Does early vigor predict drought resistance in Helianthus annuus L.?
Increased drought associated with climate change is expected to negatively impact plant survival, productivity, and fitness. Generally, faster growing plants are expected to be less tolerant of abiotic stresses such as drought than slower growing plants, particularly when strategies allowing plants to morphologically avoid drought are not favored. We investigated this using ten cultivated inbred lines of sunflower that represent a substantial portion of allelic diversity among cultivated sunflower. Specifically, we asked:
Q1: Is there variation among cultivated sunflower lines in resistance to chronic drought imposed at budding?
Q2: How does variation in juvenile growth rate under well-watered conditions relate to variation in subsequent drought tolerance?
Plants were initially grown under well-watered conditions until budding and assessed for height growth through time. At budding, treatments of continued well-watered or drought conditions were initiated, with drought imposed using an automatic irrigation system that controlled sustained low soil moisture. This timing was chosen because drought is known to strongly affect yield during reproductive development in sunflower. Drought tolerance was calculated as percent reduction in performance under drought as compared to the well-watered treatment for each trait.
Preliminary results indicate a significant effect of drought on measures of plant performance such as height (0-50% reduction), biomass (38-80% reduction), floral tissue mass (30-87% reduction), and disc diameter (8-40% reduction), but not root mass ratio. Lines differ significantly for early height relative growth rate and phenology, and final height and biomass. However, there does not appear to be a relationship between early height relative growth rate and tolerance of sustained moisture limitation during reproductive phase. Thus, over the range of relative growth rates for these cultivated lines, there does not appear to be an inherent tradeoff between drought tolerance and juvenile relative growth rate.