SURVIVAL OF RHIZOBIUM-LEGUMINOSARUM BIOVAR VICEAE SUBJECTED TO HEAT, DROUGHT AND SALINITY IN SOIL

Two strains (RCR 1001 and 1044) and a commercial inoculant (Okadin) of Rhizobium leguminosarum biovar viceae were tested for their ability to survive in autoclaved clay soil for up to four months under heat, salinity and drought stress. Resistance to heat was tested by incubating rhizobia in soil at 27, 37 and 42-degrees-C. Tolerance of rhizobia to salinity was investigated by growing rhizobia in soil salinized with 1 and 2% NaCl (m/m). Drought resistance was tested by subjecting bacteria to soil moisture contents of 20, 10 and 5%. Strain RCR 1001 was more resistant to heat and nodulated faba bean better than other tested strains. A commercial inoculant Okadin survived more (plate count method) and nodulated faba bean (plant infectivity, most probable number, MPN) at moisture content of 5% and 2% NaCl. Although, strains RCR 1001 and 1044 resisted these stress conditions (plate count) they lost their abilities to nodulate faba bean (MPN-test). There is a possibility for selection of effective rhizobia which are more tolerant to harsh conditions.