Title page for ETD etd-8297-134015


Type of Document Dissertation
Author Shen, Zhengxing
Author's Email Address zshen@vt.edu
URN etd-8297-134015
Title Studies on the Plasticity of Dormancy and on Aging in Switchgrass Seeds
Degree PhD
Department Crop and Soil Environmental Sciences
Advisory Committee
Advisor Name Title
Parrish, David J. Committee Chair
Abaye, Azenegashe Ozzie Committee Member
Orcutt, David M. Committee Member
Welbaum, Gregory E. Committee Member
Wolf, Dale D. Committee Member
Keywords
  • seeds
  • switchgrass
  • panicum virgatum
  • dormancy
  • aging
Date of Defense 1997-07-02
Availability restricted
Abstract
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 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.

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