Georgios Koubouris

Olive reproductive phenology depends on the balance between winter chilling and subsequent heat accumulation, yet multi-environment Mediterranean observations to assess this dynamic across thermal regimes remain scarce. We monitored Full Budburst (FB) and Full Flowering (FF) during 2021–2024 in 670 cultivars across five germplasm banks in Greece, Italy, Morocco, Spain, and Türkiye. Median dates, periods, dispersion, and phenological stage overlap were related to bioclimatic factors and chilling and heat accumulation. The influence of the germplasm-bank environment, year, and their interaction on the timing of both stages was assessed. The Median Full Budburst (FB₅₀) and Median Full Flowering date (FF₅₀) were strongly correlated. Likewise, budburst dispersion (ID_bb) was positively associated with flowering dispersion (ID_ff), serving as descriptive indicators of phenological synchrony under varying thermal regimes. Warmer conditions between FB₅₀ and FF₅₀ were associated with a shorter transition to flowering. Conversely, warmer pre-budburst conditions and lower chilling accumulation were associated with greater budburst and flowering dispersion and reduced synchrony. These findings indicate that budburst provides an important temporal reference for flowering. Integrating budburst and flowering dispersion with transition gap (T_gap) metrics offers a quantitative framework for characterizing population-level phenological responses under contrasting thermal regimes and enhancing future olive breeding programs.

Nowadays, we live in the paradoxical situation of having abundant tools in our hands and at the same time having to deal with abundant challenges

Background Olive ( Olea europaea L.) breeding initiatives rely heavily on the extensive and correct characterisation of genetic resources to successfully achieve their goals, such as addressing climate change and emerging diseases challenges. However, the historical lack of standardised phenotyping protocols across multi-environment trials has severely hindered data interoperability and large-scale comparative analyses. Methods Within the Horizon 2020 GEN4OLIVE project, five international olive germplasm banks established a consensus-based methodological framework to systematically evaluate over 500 olive cultivars. We harmonised 14 evaluation protocols covering six fundamental dimensions: phenological and agronomic traits, abiotic stress resilience, biotic stress resilience, olive oil yield and chemical quality, table olive quality assessment, and morphological characterisation and photography. While most protocols were adapted from previously published literature to ensure ease of implementation across different facilities, novel methodologies for frost tolerance and standardised photography were developed de novo. Results The implementation of these consensus methods across five countries proved highly successful. This methodological framework enabled the generation of the largest harmonised, publicly available dataset on olive genetic resources to date, effectively making possible the correct comparation and ranking of the olive cultivars based on their specific characteristics. Conclusions This compendium of methods provides a robust, highly replicable reference point for the standardisation of olive germplasm characterisation and use of shared benchmark cultivars as an effective way for data normalization and comparation. It facilitates future global pre-breeding efforts, ensures international data interoperability, and supports the discovery of resilient cultivars to secure the future of the olive sector.

The cultivation of olive trees is concentrated in regions with a Mediterranean climate commonly characterized by drought and relatively high soil salinity. Scarce water supply, along with the accumulation of Sodium (Na+) ions in plant tissues, triggers various changes in plant mineral element concentrations. Three months of experimental treatments, consisting of deficient irrigation and saline water application on potted trees of three Greek Olea europaea L. cultivars (‘Lefkolia Serron’, ‘Amfissis’ and ‘Mastoidis’), led to statistically significant changes in Calcium (Ca), Copper (Cu), Iron (Fe), Manganese (Mn), Zinc (Zn), and Nitrogen (N) leaf concentrations. The correlation of hyperspectral leaf reflectance with Potassium (K) and Magnesium (Mg) appeared to be significant, which indicates a potential application for early and non-destructive detection of plant nutritional status. Additionally, customized Vegetation Indices, created as normalized ratios between wavelengths with the highest and lowest correlation with each element concentration, resulted in higher correlations than conventional, widely used indices (NDVI, WI, and PRI), a finding that emphasizes the importance of using individualized rather than generalized indices.

Salinization of olive orchards constitutes a front-line agronomic challenge for farmers, consumers, and the scientific community as food security, olive logistics, and land use become more unsustainable and problematic. Plantlets of two olive varieties (var. Kalamon and var. Koroneiki) were tested for their performance under soil saline conditions, in which L-methionine, choline-Cl, and L-proline betaine were applied foliarly to alleviate adverse effects. The ‘Kalamon’ variety ameliorated its photosynthetic rates when L-proline betaine and L-methionine were administered at low saline exposure. The stressed varieties achieved higher leaf transpiration rates in the following treatment order: choline-Cl > L-methionine > L-proline betaine. Choline chloride supported stomatal conductance in stressed var. Kalamon olives without this pattern, which was also followed by var. Koroneiki. Supplementation regimes created a mosaic of responses on varietal water use efficiency under stress. The total phenolic content in leaves increased in both varieties after exogenous application only at the highest levels of saline stress. None of the substances applied to olive trees could stand alone as a tool to mitigate salinity stress in order to be recommended as a solid agronomic practice. The residual exploitation of amino acids by the olive orchard microbiome must also be considered as part of an environmentally friendly, integrated strategy to mitigate salinity stress.

During recent years, agriculture has been undergoing a significant transformation in response to contemporary economic pressures and the escalating impact of climate change

A set of twenty-four Psidium guajava genotypes including exotic cultivar had been genetically characterized using a total of twenty microsatellite (SSR) markers spanning a total of 11 chromosomes. The average number of alleles per locus was 2.93. Fifteen markers (out of the twenty used) were highly polymorphic and could discriminate local cultivars and exotic collection. Two markers, mPgCIR352 and mPgCIR175, showed the highest level of polymorphism, whereas marker mPgCIR352 showed the maximum marker index for high level of resolving capacity amongst all markers tested. Marker mPgCIR321, with 0.778 PIC value present on linkage group 11, has been identified to be associated with fruit yield. Molecular variance study resulted at 92% genetic variance within population and 8% between population. First three axes explained 53.32% variation through principal coordinate analysis. This study explains variation among the existing popular cultivar, local cultivar, and few exotic cultivars which can be helpful in designing cross breeding programmes through the selection of the superior parental varieties.

Genetic improvement and the identification of drought-tolerant cultivars are crucial in perennial ryegrass (Lolium perenne L.) turfgrass to enhance germplasm reserves for molecular breeding and the development of sustainable landscapes in arid and semi-arid green spaces. Cytokinins (CKs) are plant hormones that regulate various physiological processes, including cell division, shoot growth, and leaf senescence, and also are known to regulate plant responses to drought stress. This study aimed to enhance drought tolerance in perennial ryegrass cultivars by utilizing the drought-inducible RD29A promoter to drive the expression of the IPT gene, which boosts cytokinin levels. The research also compared the performance of these transgenic plants with wild-type (WT) plants and local perennial ryegrass accessions under varying irrigation conditions. Results showed that certain transgenic plants and local accessions displayed higher drought tolerance based on turf quality, physiological, and biochemical characteristics. The expression of the IPT gene was confirmed in transgenic plants exposed to drought stress. Transgenic lines including GM24, GM12, GC8, GC6, NC12, NC14, NS14, and GC3 exhibited increased drought tolerance, maintaining higher levels of cytokinins in the leaves, improving water content, photosynthetic rate, and antioxidant activity while reducing damage indicators. Catalase and superoxide dismutase activities were more influential than peroxidase in drought adaptation and recovery. The efficiency of the RD29A promoter and the use of the UBQ10 intron in the IPT gene construct affected gene expression. Moreover, the significant genotypic variation among local accessions indicates opportunities for improving drought tolerance through targeted breeding in sensitive and moderately tolerant genotypes. Further research is recommended to investigate hormonal balance and osmoregulation in transgenic and wild-type plants under multiple stresses. Additionally, identifying candidate genes involved in drought tolerance, particularly in local ryegrass accessions, should be a focus for future studies.