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Relationship between accumulated hydrothermal time during seed priming and subsequent seed germination rates

Published online by Cambridge University Press:  19 September 2008

Kent J. Bradford  and
Anthony M. Haigh
Kent J. Bradford*
Affiliation:
Department of Vegetable Crops, University of California, Davis, CA 95616-8631, USA
Anthony M. Haigh
Affiliation:
Faculty of Horticulture, University of Western Sydney, Hawkesbury, Richmond, NSW 2753, Australia
*
* Correspondence
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Abstract

Seed germination rates are sensitive to both temperature (T) and water potential (ψ). The times to germination of seeds imbibed at suboptimal T and/or reduced ψ are inversely proportional to the amounts by which T exceeds a base temperature (Tb) and ψ exceeds a base water potential (ψb). Germination rates across a range of suboptimal T and ψ can be normalized on the basis of the hydrothermal time accumulated in excess of these thresholds. However, seeds can also progress metabolically toward germination even at T or ψ too low to allow radicle emergence to occur. Seeds preimbibed at low ψ and dried back, or primed, germinate more rapidly upon subsequent reimbibition. We show here that the increase in germination rates of tomato (Lycopersicon esculentum Mill.) seeds resulting from seed priming is linearly related to the hydrothermal time accumulated during the priming treatment. The threshold temperature (Tmin = 7.05°C) and water potential (ψmin = −2.50 MPa) for metabolic advancement were considerably lower than the corresponding thresholds for radicle emergence of the same seed lot (Tb = 11°C; ψb = −0.71 MPa), allowing the accumulation of hydrothermal priming time that is subsequently expressed as more rapid germination when T or ψ increase. The hydrothermal time model can now be applied to quantify and analyse germination rates of seeds across the entire range of suboptimal T and ψ at which metabolic progress toward radicle emergence is possible.

Keywords

Hydrothermal timeLycopersicon esculentum Millseed germinationseed primingtemperaturetomatowater potential
Type
Research Papers
Information
Seed Science Research , Volume 4 , Issue 2 , June 1994 , pp. 63 - 69
Copyright
Copyright © Cambridge University Press 1994

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