Restoration of Growth of Durum Wheat (Triticum durum var. waha) Under Saline Conditions Due to Inoculation with the Rhizosphere Bacterium Azospirillum brasilense NH and Extracts of the Marine Alga Ulva lactuca

Inoculation with the rhizosphere bacterium Azospirillum brasilense NH, originally isolated from salt-affected soil in northern Algeria, greatly enhanced growth of durum wheat (Triticum durum var. waha) under saline soil conditions. Important plant parameters like the rate of germination, stem height, spike length, dry weight of roots and shoots, chlorophyll a and b content, proline and total sugar contents, 1000-seed weight, seed number per spike, and weight of seeds per spike were measured. At salt stress conditions (160 and 200 mM NaCl) A. brasilense NH restored almost completely vegetative growth and seed production. The combination with extracts of the marine alga Ulva lactuca resulted in even more improved salt tolerance of durum wheat. Proline and total sugar accumulation, a sign of physiological plant stress under inhibitory salt conditions, was reduced in plants inoculated with A. brasilense NH with and without addition of algal extracts. Inoculation with the salt-sensitive A. brasilense strain Sp7 could not restore salt-affected plant growth at 200 mM NaCl. Furthermore, it could be demonstrated by fluorescence in situ hybridization and confocal laser scanning microscopy that A. brasilense NH is able to colonize roots of durum wheat endophytically under salt-stressed conditions. Thus, the salt-tolerant rhizobacterium A. brasilense NH could effectively provide alone or in combination with extracts of U. lactuca a promising solution to overcome salt inhibition which is a major threat hindering productive wheat cultivation in arid saline soils.