Field-Based Portable Heat Chambers for the Determination of Day-Time Heat Stress in Canola (Brassica napus L.)

To cope with future changing climates, it is paramount to not only breed for heat-tolerant germplasm but also test the heat tolerance of crops in reliable field-based experiments for commercial adoption of the research. There is little published research assessing the day-time heat stress in canola during the optimal growing period under field conditions. Additionally, the impact of heat stress and its interaction with water availability at critical reproductive growth stages appears severely understudied in field experiments. Therefore, a novel system for simulating heat stress was specifically developed and tested for canola plots. Eight portable heat chambers were constructed with clear polycarbonate sheets, fitted with two fan heaters and a ceiling fan that were controlled by a commercial thermostat. Heat stress of 33°C was simulated as heat waves for the eight-day period during key reproductive stages (start of flowering, mid-flowering, end of flowering, and late-podding). The heating system was able to elevate and maintain high temperature consistently across water regimes, validating the system's successful imposition of heat stress. The impact of heat stress was confirmed through a statistically significant plot grain yield reduction that was associated with a reduction in total pods, fertile pods, and seed number. Averaged across different water regimes, heat stress at advanced reproductive developmental stages resulted in grain yield reduction ranging from 39.9% at mid-flowering to 56.2% at the end of flowering compared to the non-stressed control. While the system and methodology developed are successful in canola heat tolerance breeding programs, there is potential that this methodology is scalable to other crops or plants.