摘要
Soil bacteria Sinorhizobium meliloti had enormous agricultural value, due to their ability in fixing nitrogen symbiotically with an important forage crop legume--alfalfa. The aims of the present study were （1） to isolate indigenous S. meliloti from different field sites in lraq; （2） to evaluate the isolates tolerance to induced drought using polyethylene glycol-6000; （3） assessing genetic diversity and genetic relationships among isolates of natural population with drought tolerant abilities. Drought tolerance study revealed vast variations between Sinorhizobium isolates, the highest tolerant isolates to drought were 12 from total thirty （40%）, tolerated from -3 up to -4 MPa, while the drought sensitive isolates tolerated up to -1.5 MPa, except isolate Bs 58 which tolerated up to -1 Mpa water potential. The growth declined with the increase of drought stress. Cluster analysis based on Polymerase Chain Reaction-Restriction Fragment Length Polymorphism （PCR-RFLP） of the 16S rDNA showed two divergent groups with 41% similarity, the first group included three drought sensitive isolates （Bs 44, Bs 54 and Bs 58）, the second group comprised the rest nine isolates （moderate and high drought tolerant）, except for Bs 55 which was drought sensitive isolate, all isolates in the two groups showed no differences between them. The PCR-RFLP of 16S rDNA method revealed a genetic variance between the drought sensitive and tolerant isolates.
