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(American Journal of Botany. 2010;97:15-26.) doi: 10.3732/ajb.0900213 © 2010 Botanical Society of America, Inc.

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Recalcitrancy and a new kind of epicotyl dormancy in seeds of the understory tropical rainforest tree Humboldtia laurifolia (Fabaceae, Ceasalpinioideae)¹

² Department of Botany, University of Peradeniya, Peradeniya, Sri Lanka ³ Department of Biology, University of Kentucky, Lexington, Kentucky 40506 USA ⁴ Department of Plant and Soil Sciences, University of Kentucky, Lexington, Kentucky 40546 USA

ABSTRACT

We report a new kind of seed dormancy and identify the storage behavior category for an important understory rainforest tree that also is used as an ornamental. While studying seed dormancy of Fabaceae species in Sri Lanka, we observed a considerable delay in emergence of the plumule following radicle emergence in Humboldtia laurifolia. Because epicotyl dormancy has not been reported in Fabaceae, we undertook a detailed morphological study of seed germination in this species. Our aims were to document desiccation tolerance/intolerance and epicotyl dormancy in seeds of H. laurifolia. Drying and low temperature storage were used to evaluate storage behavior of the seeds and imbibition, germination, and seed coat anatomy to categorize seed dormancy in two seed collections. Plumule development before its emergence and effects of light and temperature on plumule emergence were monitored. All seeds that were dried to 15% moisture content or stored at –1°C lost viability. Plumules began to grow 20 ± 5 d from radicle emergence and emerged after 40 ± 3 d. Dark and high illuminance further delayed plumule emergence. Seeds are recalcitrant and have a hitherto unreported kind of epicotyl dormancy, for which we propose the formula .

Key Words: epicotyl dormancy • Fabaceae, Humboldtia laurifolia • plumule emergence • recalcitrant seeds • seed germination

Received for publication 16 July 2009. Accepted for publication 9 October 2009.

FOOTNOTES

¹ The authors thank Prof. N. K. B. Adikaram, Department of Botany, University of Peradeniya, for allowing G.J. and A.W. to use the laboratory facilities; Mr. Manjula Wijesundara, Department of Botany, University of Peradeniya, for preparing the diagrams of Humboldtia laurifolia plumule development; Prof. I.A.U.N. Gunatilleke, Prof. C.V.S. Gunatilleke, Prof. D. M. D. Yakandawala, and Dr. G. A. D. Perera, University of Peradeniya, for providing information about habitat conditions of H. laurifolia; and Mrs. I. M. Gunathilaka, Ms. A. S. Gunathilaka, and Ms. C. N. Gunathilaka for collecting seeds.

⁵ Author for correspondence (e-mail: gejaya{at}gmail.com), phone: +94-81-2394527, fax: +94-81-2388018

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