Theses and Dissertations Collection

AbstractEndophytes are microbes living symbiotically within plant tissues. They have been shown to have profound effects on plant growth and defense, yet the ecological and managerial implications of these interactions have only recently been discovered. Scientific observation and discovery in this field is sometimes difficult because interactions between the same two species can have radically different outcomes depending on any number of factors, both biotic and abiotic. Soil, light, temperature, genetics, and the presence or absence of other plants and microbes can all dramatically change the outcome of an interaction from mutually beneficial to neutral or even pathogenic. It’s important to study these interactions further and determine how these interactions can affect plant and human health. This thesis examines the effects of microbes on the growth of a common crop plant and the potential applications for human health, as well as the exclusionary interactions between endophytic bacteria and fungi present in a commercially valuable tree species with a declining population. The first chapter reports the results of a study comparting the antagonism of bacteria from different plant tissues. Pinus monticola, commonly known as Western White Pine, was chosen the model system due to its high commercial value and its declining population due to susceptibility to white pine blister rust. White pine blister rust is a devastating plant disease caused by a biotrophic stem rust, Cronartium ribicola. It was found that bacteria isolated from seed were more antagonistic towards endophytic fungi than those isolated from needles. These findings may be useful for furthering efforts to manage plant pathogens such as Cronartium ribicola with further testing and development. The second chapter of this thesis describes the results of interactions between strains of Bacillus subtilis and Raphanus sativus as a model domesticated crop plant. The goal of the study was to determine if a probiotic train of human origin could have the same effects on plant growth and health as strains isolated from plant sources. The results indicate that the strains have similar affects, regardless of origin. This could have applications in agriculture as not only potential plant growth promoters, but as a novel way to deliver health promoting bacteria to human consumers.