Evaluation of Baja Peninsula seaweeds against plant pathogens

Abstract The widespread use of synthetic pesticides to control pests has generated serious consequences on the environment and human health. Currently, efforts focused on the search for new pesticides with less impact on the environment have been doubled. Marine algae synthesize compounds with activity against various agricultural pests (insects, nematodes, and fungi); however, marine pesticides are an underdeveloped alternative. This represents an opportunity to explore new sources of compounds. The objective of this work is to evaluate the antimicrobial, nematicidal and insecticidal activity of seaweed extracts against pathogens of agricultural importance. Therefore, 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. Nematicidal activity was assessed by egg hatching inhibition on Meloidogyne incognita and insecticidal activity against maize weevil Sitophilus zeamais. Regarding the antibacterial potential, Laurencia johnstonii, Asparagopsis taxiformis and Dictyota dichotoma showed higher inhibition against all the strains. Padina concrescens exhibited the highest percentage of egg hatching inhibition against M. incognita (59%) followed by L. johnstonii (48%). All the seaweeds cause mortality of S. zeamais. However, the highest insecticidal activity was found on L. johnstonii (71.9%). Red and brown seaweeds showed in general higher content of total phenolic compounds. Red and brown seaweed showed great potential for the control of phytopathogens through appropriate agricultural practices. However, further research is necessary to identify the active compounds.