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First published online May 12, 2009; doi:10.3732/ajb.0800379 American Journal of Botany 96: 1086-1095 (2009) © 2009 Botanical Society of America, Inc.

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Temperature requirements differ for the two stages of seed dormancy break in Aegopodium podagraria (Apiaceae), a species with deep complex morphophysiological dormancy¹

² Environmental Horticulture and Landscape Architecture, Graduate School of Agriculture, Hokkaido University, Sapporo, Japan 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

Only a few studies have considered the possibility that low temperature requirements may vary among stages of dormancy break in seeds with morphophysiological dormancy (MPD). We show that this lack of consideration in previous studies on seed dormancy and germination of Aegopodium podagraria might explain the low germination percentages and/or the relatively long periods of incubation needed for germination. Under natural temperatures, embryos began to grow in September and were fully elongated by late December; most growth occurred when the average daily mean temperature was about 10°C. Radicles emerged under snow in late winter, and cotyledons emerged after snowmelt in early spring. In laboratory experiments, 100% of the embryos grew to full length at both 0 and 5°C, whereas 0°C was much more effective than 5°C in overcoming the physiological dormancy in seeds after embryos were fully elongated. Following radicle emergence, cotyledons emerged readily in a wide range of temperatures 5°C. GA₃ did not substitute for the low temperature requirement for dormancy break. Seed dormancy in A. podagraria fits Nikolaeva’s formula for deep complex MPD, i.e., C₃B-C₃. Better germination of seeds pretreated at 0° than at 5°C has practical implications for cultivating this species.

Key Words: Aegopodium podagraria • Apiaceae • germination phenology • gibberellic acid • invasive species • morphophysiological dormancy • underdeveloped embryo

Received for publication 11 November 2008. Accepted for publication 23 January 2009.

FOOTNOTES

¹ S.S.P. thanks the Japanese Society for the Promotion of Science (JSPS) for a Postdoctoral Fellowship (P06195).

⁵ Author for correspondence (e-mail: shyamphartyal{at}gmail.com); present address: Department of Forestry, PO Box. 59, H.N.B. Garhwal University, Srinagar-Garhwal (UK) 246174, India

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