Document Type

Thesis

Date of Degree Completion

Winter 2020

Degree Name

Master of Science (MS)

Department

Biology

Committee Chair

Jennifer Dechaine

Second Committee Member

Mary E. Poulson

Third Committee Member

Eric A. Graham

Abstract

Longer and more intense droughts are predicted to become more common in the coming century due to anthropogenic climate change. Drought can reduce crop yield and decrease food security. In order to mitigate the negative effects of drought on crop production, it is important to elucidate the underlying mechanisms that promote drought stress resistance in crop plants. Floral traits impact yield, especially in oilseed crops such as sunflower (Helianthus annuus), but their susceptibility to drought stress is understudied. The goal of this study was to describe the floral trait architecture of H. annuus crop lines under drought versus well-watered conditions and examine the relationship between these traits and drought resistance. Forty H. annuus lines from the Sunflower Association Mapping population were assessed for size traits (height, stem diameter, head diameter and mass) and floral traits (floret lengths, nectar volume and concentration) in a field experiment under well-watered and drought conditions. Drought stress resulted in a decrease for most size traits, as well as shorter corollas and styles, and a decrease in average nectar volume. Floral sucrose concentration was unaffected by drought stress; however, line and line by treatment variation was observed for this trait and for average nectar volume. Line effects were highly significant for each trait, indicating that all traits measured have a strong genetic component. Lines differed significantly in their response to drought for head diameter at time of flowering, anther length, and days to flower. Larger size generally increased drought resistance. Nectar sucrose concentration had a significant positive correlation with final height of the plant and seed total in the watered treatment, indicating that larger plants with higher seed totals had higher nectar sucrose concentrations by volume than those in the drought treatment. The results involving shortened corolla and style lengths during drought should be studied further to determine whether there is an advantage for agricultural pollinators. Anther length was the only floral trait correlated with drought resistance. Anther length should be studied further in order to determine if its conservation across treatments can be useful for improving future H. annuus marker assisted selection efforts.

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