Seed dormancy-breaking and germination requirements of Drosera anglica, an insectivorous species of the Northern Hemisphere

Seeds of Drosera anglica collected in Sweden were dormant at maturity in late summer, and dormancy break occurred during cold stratification. Stratified seeds required light for germination, but light had to be given after temperatures were high enough to be favorable for germination. Seeds stratified in darkness at 5/1 degreesC and incubated in light at 12/12 h daily temperature regimes of 15/6, 20/10 and 25/15 degreesC germinated slower and to a significantly lower percentage at each temperature regime than those stratified in light and incubated in light. Length of the stratification period required before seeds would germinate to high percentages depended on (1) whether seeds were in light or in darkness during stratification and during the subsequent incubation period, and (2) the temperature regime during incubation. Seeds collected in 1999 germinated to 4, 24 and 92 % in light at 15/6, 20/10 and 25/15 degreesC, respectively, after 2 weeks of stratification in light. Seeds stratified in light for 18 weeks and incubated in light at 15/6, 20/10 and 25/15 degreesC germinated to 87, 95 and 100 %, respectively, while those stratified in darkness for 18 weeks and incubated in light germinated to 6, 82 and 91 %, respectively. Seeds collected from the same site in 1998 and 1999, stratified in light at 5/1 degreesC and incubated in light at 15/6 degreesC germinated to 22 and 87 %, respectively, indicating year-to-year variation in degree of dormancy. As dormancy break occurred. the minimum temperature for germination decreased. Thus, seed dormancy is broken in nature by cold stratification during winter, and by spring, seeds are capable of germinating at low habitat temperatures, if they are exposed to light. (C) 2001 Editions scientifiques et medicales Elsevier SAS.