Morpho-anatomical evaluation of Teramnus labialis seeds: strategies to overcome physical dormancy

Teramnus labialis (Leguminosae) is an underutilized species that has the potential to play an important role in diverse agro-ecosystems as a protein supplement for animal feed and a cover crop to conserve soil health. However, the establishment of this plant is difficult due to low levels of seed germination as a consequence of seed dormancy. The present report describes morpho-anatomical traits and dormancy breaking requirements of T. labialis seeds. General seed anatomical characteristics revealed a thick seed coat enclosing endosperm and cotyledons. Externally, the hilar region was observed, with a well-defined hilar fissure. Morphologically, the embryo is composed of an embryonic axis, which occupies less than half the length of the cotyledons embedded within two thick cotyledons. The cotyledons are inserted into the embryonic axis just below the plumule and serve as protection for it. The embryonic axis is of the bent type, with an embryonic root (radicle) and plumule (apex) visible. Histological analysis showed the presence of a thin cuticle (2.5 mu m), a layer of compact macrosclereids (69.6 mu m) and osteosclereid cells (38.8 mu m). It is proposed that the presence of the macrosclereid and osteosclereid cells confers the impermeability characteristic to seeds. From the scarification treatments tested, immersion in liquid nitrogen and abrasion with sandpaper were found to produce high levels of synchronous germination. However, the latter method is not recommended when large numbers of seeds have to be processed.