Six different strains isolated from Vigna radiata (IARI-1 UU-2, UU-4, UU-7, UU-10 and UU-13) and seven strains from Arachis hypogea (IARI-16, UU-17, UU-18, UU-19, UU-20, UU-21 and UU-22) were selected to assess their capability to tolerate environmental variables like pH, temperature, salinity (NaCl), iron (Fe), phosphate (K2HPO4), and nitrate (NaNO3). The bacteria under investigation expressed noticeable ability to grow under these stress factors examined. The rhizobial isolates were compared to two reference rhizobial strains of specific host collected from IARI, India. Rhizobium UU-4 from Vigna radiata was found to be most tolerant species to high and low temperature, high salinity, relatively higher phosphate and higher nitrate concentrations but was sensitive to lower pH. UU-2 from the same host tolerated maximum to lower temperature, alkaline pH, phosphate deficiency and to higher concentration of iron but was very sensitive to a little raise in salinity. UU-10 was tolerant to lower pH, low nitrate, relatively higher phosphate, non-saline conditions and low iron concentration in the media. UU-13 grew well only in the presence of higher phosphate and low iron and was sensitive to lower temperature, acidic pH, phosphate deficiency and to the presence of nitrate in the media. UU-1 was most sensitive to higher temperature, alkaline pH, non-saline condition, higher concentration of phosphorous and nitrate, and was tolerant to higher level of salinity. UU-22 from A. hypogea was most tolerant to lower as well as higher temperatures, but sensitive to salinity and higher nitrate concentration. UU-21 was very sensitive to low temperature, salinity, presence of iron and also grew only when the nitrate concentration in the media was more than 50 µg/ml, but was tolerant to alkaline pH. UU-16 grew well in salinity free conditions, tolerant to low iron and also grew well in higher nitrate (up to 200 µg/ml) and phosphate deficiency, but was very sensitive when the concentrations of iron became higher. UU-17 preferred lower pH, lower temperature, moderate salinity, higher iron, phosphate deficiency and also grew comparatively well in presence of nitrate. UU-20 though was sensitive to lower pH and phosphate deficiency, was tolerant to higher salinity and also grew well in presence of nitrate. Based on the above results, Rhizobium strains UU-22 from A. hypogea and UU-13 from V. radiata may be effective for nodulation as well as yield of two leguminous crops.
Key words: Rhizobia, region specific, environmental stress, Arachis hypogea, Vigna radiata.
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