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.

Comparative analysis of cultivated and wild olive genotypes to salinity and drought stress.

The Mediterranean region's harsh conditions, characterized by low rainfall, high solar radiation, and elevated temperatures, pose challenges for vegetation, particularly in the face of climate change. Cultivated olive (Olea europaea subsp. europaea var. europaea) holds historical and economic significance as one of the oldest crops in the Mediterranean. Due to their high germplasm diversity and greater flowering abundance compared to the offspring of cultivated olives, wild olives (Olea europaea subsp. europaea var. sylvestris) could be utilized for selecting new olive cultivars capable of adapting to a changing climate. This research aimed to compare the effects of salt and drought stress on wild and cultivated genotypes by analyzing morphological, physiological, and biochemical parameters. Results showed that shoot length, shoot dry mass, and leaf area are key drought stress indicators in wild olive trees. The results indicated the olive trees more susceptible to salinity stress had lower Na+ and Cl- concentrations in their leaves and took longer to stabilize salt ion levels. Decreased K+ content in roots across all treatments indicated a general stress response. The uptake of Ca2+ appears to be the most energy-efficient response of olive trees to short-term salinity and drought. In contrast to proline and malondialdehyde, trends in superoxide dismutase activity suggest that it is a reliable indicator of salinity and drought stress. Regarding olive adaptability to salinity stress, promising results obtained with two wild olive genotypes merit their further physiological study.

Mechanisms of Kale (Brassica oleracea var. acephala) Tolerance to Individual and Combined Stresses of Drought and Elevated Temperature.

Rising temperatures and pronounced drought are significantly affecting biodiversity worldwide and reducing yields and quality of Brassica crops. To elucidate the mechanisms of tolerance, 33 kale accessions (B. oleracea var. acephala) were evaluated for individual (osmotic and elevated temperature stress) and combined stress (osmotic + temperature). Using root growth, biomass and proline content as reliable markers, accessions were evaluated for stress responses. Four representatives were selected for further investigation (photosynthetic performance, biochemical markers, sugar content, specialized metabolites, transcription level of transcription factors NAC, HSF, DREB and expression of heat shock proteins HSP70 and HSP90): very sensitive (392), moderately sensitive (395), tolerant (404) and most tolerant (411). Accessions more tolerant to stress conditions were characterized by higher basal content of proline, total sugars, glucosinolates and higher transcription of NAC and DREB. Under all stress conditions, 392 was characterized by a significant decrease in biomass, root growth, photosynthesis performance, fructan content, especially under osmotic and combined stress, a significant increase in HSF transcription and HSP accumulation under temperature stress and a significant decrease in NAC transcription under all stresses. The most tolerant accession under all applied stresses, 411 showed the least changes in all analyzed parameters compared with the other accessions.

Physiological and Biochemical Response of Wild Olive (Olea europaea Subsp. europaea var. sylvestris) to Salinity.

In the face of climate change, water deficit and increasing soil salinity pose an even greater challenge to olive cultivation in the Mediterranean basin. Due to its tolerance to abiotic stresses, wild olive (Olea europaea subsp. europaea var. sylvestris) presents a good candidate in breeding climate-resilient olive varieties. In this study, the early response of the native Croatian wild olive genotype (WOG) to salinity was evaluated and compared with that of well-known cultivars (cv.) Leccino and Koroneiki. Potted olive plants were exposed either to 150 mM NaCl or 300 mM mannitol for 3 weeks to distinguish between the osmotic and ionic components of salt stress. To determine the impact of the plant age on salinity, 1-, 2-, and 3-year-old WOG plants were used in the study. The growth parameters of both the cultivars and WOG of different ages decreased in response to the mannitol treatment. In contrast to cv. Leccino, the NaCl treatment did not significantly affect the growth of cv. Koroneiki or WOG of any age. The contents of Na+ and Cl- were considerably higher in the salt-treated WOG, regardless of age, compared with the cultivars. However, while both treatments significantly reduced the K+ content of cv. Koroneiki, that nutrient was not significantly affected in either cv. Leccino or WOG. Unlike the cultivars and older WOG, the NaCl treatment caused a significant decline of photosynthetic pigments in the 1-year-old WOG. The cultivars and WOG of different ages experienced a similar drop in the chlorophyll a content under the isotonic mannitol treatment. The absence of lipid peroxidation, modulation of superoxide dismutase, and guaiacol peroxidase activity were noted in all WOG ages under both stressors. These data suggest that WOG resilience to salinity is associated with its large leaf capacity for Na+ and Cl- accumulation, K+ retention, and its adaptable antioxidative mechanisms. The results are promising with regard to obtaining a new olive cultivar with better resilience to soil salinity.