Identifying superior photosynthetic efficiency traits in canola (Brassica napus L.) germplasm
Creators: Guerrero Zurita, Fernando
Publisher: name: University of Alberta Library
Year: 2024

<p>Canada is the world’s largest producer of canola (Brassica napus), contributing 54% of global production in 2021. However, Canada’s canola yield is not growing at the required pace to reach the targets and compete with other canola producers. To address this issue, multifaceted approaches must be designed to develop high-yielding canola cultivars. Improving the photosynthesis of the crop is a promising pathway to reach the goal. However, photosynthetic efficiency of the crop is often threatened by extreme weather fluctuation resulting from climate change. In that sense, deepening our understanding on the physiological mechanisms of photosynthesis under challenging environmental conditions would be crucial to optimize and better design efforts to enhance canola yield. <br>
The first objective of this study was to conduct a comprehensive meta-analysis to i) quantify the effect of single and combined abiotic stresses on chlorophyll fluorescence (CF) and gas exchange (GE) parameters, and ii) to identify the interaction of drought, temperature, and light as combined stresses on CF and GE parameters in a wide variety of plant species. Plants respond differently when exposed to individual or combined stresses. In the presence of two abiotic stresses, plant responses can either be antagonistic or synergistic: combined drought and light stress resulted mostly in synergistic interactions; high light intensities alleviate drought stress at the stomata level but at the thylakoid level, photosystem II (PSII) is photoinhibited. Combined drought and heat stress also indicated that drought had a more predominant effect than heat stress. Combined temperature and light stress were predominantly antagonistic at the thylakoid level, due to heat dissipation and the upregulation of photosystem I, triggered by heat-induced photoinhibition of PSII.<br>
The second objective was to screen 168 genetically diverse canola accessions using CF, GE, and agronomic parameters to identify the accessions carrying superior and heritable PE traits for use in breeding. For this, five rainfed field experiments were conducted during the 2021, 2022, and 2023 growing seasons in Edmonton, Canada. Three distinct groups of accessions with contrasting PE physiology were identified: high-yielding accessions with optimized stomatal behavior (leaf transpiration as a superior trait), useful for drought tolerance; high-yielding accessions with enhanced excess energy dissipation (non-photochemical quenching as a superior trait), beneficial for temperature and light stress tolerance; and moderate-yielding accessions with increased photosystem II (PSII) efficiency (maximum photochemical yield of PSII as a superior trait), valuable for enhanced light-harvesting under optimal conditions.<br>
    This study offers a new perspective on the role of photosynthesis to enhance canola yield under changing environmental conditions due to climate change. Focusing on combined abiotic stresses at varying severity levels, in conjunction with climate data, can aid policymakers in designing more effective climate change mitigation strategies. The next step in canola breeding should involve integrating insights from diverse PE physiology with high-throughput tools and remote sensing for rapid photosynthesis measurement. This approach would enable breeders to develop PE-oriented strategies to create multi-stress-tolerant genotypes, ultimately leading to improved canola yields that benefit crop producers.</p>