Somatic stress memory: Investigating the adaptive responses of old and modern wheat genotypes to recurrent combined heat and deficit irrigation stress

• No priming effects in photosynthetic and fluorescence parameters, but yield traits showed priming responses. • Additive stress effects in physiological parameters in plants primed at stem elongation (SE+HD), but not in plants primed at booting (B+HD). • Yield parameters showed stronger priming responses under SE+HD than B+HD stress. • Modern genotypes outperformed old in many physiological traits under heat stress. • LM20 outperformed the old genotypes in some photosynthetic and fluorescence traits under B+HD, though a gradient remained between tolerant and susceptible lines. In view of the importance of stress memory in plant adaptation to extreme weather events, our study focused on capturing the priming effects on stress responses at later developmental stages in diverse wheat genotypes. Two modern (LM20, LM17) and two old (KU19, KU12) genotypes, out of which LM20 and KU19 are heat tolerant, and LM17 and KU12 are heat susceptible. Plants were exposed to moderate combined heat (30/23 °C DT/NT) and deficit irrigation (50 % PHC) (priming at the stem elongation or booting stages), followed by recurrent combined heat (35/28 °C) and deficit irrigation (50 % PHC) at post-anthesis. The results showed that primed plants retain stress memory and outperformed non-primed plants in yield traits. Priming stress at different phenophases elicited varied stress responses under extreme post-anthesis stress. Tolerant genotypes primed at booting maintained both the photosynthetic and chlorophyll fluorescence parameters during post-anthesis stress (B+HD), while plants primed at stem elongation followed by recurrent post-anthesis stress (SE+HD) achieved higher yields. Modern genotypes outperformed old genotypes in many photosynthetic parameters under heat stress. The modern genotype LM20 excelled under B+HD stress due to improved biochemical regulations and sustained better dry biomass and yield under SE+HD stress than old genotypes. Despite the new outperforming old genotypes, a gradient was seen between tolerant and susceptible genotypes. These findings show that stress priming can enhance yield resilience in wheat under recurrent combined heat and deficit irrigation, with the extent of benefit depending on genotype and priming stage.