Selection of stress-tolerant rhizobial isolates of wild legumes growing in dry regions of Rajasthan, India.

Abstract

An attempt has been made to evaluate the effect of abiotic constraints (salt, pH and temperature) on the growth of rhizobia isolated from Leucaena leucocephala, Tephrosia purpurea and Crotalaria medicaginea grown in arid and semiarid regions of Rajasthan with a view to screen out stress tolerant isolates. A total of 27 isolates have been used for screening their stress tolerating ability with contrast to environmental abiotic soil conditions commonly prevailing in arid and semiarid regions of Rajasthan. All the isolates were phenotypically and biochemically characterized followed by their plant assay test in growth pouches and pot experiment under controlled environmental conditions. Growth of pure rhizobial isolates on Yeast Extract Mannitol (YEM) medium having variable range of pH (4.0 to 10.0) and different concentrations of NaCl (0.01-4.5 %) were recorded at 540 nm using UV-VIS spectrophotometer after incubation at 28± 2C for two days. Survival of rhizobial isolates under variable stress of temperature was also selected using Thermal Death Point (TDP) process. On the basis of comparison of growth under varied stress conditions, five rhizobial isolates from each salt and pH stress study (salt tolerant: ALL-1, ALL-4, ALL-5, BLL-1 and BLL-2; pH tolerant: ATP-2, ATP-3, ATP-4, ATP-9 and ACM-2), where as seven root nodulating bacteria from temperature tolerant: ALL-1, ALL-2, BLL-1, BLL-7, ATP-2 ATP3, and ATP9) were screened out. The stress tolerant traits of these rhizobia are of potential value from the point of view of biofertilization of legume seedlings during a forestation of degraded areas in arid and semi-arid tropics of Rajasthan.