Epsilon Archive for Student Projects

Abstract

Plant growth promoting rhizo-bacteria (PGPR) affect plant growth by producing and
releasing secondary metabolites (plant growth regulators/phytohormones/biologically
active substances), facilitating the availability and uptake of certain nutrients from the root environment and inhibiting plant pathogenic organisms in the rhizosphere. At the same time, plants produce root exudates containing e.g. sugars, amino acids, organic acids, vitamins, enzymes and organic or inorganic ions. Those substances in turn influence the rhizosphere microflora and also the behaviour of PGPR. In this work, I examined the potential use of legume bacteria, rhizobia as PGPRs since it has been shown that rhizobia (legume bacteria) can function as PGPR in non-nitrogen fixing plants.

In the present study, the interactions of nine different rhizobial strains with six different mixed non-nitrogen fixing plant species were examined in laboratory and greenhouse experiments. Mixed botanical plant's seeds were inoculated with same concentration of different rhizobial strains. Significantly increased plant biomasses indicate that rhizobia have naturally potential ability to promote the growth of non-nitrogen fixing plant. The concentration level of rhizobial inoculation is another important factor for seed germination and plant growth. In addition, linseed was inoculated with only one rhizobial strain of different concentrations. To complement experiments were conducted, one was for rhizobial growth and the other one was for interactions between rhizobia and pathogenic fungi. None of the strains tested prevented in vitro fungal growth towards bacterial colonies but after some days of contact between rhizobia and fungi, some strains showed a tendency to dissolve the fungal mycelium. The results showed that Sinorhizobium meliloti strains were the most effective and could be suggested to act as PGPR. The inoculation concentration of the rhizobial strain was crucial. A concentration of 104 cfu mL-1 of Sinorhizobium meliloti proved to be optimal for successful seed germination and growth of linseed.