Increasing the potassium use efficiency of crops

Increasing the potassium use efficiency (KUE) of crops will be important in satisfying growing demand for food that is cost-effective and has minimal environmental consequences. The work presented in this thesis contributes to this aim by exploring the measurement of KUE and identifying drivers responsible for differences in KUE between rice genotypes at the physiological and genetic levels. In Chapter 2, a mathematical model was constructed based on growth experiments using cv. IR64 rice plants. Subsequently, sensitivity analysis was used to assess how best to measure KUE experimentally, showing how KUE could be comprehensively measured using a small selection of metrics. KUE was then quantified in over 300 rice genotypes in Chapter 3. From this, high performing rice genotypes were identified along with associations between KUE metrics and physiological traits. While key physiological drivers of differences between genotypes differed with metrics, the replacement of potassium by sodium was consistently found to aid KUE. In Chapter 4, differences in KUE between rice genotypes were then explored at the genetic level, using genome-wide association studies (GWAS) to describe the genetic underpinnings of KUE for the first time. This resulted in the identification of KUE-relevant quantitative trait loci (QTLs) and candidate genes. Both novel and previously described QTLs for KUE were found and links between the sub-population structure present in rice and the genetic architecture of KUE were uncovered. Furthermore, several genes coding for proteins with regulatory functions were identified in GWAS analyses, as were genes for sodium transport proteins. Taken together, the findings of the work presented in this thesis could be used to inform future KUE studies as well as providing candidate physiological traits and genetic loci for crop improvement.