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Abstract
Salinity and drought are two abiotic stresses that reduce crop productivity globally. It is generally expected that crops are less stress tolerant than their wild relatives, suggesting traits from wild germplasm can be used to improve crop stress tolerance. My dissertation focuses on crops and their wild counterparts’ responses to abiotic stress and the relationships of morphological and physiological traits with tolerance. I explored salinity and drought stress responses in wild and cultivated Helianthus annuus in separate greenhouse experiments and assessed drought recovery in cultivated H. annuus in another experiment. For comparisons of cultivated and wild H. annuus, stress tolerance was measured in two ways: as the proportional reduction in total biomass and as the deviation from expected performance under stress based on its vigor (expectation-deviation tolerance). When tolerance was assessed as proportional reduction, I found that wild H. annuus were more tolerant than cultivated to both salinity and drought. However, when assessed as expectation-deviation tolerance, I found no difference between cultivated and wild H. annuus under salinity stress, due to an association between vigor and proportional reduction in biomass, whereby more vigorous accessions (generally cultivated) decreased more under stress. Under drought, I found no such relationship. Overall, trait responses differed between wild and cultivated accessions under salinity stress but not under drought. Associations between traits and tolerance were generally lacking, regardless of stress type or domestication status. During drought recovery, I found previously droughted cultivated genotypes increased their growth rate, partially compensating for growth losses during drought. Higher growth rate was associated with increased photosynthesis and greater allocation to leaves. In summary, I found support for the expectation that cultivated sunflowers are less stress tolerant than their wild progenitors, but conditionally based on stress type and metric of tolerance. Moreover, linking specific traits to tolerance remains challenging, making it difficult to select specific traits from wild germplasm to introduce into crops. My results on drought recovery highlight the assessment of growth during stress and during rehydration, as stresses can be transient. Though difficult, understanding plant responses to abiotic stress is vital research needed to meet increased global food demands.