| Summary: | Soil salinization is a globally growing problem, and several approaches have been proposed to mitigate its effects on the productivity of plants of economic interest. The use of halophilic or halotolerant bacteria as plant growth promoters is one of the strategies recommended for the mitigation of salt stress. However, halotolerant bacteria isolated from the rhizosphere of halophyte plants are the most commonly used inoculum. The objective of this work was to evaluate the potential of halophilic bacteria, isolated from a salt pan, in the attenuation of saline stress Lactuca sativa, used as a model crop glycophyte. A collection of strains isolated from Santiago da Fonte saltpans (Aveiro) representing the genera Bacillus, Halobacillus, Idiomarina and Marinobacter, was analyzed for some characteristics considered as advantageous in the colonization and promotion of growth of host plants. The production of extracellular enzymes in presence of 0, 20 and 100 NaCl, as well as the ability to solubilize phosphate and produce 1-aminocyclopropane-1-carboxylate deaminase were tested. H. locisalis and I. seosinesis, considered as more interesting in terms of plant growth promoting traits, were tested separately and together as inoculum in lettuce seeds. A factorial experimental design was applied to test the effect of inoculation and salinity of the irrigation water on the efficiency of seed germination and plant growth. Germination efficiency was strongly affected by salinity and no significant effects of inoculation were observed. The germination efficiency was lower at 10 NaCl than at salinity 0 and the weight of the plants was significantly lower in the plants inoculated with the consortium of isolates than in the uninoculated plants. Plants inoculated with the consortium and grown at salinity 10 had lower water content. When used separately, H. locisalis or I. seosinesis caused an increase in leaf size in plants cultivated in salinity, in relation to the inoculated control. Inoculation did not cause a significant effect on chlorophyll fluorescence. Although no evidence of attenuation of saline stress by inoculation was detected, H. locisalis inoculum showed a positive effect on the growth of plants in non-saline conditions, indicating a potential as a growth promoting bacterium of plants of agricultural interest.
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