Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 13, 2001
Publication Date: September 1, 2001
Interpretive Summary: Eastern gamagrass is recognized as one of the most productive native grasses in North America; however, its potential has not been reached due to difficulty in establishment from seed. We investigated the seed germination and dormancy in 'Iuka' and 'Pete' eastern gamagrass. Seed germination was affected only by caryopsis weight. Seed dormancy of the two cultivars studied was attributed to the fruit case. Under natural conditions, a caryopsis must first overcome the integrity of the cupulate fruit case to germinate. 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. Given that the force required to open the cupulate fruit case did not significantly change after a 4-wk moist prechill at 0 to 5 deg C, late winter plantings would be adequate if soil temperatures and moisture were favorable. Planting prechill- conditioned seed in early spring would be an alternative if soil temperatures and moisture were unfavorable in late winter.
Technical Abstract: Eastern gamagrass is an important native rangeland species and could be a better improved pasture grass. Stand establishment is slow and can take three years before a full stand is attained. The objectives of our study were to determine the caryopsis weight distribution, the effects of caryopsis weight on 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 and separated into five weight classes and germinated. Differences in percentage 7- and 14-d actual germination and total potential germination were attributed only to caryopsis weight (P <0.05). No caryopsis weight x cultivar interaction occurred, suggesting homogeneity of slopes for cultivars (P >0.25). To test the role of the cupulate fruit case in germination, an artificial fruit case (band) was fashioned from an extruded plastic hexagonal tube an a caryopsis placed inside. The germination of unbanded caryopses (44.8 %) was greater than banded caryopses (6.3 %, P < 0.05). A lever and fulcrum were used to find the force required to open the fruit case. The relationship of the force (N) required to open a fruit case (Y) and the duration of prechill in weeks (x) was Y = 4.05 + 2.41 exx-x, rxx2=0.41. Seed dormancy is likely mechanical for these cultivars. Given that the force required to open the fruit case did not change significantly after 4- wk of moist prechill, the effects of the prechill may largely involve predisposing the cupule to subsequent deterioration from other factors, such as light, alternating temperatures, freezing and thawing, fire, rodents, and soil microorganisms may be involved in its decay.