Root and crown rot caused by oomycetes: an emerging threat to olive trees

Soilborne diseases are an increasing threat to agriculture and natural ecosystems. Olive root and crown rot (ORCR) caused by pathogenic oomycete species has recently been reported in several olive-growing countries as an emerging phytopathological problem causing leaf yellowing, defoliation, twig dieback, and the development of wilting followed by decline of olive trees. Within the oomycetes, several Phytophthora and Pythium species have been reported to cause root and crown rot of cultivated and wild olive trees. Studies have shown that the disease is particularly severe in young olive groves located on poorly drained, occasionally waterlogged clay soils. Modernization of olive orchards induced by the introduction of irrigation, planting on more favourable and heavier soils, and intensification may increase the risk to cultivated olive trees. In addition, the potential for the spread of these oomycetes, as well as changes in precipitation patterns with more frequent heavy rains, would facilitate the development of infections in wild olive forests and olive groves. Therefore, this review summarizes the latest findings and advances regarding the causative agents of ORCR, detection and diagnosis tools, symptoms, disease cycle, epidemiology, and potential management strategies.