Azospirillum, a well known plant growth, promoting rhizobacteria, has been widely used as an agricultural bioinoculant. The application of the bioinocualnt enhances the plant growth through the production of growth regulators and by supplying biologically fixed nitrogen to the host plant. However, the lack of stress tolerance and poor survivability in soil of the introduced bacteria results in poor performance of the bioinoculant under stress soils. To ensure the good quality bioinoculant production, physiological status of the microorganism play a vital role rather than the cell numbers. It has been proposed that flocculation and concomittant accumulation of poly-b-hydroxybutyrate, a cellular reserve material, in Azospirillum cells rendering more resistance during environmental stresses and use of the flocculated cell forms of Azospirillum, as agricultural bioinoculant, is considered to be the novel bioinoculant technology in stress soils.
In the present study, it was observed that Fructose and KNO3, as sole carbon and nitrogen source, physiologically augmented more flocculation in Azospirillum cells. Moreover, addition of Strychnos potatorum seed material, as plant seed flocculant, non-physiologically inducted more flocculation of Azospirillum cells in a shorter period. The harvested Azospirillum bioflocs, exhibited higher desiccation and thermal tolerance when compared to the vegetative cell forms.
It was concluded that Azospirillum biofloc, as a novel formulation of agricultural bioinoculant, exhibited more tolerance to temperature and desiccation which are the two critical environmental stress conditions responsible for the poor performance of agricultural bioinocula in natural environments.
Azospirillum, Bioflocs, Plant seed, flocculants, Desiccation and Thermal tolerance
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