Application of liquid microbial inoculants on legume seeds is a sustainable agricultural practice that can improve plant nutrient uptake and increase crop productivity. Inoculants should provide long-term survival of rhizobia in the final product and after application, to legume seeds. Ten different medium formulations of microbial inoculants were examined (yeast mannitol broth with the addition of agar, sodium-alginate, calcium chloride, glycerol or ferric chloride and combinations thereof) for the survival of the efficient nitrogen-fixing rhizobium, Sinorhizobium (Ensifer) meliloti L3Si strain. The most suitable liquid inoculant for survival of L3Si during a storage time of 150 days was the medium formulation containing glycerol in combination with agar or sodium-alginate. Alfalfa seeds were pre-inoculated with four formulations (yeast mannitol broth (YMB), YMB with agar (1 g L-1), YMB with 1 or 5 g L-1 sodium-alginate) for up to three months. Seeds pre-inoculated and stored for one month produced successful alfalfa plants. The nitrogen content in alfalfa obtained from pre-inoculated seeds one month before sowing was adequate and ranged from 3.72-4.19%. Using S. meliloti-based liquid inoculants for alfalfa and application of the pre-inoculation technique can increase the quality of alfalfa crops and reduce cultivation cost.
A diverse group of soil bacteria found in the rhizosphere which can colonize plant roots and improve plant growth are designated as plant growth promoting rhizobacteria. The aim of this study was isolation and screening of different rhizobacterial strains for plant growth promoting characteristics and their ability to improve growth of two grass species, orchardgrass (Dactylis glomerata L.) and meadow fescue (Festuca pratensis Huds.). The strains investigated, belonging to the genera Azotobacter, Bacillus, Pseudomonas and rhizobial bacteria, showed various plant growth promoting traits, such as phosphate solubilisation, siderophore production, and indole-3-acetic acid (IAA) production. Co-inoculation of meadow fescue with Azotobacter chroococcum A2 and Sinorhizobium meliloti or Pseudomonas sp., and A. chroococcum A5 with S. meliloti, significantly increased shoot dry weight (SDW)(25-33%), as well as total N (26-33%), P (24-31%) and K (26-28%) contents in plants (mg pot ), compared to uninoculated control. In addition, inoculation of orchardgrass with A. chroococcum strain A1, as well as co-inoculation with B. megaterium and A. chroococcum A1 or A31, significantly increased SDW (51-59%) and total N (54-59%), P (51-74%) and K (49-55%) contents, compared to uninoculated control. Nitrogen percentage in SDW was slightly higher than sufficiency ranges, while K percentage was optimal in all treatments in both species. Phosphorous percentage was lower than sufficiency ranges as a consequence of very low soil P content. The results emphasize the potential of particular rhizobacteria to improve the growth of forage grasses.
This study was conducted to test the hypothesis that plant growth promoting rhizobacteria (PGPR) can promote the growth of Italian ryegrass, Lolium multiflorum Lam. as well as the growth and nodulation of subsequent alfalfa, Medicago sativa L. In a pot experiment, the influence of PGPR on yield and nitrogen content of Italian ryegrass and alfalfa was studied with the aim to improve their growth and provide effective alfalfa nitrogen fixation under unfavourable soil conditions. Plants were inoculated with seven strains belonging to Sinorhizobium meliloti, Azotobacter spp. and Enterobacter sp. A beneficial effect on yield and N-assimilation in Italian ryegrass was obtained due to the inoculation of the plants with Azotobacter vinelandii and some Sinorhizobium meliloti strains. In addition, Italian ryegrass seed inoculation with particular rhizobial strains the year before alfalfa growing provided abundant nodulation and better growth of alfalfa.
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