Rhizospheric bacteria alleviate salt-produced stress in sunflower.

The effect of isolate Pseudomonas fluorescens biotype F and P. fluorescens CECT 378(T) inoculation on fresh weight and ions accumulation was studied in sunflower plants grown in sand:peat substrate with addition of 100mM NaCl. The inoculation resulted in an increase in fresh weight of more than 10% in salt treatments and in an accumulation of less Na(+) and more K(+) in plant tissues in all cases. The bacterial inoculants favoured the K(+)/Na(+) ratio in all plant parts and in the case of the isolate CECT 378(T) conducted to 66% increment in leaves, 34% in stems and 16% in roots, while the effect of isolate inoculation was (only) more evident in leaves and stems with 30% and 26%, respectively. Both strains were found to produce indoleacetic acid and siderophores in in-vitro tests, thus the production of indoles was highly dependent on the exogenous tryptophan in the medium. The results suggest that salt stress in sunflower plants was alleviated partially by the inoculation with strains that produce indoles and siderophores, having also a positive effect on the K(+)/Na(+) ratio in the shoot. Moreover, those plants were characterized with better-developed roots.