In vitro antifungal effect of plant-based and Ulva sp. extracts on Aspergillus flavus growth and conidia germination

Mycotoxins in cereals, particularly maize, represent a major threat to food safety and agricultural sustainability, a challenge expected to intensify under climate change. In this context, the development of environmentally friendly and sustainable mitigation strategies is urgently needed. Plant waste materials and seaweed biomass represent promising renewable sources of bioactive phytochemicals that can be used as sustainable agricultural approaches to control fungal pathogens. This study investigated the in vitro antifungal activity and chemical composition of hydroalcoholic extracts from plant waste materials and seaweed ( Ailanthus altissima (Mill.) Swingle leaves, Humulus lupulus L. trub, Olea europaea L. leaves, and Ulva sp. thallus). Except for Olea europaea , all extracts inhibited the growth of Aspergillus flavus , with those from Ulva showing the highest efficacy (EC 50 = 14.2 mg/mL). Total Phenolic (TPC) and Flavonoid (TFC) contents were quantified, revealing distinct chemical profiles across the extracts. Despite a TPC nearly three times lower (3.80 µg GAE/mg DW) than that from Humulus trub and Ailanthus (~ 11 µg GAE/mg DW), the superior activity of Ulva extract was attributed to its unique chemical composition. While the plant-derived extracts were enriched in glycosylated flavonols, the Ulva extract was characterized by specific phenolics, such as rosmarinic and p -hydroxybenzoic acids, and a dominant polysaccharide fraction; 1 H and 13 C NMR analysis confirmed the presence of sulfated ulvans, identified by characteristic rhamnose, xylose, and uronic acid units. These findings highlight the potential of plant residues and seaweed biomass as sustainable sources of antifungal compounds. In particular, Ulva extracts emerge as promising candidates for the development of eco-friendly strategies to control Aspergillus flavus infections, supporting greener crop protection and future applications in agricultural and post-harvest systems.