Phytotoxicity Assessment of Olive Mill Wastewater on Seed Germination and Early Seedling Growth of Atriplex halimus and Achillea fragrantissima Dryland Plants

Most of Jordan’s arid and semi-arid areas have suffered land degradation and a decline in plant biodiversity, making non-conventional water resources essential for enhancing dryland productivity. Olive oil production in Mediterranean countries generates large amounts of olive mill wastewater (OMW), locally known as “Zibar,” a source of environmental pollution due to its high acidity and heavy loads of polyphenols and organics. We assessed the phytotoxicity of OMW at five concentrations (0–100%) on seed germination and early seedling growth of two dryland native plants, Atriplex halimus and Achillea fragrantissima, to evaluate their suitability for revegetation of OMW-affected sites. The final germination percentage was unaffected by OMW concentration in either species, but the seedling vigor index declined significantly under treatment in both. In Achillea fragrantissima, the germination index, root length, and fresh weight were significantly reduced even at the lowest OMW concentration tested, indicating high sensitivity. In Atriplex halimus, significant reductions in shoot length and fresh weight emerged mainly at higher concentrations, indicating comparatively greater tolerance. These results suggest Atriplex halimus is a more promising candidate for further evaluation in diluted OMW reuse, while highlighting the need for species-specific testing before recommending dryland plants for OMW-affected environments.