Submitted to: Seed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 24, 1999
Publication Date: N/A
Interpretive Summary: The genus Cuphea includes a diverse array of plants with potential ornamental, nutritional, medicinal, and industrial value. A considerable amount of research has been directed towards the development of Cuphea as a commercial oilseed crop. To support research and development efforts, the North Central Regional Plant Introduction Station in Ames, Iowa, maintains hundreds of seed samples representing the genetic diversity found within this genus. One of the challenges in conserving these seed samples is that Cuphea shows complex patterns of seed dormancy. This limits our ability to measure seed quality, viability, and longevity, because existing seed-germination tests rely on embryo excision and are slow and labor intensive. We developed a series of experiments testing various combinations of possible dormancy-breaking techniques in order to develop rapid, reliable alternatives to our standard, embryo-excision protocol. Although we have so far been unable to develop protocols as reliable as our existing test, we have found that Cuphea seeds germinate nearly as well when treated for two weeks under high humidity and germinated in light under widely fluctuating temperatures or when given two weeks' moist, cold treatment combined with the growth regulator, gibberellic acid. The results of our experiments help clarify mechanisms of seed dormancy in Cuphea. They can serve as the basis for additional research to develop improved seed-viability tests, which ultimately should reduce the cost of maintaining our Cuphea collections and may be more widely applied in the event that Cuphea becomes a commercial crop.
Technical Abstract: Several species of Cuphea exhibit primary seed dormancy. This hampers viability testing and seed regeneration for germplasm managers, plant breeders, and other researchers. An accurate viability test involving embryo excision has been developed. This research explores alternatives to that labor-intensive technique. Seeds of C. viscosissima Jacq. lost much of their dormancy after 4 to 6 months of cold, moist storage or after four years of dry storage at room temperature. In either situation, an alternating temperature regimen with light was required during the germination test for optimal nonexcised results. Seeds of C. viscosissima, after-ripened at room temperature for seven weeks after harvest, responded well to an alternating temperature regimen with light, if the seeds were first placed under high-humidity conditions in accelerated aging boxes (termed herein as accelerated after-ripening). Response to accelerated after-ripening treatments by older samples of nine other species of Cuphea, obtained from the germplasm collections of the North Central Regional Plant Introduction Station, was generally inferior to results obtained by the use of embryo excision. Possible causes for this difference related to the dynamics of seed production and variation in seed handling methods are discussed.