The antifungal properties of extracts of algae were examined to evaluate their ability to protect wheat plants against Bipolaris sorokiniana. Our main objectives were to determine their effects on the in vitro growth of the pathogen and their aptitude for controlling Helminthosporium leaf blights and activating plant defense responses in the greenhouse. According to the screening carried out on the 23 species of algae, the extracts of the 4 algae (Fucus spiralis, Laminaria Ochroleuca, Gracilaria sp., and Ellisolandia Elongata) showed a very high inhibition of fungal growth in vitro of B. sorokiniana. In the greenhouse, they induced high protection against the fungal strain when applied twice by leaf sprays at 5g/L, 10g/L, and 20g/L, which reduced the alteration index of the leaves by about 75 %, and the stunting index was reduced in plants treated with the ESA. In addition, its protective capacity was associated with the accumulation of H₂O₂, as well as the potentiation of the activity of polyphenol oxidase and peroxidase.  After the in vitro test of the fractions obtained from the Lancelot fractionation, it was concluded that the molecules responsible for the activity are located in the low molecular weight fraction. Algae extracts (macroalgae) sprayed on plants were reported to reduce the incidence of Erysiphe polygon (powdery mildew) on turnips and damping-off of tomato plants, Botrytis cinerea (gray rot) on plants of strawberries. These results demonstrated that the aqueous seaweed extracts (ASE) harvested from the coast of El Jadida (Sidi Bouzid) resulted in an improvement of the resistance in wheat plants by both inhibiting the growth of Bipolaris sorokiniana and activating plant defense responses.