Some environmental factors influencing the survival of Rhizobium leguminosarum bv. viceae.

Investigations were carried out to monitor the sensitivity of Rhizobium leguminosarum bv. viceae strains to various environmental stress-factors (salinity, pH, Al3+, Ca2+, Mg2+) and select them as potential candidates for Vicia faba inoculation. In the range between pH 5.0 and 10.0, the salt effect of 10-500 mM NaCl, Ca2+, Mg2+ (as chlorides and sulphates), Al2O3 and KAl (SO4)2 (25-400 microM) were tested in modified yeast-mannitol (YEM) liquid medium. Cell density of the suspensions inoculated with R. leguminosarum bv. viceae strains (initial cell-number 10(6) CFU/ml) were measured spectrophotometrically after 48 h incubation in a rotary shaker (rpm 150) at 28 degrees C. Data of optical density (OD550) are shown as percent of control (inoculated, free from treatments, pH 7.0) tubes. It was established, that results of tolerancy were in agreement with those found earlier for Rhizobium sensitivity. Strain of Lóbab Z (isolated in Hungary) however proved to have an especially outstanding survival in any media tested in vitro. Lowest observed effect concentrations (LOECs) were: 500 mM NaCl, 200 microM Al3+ (as Al2O3 or KAl (SO4)2), 50-100 mM Mg2+, and 200-300 mM Ca2+. For the Al3+, Ca2+ and Mg2+ cations, there was no variation between the stress-effect of sulphate and chloride anions. Both forms of Ca2+, however significantly reduced the growth potential of R. leguminosarum bv. viceae strains.