Tansley Review - New Phytologist 171: 501-523 (2006)

Seed dormancy and the control of germination

William E. Finch-Savage (1), Gerhard Leubner-Metzger (2)

(1) Warwick HRI, Warwick University, Wellesbourne, Warwick CV35 9EF, United Kingdom, Web: 'Seed Science Group' http://www2.warwick.ac.uk/fac/sci/hri2/research/seedscience/

(2) Institut für Biologie II (Botanik/Pflanzenphysiologie), Albert-Ludwigs-Universität Freiburg, Schänzlestr. 1, D-79104 Freiburg i. Br., Germany, Web: 'The Seed Biology Place' http://www.seedbiology.de

Received February 23, 2006; accepted March 27, 2006; published

Effects of temperature and water potential on germination rate

Figure 7. Schematic illustration of the effects of temperature (A) and water potential (B) on germination rate. G10 (dotted lines), G50 (dashed lines) and G90 (solid lines) represent individual seeds in the population at percentiles 10, 50 and 90 respectively. Germination rate increases linearly with temperature above a base (Tb). The slopes of these lines are the reciprocal of the thermal times to germination (1/theramal germination). As temperature increases above an optimum (Topt), rate of germination decreases to a ceiling temperature (Tc). Rate of germination also decreases linearly with water potential (waterpotential) to a base (waterpotential base). Tb is often the same for all seeds in the population, but 1/thermal germination, Tc and waterpotential base vary between seeds in a normal distribution (C, sigma). (D) Schematic representation of the relationship between the water potential of the fiftieth percentile ( waterpotential base(50)) and temperature and their effect on the germination rate of percentile G(50). Figures A-D are modified from (Finch-Savage, 2004) and printed with permission from The Haworth Press, Inc., Binghamton, NY, USA; article copies available from The Haworth Document Delivery Service: 1-800-HAWORTH, E-mail address: docdelivery@haworthpress.com. (E, F) An illustration of the effect of waterpotential base values changing at higher temperatures on cumulative germination. Each seed in the distribution will respond by the extent to which ambient conditions exceed their individual threshold sensitivity (Alvarado and Bradford, 2002). The black line (W) shows sigma waterpotential base of a non-dormant seed population at optimum temperature (E) with rapid germination of all seeds (F). As temperature increases above optimum the distribution (W) shifts to the right (grey line; X) and seeds germinate more slowly. Further increases in the temperature (dashed; Y then dotted lines; Z), further reduce germination rate and the percentage of seeds that can germinate is also progressively reduced as waterpotential base exceeds ambient water potential. These seeds at high temperature are not dormant, but limited by their environment. However, the same illustration shows how other environmental conditions can also increase and decrease sensitivity (shift the distribution of waterpotential base) in the same way to induce or break dormancy (movement to the right or left respectively). waterpotential base values greater than 0 MPa cannot be measured, but are an extrapolation based upon those seeds that can germinate (Bradford, 1996).

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   Abstract    Fig. 1               Fig. 2
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