Resilience of rapeseed to heat stress during grain filling in a high yielding environment

Global climate change is driving the temperature increase, which negatively impacts on crop production. Most heat stress studies in rapeseed have been conducted under controlled conditions, limiting their results to true field crops. This study aimed to assess the sensitivity of rapeseed to temperature increase during two phases of the grain filling period in southern Chile, a high-yield potential environment. To our knowledge, this is the first field study evaluating the effects of heat stress at different phases of grain filling in rapeseed. Three field experiments were conducted with two adapted spring rapeseed hybrids, Lumen and Solar CL, under three temperature treatments: a control at ambient temperature, a 5{degrees}C increase from the beginning of flowering to 15 days after flowering (DAF), and the same increase from 15 to 30 DAF. Crop and climate variables, including air temperature and solar radiation were recorded along the experiments. Slight effects on grain yield due to heat stress were found, however, the hybrids exhibited different sensitivities, with Lumen being less affected than Solar CL. Grian yield of the last hybrid showed positive association with photothermal quotient and negatively with temperature, while Lumen did not show relationship. The most significant impact on grain yield occurred during the first half of grain filling (0-15 DAF), resulting in a reduction of 26.8% of grain number in Solar CL, compared to a 6.0% reduction in Lumen across experiments. Grain weight remained little affected by thermal stress, indicating its conservative behaviour and tolerance in southern Chile conditions. Grain oil concentration was scarcely sensitive, while grain protein concentration increased under heat stress. The low impact on the crop outcomes of our studies may be attributed to the lower background temperature of southern Chile, suggesting that this environment may confer greater rapeseed heat tolerance during grain filling than in other agroecosystems.