DROUGHT TOLERANCE OF RHIZOBIUM-LEGUMINOSARUM AND RHIZOBIUM-MELILOTI

Cell suspension of Rhizobium leguminosarum bv. viciae D-253, R. legumi nosarum bv. D-560 and R. meliloti D-557 were incorporated into sterile diatomaceous earth (DE) and dried at room temperature. Initial number s of colony-forming units (CFU), expressed as log10, were 8.27, 8.36 a nd 8.51, respectively. After 5 months of storage the CFU numbers were 0.00, 5.99 and 7.43, respectively. R. meliloti D-557 showed only minor lowering of the CFU number even after 16 months of storage (log10 = 7 .07). After 7 months of storage in DE some single-colony isolates of D -253 produced 10 - 100 times higher CFU numbers than the original stra in. The isolates of D-560 were much more drought-tolerant. The cells o f the original strain died after 7 months of storage, log10 of CFU was 6-7 in the isolates. In both strains some of their drought-tolerant i solates had the same specific acetylene-reducing activity of nodule ti ssue as the original strains. Diatomaceous earth seems to be a prospec tive carrier for the formulation of bacterization preparations.