Eight Polysaccharides Enriched Extracts (PEEs) obtained from Moroccan seaweeds were selected to test their effectiveness on the natural defense of tomato plants. Firstly, we examined the effect of the 8 PEEs at 4 concentrations (0.02, 0.05, 0.1 and 0.2 mg. mL-1) with 3 application methods (T1: root irrigation, T2: foliar spray, and T3: combining the 2 methods T1 and T2) on protein content and plant defense enzyme: Phenylalanine Ammonia-lyase (PAL) on tomato plants in absence of a pathogen. In the second part, we analyzed the ability of PEEs to induce protection against Botrytis cinerea, causative agent of gray mold, by testing PEEs on detached tomato leaves. Results showed that the PEEs obtained from Codium tomentosum, Ulva rigida, and Bifurcaria bifurcata at 0.1 mg. mL-1 and Gelidium crinale, Schizymenia dubyi and Fucus spiralis at 0.02 mg. mL-1 were the best treatments that significantly stimulated protein content and PAL activity in tomato plants with the three application methods. The same extracts at the same concentrations, in addition of PEEs from G. pistillata at 0.02 mg. mL-1 were the treatments having the greatest inhibitory effect on the diameter lesion of B. cinerea in detached leaves when compared to the control. The principal component analysis showed a correlation between PAL content and the reduction of diameter lesion. The comparison of the application method in our study did not show differences. These findings confirmed that these algal polysaccharides treatments could be a promising method to reduce dependency on synthetic fungicides. The presence of uronic acid and sulfated groups in the extracts could explain the elicitation mechanism induced in plant cells.