Typing of Rhizobium with two different phage dilutions.

The sensitivity of 223 Rhizobium strains to 28 phages in concentration 4xRTD and 0.4xRTD was compared. Depending on their sensitivity to the different phages the strains were divided into three groups: 1. Rhizobium trifolii strains, Rhizobium leguminosarum for pea, vetch and horse bean and Rhizobium phaseoli, 2. R. trifolii strains and R. leguminosarum for pea and vetch, 3. R. meliloti strains, R. lupini and R. meliloti mutants. The use of 4xRTD distinguished 50 different phage types among the 223 strains tested. To the lower phage concentration, i.e. 0.4xRTD responded 155 Rhizobium strains and this concentration gave 48 new sensitivity patterns to phages besides 19 determined with 4xRTD. The use of lower phage concentration resulted in further differentiation within some phage types of the first group though most the strains of this group were not lysed by phages in this concentration. Much greater differentiation was observed among the R. trifolii mutants of the second group. Wild-type and mutant R. meliloti strains of the third group showed similar number of phage sensitivity patterns in the case of both 0.4xRTD and 4xRTD.