Growth and Survival of Rhizobium spp. in Peat Culture

SUMMARY The growth and survival in peat culture of 3 strains of Rhizobium representing 3 inoculation groups, were affected by the source of the peat, pH and method of pH adjustment, method of sterilization, drying temperature and moisture content. The choice of a peat for culture production can be made only on actual tests of its suitability as a medium for rhizobial growth and survival. Sterilization always permitted more rapid growth of the rhizobia and favoured their viability during storage. For the cowpea strain sterilization was essential. Sterilization by γ radiation was generally superior to autoclaving: temperatures > 100° at the time of drying adversely affected survival and multiplication. Heat of wetting, which kills many of the added rhizobia, and the production of inhibitory substances, which prevents subsequent multiplication and accelerates death during storage, are important factors. Temperatures of 80–100° were safe and sufficient to dry peat spread in a thin layer. A moisture content of 40–50% (on a wet weight basis in the finished culture) was optimal.