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Coat thickness and hard-seededness in some Medicago and Trifolium species

Published online by Cambridge University Press:  19 September 2008

L. Russi ,
P. S. Cocks  and
E. H. Roberts
L. Russi*
Affiliation:
International Center for Agricultural Research in the Dry Areas (ICARDA), PO Box 5466, Aleppo, Syria
P. S. Cocks
Affiliation:
International Center for Agricultural Research in the Dry Areas (ICARDA), PO Box 5466, Aleppo, Syria
E. H. Roberts
Affiliation:
Department of Agriculture, University of Reading, Earley Gate, PO Box 236, Reading RG6 2AT, UK
*
* Present address and correspondence Istituto di Miglioramento Genetico Vegetale, Universita di Perugia, Borgo XX Giugno, 74 06100 Perugia, Italy
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Abstract

The seeds of three medics (Medicago orbicularis, M. rigidula and M. rotata) and three clovers (Trifolium stellatum, T. campestre and T. tomentosum) were collected from a pasture in north-west Syria on three occasions: immediately after seed set, at the end of the dry season, i.e. 4 months after seed set, and 16 months after seed set. Complete and sectioned seeds were observed with a scanning electron microscope. Morphological changes and differences in thickness of the seed coat were related to the hard-seededness of the samples collected in the seed bank before the onset of the rainy season. The morphology and structure of the seed coat of all six species were typical of papilionoid legumes. The species with the softest seeds (T. stellatum) showed a very thin and discontinuous cuticular layer at seed maturation (0.16 μm), while a thick and continuous cuticle (4.24 μm) was characteristic of the hardest-seeded species (M. orbicularis). The lens region of seed of all species except T. campestre was weakened after a few months in the field. This weakening was also found in seeds which were certainly hard, but the cracks in the lens region were apparently not deep enough to allow imbibition. Even when large areas of the palisade layer were removed from the lens region of seeds of M. rotata, this was not sufficient to permit water uptake. Differences in the seed coat thickness of the six species accounted for differences in seed dormancy only when seed mass was taken into account.

Keywords

hard seedsMedicagopasture legumesscanning microscopyseed coatTrifolium
Type
Research Papers
Information
Seed Science Research , Volume 2 , Issue 4 , December 1992 , pp. 243 - 249
Copyright
Copyright © Cambridge University Press 1992

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Footnotes

†

Present address Crop and Pasture Science Department, University of Western Australia, Nedlands, Perth WA 6009, Australia

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