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Annual Changes in Temperature and Light Requirements for Germination of Palmer Amaranth (Amaranthus palmeri) Seeds Retrieved from Soil

Published online by Cambridge University Press:  20 January 2017

Prashant Jha*
Affiliation:
Department of Research Centers, Southern Agricultural Research Center, Montana State University, 748 Railroad Highway, Huntley, MT 59037
Jason K. Norsworthy
Affiliation:
Department of Crop, Soil, and Environmental Sciences, University of Arkansas, 1366 West Altheimer Drive, Fayetteville, AR 72704
Melissa B. Riley
Affiliation:
Department of Entomology, Soils, and Plant Sciences, Clemson University, 120 Long Hall, Clemson, SC 29634
William Bridges Jr.
Affiliation:
Department of Applied Economics and Statistics, Clemson University, 243 Barre Hall, Clemson, SC 29634
*
Corresponding author's E-mail: pjha@montana.edu

Abstract

Experiments were conducted on Palmer amaranth seeds collected in 2004 and 2006 from a natural population near Pendleton, SC, to determine the temperature and light requirements for germination of seeds retrieved from soil surface or from 10-cm depth in the field. A cyclic change in seed germination of Palmer amaranth in response to temperature and light occurred during a 12-mo after-ripening period. Freshly matured seeds collected in November required mean temperatures ≥ 25 C, and natural or red (R) light for increased germination. Following after-ripening in winter, seeds experienced a reduction in dormancy and germinated higher at 25 to 35 C mean compared with 10 to 15 C mean. With after-ripening for an additional 3 mo in May, seeds experienced a broadening of thermal range (10 to 40 C mean), and germination in natural light or R light was more than twice the germination in the absence of light. Fluctuating temperatures (7.5 C amplitude) improved germination over constant temperatures, except in summer and fall (9 and 12 mo after seed maturation). Exposure of seeds to high temperatures during summer caused secondary dormancy induction. Averaged over thermal amplitudes, seeds retrieved in fall required mean temperatures > 25 C for increased germination. Burial in spring for 3 to 6 mo induced seed dormancy, and the relative germination in fall (12 mo after seed maturation) was at least 50% higher for seeds retrieved from soil surface compared to seeds exhumed from 10-cm soil depth. Seeds retrieved in late summer and fall required natural light or R light for promoting germination, whereas far-red (FR) light or darkness inhibited germination. Furthermore, the effect of R and FR light was reversible, indicating a partially phytochrome-mediated germination response of Palmer amaranth seeds following 9 to 12 mo of after-ripening in the field.

Information

Type
Weed Biology and Ecology
Copyright
Copyright © Weed Science Society of America 

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