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Watermelon seed germination. 1. Effects of light, temperature and osmotica

Published online by Cambridge University Press:  19 September 2008

C. A. Thanos  and
K. Mitrakos
C. A. Thanos*
Affiliation:
Institute of General Botany, University of Athens, 15784 Athens, Greece
K. Mitrakos
Affiliation:
Institute of General Botany, University of Athens, 15784 Athens, Greece
*
* Correspondence
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Abstract

Seeds of watermelon (Citrullus lanatus cv. Sugar Baby) germinated optimally in the dark, throughout the range 20–40°C. Germination was inhibited by continuous (c) irradiation with farred (FR), blue or white incandescent light; short pulses were ineffective. Intermittent FR could fully substitute for cFR; the effect of alternating red and FR pulses during 30-min dark cycles depended upon the timing of the illuminations within each cycle. It is concluded that germination in watermelon is controlled by the low-energy reaction of phytochrome. However, continuous and intermittent red light resulted in partial reductions in germinability. Opening the seed coat at the radicle end enhanced germination in the dark and reduced photosensitivity towards FR. The outer, lignified part of the testa exerted a mechanically restrictive force upon the expanding radicle; this force was estimated to be equivalent to 0.3 MPa. The kinetics, at 25°C in the dark, of the time course of germination and the escape from the inhibitory actions of cFR and osmoticum (0.5m mannitol) were all sigmoid curves, which, upon transformation to normal distributions, had different means, but statistically similar variances. The cFR-irreversible activation of germination by phytochrome and the mannitol-irreversible onset of radicle elongation preceded radicle protrusion (mean at 32 h, 25°C) by 8 and 6 h, respectively. From the results and data on imbition, it is concluded that activation of germination in watermelon takes place during the second, stationary phase of imbibition (20–30 h after sowing at 25°C).

Keywords

Citrullus lanatusosmotic inhibitionphotoinhibitionphytochromeseed coatgerminationwatermelon
Type
Research Papers
Information
Seed Science Research , Volume 2 , Issue 3 , September 1992 , pp. 155 - 162
Copyright
Copyright © Cambridge University Press 1992

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