Résumé:
Alfalfa (Medicago sativa L.) is being grown in harsh environment in Iraq and is mostly subjected to abiotic stresses such
as drought, salinity, pH and temperature. Both alfalfa and its nitrogen fixing symbiotic bacteria Sinorhizobium meliloti are affected
by these environmental stresses. Enhancing nitrogen fixation biologically could be achieved through selection of tolerant strains of S.
meliloti to these environmental stresses and inoculating them to the crop, also growing tolerant cultivars. This study examines
phenotypic diversity for tolerance to drought, salinity, temperature and pH. Sixty isolates sampled from different areas of Iraq. The
results revealed high degree of phenotypic diversity in Sinorhizobium populations. Furthermore, the isolates which showed tolerance
to drought stress also showed tolerance to salinity and high degree of temperature, indicating direct relationship between three
physiological path ways. Also 58.3% of drought tolerant isolates were alkaline tolerant they tolerated up to pH 9, point to say almost
all drought tolerant isolates in this study illustrated strong + positive reaction to catalase enzyme. And 91.6% themes were negative
for Gelatinase enzyme test. While only 50% of drought sensitive isolates were negative for drought sensitive isolates could grow at
high temperature (42 °C).
