Files
Abstract
Drought is major agricultural stress that reduces crop productivity and is predicted to increase in frequency and severity due to climate change. As such, we need crops that can withstand drought to feed a growing population. In this dissertation, I explore variation in leaf anatomy across cultivated and wild sunflower (Helianthus annuus L.). Stomatal and vein traits are important for plant-water relations, influencing both gas exchange and water transport. I quantified trait variation across the cultivated sunflower gene pool and associated it with genomic regions, finding associations for numerous traits but limited colocalization between traits despite pervasive trait-trait correlations. However, I was able to map major axes containing traits relating to gas exchange and leaf construction. Next, I used a subset of lines to investigate trait variation and plasticity under multiple levels of drought stress. I again found substantial variation in traits and that trait plasticity increased with increasing drought stress, along with the same major axes of trait variation. This suggests the existence of persistent functional relationships among traits. I also found that four key leaf traits were strongly predictive of plant performance. Finally, I analyzed leaf trait variation and its relationship withenvironmental variables and performance in wild sunflower in a common garden setting. Once again, I found substantial variation across traits, with significant population effects indicating the existence of genetic variation for the majority of these traits across the wild sunflower range. Growth/biomass-related traits showed much stronger environmental associations compared to finer-scale leaf traits. I also found that many of the same traits that exhibited predictive power in cultivated sunflower could be used to predict plant performance in wild sunflower. Taken together, my results show that there is variation in leaf anatomical traits that are important for plant-water relations in both cultivated and wild sunflower, and that these traits exhibit substantial plasticity under drought. This sort of information on the extent and nature of trait variation and covariation has the potential to influence breeding strategies aimed at modifying leaf traits in response to looming environmental challenges.