WHEATZARD (WHEAT ZEROING IN ON ADAPTIVE RESPONSE TO DROUGHT): A STUDY TO EVALUATE WATER STRESS IMPACT ON WHEAT PHENOLOGY SIMULATIONS || WHEATZARD (WHEAT ZEROING IN ON ADAPTIVE RESPONSE TO DROUGHT): UNO STUDIO PER LA VALUTAZIONE DELL'IMPATTO DELLO STRESS IDRICO SULLE SIMULAZIONI FENOLOGICHE DEL FRUMENTO

Plants’ phenological development depends on air temperature as major driving cue. The relationship between air temperature and plants phenology has been formalized via the Growing Degree Days (GDDs) concept, defined as the thermal time accumulated during a time step, generally one day (24 hours). Traditional GDD models do not take into account other constraining factors than temperature as vernalization, photoperiod and water stress (WS). Despite several experimental evidences have demonstrated that phenology can be hastened or slowed down by WS, its representation in plant phenology model is still debated. One potential approach is to modulate the accumulation of GDDs using a "water stress factor," analogous to existing adjustments for vernalization and photoperiod. This is particularly relevant given that the occurrence of WS, considering its timing, duration, frequency, and severity throughout the crop life cycle, varies markedly across environments and agricultural seasons, thereby complicating the identification of consistent phenological patterns. The objectives of this study were to evaluate the phenological responses of wheat to WS using a 20-year dataset (2003–2023) of field observations collected in a long-term experiment located in Bologna (Emilia-Romagna). A hourly time step phenological model was calibrated and validated to account for temperature, vernalization, and photoperiod effects. Then, a simplified WS model has been used to study the dynamic correlation of WS during the growing season in order to understand its influence on the timing of key developmental stages. The results showed that the correlation between WS and wheat phenology strongly varied during the crop cycle, both in terms of direction and intensity. Overall, results showed the tendency of the crop to alternate an initial phases of drought avoidance, in which phenology was slowed down, with a phase of drought escape, in which the opposite behavior, i.e., accelerating phenology, was implemented. Incorporating a WS factor could enhance the model’s responsiveness to water-limited conditions and potentially reduce prediction errors.