Temporal phenotypic responses of early vegetative maize to heat, drought, and combined stresses

Understanding how maize responds to heat, drought, and the combination of stresses is essential for developing resilient cultivars for future climates. We characterized temporal phenotypic responses of 47 genetically diverse Zea mays inbred lines grown under control, drought, heat, and combined drought-heat stresses for 13 days in a high-throughput phenotyping platform. Plant area was modeled over time using Bayesian hierarchical growth analysis. Treatment explained the largest proportion of phenotypic variance, while genotype × treatment interaction accounted for up to 35% of color variation. Growth and development responses were strongly genotype-dependent, and combined-stress responses were more closely related to heat rather than drought responses. Heat primarily reduced height and impacted growth but not development, whereas drought reduced leaf number and greenness and impacted both growth and development, indicating distinct physiological effects. Despite strong genotype effects, subpopulation explained differences only in drought responses. In follow-up experiments, these early vegetative stresses had a significant impact on days to anthesis and plant area even long after the stresses had stopped. Collectively, these results emphasize that combined-stress tolerance cannot be inferred from a single-stress, and that there is potential for improving early environmental stress tolerance that will impact later plant phenotypes.