A Study On The Stress Tolerant Rhizobial Isolates From Sesbania bispinosa

The present investigation was carried out to study the extremely diversified characteristics of rhizobial strains isolated from locally produced legume Sesbania bispinosa, a well-known green manure of Bangladesh, commonly known as Dhaincha. It was important to study the rhizobial isolate of this less studied plant of Bangladesh in order to learn about its association and to increase soil fertility. An attempt had been made to evaluate the effect of abiotic constraints (salt, pH and temperature) on the growth of rhizobia isolated from Sesbania bispinosa growing in different region of Bangladesh with a view to screen out stress tolerant isolates. Growth of pure rhizobial isolates on Yeast Mannitol Agar (YMA) medium having different concentration of NaCl (2%, 2.5%, 3%, 4%, 5%, 6% and 8%) and variable range of pH (4.5, 5.5, 6.5, 8.5, 9.5 and 10.5) were recorded after incubation at 30ËšC for 24-48 hours. The growth of rhizobial isolates were also observed after incubation at 25ËšC, 30ËšC, 37ËšC, 45ËšC and 55ËšC temperature, respectively. All the 46 isolates were able to tolerate up to 3% salt concentration. However it was observed that with increasing salt concentration isolates were found to be decreasing. It was further observed that, acidic and alkaline pH could not suppress the growth of these isolates. All isolates were found to grow upto 37ËšC. However, 42 out of 46 isolates were able to tolerate 45ËšC. The highest temperature (55ËšC) was found to inhibit growth of about 43% isolates. The stress tolerant traits of these rhizobia are of potential value from the point of view for using Sesbania sp. as bio-fertilizer in different region of Bangladesh.