Chloroplast DNA polymorphisms in switchgrass, Panicum virgatum L. and other Panicums

Switchgrass is a native species that has an array of ploidy levels and ecotypes. The first objective of this dissertation research was to determine if restriction fragment length polymorphisms (RFLP\u27s) exist in switchgrass chloroplast DNA (cpDNA) among accessions differing in nuclear DNA content. Eighteen switchgrass cultivars were surveyed using four restriction endonucleases and 20 sorghum cpDNA probes. No cpDNA polymorphisms existed among upland cultivars regardless of DNA content. Lowland cultivars did differ from upland cultivars by a single cpDNA restriction site change. The two cytotypes have been designated as U (upland) or L (lowland) cytotype. These results demonstrate that cpDNA differs among switchgrasses and that this variation is associated with ecotype variation. The second objective of this research was to determine if DNA content and cpDNA polymorphisms existed among and within switchgrass accessions from remnant midwestern prairie sites. Twenty-eight switchgrass accessions were surveyed for DNA content, and for the U or L cpDNA cytotype. The midwestern remnant prairies contained mostly the U cytotype with one exception, IA 31. This accession has both cytotypes. Flow cytometric analysis of nuclear DNA content indicated that switchgrass populations can be a mixture of ploidy levels, with either 3 or 6 pg of DNA per cell. These results dictate that collected prairie germplasm needs to be identified according to DNA content and cytotype, before it is utilized by plant breeders. The third objective of this dissertation was to examine the potential use of cpDNA RFLP\u27s to determine relationships in the genus Panicum L. Chloroplast DNA from eighteen species was digested with three restriction endonucleases, revealing twenty-six polymorphisms. These polymorphisms made it possible to divide the taxa into two groups: (1) the $\rm C\sb3,\ C\sb3/C\sb4$\u27s and (2) the C$\sb4$\u27s. Results did provide a relatively good congruence with taxonomic perceptions based on morphological traits. The cpDNA RFLP\u27s have shown that they have potential as a molecular marker that will aid in separating the genus into more discrete units