Sir according to the study conducted by Kumaresan & Reetha (2011) "Liquid Azospirillum bioinoculant formulated with trehalose (10mM) promoted long term survival of Azospirillum followed by glycerol (10 mM) gum arabica (0.3%) and PVP (2%) and they supported 108 cells/ml up to 11 months of storage under ambient temperature (28°C to 32°C), whereas PEG (1%), PVA (0.5%) and control (lignite carrier) recorded the same population up to 8 months, 6 months and 5 months respectively."

I think this might be helpful to you.. I have also attached the link to the same article here for your kind reference:

Article Survival of Azospirillum brasilense in liquid formulation am...