Effect of combined abiotic factors on the growth of PGPR associated with Medicago Sativa

Ten Plant growth promoting rhizobacteria (PGPR) were isolated from Medicago Sativa plants grown in two arid sites in south Morocco. Strains were recovered from functional root nodules, purified and checked for growth: they were all slow growing. They were evaluated for nodulation efficiency under controlled conditions: they were all infective and efficient with the host plant. Strains exhibited a wide tolerance to the main abiotic factors: half of the strains presented a good growth at 510 mM NaCl and 10% of strains tolerated levels up to 850 mM NaCl. All strains were able to grow at 32 °C and 10% of strains showed to be tolerant at 40 and 45 °C. Strains showed to be tolerant to alkaline pH: 50% of strains were all able to grow at pH 8.5 and 30% at pH 9. In vitro experiments of combined effects of NaCl x pH, NaCl x temperature and NaCl x pH x temperature indicated that pH and NaCl affected more growth than temperature. The combined effect of the three factors resulted in the decrease of growth; however, some strains showing a good performance were selected for subsequent inoculation tests under adverse environments.