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Abiotic stresses, including salinity stress, affect numerous crops, causing yield reduction, and, as a result, important economic losses. Extracts from the brown alga <i>Ascophyllum nodosum</i> (ANE), and compounds secreted by the <i>Pseudomonas protegens</i> strain, CHA0, can mitigate these effects by inducing tolerance against salt stress. However, the influence of ANE on <i>P. protegens</i> CHA0 secretion, and the combined effects of these two biostimulants on plant growth, are not known. Fucoidan, alginate, and mannitol are abundant components of brown algae and of ANE. Reported here are the effects of a commercial formulation of ANE, fucoidan, alginate, and mannitol, on pea (<i>Pisum sativum</i>), and on the plant growth-promoting activity of <i>P. protegens</i> CHA0. In most situations, ANE and fucoidan increased indole-3-acetic acid (IAA) and siderophore production, phosphate solubilization, and hydrogen cyanide (HCN) production by <i>P. protegens</i> CHA0. Colonization of pea roots by <i>P. protegens</i> CHA0 was found to be increased mostly by ANE and fucoidan in normal conditions and under salt stress. Applications of <i>P. protegens</i> CHA0 combined with ANE, or with fucoidan, alginate, and mannitol, generally augmented root and shoot growth in normal and salinity stress conditions. Real-time quantitative PCR analyses of <i>P. protegens</i> revealed that, in many instances, ANE and fucoidan enhanced the expression of several genes involved in chemotaxis (<i>cheW</i> and <i>WspR</i>), pyoverdine production (<i>pvdS</i>), and HCN production (<i>hcnA</i>), but gene expression patterns overlapped only occasionally those of growth-promoting parameters. Overall, the increased colonization and the enhanced activities of <i>P. protegens</i> CHA0 in the presence of ANE and its components mitigated salinity stress in pea. Among treatments, ANE and fucoidan were found responsible for most of the increased activities of <i>P. protegens</i> CHA0 and the improved plant growth.