The aim of this study was the isolation of Pseudomonas sp. and Bacillus sp. strains from rhizospheric soil and monitoring the impact of two isolates denoted as P12 (Pseudomonas sp.) and B1 (Bacillus sp.) on the parameters of the English ryegrass (Lolium perenne) yield and activity of the soil microbial communities. During 2012-2014, the plot experiment was set up following randomized block system. Better effect on the plant growth was recorded with the use of Pseudomonas sp. P12 isolate than with Bacillus sp. B1. Positive effect on the increase in the total number of microorganisms, aminoheterotrophs and azotobacter was also achieved. Bacillus sp. B1 increased only the number of actimycetes. Both isolates positively affected the dehydrogenase activity (DHA).
The use of plant growth-promoting rhizobacteria (PGPR) in the production of medicinal plants is crucial, because agricultural chemicals are no longer acceptable in their production. This paper discusses the results of a recent study undertaken to isolate and characterize PGPR isolates of Bacillus, Pseudomonas and Azotobacter from common thyme (Thymus vulgaris L.) rhizospheric soil and monitor the effect of their application on seed germination and plant growth. The effect of selected isolates on seed germination and initial growth of common thyme was examined in controlled conditions. The impact of the isolates on the content of biochemical stress markers (total phenols and lipid peroxidation intensity) in germinated seeds was determined. The influence of the isolates on the plant growth under well-watered conditions (watered to 80% of water holding capacity (WHC)) and under water deficit stress (watered to 40% of WHC) was evaluated by measuring plant root and stem length in semi-controlled conditions. This study confirmed that indigenous rhizospheric bacteria of common thyme have multiple plant growthpromoting (PGP) properties. Among Bacillus 10 isolates, Pseudomonas 12 isolates and Azotobacter 9 isolates, only Pseudomonas isolate (P53) had all the tested PGP properties. The applied isolates had a positive effect on the examined plant growth parameters. The highest percentage of germination was determined in the treatment with P53 isolate (96%). The highest response for vigour index was observed with isolate A1 (3807%). All isolates, except B58 and B60, reduced stress by lowering the amount of both or at least one stress related molecules. The results of the experiment led to the conclusion that isolates Azotobacter sp. A1 and Pseudomonas sp. P53, both ACC-deaminase-producing bacteria, have the best effect on plant growth under well-watered and drought-stressed conditions, which indicates their potential to be used as a biofertiliser for promoting common thyme growth.
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