|Brenner, David -|
Submitted to: Seed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 13, 2010
Publication Date: October 26, 2010
Citation: Kovach, D.A., Widrlechner, M.P., Brenner, D.M. 2010. Variation in Seed Dormancy in Echinochloa and the Development of a Standard Protocol for Germination Testing. Seed Science and Technology. 38:559-571. Interpretive Summary: The USDA-ARS North Central Regional Plant Introduction Station located in Ames, IA is a key component of the US National Plant Germplasm System. It conserves over 300 different populations of Echinochloa, a genus of grasses that includes both important agricultural weeds, such as barnyard grass, and millets used for human food. These germplasm collections include 15 species from around the world. With such diverse collections, no single germination-testing method was adequate for accurately assessing the seed viability of these samples. By manipulating light conditions, we found that some samples required light while others germinated best in darkness, but no pattern was found in this response based on plant species or improvement status (wild, weedy, or cultivated crop). Most samples showed optimal germination when tests were conducted between 25 to 30°C. However, both positive and negative responses to light were sometimes expressed, even at lower temperatures. A sequential treatment where seeds were first tested in darkness and then transferred to periodic light showed that dormancy caused by darkness was being induced in light-requiring seeds. Similarly, a sequential treatment with light followed by darkness revealed that dormancy caused by light was being induced in dark-requiring seeds. Thus, in the absence of information about the light requirements of particular samples, we conclude that side-by-side germination tests where two replicates receive periodic light and the others are tested in darkness are best. We recommend this approach for germplasm centers, seed-testing laboratories, and others working with diverse Echinochloa seedlots. It should increase the accuracy of testing and more readily identify low-quality samples requiring special attention.
Technical Abstract: The North Central Regional Plant Introduction Station maintains more than 300 accessions of Echinochloa representing 15 species from a diverse cross-section of nations and growing conditions from around the world. With such a diverse collection, no single germination-testing protocol was adequate for accurately assessing their viability. By manipulating light conditions, we determined that some accessions were light-requiring and others were dark-requiring. In addition, no pattern was found for this response based on taxonomy or improvement status. Most accessions tested showed optimal germination when tests were conducted between 25 to 30°C. However, both positive and negative photoblastic responses were sometimes expressed, even at lower temperatures. A sequential treatment of darkness followed by light revealed that skotodormancy (dormancy caused by darkness) was being induced in light-requiring seeds. Similarly, a sequential treatment with light followed by darkness revealed that photodormancy (dormancy caused by light) was being induced in dark-requiring seeds. Thus, without prior knowledge of the light requirements of a particular accession, we conclude that a side-by-side germination test where two replicates receive periodic light (12 hours at 30°C / 12 hours dark at 20°C) and the other two are tested in darkness (12 hours at 30°C / 12 hours at 20°C) is best for Echinochloa. This approach is recommended for germplasm centers, seed-testing laboratories, and others working with genetically and geographically diverse Echinochloa seedlots.