Accounting for the impact of genotype and environment on variation in leaf respiration of wheat in Mexico and Australia

An approach to improving radiation use efficiency (RUE) in wheat is to screen for variability in rates of leaf respiration in darkness (R_dark). We used a high-throughput system to quantify variation in R_dark among a diverse range of spring wheat genotypes (301 lines) grown in two countries (Mexico and Australia) and two seasons (2017 and 2018), and in doing so quantify the relative importance of genotype (G) and environment (E) in influencing variations in leaf R_dark. Through careful design, residual (unexplained) variation represented <10% of the total observed. Up to a third of the variation in R_dark (and related traits) was under genetic control. This suggests opportunities for breeders to use R_dark as a novel selection tool. In addition, E accounted for more than half of the total variation in area-based rates of R_dark. Here, the day of measurement was crucial, suggesting that day-to-day variations in the environment influence rates of R_dark measured at a common temperature. Overall, this study provides new insights into the role G and E play in determining variation in rates of leaf R_dark of one of the most important cereal crops, with implications for future improvements in carbon use efficiency and yield.