Odile Berge

Abstract A pot experiment was conducted to elucidate the effects of inoculating five exopolysaccharide (EPS)-producing bacterial strains on the dry matter yield and the uptake of K+, Na+, and Ca2+ by wheat seedlings grown in a moderately saline soil. The bacteria were isolated from the rhizosphere soil (RS) of wheat grown in a salt-affected soil and included Aeromonas hydrophila/caviae (strain MAS-765), Bacillus insolitus (strain MAS17), and Bacillus sp. (strains MAS617, MAS620 and MAS820). The inoculation substantially increased the dry matter yields of roots (149–527% increase) and shoots (85–281% increase), and the mass of RS (176–790% increase). All the strains, except MAS617, also increased the RS mass/root mass ratio as well as the population density of EPS bacteria on the rhizoplane, and both these parameters were significantly correlated with the content of water-insoluble saccharides in the RS. Inoculation restricted Na+ uptake by roots, which was not attributable to the binding of Na+ by the RS, or to the ameliorative effects of Ca2+ under salinity. The decreased Na+ uptake by roots of inoculated than uninoculated plants was probably caused by a reduced passive (apoplasmic) flow of Na+ into the stele due to higher proportion of the root zones covered with soil sheaths in inoculated treatments. Among the strains tested, MAS820 was the most efficient in all respects, whereas MAS617 was the least effective. Results suggested that inoculating selected EPS-producing bacteria could serve as a useful tool for alleviating salinity stress in salt-sensitive plants.

Abstract:  This study was conducted to isolate and identify the EPS-producing bacteria associated with the roots of three wheat lines grown in saline and non-saline soil. Results indicated the presence of various EPS-producing bacterial genera in unplanted saline and non-saline soil, rhizosphere and rhizoplane of the three wheat lines. Bacillus sp. were  more variable in unplanted  saline than non-saline soil. In contrast to uniform distribution of Bacillus sp. in unplanted soils, other EPS-producing bacterial genera isolated from rhizosphere and  rhizplane were more numerous and diversified. Frequent occurrence of Microbacterium sp. in the soil and rhizosphere of the plants invoke the desire for more research work to explore the role of this bacterium in the saline environment.