Unraveling the Mysteries of Seeds

Sarah Shank
Seeds of coyote tobacco, Nicotiana attenuata, undergoing smoke treatments.

Sometimes it takes a while to unravel the mystery of seeds; other times they present no mystery at all. Take showy stickseed (Hackelia venusta) seeds as an example of the former. The germination ecology of showy stickseed was for years a mystery. Traditional propagation techniques using cold stratification yielded poor germination rates. Researchers experimented with various scarification techniques (altering the seed coat by weakening or creating an opening) and gibberellic acid, a plant growth hormone, to stimulate germination. It took many trials and several years to develop a technique that combines cold stratification followed by embryo excision to yield germination rates over 80%. A mystery solved.

Sarah Shank
Coyote tobacco seed under the microscope.

Legume seeds are by and large seeds that appear to have no mystery, at least when it comes to dormancy. Scarify the hard seed coat so that the embryo is exposed to air and can imbibe water, and germination ensues. Rare Care’s Research and Propagation Assistant Sarah Shank, however, discovered that Whited’s milk-vetch (Astragalus sinuatus) seeds had something to teach after all. When experimenting with scarifying the seeds using sandpaper to scrape versus nicking the seed coat with a scalpel, she found that the time to germination was more consistent among the seeds whose coats were nicked, an observation that can be beneficial for handling seedlings in horticulture practice.

Working with seeds of fire adapted species presents an entirely different set of mysteries to explore. The seeds of some species need to be exposed to heat or chemicals in the smoke to stimulate germination. Sarah is currently testing seeds from several populations of coyote tobacco (Nicotiana attentuata). This is a fire-adapted species: the spring immediately following wildfire a large crop of this annual species will appear along some riparian corridors in the shrub-steppe of central Washington. To test whether smoke mediates germination of populations found in Washington, Sarah is using culinary liquid smoke and soaking seeds in a dilute solution for 24 to 48 hours before cold stratification. Unlike some genotypes tested in Utah that do not need cold stratification, our local genotypes need exposure to smoke and cold stratification to stimulate germination.

The extensive seed collection in the Miller Seed Vault offers many opportunities to explore the biology of seed dormancy in Washington’s rare plants. Our next mystery to solve? How to germinate Gray’s broomrape (Aphyllon californicum ssp. grayanum) seeds, a parasitic plant that grows with various species of the Asteraceae family. Understanding the germination requirements of rare native plants is an important step in the long-term conservation of these species, one that we unravel one species at a time.