Quantitative analysis of the thermal requirements for stepwise physical dormancy-break in seeds of the winter annual Geranium carolinianum (Geraniaceae)

N. S. Gama-Arachchige, J. M. Baskin, R. L. Geneve, C. C. Baskin

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


Background and AimsPhysical dormancy (PY)-break in some annual plant species is a two-step process controlled by two different temperature and/or moisture regimes. The thermal time model has been used to quantify PY-break in several species of Fabaceae, but not to describe stepwise PY-break. The primary aims of this study were to quantify the thermal requirement for sensitivity induction by developing a thermal time model and to propose a mechanism for stepwise PY-breaking in the winter annual Geranium carolinianum.MethodsSeeds of G. carolinianum were stored under dry conditions at different constant and alternating temperatures to induce sensitivity (step I). Sensitivity induction was analysed based on the thermal time approach using the Gompertz function. The effect of temperature on step II was studied by incubating sensitive seeds at low temperatures. Scanning electron microscopy, penetrometer techniques, and different humidity levels and temperatures were used to explain the mechanism of stepwise PY-break.Key ResultsThe base temperature (Tb) for sensitivity induction was 17·2 °C and constant for all seed fractions of the population. Thermal time for sensitivity induction during step I in the PY-breaking process agreed with the three-parameter Gompertz model. Step II (PY-break) did not agree with the thermal time concept. Q10 values for the rate of sensitivity induction and PY-break were between 2·0 and 3·5 and between 0·02 and 0·1, respectively. The force required to separate the water gap palisade layer from the sub-palisade layer was significantly reduced after sensitivity induction.ConclusionsStep I and step II in PY-breaking of G. carolinianum are controlled by chemical and physical processes, respectively. This study indicates the feasibility of applying the developed thermal time model to predict or manipulate sensitivity induction in seeds with two-step PY-breaking processes. The model is the first and most detailed one yet developed for sensitivity induction in PY-break.

Original languageEnglish
Pages (from-to)849-858
Number of pages10
JournalAnnals of Botany
Issue number5
StatePublished - May 2013

Bibliographical note

Funding Information:
We would like to express our sincere gratitude to Dr Diego Batlla, IFEVA/Cátedra de Cerealicultura, CONICET/Facultad de Agronomía, Universidad de Buenos Aires, Argentina, and Dr Bruce Downie, Department of Horticulture, University of Kentucky, USA, for pre-reviewing the manuscript and for their valuable suggestions. This work was supported in part by the Graduate Ribble fund, Department of Biology, University of Kentucky, USA.


  • Geraniaceae
  • Geranium carolinianum
  • PY-breaking mechanism
  • physical dormancy-break
  • sensitivity induction
  • stepwise PY-break
  • thermal time model
  • winter annual

ASJC Scopus subject areas

  • Plant Science


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