Genetic Variation of Sinorhizobium meliloti Isolates Differing in Their Ability to Drought Tolerance

Soil bacteria Sinorhizobium meliloti had enormous agricultural value, due to their ability infixing nitrogen symbiotically with an important forage crop legume- alfalfa. The aim of thisstudy (i) isolate indigenous S. meliloti from different field sites in Iraq, (ii) evaluate the isolatestolerance to induce drought using polyethylene glycol-6000, (iii) assessing genetic diversity andgenetic relationships among isolates of natural population with drought tolerant abilities.Drought tolerance study revealed vast variations between Sinorhizobium isolates, the highesttolerant isolates to drought were twelve from total thirty 40%, tolerated from -3 up to -4 Mpa(mega pascal), while the drought sensitive isolates tolerated upto – 1.5 Mpa, except isolate Bs58which tolerated upto -1 Mpa water potential. The growth declined with the increase of droughtstress. Cluster analysis based on RAPD-PCR showed significant differences among S. melilotiisolates, and the results gave almost identical grouping of isolates in regards to droughtexperiment. Among indigenous isolates two divergent groups could be determined, the first majorgroup included drought tolerant isolates and the second major group comprised all droughtmoderate and sensitive isolates with 40% similarity between the two major groups.