Dowling, Charlie D. 1986- (2015-12). Characterization of Overwintering Perenniality in Napiergrass: Traditional and Molecular Approaches. Doctoral Dissertation.
Napiergrass (Pennisetum purpureum Schum.) is a tropical grass limited in adaptation to the southern United States, and efforts to expand its area of production as a quality forage crop as well as a high-biomass biofuel crop are needed. Phenotypic selection and screening of napiergrass S1 inbred lines and F1 hybrids for increased winter hardiness (USDA Winter Hardiness Zones 8b to 7b) demonstrated that napiergrass is more winter hardy than expected. Variation in hardiness zone 7b winter weather patterns at Vernon, TX, and Alma, AR, resulted in 40% survival across genotypes and no winter survival, respectively, even though the minimum temperatures at both locations were similar. Winter survival in this species is associated with rhizome development. Therefore, rhizome candidate gene expression assays using quantitative polymerase chain reaction (qPCR), on fall and spring sampled rhizomes for genes associated with overwintering, rhizome development, and rhizome proliferation resulted in two cloned genes, APETELA2 (AP2) and Rare Cold Inducible 1 (RCI1) conferring detectable changes in gene expression patterns. Spring sampled rhizomes showed the greatest fold change (FC), specifically in the zone of cell division across all genotypes. Attempts to transfer genes associated with cold-tolerance from oriental fountaingrass (Pennisetum orientale L.C. Rich.) and buffelgrass [Cenchrus ciliaris (L.) syn Pennisetum ciliare Link] into napiergrass via wide hybridization were not successful because no interspecific hybrids were recovered. Analysis of pollen tube growth and pollen-pistil interactions did not reveal barriers to these hybridizations, but post- fertilization events may be the reason for the failure to recover hybrids and this needs to be investigated.