Masters Theses

Date of Award

6-1986

Degree Type

Thesis

Degree Name

Master of Science

Major

Forestry

Major Professor

Edward R. Buckner

Committee Members

Otto J. Schwarz, John Day

Abstract

Desirable wood properties once made mountain silverbell (Halesia Carolina L.) a favored species among loggers in the southern Appalachians. Showy flowers, disease resistance, and handsome form continue to make it a desirable ornamental. Delayed and erratic germination over a one to two year period, plus a poorly understood dormancy mechanism, may be responsible for limiting its commercial availability. Prolonged warm and cold stratification has been recommended as a presowing treatment, but it is not clear whether such treatments relieve dormancy by overcoming hardseededness, inhibiting chemicals, or morphological and physiological impediments within the embryo itself.

During the years 1982-84, a study was undertaken to find means of hastening germination, and to provide for a clearer understanding of dormancy. Various conventional sacrification procedures were used to quickly remove hard seed coverings, but these failed to induce germination. In vitro culturing of excised surface sterilized embryos, however, proved highly successful, yielding 100 percent germination within 7 days.

Later experimentation showed that morphological and physiological dormancy factors were absent at the time of fruit abscision in mid autumn. Exogenously applied extracts from fruit and seed layers also did not inhibit germination. The primary impediments appeared to center on the hardened endocarp which physically restricted water availability to the quiescent embryo for several months, and then mechanically prevented embryo expansion once hydration occurred.

Overwintering on the forest floor (or artificial stratification designed to mimic overwintering) gradually overcomes physical and mechanical barriers of hardseededness, especially under moist, non-sterile conditions. Embryo excision and culture expedites this process so that seedlings suitable for out-planting can be obtained within 1 year.

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