The recovery phase duration shapes plant responses to recurring heat stresses in winter oilseed rape (Brassica napus L.)

The accelerating pace of climate change increases heatwave frequency, challenging crop acclimation. A greenhouse experiment in oilseed rape investigated how prior heat exposure influences seed yield and quality after an intense heat stress (HS). Three sequences of two heat events were tested, differing in recovery duration. We hypothesized that the interval between stresses would determine the priming effect of an initial mild stress (early, intermediate, late) on subsequent HS. Results showed that yield components were not much affected by the heat modalities reflecting the high plasticity of oilseed rape. However, HS-containing sequences significantly reduced seed biomass, with the extent of reduction depending on the timing of the first mild stress. Seed concentration of fatty acids and the seed storage capacity were impacted by the cumulated duration of heat days but the sequence with the intermediate recovery duration (ca. 45°Cd before the intense heat) led to mitigate HS-induced negative effects. Dynamic measurements of fluorescence-based chlorophyll parameters were shown to be able to catch the specificities of the heat sequences and to reflect the differences in final seed biomass accumulation. Overall, our study highlights the critical role of the time interval between stress events in sustaining priming effects induced by the initial stress. More broadly, this work demonstrates the fine tuning of stress priming and advances our understanding of this often-overlooked aspect of stress memory by uncovering the climate-related determinants that shape crop acclimation strategies. • Crop performance under heat depended on prior mild stress and recovery length. • Seed biomass reduction from intense heat depended on timing of first mild stress. • Short recovery phases lessen unsaturated fatty acid loss, suggesting a priming effect • Seed storage capacity was shaped by total heat days, with short recovery easing effects. • Chlorophyll fluorescence indices reliably predict heat impacts on yield and quality.