assessment of drought-related traits for rainfed wheat under current and future climates

Objective: this research aimed to employ crop simulation modeling to identify key traits for improving water-limited yield (yw) of rainfed wheat (triticum aestivum l.) across iran's diverse agro-climatic zones under current and projected future climates.methods: using the global yield gap atlas (gyga) upscaling protocol and the ssm-icrop model, simulations were conducted for 32 reference weather stations (rwss) representing 72% of iran's national rainfed wheat area. historical (2000–2015) and future (2041–2060; rcp4.5, +1.9 °c, 500 ppm co₂) climate scenarios were analyzed to evaluate the impact of modifying physiological traits.results: under the current climate, the national mean simulated yw was 2.02 t ha⁻¹, ranging from 1.04 to 4.41 t ha⁻¹. future climate increased mean yw to 2.87 t ha⁻¹ (range: 1.54–5.33 t ha⁻¹), due to co₂ fertilization and accelerated development, alleviating terminal drought. trait analysis revealed that increasing the grain-filling duration by 20% was the most effective and consistent strategy, boosting national mean yield by 0.30 t ha⁻¹ (current climate) and 0.47 t ha⁻¹ (future climate) in high-rainfall caspian sea zones. conversely, shortening the vegetative phase by 20% increased yields by up to 0.1 t ha⁻¹ in terminal-drought regions of the zagros mountains but reduced yields in eastern and northeastern iran, with negative impacts intensifying under future climate. decreasing phyllochron provided modest yield gains (>5% in 7 rwss) under the current climate, but its benefits diminished under future warming. increasing radiation use efficiency had a limited impact under both climate conditions. spatial analysis showed the primary key trait was extending grain-filling for 13 rwss (current) and 16 rwss (future), while shortening the vegetative phase was key for 11 and 12 rwss, respectively. critically, in 9 rwss across western/northwestern iran, the optimal trait shifted with climate change, underscoring strong g×e interactions.conclusion: breeding for enhanced grain-filling duration offers a robust, climate-resilient strategy for most parts of iran. in contrast, manipulating vegetative growth duration requires precise, region-specific targeting due to its variable and sometimes negative effects. these results provide a spatially explicit blueprint for trait-based breeding to enhance the productivity and climate resilience of iran's rainfed wheat systems.