**3. Conclusions**

The crude fucoidans from the brown algae, *F. spiralis* and *B. bifurcata* tested on the date palm roots, display potential elicitor activity on the phenolic metabolism due to the induction of PAL activity. Thus, leading to mobilisation of the phenlypropanoids pathway and to the accumulation of phenolic compounds and lignin. The elicitor effect of studied fucoidans was related to their highly sulfated structures with a small molecular weight (*M*W). In addition, the simple and innovative elicitation model adopted in this paper highlighted the elicitor effect of fucoidans without stressing the roots, which could be applied in the field. These results open prospects for the formulation of a biological product, leading to a preventive control of date palm Bayoud disease.
