| Summary: | Upland cotton (Gossypium hirsutum) is cultivated in many contrasting production environments and is often subjected to a combination of abiotic stresses such as high temperature (heat) and water deficit (drought) stress. In the present dissertation, two recombinant inbred line populations were constructed from heat-tolerant and -susceptible parental lines and evaluated in multiple environments under the presence of two treatments, well-watered (heat stress) and water-limited in the presence of high temperature (combination of heat and drought stresses). We assessed two agronomic traits, seed cotton yield and lint yield, as well as six fiber traits, lint percent, micronaire, length, strength, uniformity, and elongation. Fiber traits had moderate to very high broad-sense heritabilities, while heritabilities of agronomic traits were lower for both populations in each irrigation regime. Correlations between traits were not effected by the irrigation regimes. A stability analysis across the range of environments tested demonstrated that high seed cotton yield performance and greater stability may play a role in tolerance to the combination of heat and drought stresses. Additionally, we constructed linkage maps for both recombinant inbred line populations and mapped QTL controlling variation all eight traits. A total of 138 QTL were identified across populations for the eight traits. Climate change in the form of rising temperatures and reduced water availability will increase the occurrence of the combination of heat and drought stresses in a farmer's field. Thus, current cotton breeding programs will need to focus on the development of cotton varieties tolerant to heat, drought, and the combination of the two.
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