Algal extract as a key protective agent: Jania rubens–enriched PVA/CMC coatings for postharvest onion disease control

Onion (Allium cepa L.) is one of the major vegetable crops that are damaged and lost by pathogenic fungal infection during storage due to a lack of proper storage conditions. This study investigates the antifungal potential and mechanism of action of Jania rubens extract against two onion pathogens, Aspergillus niger and Talaromyces calidominioluteus. The acetone extract (AE) of Jania rubens demonstrated notable inhibitory effects against the tested fungi, exhibiting potential antifungal activity relative to the fungicide fluconazole. Gas Chromatography-Mass Spectrometry (GC–MS) profiling revealed a rich composition of bioactive compounds, including phytol, thymol, estragole, and fatty acids, known for their antimicrobial properties. In practical application on onion bulbs, dipping in polyvinyl alcohol/carboxymethyl cellulose (PVA/CMC) incorporated with Jania rubens extract significantly improved the physiological status (fresh and dry weight), provided a stronger and more sustained reduction in oxidative stress markers (H2O2 and MDA), and a prolonged decrease in fungal colony-forming units over two months compared to infected onion and PVA/CMC coating. At the morphological level, Transmission Electron Microscopy (TEM) confirmed the direct antifungal action, showing severe ultrastructural damage in fungal hyphae, including cell wall degradation, plasma membrane detachment, and cytoplasmic disorganization. Additionally, molecular analysis provided further clarity, revealing the extract's ability to downregulate key fungal genes: FKS1, CHS2, and CHS (Cell Wall Biosynthesis), ERG11 (Ergosterol Biosynthesis), SOD5 (Antioxidant Defense). Collectively, these findings confirm that Jania rubens extract exerts a potent antifungal effect by simultaneously targeting the fungal cell wall, membrane, and antioxidant pathways. The extract represents a promising, eco-friendly alternative for the effective postharvest management and preservation of stored onions.