Thursday, January 2, 2014

Regenerating a Rare Sunflower


In my mind, the sunflower may be the most iconic American plant. It’s a plant of summer, a plant of fall, a plant chewed on the ball field (and a healthier one than the other plant commonly chewed on the diamond, Nicotiana tabacum). My earliest gardening memories are of a sunflower; of planting a seed in a Dixie cup with my preschool class and watching it grow in my parent’s garden till it towered over my head.  It was fitting that one of the first plants that I worked with at Rancho Santa Ana Botanic Garden (RSABG) was a sunflower.

Flowers of Helianthus inexpectatus
The seed bank at RSABG is always adding new seeds to its collection. Each of these new seed collections must be tested to make sure that the seeds are alive. There are several ways to test whether or not a seed is alive.  The method that we use for most of our seed collections is germination testing. This process is fairly straightforward. We take a small sample of seeds, and germinate them under very specific and controlled conditions. By looking at the ratio of seeds which sprout compared to the total amount of seeds which were sown and dissecting and making observation about any ungerminated seeds we can get a good estimate of the percentage of viable (living) seeds in a collection. On my first day at RSA, an assortment of interesting seeds was ready and waiting to be tested. One of these was a sunflower, and a rather unusual one…

The Newhall Ranch Sunflower (Helianthus inexpectatus) wasn’t formally described until 2010, when David Keil and Mark Elvin published a description in  Aliso, the scientific journal of RSABG. Before the description, there was some confusion about what this plant actually was. It was found at Newhall Ranch, an interesting and controversial piece of land just south of the grapevine along the I-5. When they were discovered, there was some confusion about the taxonomic identity of these plants. Based on pollen size, chromosome counts that differed from closely related species and other factors, the plants were described as an entirely new sunflower.

Since the seeds came from such an unusual plant, we used a very small sample to test their viability. 30 seeds were sown, 17 of which germinated. This gave us our baseline of viability for the collection, and the added bonus of 17 tiny plants. In some of our tests, the plants which are produced inevitably end up being discarded, often in a spectacular display of fungal attack, but with these unusual seeds we knew that we wanted to grow them on. The plants were grown in small two inch pots for several weeks and were tended to with care by our talented nursery staff. Once they were large enough, we transferred them to raised beds, where we could grow them to maturity.

Seeds of Helianthus inexpectatus
Seed regeneration, also known as seed bulking, is the process of taking a small amount of seeds, growing plants from them, and collecting and storing the seed that those plants produce. The 17 plants that were produced during germination testing were used for this purpose. After a long summer of frequent watering and the occasional threat of insect attack, the plants flowered and began to set seed. We harvested seed over the course of approximately one month, collecting mature flower heads and storing them in a dry area in paper bags. Many of the seeds were found to be unfilled and non viable, but some were healthy and normal. Altogether we were able to harvest more than 2,500 viable and healthy seeds from the 30 seeds that we started with in our germination test. The seeds that we produced will be stored at the RSABG seed bank, and will be available to the botanical researchers and conservationists. 

Susanna Bixby Bryant, the founder of RSABG, envisioned an organization that would “…replenish the depleted supply of some of the states rarest plants.” Many years after she wrote those words, it is an honor to be continuing this work, methodically collecting, storing, growing, and regenerating our states rarest plants.

No comments:

Post a Comment