• Energy Research

AbstractCultivated olive, a typical fruit crop species of the semi-arid regions, could successfully face the new scenarios driven by the climate change through the selection of tolerant varieties to salt and drought stresses. In the present work, multidisciplinary approaches, including physiological, epigenetic and genetic studies, have been applied to clarify the salt tolerance mechanisms in olive. Four varieties (Koroneiki, Royal de Cazorla, Arbequina and Picual) and a related form (O. europaea subsp. cuspidata) were grown in a hydroponic system under different salt concentrations from zero to 200 mM. In order to verify the plant response under salt stress, photosynthesis, gas exchange and relative water content were measured at different time points, whereas chlorophyll and leaf concentration of Na+, K+ and Ca2+ ions, were quantified at 43 and 60 days after treatment, when stress symptoms became prominent. Methylation sensitive amplification polymorphism (MSAP) technique was used to assess the effects of salt stress on plant DNA methylation. Several fragments resulted differentially methylated among genotypes, treatments and time points. Real time quantitative PCR (RT-qPCR) analysis revealed significant expression changes related to plant response to salinity. Four genes (OePIP1.1, OePetD, OePI4Kg4 and OeXyla) were identified, as well as multiple retrotransposon elements usually targeted by methylation under stress conditions.

Climate change, currently taking place worldwide and also in the Mediterranean area, is leading to a reduction in water availability and to groundwater salinization. Olive represents one of the most efficient tree crops to face these scenarios, thanks to its natural ability to tolerate moderate salinity and drought. In the present work, four olive cultivars (Koroneiki, Picual, Royal de Cazorla and Fadak86) were exposed to high salt stress conditions (200 mM of NaCl) in greenhouse, in order to evaluate their tolerance level and to identify key genes involved in salt stress response. Molecular and physiological parameters, as well as plant growth and leaves’ ions Na+ and K+ content were measured. Results of the physiological measurements showed Royal de Cazorla as the most tolerant cultivar, and Fadak86 and Picual as the most susceptible ones. Ten candidate genes were analyzed and their complete genomic, CDS and protein sequences were identified. The expression analysis of their transcripts through reverse transcriptase quantitative PCR (RT-qPCR) demonstrated that only OeNHX7, OeP5CS, OeRD19A and OePetD were upregulated in tolerant cultivars, thus suggesting their key role in the activation of a salt tolerance mechanism.

Olive (Olea europaea L.) is one of the most cultivated tree species in Iran. This plant is characterized by its tolerance to drought, salt, and heat stresses while being vulnerable to frost. During the last decade, periods of frost have occurred several times in Golestan Province, in the northeast of Iran, which caused severe damage to olive groves. This study aimed to evaluate and individuate autochthonous Iranian olive varieties with regard to frost tolerance and good agronomic performance. For this purpose, 218 frost-tolerant olive trees were selected from 150,000 adult olive trees (15–25 years old), following the last harsh autumn of 2016. The selected trees were reassessed at different intervals, i.e., 1, 4, and 7 months after the cold stress in field conditions. Using 19 morpho-agronomic traits, 45 individual trees with relatively stable frost-tolerance were reevaluated and selected for this research. Ten highly discriminating microsatellite markers were used for the genetic profiling of the 45 selected olive trees, and, ultimately, five genotypes with the highest tolerance among 45 selected ones were placed in a cold room at freezing temperatures for image analyses of cold damage. The results of morpho-agronomic analyses evidenced no bark splitting or symptoms of leaf drop in the 45 cold-tolerant olives (CTOs). The oil content of the cold-tolerant trees comprised almost 40% of the fruit dry weight, highlighting the potential of these varieties for oil production. Moreover, through molecular characterization, 36 unique molecular profiles were individuated among the 45 analyzed CTOs that were genetically more similar to the Mediterranean olive cultivars than the Iranian ones. The present study demonstrated the high potential of local olive varieties, which would be promising and more suitable than commercial olive varieties, with regard to the establishment of olive groves under cold climate conditions. This could be a valuable genetic resource for future breeding activities to face climate changes.

AbstractOlive is a long-living perennial species with a wide geographical distribution, showing a large genetic and phenotypic variation in its growing area. There is an urgent need to uncover how olive phenotypic traits and plasticity can change regardless of the genetic background. A two-year study was conducted, based on the analysis of fruit and oil traits of 113 cultivars from five germplasm collections established in Mediterranean Basin countries and Argentina. Fruit and oil traits plasticity, broad‐sense heritability and genotype by environment interaction were estimated. From variance and heritability analyses, it was shown that fruit fresh weight was mainly under genetic control, whereas oleic/(palmitic + linoleic) acids ratio was regulated by the environment and genotype by environment interaction had the major effect on oil content. Among the studied cultivars, different level of stability was observed, which allowed ranking the cultivars based on their plasticity for oil traits. High thermal amplitude, the difference of low and high year values of temperature, negatively affected the oil content and the oleic acid percentage. Information derived from this work will help to direct the selection of cultivars with the highest global fitness averaged over the environments rather than the highest fitness in each environment separately.