizóbio; na segunda, em outro município, os efeitos de quatro doses de N (0, 30, 60 e 90 kg ha-1) e quatro de Mo (0, 40, 80 e 120 g ha-1), em um esquema fatorial; e na terceira, em seis municípios, os efeitos das combinações 0-0-0, 0-40-70, 20-0-70 e 20-40-70 de N no sulco de plantio (kg ha-1), N aplicado em cobertura (kg ha-1) e molibdênio (g ha-1), respectivamente. Em todos os experimentos, o Mo nas folhas e o N em cobertura foram aplicados aproximadamente 25 dias após a emergência das plantas. Todos os experimentos receberam 90 kg ha-1 de P2O5, na forma de superfosfato simples, e 60 kg ha-1 de K2O, na forma de cloreto de potássio, e os solos eram povoados por estirpes nativas de rizóbio. A inoculação com estirpes selecionadas de rizóbio não teve efeito no rendimento de grãos. A adubação com Mo aumentou a produtividade do feijão, levando a rendimentos máximos com doses que variaram de 70 a 100 g ha-1, dependendo da adubação nitrogenada: quanto mais N, menor a dose de Mo. A adubação nitrogenada no sulco de plantio também foi essencial, e sua falta nem sempre foi compensada pela aplicação de N em cobertura. A combinação N + Mo trouxe aumentos de produtividade de cerca de 90 a mais de 200%.

Nitrogen fixation and nodule occupancy by native strains of Rhizobium on different cultivars of common bean (Phaseolus vulgaris L.)

A field experiment under rainfed conditions was conducted in Durango, Mexico, to assess N2-fixation of three cultivars of common bean (Phaseolus vulgaris L.) using 15N-methodology. In addition, diversity of rhizobial isolates obtained from nodules of the different plant genotypes was evaluated by intrinsic antibiotic resistance (IAR), PCR using enterobacterial repetitive intergenic consensus (ERIC) primers, PCR-RFLP analysis of the 16S rRNA gene and multilocus enzyme electrophoresis (MLEE). Selected isolates were used to determine acetylene reduction and competitive ability under greenhouse conditions. The three cultivars tested did not show high variation in N2-fixation, the %Ndfa values ranged from 19 to 26%. Variability in N2-fixation efficiency among various native rhizobial isolates was very high and our results indicate that differences in competitive abilitiy exist also. PCR-RFLP of the 16S rRNA gene and MLEE revealed that most of the isolates belong to the species Rhizobium etli. Intrinsic antibiotic resistance analysis and ERIC-PCR showed high diversity among isolates. In contrast, our results using MLEE show low genetic diversity (H = 0.105).

Nodulation of Medicago Sativa L. by Different Rhizobium Strains in the Sultanate of Oman

Three native Rhizobium strains were isolated from Musandam. Buraimi and the Agricultural Experiment Station at Sultan Qaboos University in the Sultanate of Oman. An internationally known Rhizobium strain (TAI. 1373} was obtained from the Nitrogen Fixation for Tropical Agriculture I.egume Collection at the University of Hawaii. U.S.A-. for comparison. The different abilities of the strains to nodulate Medicago sativa I. were investigated. Different plant parameters namely, the fresh and dry weights of the shoot (g/plant ). the number of nodules per plant and the nitrogenase activity (u mole C2H2/sample/3hours) were measured. The results showed that the native Rhizobia were capable of nodulating M saliva. But inoculation with effective known strains such as TAL1373 enhanced nodulation.

Neighbour specificity between Lolium perenne and Trifolium repens from a natural pasture.

Five genotypes of Trifolium repens and Lolium perenne were collected as neighbouring pairs along a fertility gradient in a natural pasture. After vegetative multiplication, the 25 possible combinations of Lolium genotype x Trifolium genotype were planted in the greenhouse in order to investigate competition between the genotypes. The comparison of the five combinations whose individual components had been neighbours with the combinations of genotypes that had not coexisted before disclosed no difference in total biomass production over 7 months. However, the yield of Trifolium increased when grown with the Lolium genotype which had been its natural neighbour, while the latter showed a decrease in yield. This neighbour specificity existed even when carryover effects from the sampling site had been eliminated (preconditioning period of 18 months) and when native Rhizobium strains were not present (inoculation with a non-native strain). The complex pattern of neighbour specificity with time indicated the importance of environmental conditions for its outcome. These results are a further confirmation of positive effects on the growth of Trifolium repens when grown together with its natural neighbour. They are discussed in the context of coexistence and coevolution.