Effects of heat and drought on canola (Brassica napus L.) yield, oil, and protein: A meta-analysis

Canola (Brassica napus L.) is a major oilseed crop for edible and industrial uses. Climate change, characterized by extreme heat and drought conditions, can affect canola seed yield and quality (protein and oil), restricting grower capacity to keep pace with growing demand. However, estimating the influence of future climate on such complex traits is challenging due to biophysical interactions and crop adaptations to abiotic stresses. Current scientific literature reports contrasting impacts on the effect of heat and drought for canola productivity, mainly linked to changes in magnitude and duration of the stress. To better understand how drought and heat affect canola seed yield and quality (mainly protein and oil), a meta-analysis was executed to compile a total of 39 papers (1794 observations). The aims of this research were to i) quantify the impact of different timing and duration of heat and drought stresses on canola seed yield, oil yield, and seed quality (oil and protein concentration), and ii) study the effect of short-term stresses on seed quality, yield and its components (seed number and seed weight). This review study highlighted the magnitude and direction of overall and different stress impacts on canola; and some of the main limitations in the current scientific literature. Briefly, the main outcomes of this review highlighted that i) early heat stress(before end of flowering) had the largest impact on canola seed yield, as a short stress, ii) drought caused greatest yield impact when imposed for a long duration during flowering or a shorter duration during pod setting, and iii) short stresses had large impacts on seed oil concentration mainly during pod setting. More studies with standard stress levels and detailed information of abiotic stresses on reproductive growth stages are needed. This meta-analysis provides critical information for crop management, guiding development of cultivars linked to tolerance to abiotic stresses for breeding programs, and the future direction of canola adoption and production.