Volume 27, 327

Tropical Grasslands (1993) Volume 27, 327–334

Tropical pasture establishment.
6. Treatment of Seca stylo seed to reduce hard seed content

J.M. HOPKINSON¹ and C.J. PATON²

¹QDPI, Walkamin Research Station, Walkamin, Queensland
²QDPI, Brian Pastures Research Station, Gayndah, Queensland, Australia

Abstract

Two approaches were investigated for the reduction in hard seed content of Seca stylo (Stylosanthes scabra). One was to cause strophiole-breaching through imposition of brief high temperatures by contact with a heated metal plate, and the other scarification of the testa by hammer milling.
Numerous combinations of metal temperature and duration of contact produced a range of levels of the heat dose applied (degree-seconds above 90°C). Response curves relating heat dose to the amount of seed softening and killing were constructed. The similarity of the softening and killing curves, coupled with inconsistency in response between seed lots, explained unreliable results of treatment that were not materially improved by modifications such as prior wetting or rapid cooling after heat treatment. Two causes of inconsistency were detected: a sharp fall in the mean critical heat dose for killing as seed moisture content rose; and apparently different insulative properties of upper and lower segment seed hulls. Heat treatment, besides killing some seeds, weakened survivors and further reduced the numbers of seedlings emerging from soil Despite its effectiveness in softening seed, it was judged to be too unreliable for practical use Hammer milling, by comparison, was simple and effective. The extent of dehulling could be controlled at about 50%, with germination of dehulled seeds, raised to over 60%, and no effect on those remaining intact. Scarification is not a complete substitute for strophiole-breaching, but currently there is no way to produce breached seed commercially other than by expensively suction-harvesting fallen, already weathered seed.