Seed Germination and Dormancy in Eastern Gamagrass

Eastern gamagrass [ Tripsacum dactyloides (L.) L.] is an important native rangeland species and could be a more widely used perennial pasture grass. Stand establishment, however, is slow, and it can take 3 yr before a full stand is attained. Our objectives were to determine the caryopsis weight distribution, the relationship between caryopsis weight and percentage germination, the role of the cupulate fruit case in seed dormancy, and the force required to open the cupulate fruit case. Caryopses of ‘Iuka’ and ‘Pete’ eastern gamagrass were extracted from the cupulate fruit case by hand, individually weighed, separated into five weight classes, and germinated in a germination chamber. Differences in percentage observed germination and total potential germination at 7 and 14 d were attributed to caryopsis weight ( P > 0.05). No caryopsis weight × cultivar interaction occurred, suggesting homogeneity of slopes for cultivars ( P > 0.25). An artificial fruit case (band) was fashioned from an extruded plastic tube and a caryopsis placed inside to examine the role of the fruit case in germination. Germination of unbanded caryopses (44.8%) was significantly greater than banded caryopses (6.3%, P ≤ 0.01). A lever and fulcrum were used to find the force required to open the fruit case. We concluded that seed dormancy was likely mechanical for these cultivars. Under natural conditions, the integrity of the fruit case must be reduced before germination will proceed normally. Light, alternating temperatures, freezing and thawing, fire, rodents, and soil microorganisms, to name a few, may be involved in the decay of the fruit case.