Student name: Afonso Henriques da Silva

RUN-EU institution: Politécnico de Leiria, Portugal

Abstract

The olive tree (Olea europaea), grown globally on 12 million hectares, anchors Mediterranean economies, with Portugal’s 350,000 hectares producing 160,800 tons of olive oil by 2023. Recognised by the U.S. Food and Drug Administration (FDA) for its cardiovascular benefits, the quality and production of olive oil are threatened by fungal diseases such as anthracnose (Colletotrichum spp.), which causes economic losses and sensory defects. Copper-based fungicides, although widely used, present environmental and public health concerns. Given these limitations and the increasing restrictions imposed by the EU, there is an urgent need to develop effective, safe and sustainable alternatives. Seaweed, rich in bioactive compounds with antifungal and antimicrobial properties, is a sustainable and environmentally friendly alternative. This study evaluated extracts from A. armata, A. carterae, F. vesiculosus, C. monotis, and S. muticum (0.1, 0.5, and 1 mg/mL).

The research revealed a concentration-dependent antifungal activity of the seaweed extracts against Colletotrichum. The extract of A. carterae (1 mg/mL) showed the highest inhibition (60% at 24 h), followed by F. vesiculosus (0.5 mg/mL; 31% inhibition). The phytotoxicity tests identified specific toxicity for each species: F. vesiculosus and S. muticum extracts were non-toxic at all concentrations tested (0.1-1 mg/mL), while A. armata, A. carterae and C. monotis showed toxicity regardless of concentration.

The results demonstrate the antifungal potential of A. carterae despite its phytotoxicity, contrasting with the safer profile of F. vesiculosus. Both seaweed extracts, which are biodegradable and have low persistence, are in line with the objectives of the EU Green Deal, offering sustainable alternatives to copper fungicides. Future research should prioritise optimising the concentration of A. carterae to mitigate phytotoxicity while maintaining potency, as well as exploring other formulations with alternative solvents to improve sustainable antifungal solutions.

Keywords: anthracnose, olive tree, seaweed extracts, antifungal compounds.