Long live the seeds: Germination testing in a conservation seed bank

Seeds are alive–and like all living things, they degrade over time. As a conservation seed bank that stores millions of seeds for research, restoration, and reintroduction, testing seeds to determine their long-term viability is a key part of our work. 

The Mojave Desert Seed Bank has over 950 seed collections at our headquarters in Joshua Tree, California. We check seed vitality through germination tests at regular intervals–once when they are collected, again after one year of storage, and then every five years thereafter. In these germination tests, we attempt to recreate conditions found in the seed’s natural environment that would most likely trigger germination. Through testing, we improve germination rates and gain a greater understanding of what dormancy mechanisms are present in each species by recording how the seeds respond to the treatments we apply and adapting our methods accordingly.

A closer look

Once seeds are collected from the field, they are dried for 2-4 weeks, then cleaned by staff and volunteers–whether by hand, using a sieve, a custom-made blower, or some combination of all three–to remove the husk and other non-viable plant material that could introduce moisture or pathogens in storage.  

Seed Collections Manager Corina Godoy cleans Penstemon incertus seeds by hand, using a series of sieves with metal mesh of variable sizes. 

Once extraneous plant material is removed, we conduct sample cut tests to estimate the proportion of viable seeds in a collection before it goes into storage.  

Left: Seed Collections Manager Corina Godoy performs a cut test. Right: A well-developed desert globemallow (Sphaeralcea ambigua) embryo under the scope.

Staff perform cut tests by bisecting seeds under a microscope to assess the fill and condition of the endosperm and embryo within. If the cut tests reveal a high proportion of empty, damaged, or poorly developed embryos within the collection, we increase the level of cleaning to remove as many of the empty seeds as possible. We consider a collection to be ready for long-term storage when less than 10% of the seeds are empty.

Kickstarting the growing process

While a cut test gives us a snapshot of the condition of a collection, germination tests are much more comprehensive and give us a better understanding of its viability. 

From left: Seed Collections Manager Corina Godoy sterilizes seeds in a cleaning solution. Some seeds require special treatments prior to plating. Here, narrowleaf globemallow seeds (Sphaeralcea angustifolia) are manually scarified by gently rolling them on a fine grit sandpaper, which helps wear down the seed coat to facilitate better water absorption, improving germination rates. Different species may benefit from different treatments, and some need no pretreatment at all. Under a microscope, you can see the scarified seed coats as compared to the bottom left seed, which does not exhibit much scarification. 

Generally, seeds are first bathed in a sterilizing solution to remove pathogens or bacteria that may affect germination rates. 

Once sterilized and any necessary pre-germination treatment applied, seeds are plated on a petri dish filled with agar–a gel that provides a moist environment that encourages germination and offers a clean, controlled space for the seeds to germinate. Though agar is often more humid than our desert soil, this environment helps us see how seeds might behave under more ideal moisture conditions.

Corina arranges seeds on the agar tray using a guide to space them evenly.

Some seeds go straight into the germination chamber (affectionately nicknamed Percy) which cycles between adjustable high and low temperatures. Others go into a cold stratification treatment for 30-60 days at a constant temperature of 3°C for 30-60 days to simulate the chill of winter, after which they are put into the germination chamber to simulate the warmer conditions seen in spring. In some species, this can trigger the biological cues needed to break a seed’s dormancy.

Percy is programmable, so we run different seasonal simulations to figure out the ideal conditions that seeds need to germinate, especially when working with species that have no prior germination data.

Watch it grow

In the chamber, we monitor the seeds regularly, looking for a radicle–the tiny root that emerges during germination. For each test we run, we collect data that will help us inform changes to future tests or allow us to recreate our successful attempts. Amongst this data is the day germination is first observed, the length of the germination period, and the number of days to peak germination. If we see unusually low germination rates, we will reassess what treatment or pre-treatment to apply to future tests of that species.

Above, a radicle emerges during a germination test on our native fillaree, Erodium texanum.

Regularly testing a collection allows us to monitor viability over time. If germination rates drop, we know it’s time to use the seeds while some viability remains. Our tests also teach us whether the seeds are able to tolerate our storage conditions and what dormancy mechanisms they employ–some seeds lose viability after just one year in storage; others may go dormant in storage, requiring additional treatments to trigger germination later down the line.

A regional resource

The Mojave Desert Seed Bank is safeguarding the diverse flora of the Mojave and Colorado Deserts against the threats of climate change, habitat loss, and extinction. We have collections representing over 300 taxa, including 18 species of special concern, and are working towards becoming a living repository of the region’s 2,400+ native plant species.

Many species that we develop germination protocols for extend beyond the deserts. For example, winterfat (Krascheninnikovia lanata) ranges east to the Great Plains and north into Canada. Our research on longevity in storage is also valuable for seed banks everywhere. Taxonomic groups often have similar dormancy mechanisms, so our findings can be used by restoration practitioners to improve success wherever they work.

As climate change renders other regions increasingly arid, desert native plant adaptations to harsh conditions are becoming of greater interest to scientists elsewhere. 

Learn more.

The Mojave Desert Seed Bank: A lifeline for the California desert

This work is made possible thanks to generous support from the California Wildlife Conservation Board.