McCoy, Erik2020-08-252020-08-252020-04https://hdl.handle.net/11299/215013University of Minnesota M.S. thesis.April 2020. Major: Applied Plant Sciences. Advisors: Walid Sadok, Aaron Lorenz. 1 computer file (PDF); vii, 48 pages.Increasing soybean production to meet growing demand requires closing the current yield gap, and approaching the yield potential through genetic improvement and optimization of cultivars for specific growth conditions. Leaf traits are important targets for improvement and play key roles in the capture and usage and storage of the resources needed for yield production. Leaf area has been shown to be associated with yield through its effect on transpiration and interception of photosynthetically active radiation (PAR). Leaf shape has similar effects on transpiration through boundary layer effects, and also controls the amount of intercepted PAR by altering the canopy structure and the amount of light that penetrates through the canopy. Leaf venation determines the rate of water flow through the plant, and the geometry of vein topology likely has a significant effect on this rate, and therefore the total water transpired by the plant as a whole. Vein branching angles are thought to play a role in hydraulic conductance, and may also act as a structural constraint to leaf area development. While leaf shape in soybean is known to be controlled by the Ln locus, which in addition pleiotropically affects seed size and number, the genetic basis of whole-plant leaf area and venation topology traits are yet to be discovered. Leaf area, shape, and venation topology are closely linked during leaf development, so an understanding of their genetic basis and relationship to one another is critical to the optimization of leaf type for a target environment. The goals of this study are to identify QTL for whole-plant leaf area, leaf shape, and vein branching angle, as well as to quantify and compare the relationships between these traits. A bi-parental SoyNAM population (IA3023 x LG94-1906) consisting of 136 genotypes was grown twice over two years and measurements were taken for whole-plant leaf area, whole-plant dry mass, specific leaf area, leaflet length, leaflet width, leaflet shape, vein branching angle, and leaflet area. QTL mapping and correlation analyses were performed for all of these leaf traits. Novel QTL were identified for whole-plant leaf area and vein branching angle that co-localized with the Ln locus. QTL identified for leaflet length, leaflet width, and leaflet shape also co-localized with the Ln locus as expected, however a second, novel QTL was identified for leaflet length. These results suggest that the Ln locus may contribute to leaf area and vein branching angle determination in addition to leaf shape and seed size/number. Further investigation into the genetic basis of these traits and their interactions will help in developing cultivars with ideal leaf types. A negative correlation between vein branching angle and whole-plant leaf area was found, supporting the hypothesis that larger branching angles constrain leaf area development. Additional study on this relationship in soybean and other crops may prove this connection spans across species, and can be a useful target in breeding for ideal leaf types.enGeneticsLeaf AreaLeaf ShapeLeaf VenationQTLSoybeanThesis or Dissertation