Survival of Rhizobium phaseoli in Six Carrier Materials¹

Abstract

Abstract Peat is the most commonly used base material for Rhizobium sp. (rhizobia) inoculants; however, suitable sources of peat are not available in many developing countries. Other materials have been evaluated as alternatives to peat as carriers of rhizobia, but few of these studies have included Rhizobium phaseoli . In this study, survival of three strains of R phaseoli was evaluated in peat, ground peanut hulls, ground corn cohs, charcoal, vermiculite, and polyacrylamide gel at 4, 25, and 45 C. Numbers of viable cells of rhizobia were determined in the carrier materials by the plate count procedure at time zero and periodically up to 30 weeks. Survival of each strain was much better in peat, charcoal, and vermiculite than in peanut hulls or corn cohs. Die‐off in polyacrylamide gel was rapid for strain CIAT 75 survival was better for strains 3644 and 650R, but bacterial contamination was a severe problem. For peat, charcoal, and vermiculite, survival was good at 4 and 25 C for strain 3644; for CIAT 75 and 650R survival was good in these carriers at 25C but not at 4 C. Survival was very poor in all carriers at 45 C; no viable cells were detected after 3 days. None of the materials tested was superior to peat as carriers of R phaseoli , but the results indicate that charcoa and vermiculite can be used as inoculant carriers with relative success. Storage of inoculants in these carriers is feasible at room temperature.