Melon growth-promoting rhizobacteria under saline stress

The aim of this study was to evaluate melon growth promotion by fluorescent rhizobacteria of Pseudomonas spp. under saline stress. Soil samples were collected in agricultural properties of Juazeiro/BA, Petrolina/PE and Curaca/BA in the Submedium Region of the Sao Francisco Valley to conduct sampling of bacterial isolates. The obtained isolates were analyzed regarding cultural characteristics and tolerance to salinity in the following NaCl concentrations: 0; 250, 500, 750, 1000, 1250 and 1500 mM. Among the isolated bacteria, 20 were identified and used to evaluate growth promotion on melons in a protected environment. This experiment was conducted in a completely randomized 21 x 4 factorial design, with 20 bacterial isolates, one control without inoculation and four salinity levels (0.2, 2.0, 4.0 and 6.0 dS m(-1)), and it was replicated seven times. A total of 147 bacterial isolates were obtained from soil samples with electric conductivity ranging from 0.8 to 60.4 dS m(-1). Cell growth was inhibited starting at 750 mM of "in vitro" saline concentration, with tolerance observed up to 1500 mM. Pseudomonas spp. isolates were capable of promoting melon growth under non-saline conditions and of mitigating the harmful effects of excessive concentrations of soluble salts in the growth substrate.