Inhibitory activity of aqueous extracts from Anabaena minutissima, Ecklonia maxima and Jania adhaerens on the cucumber powdery mildew pathogen in vitro and in vivo

Aqueous extracts from Anabaena minutissima BEA 0300B (ANA), Ecklonia maxima (ECK) and Jania adhaerens (JAN) were evaluated for their antifungal effect against powdery mildew disease caused by Podosphaera xanthii on cucumber detached cotyledons and seedlings. All the extracts were sprayed on detached cotyledons at 2.5, 5.0 and 10.0 mg dry biomass mL−1 water and those of ANA and JAN at 5.0 and 10.0 mg mL−1 on seedlings before pathogen challenge (106 spores mL−1). ANA and JAN at 5.0 and 10.0 mg mL−1 reduced infected area and fungal sporulation on both detached cotyledons and seedlings. ANA and JAN at 5.0 and 10.0 mg mL−1 were also evaluated for their elicitation of seedling defence responses, 1, 2 and 3 days before P. xanthii inoculation. Treatments reduced disease symptoms depending on extract, concentration and application time. Both extracts differentially induced the expression of PR genes, which may have concurred to pathogen control. At all times, ANA mainly induced AePR3 and PR1 genes, at 5.0 and 10.0 mg mL−1, respectively, while JAN mainly induced AePR3 and PR4 at 5.0 mg mL−1. This suggests that both ANA and JAN activated the expression of genes within the jasmonic acid and salicylic acid pathway. Proteins, phycobiliproteins, chlorophylls, carotenoids and antioxidant activities determined in the extracts could be involved in the antifungal effect or induction of plant systemic resistance. These results demonstrate that aqueous extracts from algae and cyanobacteria may be considered for further studies as a bio-based strategy for sustainable disease management.