Date of Award
Master of Science
Moisture extremes, insect and nematode pests, and fungal pathogens have combined to limit the range of conifer species used in amenity plantings and windbreaks in Iowa and much of the Midwest. Three studies were done to screen under-used species for use in Iowa. The first study evaluated 5 different media types for growing Dothistroma pini Hulbary in culture. Five-mm plugs of D. pini were transferred to the different media in plates under sterile conditions. Colony diameter was measured every five days and conidia were harvested and counted in a hemacytometer under a microscope. Contrary to previous research, potato dextrose agar (a high-nutrient media) produced significantly more mycelium and conidia than nutrient deficient media. The second study involved determining the susceptibility of Pinus leucodermis Antoine (Bosnian pine) and Pinus koraiensis Siebold & Zuccarini (Korean pine) to Dothistroma pini Hulbary (Dothistroma needle blight). Pinus nigra Arnold (Austrian pine) was used as the comparison species. Container-grown plants were inoculated with 15 ml of conidial suspension and placed under optimum conditions for infection in a growth chamber. After 24 hours, plants were placed in the greenhouse and observed twice weekly for percent infection and infection severity for 90 days. We also measured growth (height and stem diameter) and several physiological parameters. Inoculated P. leucodermis and P. koraiensis demonstrated infection percent and severity similar to inoculated P. nigra seedlings. An outplanting study was conducted to evaluate survival and growth of Abies homolepis Siebold and Zuccarini (Nikko fir) in central Iowa. In June 2000, 148 A. homolepis and 133 Picea abies (L.) Karstens (Norway spruce) were planted at an ISU Forestry research site. Data were collected on survival, height, diameter, new growth, and lateral length. Although survival of A. homolepis was lower than P. abies, analysis indicated that this was attributable to placement of the seedlings at the field site. There was no difference between species for growth increments of surviving trees. All three experimental taxa require more screening before introduction into the nursery industry. Due to pathogen susceptibility or site-sensitivity, experimental taxa may be suitable for planting on a limited basis.
Carol Diane LaFaver
LaFaver, Carol Diane, "Evaluating under-used conifers in Iowa" (2002). Retrospective Theses and Dissertations. 17488.