Selection/ Isolation of High Temperature Tolerant Strains of Rhizobium for Management of High Temperature Stress on Rhizobium- Legume Symbiosis

Biological nitrogen fixation (BNF) is carried out by free-living, non-symbiotic, associative and symbiotic nitrogen fixing bacteria, symbiotic fixers being the major contributors. LegumeRhizobium association being most effectively and widely studied is the major area of concern with regard to BNF technology. The symbiotic association between legumes and rhizobia is highly influenced by various environmental factors, temperature being the most important one. The growth and survival of rhizobia in soils and their symbiotic association with leguminous plants are adversely affected by high soil temperatures. Therefore, the potential benefit of legume Rhizobium association is not fully exploited when soil temperatures become limiting, as is generally seen in tropical and subtropical regions, where the temperatures rise beyond 45 o C in the uppermost layers of the soil during the summer season. Isolating/ selecting temperatureresistant/ tolerant strains of rhizobia is, therefore, necessary before establishing inoculant production for these regions. The present review is aimed at understanding the effect of high temperature on Rhizobium-legume symbiosis; and at exploring the on-going efforts being employed for the management of this adverse effect.