Olive Browning Disorder (OBD) is a newly identified, non-pathogenic physiological disorder in olive (Olea europaea L.) fruit. OBD was first identified in the Israeli variety Askal, it manifests as internal browning of the endocarp and mesocarp and is caused by insufficient calcium (Ca) level during fruit development. Low fruit Ca weakens tissue structure, leading to localized collapse, oil body disintegration, and elevated free fatty acid (FFA) levels that degrade olive oil quality. The disorder typically initiates at the distal end of the fruit and progresses internally without external symptoms.
OBD appears strongly influenced by environmental and nutritional conditions. It is especially prevalent under arid and desert-like climates, where high temperatures and low transpiration reduce xylem-mediated Ca transport to fruit. Our multi-year study, conducted across experimental and commercial orchards in southern Israel, identified OBD in approximately half of the tested cultivars. These included key varieties such as Souri, Manzanilla, and Leccino, indicating widespread occurrence and possible genetic sensitivity.
Within cultivars, larger fruits were more susceptible to OBD. The disorder consistently correlated with low Ca concentrations and high nitrogen-to-calcium ratios in the fruit mesocarp. Foliar Ca applications had minimal effect on fruit Ca status, highlighting the importance of early-season Ca delivery through xylem flow.
OBD was also strongly associated with elevated FFA levels across cultivars and maturity stages, independent of ripening or pest damage. These findings underscore the need for improved early-season Ca management and cultivar screening to maintain oil quality under intensifying climate and water stress in dryland olive production systems.
