Canopy cooling traits associated with yield performance in heat-stressed oat

Abstract

In the upper U.S. Midwest, oat is a promising crop for diversifying local cropping systems and providing local consumers with a healthy food option. However, as a result of climate change, the crop is facing increasingly severe episodes of high temperature (HT) stress during reproductive development, which limit its yield potential. The goal of this 3-year field study was to identify locally-adapted HT stress-tolerant oat breeding lines, propose a parsimonious mechanistic basis for HT stress tolerance and leverage it to develop a screening method with the potential to support a breeding program. Because water supply is rarely limiting in the region, we tested the hypothesis that canopy latent cooling would be a desirable trait. To this end, we deployed “heat tents” on a core panel of 30 oat lines between booting and heading, where we measured i) grain yield and quality traits (protein, oil and beta-glucan), ii) pollen viability, percentage of filled florets, and grain number, iii) gas exchange and canopy cooling parameters (e.g., photosynthesis, transpiration rate, stomatal conductance, canopy temperature depression). Additionally, we developed a thermal imaging approach to remotely quantify canopy temperature on contrasted lines. Significant genotypic variability was detected in yield and quality trait responses to the HT stress and a physiological path model identified canopy cooling as a main process explaining superior yield performance of HT stress tolerant lines. Interestingly, pollen viability was not found to be the main driver of yield declines, suggesting a role played by other reproductive processes, including those underlying female tissue/organs sensitivity to HT stress. Finally, canopy cooling parameters correlated with geographic locations of breeding programs from which the tested germplasm originated, indicating that they are under selection. Overall, this study opens the way for a breeding program targeting the development of more climate-resilient oats adapted to northern climates.