Soil seed bank and seed dormancy in wild populations of lima bean (Fabaceae): considerations for in situ and ex situ conservation.

Seed dormancy and its impact on the soil seed bank for wild Lima bean (Phaseolus lunatus) populations were studied in the Central Valley of Costa Rica. Five populations were selected in contrasted environments. In all cases, distribution of seeds in the soil was limited to 3 cm depth. No innate dormancy was observed but combination of hard seed coat and hilum opening controlled by environmental conditions were responsible for an induced dormancy and the constitution of a persistent seed bank. Breaking of this dormancy was obtained by a brief elevation of temperature from 25° to 45°C. Impacts of this phenomenon concern both genetic and demographic aspects of in situ conservation of the species. Consequences on ex situ conservation are mainly related with the regeneration of the seed collection.