PHYSICAL ENHANCEMENT IMPROVES SEED-LOT QUALITY IN EASTERN GAMAGRASS (TRIPSACUM DACTYLOIDES)

Abstract

Eastern gamagrass [Tripsacum dactyloides (L.) L.] is a broadly adapted, warm-season perennial grass native to most of North, Central and South America. It is increasing in popularity as an ornamental, biofuel and forage crop. Less-than-adequate stands have been attributed to a combination of seed dormancy and low seed quality. The planting unit is an indurate cupule, which obscures visual caryopsis detection. The objective of this study was to assess the utility of a common laboratory blower in removing unfilled cupules and observe the influence on germination of the derived fractions. Two seed lots were selected based on low and high seed quality, 78 and 100% and 38 and 74%, cupule fill and estimated viability, respectively. Samples were fractioned at gate settings of 40-100 using a South Dakota blower and the number of cupules per fraction, mean cupule and caryopsis weight and percent germination were recorded. In both seed lots, a stepwise increase in air velocity facilitated separation based on cupule fill, cupule weight, caryopsis weight and germination of successive fractions. In the low-quality seed lot, only 31% of the cupules removed at an air velocity of 6.2 m sec-1 contained a caryopsis, but by 9.7 m sec-1 nearly all the empty cupules had been removed. Overall, cupule and caryopsis weights were increased by 107 and 35 mg and 42 and 15 mg in the low- and high-quality seed lots, respectively. Removing inferior cupules improved viability by 12 and 7% in the low- and high-quality seed lots compared to the bulk seed lot. It is clear that removing cupules that are empty or contain poorly developed caryopses will improve seed quality; however, it may be necessary to remove 40% or more of the seed-lot volume to significantly improve germination.