Challenges of Salinity Intrusion and Drought Stress on Olive Tree Cultivation on Mljet Island

Understanding genotype-specific responses to environmental stressors is vital for developing resilience strategies that ensure sustainable olive cultivation and productivity. In this work, cultivar 'Oblica' and several olive genotypes from the island of Mljet (Croatia) were exposed to short-term (21 days) salinity and drought treatments. In contrast to other olive genotypes, genotype M29 as well as cultivar 'Oblica' managed to maintain growth and chlorophyll a levels under salinity stress to the same level as the control. Drought, however, significantly reduced the growth parameters in all olive trees. Cultivar 'Oblica' accumulated the greatest amount of Na+ ions in the leaves compared to olive genotypes from the island of Mljet, demonstrating superior resistance by translocating Na+ to leaf vacuoles. The observed reduction in K+ content in the roots of olive trees under all treatments suggests a generalized stress response. On the other hand, effective Ca2+ uptake has been identified as a crucial energy-saving strategy that olive trees use to cope with brief periods of salinity and drought. The proline content and activities of superoxide dismutase (SOD) and guaiacol peroxidase (GPOX) varied among the olive trees, highlighting the importance of antioxidative capacities and stress adaptation mechanisms. According to the obtained results, stress-resistant olive genotypes like 'Oblica' and M29 show potential for breeding resilient varieties.