Two contrasting methods improve Silphium integrifolium Michx. germination rate to agronomically acceptable levels

Authors: REINERT, STEPHAN - University Of Colorado; MONEY, KENNEDY - North Dakota State University; ROCKSTAD, GRETA - University Of Minnesota; KANE, NOLAN C - University Of Colorado; VAN TASSEL, DAVID - The Land Institute; Hulke, Brent

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2018
Publication Date: 8/16/2018
Citation: Reinert, S., Money, K., Rockstad, G.B., Kane, N., Van Tassel, D.L., Hulke, B.S. 2018. Two contrasting methods improve Silphium integrifolium Michx. germination rate to agronomically acceptable levels. Euphytica. 214:256. https://doi.org/10.1007/s10681-018-2236-x.
DOI: https://doi.org/10.1007/s10681-018-2236-x

Interpretive Summary: A domesticated sunflower relative, Silphium integrifolium, is of interest as a crop-wild relative model species. It also is of interest for direct domestication into a sunflower-like perennial crop for vegetable oil production. In order to be useful, uniform and predictable seed germination is needed to evaluate various plant lines in scientific experiments and for breeding. Using prior information from sunflower, several combinations of physical and chemical treatments were conducted on three Silphium lines of diverse origin, to see if a uniform and predictable method can be developed. Two equally valuable methods, one chemical and one cold exposure, led to agronomically-acceptable levels of seed germination. These could be used for priming seed for field plantings for producers, field and lab experiments for breeders, and other study systems.

Technical Abstract: Organic dormancy, the inability of germination under favorable conditions, is a common problem in many crop species and their wild relatives, leading to more variable emergence, plant density, and growth rates, increasing costs, and lowering yield. To overcome these problems, several different methods have been developed for different crop and model plants. But in the emerging crop being bred from wild and semi-domesticated Silphium, no such method has been established thus far. The objective of this study was to identify a dormancy-breaking assay to increase the Silphium seed germination rate. Seeds of three different Silphium integrifolium Michx. genotypes were treated with five chemical treatments and one cold treatment, and dried before or after the treatment at 27 °C or 40 °C to break seed dormancy. Untreated, dried seeds were taken as control. Seeds soaked for 24 hours in a ethephon/potassium nitrate solution followed by a 72 hours heat drying step at 40 °C showed an increase of germination to up to 90% ± 2% compared to control seeds (3% ± 0% and 5% ± 1%). We also identified the minimum time frame of stratification needed to enhance seed germination in Silphium, and found that cold stratification was nearly as good as the chemical treatment. Our results provide two alternate ways to treat S. integrifolium Michx. seeds for breaking organic seed dormancy and help to facilitate future research in the Silphium domestication community. The fact that our optimal treatments were similar to protocols developed for sunflower suggests that these methods may also be applicable to many related economically-important Asteraceae species.