Maternal and burial environment determine the physical dormancy release in tropical Senna auriculata (Fabaceae) seeds

Abstract

In tropical ecosystems, species with an impermeable seed coat, i.e. physical dormancy (PY), are large in number and their seed coat is considered to be an adaptive trait for species persistence and colonization. However, only little is known about their mechanisms for breaking dormancy. The objective of this study was to understand the importance of seed maturation site and burial location in determining the PY release of Senna auriculata. Freshly collected seeds of S. auriculata from Vellore and Coimbatore, Tamil Nadu, India, germinated to 11 ± 1.5% and 19 ± 2.5% respectively and remaining seeds did not imbibe water, thus had PY. Germination of seeds from both sites following hot-water treatment for 30 s and mechanical scarification increased significantly and seeds were able to germinate at a wide-range of temperatures (5–35 °C) both in light and darkness. When incubated at 15/60 °C for 3 months, dormancy release for seeds collected from Coimbatore (72%) was greater than seeds matured in Vellore (53%). Following 1 year of burial at three different locations, seeds from Coimbatore germinated to higher percentage than Vellore seeds at all locations. In particular, the higher temperature sites released dormancy to greater extent than the lower temperature site. Our results suggest that summer temperatures (> 60 °C) prevailing in the tropics provide appropriate cues for breaking PY, but this could be greatly affected by the initial state of seeds and the burial environment.