Improving olive farming with microbial biostimulants: benefits, challenges and opportunities.

Mediterranean olive cultivation, a cornerstone of regional agriculture, is increasingly threatened by intensified farming practices, emergent vascular diseases, and severe climate change pressures, particularly drought and heat. Microbial biostimulants, specifically PGPB, offer a critical, nature-positive solution by enhancing nutrient acquisition, improving stress tolerance, and conferring biocontrol capacity to the host tree. Early studies on Olea europaea confirm the fundamental potential of these beneficial microorganisms to support olive health. This review argues that the widespread failure of conventional PGPB applications (e.g., soil drenching) in mature olive groves is not primarily a biological issue, but rather an engineering challenge. The application methods cannot effectively overcome the hostile belowground environment, intense native microbial competition, and the physical barriers of the tree's mature root and stem architecture. To unlock the full potential of PGPB for sustainable olive production, a fundamental shift in research priority is required. Future strategies must focus on advanced engineering solutions: (1) developing robust, protective nanostructured carriers to ensure microbial viability and controlled release in harsh environments; and (2) pioneering non-root delivery systems, most notably endovascular delivery (endotherapy), to bypass the soil barrier and precisely target the tree's vascular system. This review synthesizes the biological promise of PGPB in the olive sector, critically analyzes the application failures of traditional methods, and outlines a comprehensive research agenda centered on engineered delivery systems as the essential key to a resilient and sustainable future for olive cultivation under climate change.