The olive tree (Olea europaea L. subsp. europaea) is the most important perennial crop in the Mediterranean region, producing table olives and oil, both appreciated for their nutraceutical value. Although olive oil quality traits have been extensively studied, much less attention has been paid to olive drupe. Olive drupe ripening is an extremely complex process involving numerous physiological and molecular changes that are unique in this fruit crop species. This review underlines the contribution of “-omics” techniques and of the recent advances in bioinformatics and analytical tools, notably next-generation sequencing and mass spectrometry, for the characterization of the olive ripening syndrome. The usage of high-dimensional datasets, such as transcriptomics, proteomics, and metabolomics, will provide a systematical description of the molecular-specific processes regulating olive fruit development and ripening. However, the incomplete sequence of the O. europaea L. reference genome has largely hampered the utilization of omics tools towards olive drupe research. Due to this disadvantage, the most reported -omics studies on fruit trees concern metabolomics and only a few transcriptomics and proteomics. In this review, up-to-date applications of -omics technologies towards olive drupe biology are addressed, and future perspectives in olive fruit research are highlighted.

‘Lemonato’ is a Greek peach melting-flesh white-flesh cultivar with high nutritional value highly appreciated by the consumers. This study aimed to evaluate the effect of pre-harvest foliar calcium application on fruit quality, primary metabolite profile, antioxidant activity, total phenolic content, and phenolic profile of the ‘Lemonato’ peach, clone ‘Stamatis’. The experiment was conducted for two years, 2019 and 2020, in two commercial orchards at Kato Lehonia and Agios Vlasios regions, central Greece, where the ‘Lemonato’ clone ‘Stamatis’ is traditionally cultivated. The treatments were organic calcium (Ca), calcium–silicate in nanoparticles (Ca–Si), and calcium chloride (CaCl₂). Foliar application of the different Ca formulations, commonly used as a horticultural practice, were not effective at improving the fruit quality characteristics in this clone, which is characterized by fruit softening during ripening. The study revealed the sugars and organic acid composition and phenolic profile of the ‘Lemonato’ peach, clone ‘Stamatis’. Peach fruit quality, primary metabolites, and phenolic compounds of the two orchards showed a different response to organic Ca and Ca–Si, indicating that genetic or environmental factors may also be involved. A higher concentration of organic Ca and CaCl₂ increased the peach fruit phenolic compounds content and the total antioxidant activity, improving the fruit nutritional quality.

The assessment of fruit quality traits is a key factor in increasing consumer acceptance of kiwifruit. Here, an experiment was performed to evaluate the relationship between dry matter (DM) and soluble solids concentration (SSC), evaluated by both destructive (D) and non-destructive (ND) approaches, with acidity content and sensory evaluation, particularly taste, in fully ripened ‘Hayward’ kiwifruits from 20 orchards. Nutrient content and metabolomic analysis were also performed in ripened kiwifruit tissues (pericarp, placenta, and seeds) from four selected orchards of kiwifruits of high taste scores (HTS) and four orchards of low taste scores (LTS). The results suggest that ND-DM measurement positively correlated with D-DM and may serve as an indicator of kiwifruit taste. Moreover, the taste of kiwifruit was affected by both SSC and acidity. Based on the nutrient content of the pericarp and the primary metabolites of the pericarp and placenta, a clear separation was observed between kiwifruits with HTS and those with LTS, while no differences were found in seed samples. Metabolites such as fructose, maltose, mannobiose, tagatose, and citrate were accumulated in kiwifruits with a strong taste in the pericarp, whereas others, such as serine in the pericarp and placenta, have a negative impact on taste. The current study contributes to a greater understanding of the influence of dry matter, ripening characteristics, primary metabolites, and nutrient content on the taste of kiwifruits.

Flesh firmness in sweet cherries is determined using the measurement of normalized deformation force, i.e., determining the required force for a distance equal to 5 or 10% of the diameter of the cherries per millimeter. However, a firmness method involving a defined distance is quite simple and suitable for easy applications. Hence, our study focuses on the impact of fruit physiology under various and fixed distances. To assess the firmness evaluation, two sweet cherry cultivars (Canada Giant and Regina) were selected and subjected to three different levels of compression distance equal to 1%, 5%, 10% of the fruit’s small thickness dimension along with a consistent compression distance of 0.16 mm. There was a strong correlation between panelists’ preferences and the fruit that had been subjected to both a 1% deformation force and a fixed distance of 0.16 mm within each cultivar. Physiological traits, membrane integrity, and the metabolome of the fruit in these categories were mostly unaffected by the control (0%), or 1%, deformation force, as shown by clustering and PCA analysis. The control and 1% deformation force groups showed similar patterns, contrary to those of the 5% and 10% deformation force groups. Given these considerations, a fixed distance of 0.16 mm and a minimal 1% deformation force possess the potential to be employed and implemented for monitoring the firmness of sweet cherries during postharvest preservation.

Although the ripening process of climacteric fruits is well-characterized, the regulatory mechanisms underlying ripening in non-climacteric fruits, such as sweet cherry, remain poorly understood. In this study, we present an extensive physiological, biochemical and transcriptomic analysis of pedicel and fruit tissues across 8 developmental stages in the late-maturing sweet cherry cultivar “Regina,” providing a comprehensive map of tissue-specific gene expression dynamics during fruit ripening. Our data reveal widespread transcriptomic and metabolomic reprogramming, particularly in sugar metabolism within the pedicel, suggesting that cherry ripening may be partially regulated by pedicel-derived signals. Through integrative analysis, we identified key transcription factors (TFs), most notably PaWRKY57 and PaNAC29, as putative regulators of fruit development. Silencing the genes encoding these TFs at the color breaking stage in both the “Regina” and early-maturing “Carmen” cultivars resulted in delayed pigmentation and reduced fruit size. Subsequent transcriptomic and proteomic analysis of silenced fruit revealed several candidate downstream targets and regulatory networks specifically linked to anthocyanin biosynthesis. Levels of central metabolic components and major anthocyanins, particularly cyanidin glucoside and cyanidin rutinoside, were reduced alongside altered abscisic acid (ABA) levels following PaWRKY57 and PaNAC29 silencing. Furthermore, we demonstrate that PaWRKY57 and PaNAC29 interact with the promoter regions of dihydroflavonol4-reductase (PaDFR) and leucoanthocyanidin dioxygenase (PaLDOX), regulating flavonoid biosynthesis. Notably, PaNAC29 also binds to the promoters of PACLOBUTRAZOL RESISTANCE 6 (PaPRE6) and linoleate 9S-lipoxygenase 5 (PaLOX5), influencing the biosynthesis of ABA and aroma-related volatile compounds. This work provides insights into tissue-specific regulatory dynamics in sweet cherry, establishes a framework for non-climacteric fruit ripening, and identifies promising targets for improving cherry yield and fruit quality.

Native tomato landrace varieties (Solanum lycopersicum L.) are sources of high genetic diversity and are adaptable to local environmental conditions. The in vitro propagation system can be used as a tool to produce disease-free, high-quality propagation material and preserve the unique characteristics of commercial Greek tomato varieties, such as the variety Areti and the traditional landrace variety Makedonia, both of exceptional quality and economic importance. Twenty- and 27-day-old cotyledon and leaf explants were cultivated in 4 regeneration media supplemented with 0 or 0.1 mg∙L⁻¹ indole-3-acetic acid and 0.5 or 1 mg∙L⁻¹ zeatin. Regeneration efficiency was dependent on variety, explant type and age, and regeneration media. Areti was a more appropriate target genetic material, exhibiting a six-fold greater response to regeneration compared to Makedonia, regardless of media and explant age. The regenerated shoots of both varieties were successfully rooted (60%) and acclimatized (98%). This regeneration protocol would be valuable in the production of propagation material for commercial and conservation practices and in breeding programs for genetic improvement.