Moist Heat Overcomes Physical Dormancy at the Seed Coat Lens in Schizolobium parahyba var. amazonicum

ABSTRACT Schizolobium parahyba var. amazonicum (Huber ex Ducke) Barneby (Fabaceae-Caesalpinoideae) is a tree of the Amazon region with pioneer characteristics and large seeds with physical dormancy. Using Accelerated Ageing (AA) methodology, seeds were exposed to Moist Heat (40 °C; >97% Relative Humidity; RH) or Dry Heat (40 °C; 22% RH). Furthermore, it was also investigated dormancy release and the primary site of water entrance into the seeds. Seeds tolerate these conditions for up to six days without any reduction in vigour, however, only Moist Heat could overcome seed dormancy, allowing germination. The lens is the water-gap for primary water entry (where the palisade layer is thinner), as seeds with blocked lens did not imbibe. An unusual multi-layered hypodermis of osteosclereids in the seed coat was observed. Our results suggest that the combination of high temperature with high RH is a key factor involved in overcoming dormancy in the natural habitat of this Amazonian species.