Variation in seed dormancy in Echinochloa and the development of a standard protocol for germination testing
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. However, 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, but 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 seed lots.