Evolution and development of vegetative architecture: Broad scale patterns of branching across the grass family (Poaceae) and characterization of architectural development in Setaria viridis L. P. Beauv

Scope and Method of Study: The objectives of this research were to identify patterns of vegetative architecture across the grass family (Poaceae) and investigate the pattern of architectural development in foxtail ( Setaria italica (L.) P. Beauv.) and green millet (S. viridis (L.) P. Beauv.). A dataset for four markers (ndhF, phyB, ITS and rbcL) was retrieved from NCBI, representing 132 species of the 65 grass genera that were examined for branching characteristics, as well as one outgroup genus. A partitioned Bayesian analysis was conducted with a GTR model with six nucleotide substitution types and a gamma distribution with 4 rate categories. Morphological character data observed in live and herbarium specimens at the Oklahoma State University and Missouri Botanical Garden herbaria were then optimized onto the phylogeny to examine the evolution aerial branching.;I examined differences in branching between green millet and its domesticated relative foxtail millet in three field and greenhouse trials to investigate the changes in branching brought about by domestication. I also conducted three controlled experiments to determine the pattern of architectural development and phenotypic plasticity for green millet in response to changes in temperature, light intensity and planting density.;Findings and Conclusions: My work suggests that the ancestral state of branching in the Poaceae is for plants to produce tillers but not aerial branches. In addition, patterns of aerial branching are present across the grasses that are consistent with phylogenetic relationships in the family, with panicoid grasses exhibiting aerial branches and pooid grasses lacking them. Examination of live specimens suggests variation not only in the elongation of axillary buds, but also in the initiation of meristems which may be attributed to genetic or developmental variation and possibly sensitivity to environmental factors.;Foxtail millet differs from green millet in the number of tillers produced (very few to none), and a complete lack of aerial branching in foxtail millet. Green millet exhibits a stable, orderly pattern of development. Changes in temperature influence the rate of development but not the order of branch production whereas changes in light intensity influence the rate of development and the size of the plant. Under increased planting density, plants are on average shorter and produce fewer branches.