Early drought stress triggers contrasting trait responses in spring barley

Drought stress tolerance in plants, a complex trait influenced by various factors, poses significant challenges for breeding. Increasingly frequent droughts during early plant development emphasize the need to understand how traits interact under stress conditions. This study aims to investigate traits of interest for early drought stress tolerance and the relationship of physiological and yield-related traits in spring barley. A diverse set of barley genotypes were grown under greenhouse and field conditions using a rainout-shelter for two years. Drought stress was applied at the third leaf stage with soil water capacity set at 20 %, while the control group was watered until 50 %. Traits such as stomatal conductance, proline content, and yield (here grain biomass) were analyzed. Results showed high genotypic variation in traits like plant biomass, water use efficiency, and grain biomass under early drought stress. Notably, proline content was negatively correlated with grain biomass (r = -0.66). Plant height had the highest heritability (h² = 0.96), and both plant height and grains per ear had strong correlations between greenhouse and field conditions (r = 0.78 and r = 0.84). Early drought tolerant genotypes were identified by their fast adaptation to re-watering through high water use, while sensitive genotypes were characterized by elevated proline content. Understanding the response and relationship between physiological and yield-related traits is crucial for selecting barley lines with improved early drought tolerance for breeding. • Physiological and yield traits of barley were significantly affected by early drought with notable genotypic variation. • Results revealed three drought-tolerance clusters, with water use efficiency and grain biomass as key traits. • Early drought-tolerant genotypes performed strongly in traits during recovery rather than during drought stress. • Water use efficiency, plant height and grains per ear showed the strongest greenhouse-field correlation under early drought.