Effect of Seasonal Temperature Changes on Germination Responses of Buried Seeds of Agalinis fasciculata (Scrophulariaceae), and a Comparison with 12 Other Summer Annuals Native to Eastern North America(Reproductive Biology)

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Seeds of Agalinis fasciculata, a native eastern North American summer annual, were dormant at maturity in autumn and thus did not germinate in light or in darkness at 12/12 h daily temperatures of 15/6, 20/10, 25/15, 30/15 and 35/20℃. Buried seeds exposed to natural temperature changes in Lexington, Kentucky (USA) for 53 month came out of dormancy in late autumn and winter and re-entered it in late spring and early summer of each year. Nondormant seeds germinated to 60-100% in light at 20/10℃. Stratification at 5℃ broke dormancy, and nondormant seeds entered dormancy during exposure to 25/15 or 30/15℃. Light was required for germination, but some seeds could be light-stimulated during stratification. Seeds stratified in light had a broader temperature range for germination than those stratified in darkness and tested in light. Buried seeds of 11 of the 12 previously-studied native eastern North American summer annuals exhibited seasonal changes in their dormancy states. As buried seeds of the 12 species began to come out of dormancy during winter, they germinated only at high temperatures, but with additional stratification the minimum temperature for germination decreased, which is a Type 2 temperature response pattern. As seeds of A. fasciculata began to come out of dormancy during stratification, they germinated at an intermediate temperature (20/10℃), but with additional stratification the maximum temperature for germination increased and the minimum temperature decreased, which is a Type 3 pattern. This is the first report of a Type 3 pattern in a summer annual and in the Scrophulariaceae. However, the ecological significance, if any, of Type 3 in A. fasciculata seeds is unknown and may reflect more about the past history of the species or its ancestors than it does about present-day ecological adaptations to the habitat.
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Effect of Seasonal Temperature Changes on Germination Responses of Buried Seeds of Agalinis fasciculata (Scrophulariaceae), and a Comparison with 12 Other Summer Annuals Native to Eastern North America(Reproductive Biology)

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