Source-ID Seed Development

Step 1: Collecting seed from unplowed remnant prairies

 

Whenever possible, we follow these guidelines to make genetically diverse collections that should not harm remnant plant populations:

• Develop expertise in identification of target species.
• Collect seed at peak maturity or make repeated collections.
• Collect from 50 or more widely spaced plants across a site.
• Collect up to 30% of the seed from each maternal plant.
• Take a voucher specimen and/or geolocated photographs to confirm the identification.
• Dry, clean, and store seed properly.
• Maintain records on all seed collections.

Step 2: Germinating seed and growing transplants in greenhouse

We use these practices to avoid unintended selection during this crucial step:

• Investigate known strategies for breaking seed dormancy and apply them.
• Carry out small trials to test techniques.
• Start seed from each prairie in a separate germination tray.
• Transplant seedlings into plug flats as they emerge.
• Retain germination trays for first full growing season and add later emerging plants to plugs.
• Maintain good greenhouse hygiene to promote plant health.
• Keep records of practices.

Step 3: Planting and maintaining production fields

We use the following practices in the field:

• Prepare fields through repeated tillage.
• Lay plastic mulch for weed control in late spring (most plots).
• Transplant about 600 plugs in a typical 150-ft row.
• Aim for roughly equal representation of plants from each prairie.
• Use drip irrigation for wet prairie species.
• Maintain plots with mowing, trimming, and hand weeding.
• Scout frequently for insect pests, diseases, and plant condition.
• Arrange for field inspection for source-identified certification.

Step 4: Seed harvest

‌Harvest is a crucial step for avoiding unintended selection. We follow these basic practices:

• Taking care not to exclude from harvest individuals that are atypical in traits such as height or timing of maturation.
• Harvest at peak maturity or repeatedly as the stand matures over time.
• Use mechanical harvesting equipment or hand methods, depending on the species and field conditions.
• Thoroughly air dry harvested material.

Step 5: Seed processing

We use a variety of methods and equipment to separate seed from other harvested material. To avoid selection at this step while producing pure seed, we:

• Check all outputs of each machine for the presence of filled seed and modify settings to extract that seed and return it to the seed lot.
• Maintain records of seed cleaning settings and adjust to year-to-year differences based on variation in growing conditions.

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Step 6: Seed storage

To promote seed longevity, we store cleaned stock seed in a walk-in cooler set at 4 degrees Celsius and 45% relative humidity.

We reserve subsamples from each first generation seed lot (grown from remnant collections) and store them in a freezer at -20 degrees C. 

When the stock seed inventory is depleted or declines in viability (determined through seed testing), we use reserved first generation seed to produce a second generation of stock seed. 

The Iowa Ecotype Project divided the state into three eco-zones based on latitude. These zones were chosen because differences in temperature and growing season length from north to south are likely to affect the timing (phenology) of plant growth and reproduction as well as their relationships with pollinators. Smaller zones could have been drawn, reflecting Iowa landform regions, however, these were deemed too small to be economical for commercial production of diverse species of seed.

To create an Iowa Ecotype, parent seed is collected from several (preferably >10) remnant prairies within a zone in order to maximize genetic diversity.

Seed sourcing and transfer zones are topics of continuing discussion in the restoration community. See for example: Bower, et al. 2014. Generalized provisional seed zones for native plants. Ecological Adaptations 24(5), pp. 913-919

In recent years, the Plant Materials Program has adopted the Provisional Seed Transfer Zones of the US Forest Service to define the boundaries of zones for new "Iowa Ecotypes" in production. This approach divides most of Iowa into two zones, north to south, based on winter minimum temperatures that correspond roughly to latitude. The zones continue across political boundaries, extending into neighboring states. The map below shows locations of the 11 remnant prairies across northern Iowa from which we collected seed of Doellingeria umbellata, parasol whitetop, in 2020 and 2021.