Development and standardization of cyst based liquid formulation of Azospirillum bioinoculant

Abstract

Azospirillum bioinoculant is well known for its high nitrogen fixing and plant growth promoting characters. The carrier based bioinoculants generally suffer from shorter shelf life, poor quality, high contamination and low field performance. Therefore, it is necessary to develop alternative new formulation of inoculants where cyst based inoculants can play significant role. The cyst based liquid formulation was developed by inoculating Azospirillum into the cyst inducing minimal salts medium (MSM). One hundred per cent conversion of vegetative cells into cyst cells was noticed in 96 h. The survival of cyst cells in the MSM was observed up to one year and two months and interestingly, the population level of 10(8) was maintained till the final observation. The cyst cells of Azospirillum accumulated poly-beta-hydroxybutyrate (PHB) granules and exhibited desiccation tolerance up to 20 days and temperature tolerance up to 40 degrees C. Thus the cyst based liquid formulation has twin advantage of longer shelf life and tolerance to harmful environmental conditions. Regeneration of cyst cells into vegetative cells in different media viz., tap water, sterile water, rice gruel and nutrient broth was studied. The changes started within 3 h and complete return of vegetative cells was observed at 24 h. Although all the media tested favoured regeneration, comparatively quicker regeneration was observed in nutrient broth and followed by rice gruel. Thus, cyst based liquid formulation of Azospirillum has all the survival advantages and can be used as a potential bioinoculant.