​Optimized Bioprocess for the Formulation of Liquid Microbial Inoculants for Forage Cowpea and Insight of Plant-microbe Interaction by SEM

Abstract

Background: In the present investigation bioprocess for the formulation of liquid microbial inoculants with escalated shelf stability for forage cowpea has been standardized. The forage cowpea can make a relevant contribution towards livestock fodder and supply nitrogen to the soil. Methods: In the present study viability of Burkholderia seminalis, Burkholderia sp. and Bradyrhizobium sp. was evaluated for one month in a basal medium amended with different concentration of polyvinyl alcohol (PVA) (0.5%, 1%, 2% and 3%), trehalose (5 mM, 10 mM, 15 mM and 20 mM), polyethylene glycol (PEG) (0.5%, 1%, 2% and 3%) and glycerol (1%, 3%, 5% and 7%). Result: At 30th day, maximum growth and survival was observed in the basal medium amended with 5 mM trehalose for all the three test cultures. Further, Liquid microbial inoculants of Burkholderia seminalis, Burkholderia sp. and Bradyrhizobium sp. were prepared using trehalose (5 mM) in basal medium and viability retention was studied up to 180 days of storage and compared to charcoal carrier based formulations at room temperature. Furthermore, Scanning electron microscopy provided insight of root colonization of forage cowpea by liquid microbial inoculants under gnotobiotic conditions, maximum root surface colonization was observed by liquid microbial inoculants of Burkholderia seminalis followed by Burkholderia sp. and Bradyrhizobium sp. Therefore, the optimized bioprocess can be used for the formulation of liquid microbial inoculants with enhanced shelf stability and could play a pertinent role in integrated nutrient management of forage cowpea for enhanced productivity and quality.