Evaluation of some seaweed extracts from Baja Peninsula, Mexico, against plant pathogens.

Background. The widespread use of synthetic pesticides to control pests has generated serious consequences on the environment and human health. Currently, efforts focused on searching for new pesticides with less environmental impact have been doubled. Marine algae synthesize chemical compounds with biological activity, antibacterial and antifungal, and recent studies on brown seaweeds have reported activity against some agricultural pests, insects, and nematodes. However, marine pesticides are an underdeveloped alternative. This represents an opportunity to explore new sources of active compounds. Goals. Evaluate the antibacterial, antifungal, nematicidal, and insecticidal activity of seaweed extracts against pathogens of agricultural importance. Methods. Seaweeds were collected from different locations at the Baja California peninsula, Mexico, and ethanolic extracts were obtained. The antibacterial and antifungal activity against five phytopathogenic strains and Fusarium oxysporum was evaluated by disc diffusion on agar. The nematicidal activity was assessed by egg hatching inhibition on Meloidogyne incognita and insecticidal activity against maize weevil Sitophilus zeamais. Additionally, the total phenolic content of the seaweed extracts was assessed. Results. Regarding the antibacterial potential, Laurencia johnstonii, Asparagopsis taxiformis, and Dictyota dichotoma showed the highest inhibition against all the phytopathogenic strains and the fungus F. oxysporum. Regarding egg hatching inhibition against nematode M. incognita, the extract of Padina concrescens exhibited the highest percentage of inhibition (59 %) followed by L. johnstonii (48 %). All the seaweeds cause the mortality of the insect S. zeamais. However, the highest insecticidal activity was identified on L. johnstonii (71.9%). In general, red and brown seaweeds showed a higher content of total phenolic compounds. Conclusions. This study showed that species of red and brown seaweeds evaluated have a great potential for controlling the phytopathogens evaluated. However, further research is necessary to identify the active compounds and established lethal doses.