Samenvatting

Drought, caused by climate change, poses a significant threat to the production of barley. To ensure high yields, drought adaptation in barley is critical. Roots are primarily responsible for water uptake, and during drought, when water levels are low, deep rooting traits are crucial for developing drought-tolerant crops. However, roots are difficult to study due to their location and therefore a
different phenotyping technique using above-ground traits is essential to determine the root system architecture (RSA) of barley during drought. In this study, the relationship between canopy temperature (CT) and rooting depth is explored through thermography. A controlled lysimeter experiment with four genotypes under both drought and well-watered conditions, as well as the
results of a large-scale rainfed field trial with 20 genotypes, were used to grow and measure the CT of barley across drought, well-watered, and wet environments. The lysimeter experiment revealed significant differences in CT between climatic treatments (P<.001), with barley cultivars under drought experiencing warmer canopies. Additionally, some significant differences in CT were also
observed between genotypes (P <.05). Barley cultivars with shallow root systems displayed cooler canopies in wet field conditions. Well-watered CT traits were positively correlated with the wet CT traits of the field trial while drought CT traits were negatively correlated with the field CT. Although deeper rooting systems and cooler canopies during drought were suggested by a decrease in CT and an increase in stomatal conductance around flowering time, further research and analyses of the root samples grown under drought conditions are essential to confirm these results. In this study, CT has proven to be a reliable and high-throughput method for breeders to screen root traits and develop future drought-tolerant barley cultivars.