Seed pressing to remove cupules and obtain caryopses in eastern gamagrass

Conventional seed dehulling equipment is not effective for separating caryopses from intact cupules of eastern gamagrass (Tripsacum dactyloides). The objective of this study was to investigate the physical and mechanical characteristics of eastern gamagrass seed, and evaluate the effect of seed pressing on cupule removal and caryopsis viability in order to optimise the seed pressing process. Intact cupules examined were approximately twice as long as the caryopses, and when pressed longitudinally, the rupture force of intact cupules was half that of the caryopses. In addition, longitudinal compression forces the cupules to bend outwards thus enabling caryopses to be separated from cupules with little damage. Seed pressing tests indicated that pressing displacement had significant effects (P < 0.01) on percentage separation, percentage damage and percentage separation without damage. Pressing displacement of 4 and 5 mm resulted in the highest percentage separation without damage for the diploid variety, Pete (87%) and the tetraploid variety, Meadowcrest (84%), respectively. Viability of the separated, non-damaged caryopses was not affected by mechanical pressing. Seed sizing by length and pressing at different displacement for each fraction further improved percentage separation without damage of the Pete variety to 95%.