A methodological framework for the standardised evaluation of olive genetic resources: GEN4OLIVE harmonized protocols.

Olive (Olea europaea L.) covers more than 10 million hectares and encompasses over 2,000 traditional varieties. The olive pre-breeding initiatives rely heavily on the extensive characterisation of genetic resources to confront climate change and emerging diseases. However, the historical lack of standardised phenotyping protocols across multi-environment trials has severely hindered data interoperability and large-scale comparative analyses. Within the framework of the Horizon 2020 GEN4OLIVE project, five major Mediterranean germplasm banks (located in Spain, Greece, Italy, Turkiye, and Morocco) 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 photographing and morphological characterisation. While most protocols were adapted from previously published scientific literature to ensure ease of implementation, replicability, and easy and fast phenotyping across different research facilities, novel methodologies for frost tolerance and standardised artistic and technical photography were developed de novo. The implementation of these consensus methods across five different countries proved highly successful. This methodological framework enabled the generation of the largest harmonised, publicly available dataset on olive genetic resources to date, effectively mitigating genotype-by-environment (GxE) interaction distortions through the systematic use of shared benchmark cultivars (known also as reference cultivars). So, this compendium methods provides a robust, highly replicable reference point for the standardisation of olive germplasm characterisation, facilitating future global pre-breeding efforts and ensuring international data interoperability.