New publication - Experimentally assessed chill and heat requirements for Prunus cultivars vary by region. New publication - Experimentally assessed chill and heat requirements for Prunus cultivars vary by region.

In a new study, we experimentally assessed the chill and heat requirements of four Prunus species across contrasting Mediterranean climates. The work focused on almond, apricot, Japanese plum and sweet cherry, covering 17 cultivars that are important to commercial production. Measurements were carried out in research orchards in Spain, Morocco and Tunisia within the AdaMedOr project (Adapting Mediterranean Orchards).

The study, led by Alvaro Delgado from CEBAS-CSIC (Murcia, Spain) and Erica Fadón from CITA (Zaragoza, Spain), applied a standardized protocol for dormancy assessment, also developed in AdaMedOr. Throughout winter, young branches were sampled and transferred to greenhouse conditions to monitor bud development under warm temperatures. This approach allowed us to track dormancy progression and quantify the chill and heat needed for flowering. 

We found that the same cultivar can express different combinations of chill and heat requirements depending on where it is grown. Local climate played a stronger role than year-to-year variation in shaping agroclimatic requirements. Endo-dormancy duration varied across sites, yet cultivars often reached flowering at similar times, showing that chill deficits can be compensated by additional heat. This compensation was not uniform across species or cultivars, highlighting that plasticity differs within the Prunus group. Interestingly, longer endo-dormancy periods did not always coincide with higher chilling requirements, challenging common assumptions about chill sensitivity.

Overall, the results reveal substantial phenological flexibility, which enables cultivation of the same cultivar across a wide range of Mediterranean environments. At the same time, they underscore the need to account for climate-specific responses when selecting cultivars and designing orchards. These findings provide valuable experimental data for improving chill and heat models and contribute to understanding how fruit trees adjust to warming winters. They also support the development of resilient orchard systems across the Mediterranean under both current and future climates.

For more details, please refer to our open-access paper:

Delgado, A., Ruiz, D., Rodrigo, J., Luedeling, E., Fernandez, E., Mojahid, H., Guerro, B.I., Guerra, E., Santolaria, N., Irisarri, P., Egea, J.A., Caspersen, L., Ben Mimoun, M., Hajjioui, H., Erami, M., Kodad, O., El Yaacoubi, A., Ghrab, M., Benmoussa, H., Borgini, N., Elloumi, O., Fadón, E. (2026): Cultivar plasticity in temperate fruit trees across the Mediterranean region: Different combinations of chill and heat lead to dormancy release. European Journal of Agronomy 172, 127884. https://doi.org/10.1016/j.eja.2025.127884