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The oxidative stability index (OSI) and fatty acid (FA) composition of extra virgin olive oils (EVOOs) are key parameters in the characterization of new varieties in breeding programs. Their determination through traditional methods (Rancimat and gas chromatography, respectively) is expensive and time-consuming. Therefore, there is a need to develop rapid and cost-effective analytical procedures. This study aimed to evaluate the potential use of near-infrared spectroscopy (NIRS) for analyzing OSI and FA composition in EVOOs. A total of 318 samples sourced from different origins were evaluated using both FT-NIR MPA and MicroNIR instruments in transmittance mode, with wavelengths ranging from 1100 to 2500 nm and 908 to 1676 nm, respectively. Different accuracies were obtained in the models developed for the different evaluated traits, with simpler models (using a lower number of latent variables) for the MPA analyzer in all cases. Additionally, consistent results between instruments for the partitioning of the variance and heritability estimation, and the reliable ranking of genotypes were obtained from one of the sample sets tested. In summary, models derived from PLS regression using spectroscopic data of both instruments demonstrated promising results in determining these EVOO traits, facilitating their evaluation and selection of genotypes, particularly in breeding programs.

The large amount of olive cultivars conserved in germplasm banks can be used to overcome some of the challenges faced by the olive growing industry, including climate warming. One effect of climate warming in olive is the difficulty to fulfill the chilling requirements for flowering due to mild winter temperatures. In the present work, we evaluate seven olive cultivars for their adaptation to high winter temperatures by comparing their flowering phenology in the standard Mediterranean climate of Cordoba, Southern Iberian Peninsula, with the subtropical climate of Tenerife, Canary Islands. Flowering phenology in Tenerife was significantly earlier and longer than in Cordoba. However, genotype seems to have little influence on the effects of the lack of winter chilling temperatures, as in Tenerife. This was found even though the cultivars studied had a high genetic distance between them. In fact, all the cultivars tested in Tenerife flowered during the three-year study but showed asynchronous flowering bud burst. ‘Arbequina’ showed an earlier day of full flowering compared with the rest of the cultivars. The results observed here could be of interest to refine the phenological simulation models, including the length of the flowering period. More genetic variability should be evaluated in warm winter conditions to look for adaptation to climate warming.

Extra virgin olive oil (EVOO) is renowned for its numerous minor compounds, particularly phenols, which contribute to its health-promoting properties and commercial quality. The phenolic composition of EVOO largely relies on the initial phenolic content of the olive fruits, which represents, therefore, an important trait to be considered in olive breeding programs. However, only limited studies have been conducted so far to compare the relative influence of genotype and environment in the variability of this trait. For that reason, this study aims to assess the influence of genotype (cultivars ‘Arbequina’, ‘Coratina’, ‘Hojiblanca’, ‘Koroneiki’, ‘Martina’, and ‘Picual’) and environment (harvest date, season, and location) on the fruit phenolic content and composition. A wide general variability was obtained in the whole dataset, with total phenols ranging from 6019 to 38,380 μg/g. A stronger effect of the genotype than the environment was observed for total phenolic content (representing 76–90% of total sums of squares) and the different groups of compounds. Notably, significant variations were found among cultivars not only in the total phenol content but also in the percentage of individual compounds within each main phenolic group. Overall, taking into account the entire dataset available, a clear grouping of samples according to genotypes was observed. The results obtained highlight the prominent influence of the genotype (cultivar) over the environment and genotype–environment interactions on the phenolic content and composition in olive fruits; even when considering very contrasting environments as the Mediterranean and subtropical in the present work. These findings suggest the feasibility of breeding selection of new cultivars with distinctive phenolic content and composition.

Olive is one of the most cultivated species in the Mediterranean Basin and beyond. Despite being extensively studied for its commercial relevance, the origin of cultivated olive and the history of its domestication remain open questions. Here, we present a genealogical and kinship relationships analysis by mean of chloroplast and nuclear markers of different genera, subgenus, species, subspecies, ecotypes, cultivated, ancient and wild types, which constitutes one of the most inclusive research to date on the diversity within Olea europaea species. A complete survey of the variability across the nuclear and plastid genomes of different genotypes was studied through single nucleotide polymorphisms, indels (insertions and deletions), and length variation.

The fruit size of a cultivated olive tree is consistently larger than its corresponding wild relatives because fruit size is one of the main traits associated with olive tree domestication. Additionally, large fruit size is one of the main objectives of modern olive breeding programs. However, as the long juvenile period is one main hindrance in classic breeding approaches, obtaining genetic markers associated with this trait is a highly desirable tool. For this reason, GWAS analysis of both genetic markers and the genes associated with fruit size determination, measured as fruit weight, was herein carried out in 50 genotypes, of which 40 corresponded to cultivated and 10 to wild olive trees. As a result, 113 genetic markers were identified, which showed a very high statistically significant correlation with fruit weight variability, p < 10−10. These genetic markers corresponded to 39 clusters of genes in linkage disequilibrium. The analysis of a segregating progeny of the cross of “Frantoio” and “Picual” cultivars allowed us to confirm 10 of the 18 analyzed clusters. The annotation of the genes in each cluster and the expression pattern of the samples taken throughout fruit development by RNAseq enabled us to suggest that some studied genes are involved in olive fruit weight determination.

In Spain, several local studies have highlighted the likely presence of unknown olive cultivars distinct from the approximately 260 ones previously described in the literature. Furthermore, recent advancements in identification techniques have significantly enhanced in terms of efficacy and precision. This scenario motivated a new nationwide prospecting effort aimed at recovering and characterizing new cultivated germplasm using high-throughput molecular markers. In the present study, the use of 96 EST-SNP markers allowed the identification of a considerable amount of new material (173 new genotypes) coming from areas with low intensification of production in different regions of Spain. As a result, the number of distinct national genotypes documented in the World Olive Germplasm Bank of IFAPA, Córdoba (WOGBC-ESP046) increased to 427. Likewise, 65 and 24 new synonymy and homonymy cases were identified, respectively. This rise in the number of different national cultivars allowed to deepen the knowledge about the underlying genetic structure. The great genetic variability of Spanish germplasm was confirmed, and a new hot spot of diversity was identified in the northern regions of La Rioja and Aragon. Analysis of the genetic structure showed a clear separation between the germplasm of southern and northern-northeastern Spain and indicated a significantly higher level of admixture in the latter. Given the expansion of modern olive cultivation with only a few cultivars, this cryptic germplasm is in great danger of disappearing. This underlines the fact that maintaining as many cultivars as possible will increase the genetic variability of the olive gene pool to meet the future challenges of olive cultivation.

Verticillium wilt of olive (VWO) is one of the most widespread and devastating olive diseases in the world. Harnessing host resistance to the causative agent is considered one of the most important measures within an integrated control strategy of the disease. Aiming to understand the mechanisms underlying olive resistance to VWO, the metabolic profiles of olive leaves, stems and roots from 10 different cultivars with varying levels of susceptibility to this disease were investigated by liquid chromatography coupled to mass spectrometry (LC-MS). The distribution of 56 metabolites among the three olive tissues was quantitatively assessed and the possible relationship between the tissues’ metabolic profiles and resistance to VWO was evaluated by applying unsupervised and supervised multivariate analysis. Principal component analysis (PCA) was used to explore the data, and separate clustering of highly resistant and extremely susceptible cultivars was observed. Moreover, partial least squares discriminant analysis (PLS-DA) models were built to differentiate samples of highly resistant, intermediate susceptible/resistant, and extremely susceptible cultivars. Root models showed the lowest classification capability, but metabolites from leaf and stem were able to satisfactorily discriminate samples according to the level of susceptibility. Some typical compositional patterns of highly resistant and extremely susceptible cultivars were described, and some potential resistance/susceptibility metabolic markers were pointed out.

The characterization of tree canopy traits represents a key step to identify potential cultivars adaptable to a specific growing system. Developing methodologies to rapidly evaluate canopy traits allows to classify cultivars in germplasm banks and facilitates selections in breeding programs. In the present work, the ability of low-cost unmanned aerial vehicle (UAV) was compared with on-ground traditional methodology for measuring canopy traits (namely crown diameters, tree height and crown volume) in trees of the Worldwide Olive Germplasm Bank of Córdoba. The evaluated trees belonged to a wide range of cultivars and were planted in three different dates. A wide variability was found for the four parameters measured with both on ground and UAV methodologies. Besides, a significant linear correlation was observed at tree and cultivar level, with relative errors that ranged from 4.44 to 13.9 % for axial parameters or from 17.0–29.0% for volume, depending on the planting date considered. ANOVA and Tukey's results showed a high agreement between both methodologies in identifying cultivars with similar vigour values. When comparing means over time, the UAV-based data allowed a slightly better detection of significant differences than on-ground data. The results provided by the present research indicated that the use of UAV is a reliable methodology to study tree canopy traits in olive germplasm banks, supporting breeders to the identification and definition of the genetics behind crop variability. The evaluation here performed indicates that there is a wide variability on canopy traits on the cultivated olive germplasm that could be exploited to select potential cultivars for different growing systems.

Despite the importance of flowering for fruit formation, it has been considered very little in breeding programs involving fruit species, including olives. We evaluated the principal morphological flower-quality components in the olive cultivars, 'Arbequina' and 'Picual', and in the progenies of their crosses. Wide ranges of variation were obtained for all the inflorescence traits and ovary tissue sizes. An analysis of variance indicated that the residual error was the main contributor to the inflorescence traits, except for the number of perfect flowers, underlining the need to evaluate adequate numbers of inflorescences for accurate measurements of these traits. However, the high repeatability obtained for the inflorescence traits suggests that simple evaluation procedures could be accurate enough for genotype characterization. The average values for 'Arbequina' were in the upper range for all the traits; the opposite occurred for 'Picual', and the values for most of the progenies were intermediate. No significant differences between the maternal and paternal effect on inheritance were found. Some interesting transgressive segregants showed a higher flower number, greater ovary and mesocarp size, or percentage of ovaries with all four fully developed ovules. The correlations among the parameters may have reflected a relatively consistent distribution of the ovaries' structural components and a close relationship between the ovaries and their mesocarp growth.

El aceite de oliva virgen extra (AOVE) cuenta en su composición con un gran número de compuestos minoritarios relacionados con sus propiedades saludables, entre ellos, los compuestos fenólicos. Dichos compuestos están asimismo relacionados con la estabilidad y propiedades organolépticas del AOVE, siendo, por tanto, constituyentes de primordial importancia con respecto a la calidad comercial. La composición fenólica del AOVE depende en gran medida de la composición inicial en dichos componentes de los frutos, que posteriormente sufre una serie de transformaciones enzimáticas durante el proceso de extracción en la almazara. En el presente trabajo se compara la variabilidad del contenido y composición en fenoles en frutos recolectados en dos épocas en seis variedades (‘Arbequina’, ‘Coratina’, ‘Hojiblanca’, ‘Koroneiki’, ‘Martina’ y ‘Picual’) cultivadas en condiciones contrastantes con clima mediterráneo de Córdoba y subtropical de Tenerife, con el objetivo de estudiar la influencia de los factores genético y ambiental en la composición fenólica de los frutos. En todos los casos se ha observado un descenso acusado del contenido total de fenoles en la fecha de recolección más tardía (Figura 1), descenso que afectó de manera similar a todos los grupos de compuestos analizados que no variaron significativamente su proporción en las dos fechas analizadas (Tabla 1). El contenido total de fenoles estuvo significativamente influenciado por ambos factores: variedad, con los valores más altos en ‘Coratina’ y localidad, con valores más altos en Tenerife, sin que exista interacción entre ambos factores (Tabla 2, Figura 1). En cuanto a la composición fenólica, en general se observó un efecto genético (variedad) más importante que el ambiental para todos los grupos de compuestos (Tabla 2). En particular, aunque no hubo diferencias significativas entre variedades para los tres grupos principales de compuestos fenólicos (derivados de hidroxitirosol, derivados de tirosol y flavonas), sí

Hedgerow orchard is an olive growing system where trees are planted at a super high-density higher than 20-fold (i.e., 1200–2500 trees ha−1) compared to the traditional density of olive orchards (usually 50 to 160 trees ha−1). It is dominating a great proportion of new plantations because harvesting can be fully mechanized, it is early bearing and has a relatively constant high productivity. However, there are a limited number of cultivars with sufficiently low vigour to be suitable for such plantation densities. For that reason, a set of low vigour cultivars and breeding selections has been used in a field experiment as rootstocks for reducing the vigour of “Picual”, the most frequent cultivar planted in Spain. Tree vigour was characterized by measuring crown height, projected and side areas, and volume through the analysis of photogrammetric point clouds created from images acquired with an unmanned aerial vehicle. A significant reduction of the ‘Picual’ vigour was observed in most of the rootstocks tested, with canopy volume reduced up to one half. High variability on vigour, first harvesting and their relative relationship was observed between the different rootstocks used. This indicates there might be enough genetic variability to perform breeding selection for dwarfing rootstocks on ‘Picual’ olive cultivar.

The long juvenile period in olive (Olea europaea L.) delays the evaluation of characters of interest and prolongs the selection of new cultivars in the breeding programs. Therefore, it is important to use accurate selection criteria and appropriate selection pressure to make an effective identification of the superior genotypes and to identify which parents transmit lower juvenile periods to their descendants. In this study, the juvenile period, vigor, fruit fresh weight, and oil content of fruit on a dry weight basis were evaluated in 1568 genotypes from two independent open-pollinated populations; G07, that included 520 genotypes from 25 cultivars and 1 breeding selection and G14, with 1048 genotypes from 13 cultivars. This evaluation was used to test different selection criteria and define optimal selection pressure at the initial stage of an olive breeding program. Wide ranges of variation were obtained for all the characters measured, with higher variability within progenies than between progenies. "Askal" and "Barnea" seem to be the cultivars transmitting the shorter juvenile period to the descendants. In the case of fruit fresh weight and oil content, transgression of variability limits of the parents was observed. Significant correlation was found between mean values of fruit fresh weight of progenies and their parents for G07 (0.59) and G14 (0.95). Selection was made using two selection index formulas (SI1 and SI2). A high coincidence was found between the individuals selected by both formulas and the correspondent selection pressures applied; 15% for SI1, and 14% for SI2. A wide variability in the percentage of selected genotypes was found, from no individuals selected from some progenies to more than 20% of genotypes selected in some others. These results underline the need to explore the wide genetic variability currently hosted in germplasm collections for an optimal choice of parents in olive breeding works.

Olive, the emblematic Mediterranean fruit crop, owns a great varietal diversity, which is maintained in ex situ field collections, such as the World Olive Germplasm Bank of Córdoba (WOGBC), Spain. Accurate identification of WOGBC, one of the world's largest collections, is essential for efficient management and use of olive germplasm. The present study is the first report of the use of a core set of 96 EST-SNP markers for the fingerprinting of 1273 accessions from 29 countries, including both field and new acquired accessions. The EST-SNP fingerprinting made possible the accurate identification of 668 different genotypes, including 148 detected among the new acquired accessions. Despite the overall high genetic diversity found at WOGBC, the EST-SNPs also revealed the presence of remarkable redundant germplasm mostly represented by synonymy cases within and between countries. This finding, together with the presence of homonymy cases, may reflect a continuous interchange of olive cultivars, as well as a common and general approach for their naming. The structure analysis revealed a certain geographic clustering of the analysed germplasm. The EST-SNP panel under study provides a powerful and accurate genotyping tool, allowing for the foundation of a common strategy for efficient safeguarding and management of olive genetic resources.

Olea europaea subsp. cuspidata has a relatively low commercial value due to the low size and pulp to stone ratio of its drupes compared to commercial olive cultivars. Nevertheless, this subspecies could represent a valid source of useful traits for olive breeding. In the current work, the drupe metabolic composition (secoiridoids, flavonoids, simple phenols, triterpenic acids, etc.) of a progeny of 27 cuspidata genotypes coming from free pollination and their female parent was evaluated by applying a powerful LC-MS method. A total of 62 compounds were detected within the profiles; 60 of them were annotated and 27 quantified. From a quantitative point of view, the genotypes from the progeny of cuspidata showed quite different metabolic profiles to olive common cultivars ("Arbequina", "Frantoio", "Koroneiki" and "Picual") used as controls. Cuspidata drupes were richer in terms of several bioactive compounds such as rutin, hydroxytyrosol glucoside, a few interesting secoiridoids and the compounds of m/z 421 and 363. The relationships among several secondary metabolites determined in the progeny inferred from the results of both PCA and cross-correlation analysis were explained according to metabolic biosynthesis pathways in olive drupes. These outcomes underlined the potential of cuspidata genetic resources as a source of potentially interesting variability in olive breeding programs.