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Abstract
Climate change is expected to increase the frequency and severity of many abiotic stressors on plants. The common sunflower (Helianthus annuus L.) is an economically important oilseed crop grown in many regions which are subject to these climate change related stressors. The wild progenitor of cultivated sunflower (also H. annuus L.) is native to North America and thrives in many different environments. In this dissertation, I explore the phenotypic and transcriptomic responses of both wild and cultivated sunflower to several climate change related abiotic stresses. I demonstrate an association between the expression levels of two stearoyl-ACP desaturase genes and a latitudinal gradient in the saturated to unsaturated fatty acid ratio of wild sunflower seeds. I also examine how three osmotic related stresses, a dry-down stress, a salt stress, and a common simulated drought stress via polyethylene glycol (PEG), compare to a generalized nutrient stress. Those results show how varied the phenotypic and transcriptomic response can be to three putatively related stress, and in particular, provide evidence that PEG invokes a transcriptomic response quite different from that of a dry-down stress, suggesting that PEG is not useful as a means of simulating drought stress in plants. Furthermore, I explore the relationship between drought stress, heat stress and the two stresses in isolation, showing that the effects of a combined heat and drought stress are distinct from that of either stress in isolation. Finally, I describe how in vitro pollen tube growth varies across genotypes and temperatures. In summary, my results make significant contributions to our understanding of how sunflowers respond to abiotic stress and provide insight into the ways in which breeders should approach the development of abiotic stress tolerant cultivars in the future.