Communications Project

Document Type:Dissertation
Name:Zhengxing Shen
Degree:Doctor of Philosophy
Department:Crop and Soil Environmental Sciences
Committee Chair: David J. Parrish
Chair's email:davp@vtvm1
Committee Members:Azenegashe O. Abaye
David Orcutt
Gregory E. Welbaum
Dake D. Wolf
Keywords:seeds, switchgrass, panicum virgatum, dormancy, aging
Date of defense:July 02, 1997
Availability:Release the entire work for Virginia Tech access only.
After one year release worldwide only with written permission of the student and the advisory committee chair.


The dormancy of switchgrass (Panicum virgatum L.) seeds may be broken by a variety of treatments, including after-ripening and stratification. This study was conducted to investigate and characterize more systematically factors affecting both after-ripening and stratification effectiveness, and the aging that can occur concomitantly with after-ripening. More than one year of after-ripening at ambient temperature and humidity was necessary for germination of newly harvested seeds to increase from as low as 5% to around 80%. After-ripening was not accelerated at temperatures above ambient for seeds stored in paper bags, which permitted the loss of seed moisture at the increased temperatures. Both after-ripening and aging accelerated with increases in temperature (5 to 60 °C) and seed moisture content (50 to 130 g kg-1), except that there was evidence of a moisture optimum for after-ripening that shifted downward as temperature increased. For many seedlots, storage at 60 °C and 50 g kg-1 seed moisture content for about 1 mo broke most of the dormancy and resulted in acceptably low numbers of abnormal (aged) seedlings. Decreases in germinability caused by post-stratification drying of switchgrass seeds (described herein as "reversion", in which the reverted seeds could be made germinable again by further stratification) increased as the desiccation increased. Revertibility decreased as stratification or after-ripening time increased. Stratification and after-ripening worked additively to release switchgrass seeds from dormancy. Reversion (germination with stratification minus germination after stratification followed by drying) may reveal seedlot differences and changes over time and moisture content that can not be seen otherwise. Imbibed, dormant seeds placed at 21 or 30 °C were induced into deeper dormancy, as indicated by length of stratification needed to break the dormancy. Dormancy deepened more as storage temperature and time increased for imbibed seeds. There are transitional temperature and seed moisture ranges where opposing processes (aging vs. after-ripening, stratification vs. dormancy deepening) appeared to overlap or surpass one another. Switchgrass seeds, either on a single seed level, or on the population level, responded continuously to changing temperature and moisture conditions. Less aging was observed for switchgrass seeds stored in N2. After-ripening of switchgrass seemed not to be influenced by N2 or air. In sum, switchgrass is revealed to be remarkably plastic in its ability to move toward both greater germinability and greater dormancy.

List of Attached Files


At the author's request, all materials (PDF files, images, etc.) associated with this ETD are accessible from the Virginia Tech network only.

The author grants to Virginia Tech or its agents the right to archive and display their thesis or dissertation in whole or in part in the University Libraries in all forms of media, now or hereafter known. The author retains all proprietary rights, such as patent rights. The author also retains the right to use in future works (such as articles or books) all or part of this thesis or dissertation.