Fennel (Foeniculum vulgare Mill.) is a crucial medicinal plant that has garnered significant attention in agriculture under climate change conditions due to its high tolerance to abiotic stresses. To adapt to recurring environmental challenges, plants have evolved a sophisticated mechanism known as stress memory, whereby an initial exposure to a mild stress (priming) enhances the plantʹs response to subsequent severe stresses. However, the physiological an‎d epigenetic basis of this phenomenon in fennel remains unknown. This research was conducted to investigate salinity an‎d drought stress memory in selec‎ted genotypes from the global fennel germplasm, representing different subspecies. The study aimed to eva‎luate their morphophysiological, biochemical, an‎d epigenetic (DNA methylation) responses, an‎d ultimately to identify superior genotypes for future breeding programs. Two separate greenhouse experiments were carried out for salinity an‎d drought stress according to a ran‎domized complete block design. In each experiment, fennel genotypes were assessed under three conditions: control (N), a single severe stress (S2 for salinity an‎d D2 for drought), an‎d a double-stress/primed condition (S1S2 for salinity an‎d D1D2 for drought), where an initial mild stress was followed by a secondary severe stress. A comprehensive set of traits was measured, including morphological (shoot an‎d root biomass), physiological (leaf relative water content, photosynthetic pigments), biochemical (antioxidant enzymes, proline, malondialdehyde), ionic (sodium an‎d potassium), an‎d epigenetic (percentage of DNA cytosine methylation) parameters. The results clearly demonstrated the existence of a positive an‎d efficient stress memory in fennel. In both salinity an‎d drought studies, primed genotypes exhibited significantly better biomass production an‎d water status (RWC) compared to non-primed plants. The mechanisms underlying this memory under salinity stress were attributed to more efficient management of ionic homeostasis an‎d an optimized antioxidant defense system, which, at the epigenetic level, was directly correlated with the capacity for dynamic resetting of DNA methylation patterns. Under drought stress, memory functioned primarily through a greater investment in root biomass. Nonetheless, considerable genetic diversity for stress memory an‎d its associated mechanisms was observed within the germplasm. On the other han‎d, under salinity stress, some genotypes responded by enhancing sodium exclusion mechanisms in the roots, while others relied on increased tissue tolerance via sodium sequestration in leaf vacuoles. Furthermore, these physiological responses were directly linked to epigenetic flexibility. The genotype with positive memory (d14) demonstrated the ability to reset its DNA methylation pattern post-stress, whereas the genotype lacking memory (d15) failed to perform this epigenetic reset. Multivariate analyses an‎d tolerance indices identified genotypes a4 (subsp. azoricum, showing broad adaptation), d19 an‎d d13 (subsp. dulce, with root-based drought memory), an‎d d14 an‎d a1 (with ion-management-based salinity memory) as superior genetic resources for breeding programs. In conclusion, this research reveals that the ability to dynamically manage an‎d reconfigure physiological an‎d epigenetic networks lies at the core of successful stress memory. Sufficient genetic variation exists to treat stress memory as a selec‎table quantitative trait, which can enhance the efficiency of breeding for climate-resilient fennel cultivars.

محمد مهدي مجيدي

حسن كريم مجني , محمدرضا مصدقي